Fuel Starvation/Surging - First Gen

[XframeFX]

1 hour ago, NTX5467 said:

Thanks for that link to the Samba forum!  Interesting!

Got lucky on 1st hit for a TFI Schematic in Google Images for Lee H. I guess I should go back and read more!

 

Tissue rejection? TFIs are so cheap, I keep a spare in the glovebox. I spent more  $$$ on a vial of thermal semi-conductor paste for the heat sink. Although the TFI produces no heat with the .7 ohm canister coil.

 

Converted last winter hoping it would fix my thumping idle. Flip Flopping between ignition and fuel. Now after a summer with the TFI and a good handle on ignition, back to the fuel system.

[60FlatTop]

10 hours ago, XframeFX said:

Converted last winter hoping it would fix my thumping idle. Flip Flopping between ignition and fuel. Now after a summer with the TFI and a good handle on ignition, back to the fuel system.

I think I read that, went back over recent posts, then came back and read it another four times. I keep getting the same interpretation. It ain't fixed, right?

[XframeFX]

2 hours ago, 60FlatTop said:

It ain't fixed, right?

Nope, still an annoying issue. A low frequency resonant "thump" and can feel it through the seat bottom cushion.

 

But again, outside the passenger compartment staring at my idling Nailhead with the Hood up, it idles fine, nieghbour and others at car meets even say so.

Thinking copious amounts of DynaMat and hard motor mounts changed the dynamics. Then there's the DynaFlow because it's worse in "Drive" waiting at a Red light. Although through all this, the Dynaflow has operated flawless, not even a leak.

 

Thanks for asking!

[Cornpanzers Riv]

Swapped out the coil today. Went for a drive, and was pretty excited that it seemed the problem was solved. I was even able to get into the secondaries. Unfortunately, it only lasted a couple miles before the problem started up again.

(I did also confirm that the fuel lines in the rear are new.)

I’m pretty convinced it’s a fuel issue. It surges like it’s running out of gas. Typically ignition problems are more abrupt. I could be wrong though. It’s happened before, LOL.

I will buy a points and condenser to throw at it just to cover my bases. What’s interesting is it’s dramatically more evident when I’m driving uphill. Even at slow speeds and part throttle, long gradual grades trigger the problem immediately.

[EmTee]

Have you tested the fuel pump for pressure and volume?

[Cornpanzers Riv]

I have not, but the problem existed before, and after I bought a brand new pump from Napa. Doesn’t totally rule it out, but pretty much.

[Ronnie]

On 1/28/2024 at 4:58 PM, Cornpanzers Riv said:

If I try to accelerate quickly, it starts to surge. Get into the secondaries and forget about it. Seems like the problem is worse climbing a hill.

Sounds like a bad spray pump in the carburetor to me.

[XframeFX]

1 hour ago, Cornpanzers Riv said:

I will buy a points and condenser to throw at it just to cover my bases.

Without real-time data and diagnostic error codes (modern vehicles), all we can do is change parts, rely on experience/knowledge and use process of elimination.

It would be so nice to watch multiple parameters while driving. Then when the issue materializes say: "Ah look, input #7, Fuel pressure just dropped out".

 

Just a thought when driving uphill: Float level/drop?

 

 

 

Edited February 4 by XframeFX (see edit history)

[EmTee]

11 hours ago, Cornpanzers Riv said:

I have not, but the problem existed before, and after I bought a brand new pump from Napa. Doesn’t totally rule it out, but pretty much.

Not necessarily.  Why did you replace the pump?  At this point, I would still do pressure and volume tests to rule out potential problems such as: (1) restriction in the fuel line to the tank, (2) plugged or otherwise restricted fuel pickup sock, or (3) worn cam pump lobe or push rod.

[avgwarhawk]

13 hours ago, Cornpanzers Riv said:

Swapped out the coil today. Went for a drive, and was pretty excited that it seemed the problem was solved. I was even able to get into the secondaries. Unfortunately, it only lasted a couple miles before the problem started up again.

(I did also confirm that the fuel lines in the rear are new.)

I’m pretty convinced it’s a fuel issue. It surges like it’s running out of gas. Typically ignition problems are more abrupt. I could be wrong though. It’s happened before, LOL.

I will buy a points and condenser to throw at it just to cover my bases. What’s interesting is it’s dramatically more evident when I’m driving uphill. Even at slow speeds and part throttle, long gradual grades trigger the problem immediately.

Check the carb once again.  

[gungeey]

15 hours ago, Cornpanzers Riv said:

Swapped out the coil today. Went for a drive, and was pretty excited that it seemed the problem was solved. I was even able to get into the secondaries. Unfortunately, it only lasted a couple miles before the problem started up again.

(I did also confirm that the fuel lines in the rear are new.)

I’m pretty convinced it’s a fuel issue. It surges like it’s running out of gas. Typically ignition problems are more abrupt. I could be wrong though. It’s happened before, LOL.

I will buy a points and condenser to throw at it just to cover my bases. What’s interesting is it’s dramatically more evident when I’m driving uphill. Even at slow speeds and part throttle, long gradual grades trigger the problem immediately.

This sounds identical to a situation I once had. 

The solution was to check the sender sock again. My guess was that in my case at the prior fuel fill I got some contaminated gas. 

The fuel sock kept getting clogged with silt. Car would sit for a few days, silt would partially drop from the screen and I could do a mile or two then the problem would reoccur.

 

Fuel pump would show 5lbs pressure at a sitting idle. Fill a coffee can in ten seconds. 

It was the ongoing suction in the tank would pull the debris back again when driving. 

I believe I didn't need to change the sock but just blew it with compressed air from the inside out.  

It drove me nuts for 4 or 5 weeks. 

Edited February 4 by gungeey (see edit history)

[NTX5467]

The sending unit fuel intake should be placed at the lowest part of the tank, which is where a lot of the sediment should congregate.  As I understand it, the "sock" on the sender fuel inlet is there to keep moisture out of the rest of the fuel system, with a small enough mesh to resist water but not small enough to restrict gasoline.  Yet gunk from "phase separation" in the tank (from ethanol'd fuels reacting with moisture in the new fuel and/or condensate in the tank itself) can get through the sock, it seems.

 

When the engine is turned off, the fuel in the fuel line above that level should "wash" back into the tank, potentially removing any accumulation from the outside of the sock.

 

Perhaps the tank might need some internal cleaning?

 

Might try some moisture-removal fuel additive (which usually included some alcohol in it) and then drive the car until it needs fuel, then add fuel to the tank in 5 gallon amounts from gas cans?

 

Just some thoujghts,

NTX5467

[60FlatTop]

51 minutes ago, gungeey said:

Swapped out the coil today. Went for a drive, and was pretty excited that it seemed the problem was solved. I was even able to get into the secondaries. Unfortunately, it only lasted a couple miles before the problem started up again.

What was affected by the coil change besides the coil:

 

The coil wires was unplugged and moved. Ohm out the coil wire and check the ohms per foot value. If it is a carbon/cotton conductor try a solid core.

 

The primary lead to the distributor lead was moved. Ohm it out disconnected at both ends. Check for loose terminals and terminal crimps. Check the grommet and entry hole into the distributor hole for a short to ground.

 

Check the breaker plate for a good ground.

 

Check the ignition switch side primary lead for a loose terminal clip. Disconnect the battery and jump from the disconnected coil primary terminal to the positive terminal connector on the inner fender. Switch the ignition on an off a bunch of times watching for good continuity through the switch.

 

That doesn't take long but it should assure there are no hidden problems on the primary wiring side.

 

Does your key get hot after a long drive?

 

If it was mine I would ohm out the spark plug wires as well. I have an inductive pick up that reads secondary voltage in KV. If you have access to one look for high 2K to just over 3K at idle. Lower will show a dead wire. Higher will show a lean cylinder.

 

Having the problem appear to be resolved and then come back is one I would look forward too. I have driven some cars that were so bad I just kept hoping they would break so something would be definable.

 

Those cars will trick you. One very hot summer day my wife had driven her '62 Electra 225 90 miles to her parents. On the way back she put gas in it about 15 miles away from home to be sure she got back. She didn't. The car quit about three miles after. Towed home to our driveway it wouldn't start. I couldn't figure it out. Around dusk I went out to close the hood for the night. The sun was setting on the opposite side of the car. When I looked in I wondered "Why is the fuel in the sediment bowl rainbow looking?" Didn't take long to get her to admit she put 10 gallons of diesel fuel in it.

 

Sometimes the Sum, the Moon, and the Planets really do have to be in conjunction to find truth in the universe. It was a learning moment.

[1965rivgs]

  Substitute an alternative source of fuel, simple as a 2 gallon container secured under the hood which can be replenished mid test ride, and you will cut the troubleshooting tree by 50%. The first step is to determine if the problem is fuel, or spark related...just sayin'...

Tom Mooney

 

 

[Frank DuVal]

I've replaced enough of those Thick Film Integrated modules on Ford vehicles to say I'm not impressed. Mostly on friend's trucks, but I had my own '84 (yes, the same part number as the '94 Ford) towed home one day from a TFI failure 60 miles away.

 

GM HEI, rarely ever had to replace the module on those!

[XframeFX]

44 minutes ago, Frank DuVal said:

I've replaced enough of those Thick Film Integrated modules on Ford vehicles to say I'm not impressed

TFIs were relocated from the distributor to a heat sink mounted on a fender well because the engine would die when too hot. Most recovered when cooled. I believe a class action law suit was registered.

 

They have a direct path to the coil bypassing the electronic timing module for "Start". It can be enabled by opening a connector in the harness near the TFI module to set base timing. This path is primarily used for "Start" but is also a backup, limp mode and sends a diagnostic signal.

 

I am using only the "Run" path, no backup. Again, I keep a spare module in the glovebox.

 

If TFIs were bad back in the 90s, there are QC issues with new replacements today, even Motorcraft brand.

 

So far, I'm impressed. Operates as low as 9 Vdc (ballast resistor), will fire any coil (current limiting trigger), will power down if no pulse is present (key left ON) and rock solid dwell. Above all, a simple install. The 2 holes in the heat sink line up with two of the three holes on the fender where the Voltage Regulator was.

 

An interesting read/rant for a Ford Shutter Wheel:

https://www.promracing.com/tfi-distributor-shutter-wheel.html

[1965rivgs]

19 hours ago, gungeey said:

This sounds identical to a situation I once had. 

The solution was to check the sender sock again. My guess was that in my case at the prior fuel fill I got some contaminated gas. 

The fuel sock kept getting clogged with silt. Car would sit for a few days, silt would partially drop from the screen and I could do a mile or two then the problem would reoccur.

 

Fuel pump would show 5lbs pressure at a sitting idle. Fill a coffee can in ten seconds. 

It was the ongoing suction in the tank would pull the debris back again when driving. 

I believe I didn't need to change the sock but just blew it with compressed air from the inside out.  

It drove me nuts for 4 or 5 weeks. 

Steve,

  I've encountered this many, many times. I'm convinced that instead of pumping the debris into the tank from another source, what typically occurs is a film of surface rust forms on the walls of the fuel tank when the car is no longer in regular service. When the tank is topped off upon return to service, the fresh fuel washes the fine particles of surface rust down into the bottom of the tank where it accumulates like fine "sand" around the filter sock.

  Obviously this can occur many times over the course of several decades when the car is occasionally used but mostly sits idle; and especially if the fuel level is allowed to remain low.

  I've resurrected quite a few cars which were in long term storage and this issue doesn't present itself until numerous tank fulls are processed.

Tom Mooney

[Cornpanzers Riv]

Made some progress today. On a whim, I clamped off the return fuel line and took it for a long drive. Ran great, no surging or starvation at all.
of course, this leads to a couple questions.

 

First, The car no longer has air-conditioning… What was the purpose of the return fuel line on air-conditioning cars in the first place?

Second question… What could be causing excessive fuel to return? Perhaps float level?

third question, what prevents me from just disconnecting the return line and moving onto the next challenge? (I typically like to find root causes, but if this works, I’ve got plenty of other things I can be doing.) 

 

as usual, thank you for all the help.

[Bloo]

On the fuel filter, there should be a tiny orifice in the nipple that feeds the return line. It sounds like the filter might be missing the orifice or the hoses might be mis-plumbed. The return line prevents the carburetor from being force-fed fuel and overflowing if the fuel pump boils after a hot shutdown. Apparently it wasn't necessary on cars without A/C. It is a good idea though. I wouldn't be in a hurry to get rid of it.

 

Edited February 11 by Bloo (see edit history)

[1965rivgs]

  The return line was engineered into AC equipped cars as a method to prevent "vapor lock". By recirculating fresh fuel back to the tank via the fuel filter it helps to keep the fuel, which is momentarily stationary, in the fuel line from boiling when the inlet needle in the carb is closed; ie, in stop and go traffic on a very warm day with the AC blasting.

  If the fuel filter allowed a drop in fuel supply to the carb that could explain your symptoms but I would think this would not be a problem that would develop with time and after storage but would present itself immediately after installing a defective fuel filter.

  Perhaps cutting off the return is allowing just enough extra fuel to overcome the symptoms but I suspect you still have an overall issue with fuel supply and eliminating the fuel return is a temporary band-aid.

  The good news is now you are getting somewhere instead of just changing parts. You've just eliminated 50% of the troubleshooting chart.

Tom Mooney

[EmTee]

This discovery makes me even more suspicious of the fuel pump...

[Cornpanzers Riv]

27 minutes ago, EmTee said:

This discovery makes me even more suspicious of the fuel pump...

Me as well, but that was the first thing that I replaced when this problem started.

[EmTee]

20 years ago I would understand.  Today, I no longer implicitly trust any of the 'new' parts that I install.  What still seems to hold true is that more often than not, troubleshooting leads me back to the last item that was touched...

[1965rivgs]

21 minutes ago, Cornpanzers Riv said:

Me as well, but that was the first thing that I replaced when this problem started.

  Setup an alternative fuel source and eliminate  the tank and lines up to the fuel pump. It's not hard, just be careful; you are playing with gasoline. Everything needs to be secured and best not to have a container of fuel in the cabin.

Tom Mooney

[NTX5467]

Back in the 1990s, a motorhome appeared in our dealership service dept.  Complaint was "50mph top speed".  It seems the owner and his family left their Midland, TX location about sunrise and it had taken them way too long to get to our location on the western side of the DFW metro area.  Naturally, it had sat for months before it was loaded for the trim east, I suspect.  

 

Getting on I-20 out west, it was not possible to get to or maintain even a 60mph cruising speed on "flat land".  So they had made a few stops at dealerships to see what was wrong.  One large mechanic shop added an electric pump at the back, which helped, but not "like it used to be".  So we were a "last resort" of sorts.

 

The tech who drew the job was good.  He vice-gripped the return line and test drove it.  Sudden improvement.  HE then came into parts and asked if we had any carb jets in stock.  He was not concerned about the size.  I found a few and let him choose.  They were left over from the earlier 1970s when "lean surge" could be a cruise issue.  He came back in and said "bill it out".  I asked what was going on?  He returned after getting the customer checked-out and told me their story.

 

After inserting the carb jet into the return line at the fuel pump connection, he said they went for a test drive and now the motorhome cruised at 70mph at part-throttle, as before.  He said the customer was smiling ear-to-ear after our guy figured out what was going on and fixed it inexpensively.

 

Return lines were usually on factory a/c cars, but others could have them, too.  I had never thought about the return line attachments on the fuel pumps having a restriction in them, but apparently they do.  My '77 Type LT 305 2bbl did not have a return line from the factory, but a friend's '77 Z/28 350 did.  BOTH with factory a/c.

 

On some earlier '70s Chevrolet and Chrysler products, the return line was run from a vapor separator between the fuel pump and the carburetor.  I suspected THAT item had some sort of orifice in the return line item so excess fuel and vapor in the lines could exit easily (for return to the fuel tank).  But never suspected a similar orifice in the fuel pump return line.  BTAIM

 

If you can find a fuel-rated vacuum line sized so it can fit inside of the existing fuel return line, or even make it a "double stack" (for a smaller resulting orifice), that might be a simple thing to do, incognito.  Or as mentioned, a main jet from a parts carburetor.

 

Please keep us posted on your progress,

NTX5467

 

 

[XframeFX]

5 hours ago, 1965rivgs said:

Setup an alternative fuel source and eliminate  the tank and lines up to the fuel pump.

So to do this, remove the hood, strap a Briggs & Stratton fuel tank to a roof rack for gravity feed to the carburetor and take it for a test run. LOLing of course😃

 

I too questioned that fuel filter with the 1/4" return until helpful contributors on this Forum explained the teeny tiny orifice. In light of fuel delivery discovery here, maybe replace that filter once more, a different brand maybe.

 

From earlier observations, I understood that the mechanical fuel pump also regulates pressure between it and the carburetor. I can see a failure mode of too much pressure, overcoming float valve seat but, not too little pressure. However, I totally agree with Tom M, You've  progressed 50% in your troubleshooting.

How about a Tee between the fuel filter and carburetor for a remote fuel pressure gauge zip tied to the Driver's wiper arm since the hood is off?😃

 

Something to consider but a longshot, fuel delivery upstream of the mechanical fuel pump. It is 3/8" when the mechanical fuel pump inlet barb is 5/16". So, that flex hose must be scrinched down with a gear hose clamp. Potential for a leak even when parked as there's a head on that connection being at a low point. A leak would be easily detected and probably not the cause for fuel delivery.

[avgwarhawk]

What type of valve slows the gas while in the bowl? In other words, is the gas just blowing by/threw the carb and returning to the tank? Something internal to the carb? 

[RivNut]

1 hour ago, avgwarhawk said:

What type of valve slows the gas while in the bowl? In other words, is the gas just blowing by/threw the carb and returning to the tank? Something internal to the carb? 

The jet was inserted into the return line.  Apparently it slowed down the gas in the return line allowed some gas to return.  Similar to when it was pinched off.  If the weather is cool and there’s no chance of vapor lock. Get a filter for non-a/c car and see how the car runs with no return line.  The non-a/c cars ran fine with no return line.

[EmTee]

My take on the situation is the fuel pump has insufficient volume and/or pressure to allow for the return circuit.  Is the fuel pump in the car correct for one equipped with A/C?

[60FlatTop]

On 1/31/2024 at 10:08 AM, 60FlatTop said:

 

If you do have to go for new modern stock (NMS?) get Echlin parts from your NAPA store.

I am not much for quoting myself,but I have consistently seen the quality of Echlin parts over other right in the palm of my hand.

 

"NAPA® Echlin® engineers and manufactures more than 6 million high-quality Ignition Coils and components at our 60,000 sq. ft. facility in Bialystok, Poland every year."

 

I never looked it up the the "probably" reply inspired me to confirm the location.

[EmTee]

3 hours ago, 60FlatTop said:

"NAPA® Echlin® engineers and manufactures more than 6 million high-quality Ignition Coils and components at our 60,000 sq. ft. facility in Bialystok, Poland every year."

[Bloo]

18 hours ago, avgwarhawk said:

What type of valve slows the gas while in the bowl? In other words, is the gas just blowing by/threw the carb and returning to the tank? Something internal to the carb? 

It doesn't work like that. The carb works like a toilet tank. It shuts off when it is full. The return lines being discussed here connect effectively after the fuel pump but before the carb. The return line has to have a restriction or the fuel would all blow back to the tank and there would be no fuel pressure. The restriction is usually welded in the third port of the fuel filter or the third port of the fuel pump, whichever is used. Some in this thread that are suggesting the restrictor is separate and can be inside the return hose. That would work, and although I don't personally remember seeing any that were built that way, it's possible some were. The only requirement is that there be a fairly aggressive restriction.

 

It it often reported on the internet that this system allows any fuel vapor to escape and go back to the tank, thus keeping the lines full of liquid and the car running. I believed that 40 years ago when i added return lines to a few cars trying to combat vapor lock. If so, the return port should be as high as possible, and on a lot of factory jobs it is. On others it isn't. The idea doesn't hold up to scrutiny though. If the carburetor is dry, the float valve is open, and any vapor has a place to escape through the carb and the bowl vent. If the float valve is closed, the carburetor is completely full and the engine should start regardless of what is going on in the fuel line. It was suggested earlier in the thread that the return line helps with vapor lock by keeping fuel circulating and keeping the fuel pump cooler. I have found that to be true by trial and error, but also found it doesn't help nearly as much as you might expect. The restriction is tiny and not that much fuel circulates. To go any further with that idea, we would have to go down the "what is vapor lock" rabbit hole. It is very deep, and it would derail the thread.

 

@carbking explained somewhere what the return line is mainly about. I'd link it if I could remember where. He explained it better than I could, but I'll try. A mechanical fuel pump has 2 one-way check valves in it. One on the inlet lets fuel only in, and one on the outlet lets fuel only out. On a car with no return line, if you shut off the car hot, the carburetor is full or nearly so because the engine was just running. If the gasoline in the fuel pump body should boil, the pressure rises dramatically. The fuel vapor cannot go back to the tank because of the inlet check valve. It can only escape through the outlet check valve, headed for the carburetor. The boiling fuel in the fuel pump pushes any liquid fuel remaining in the fuel filter and fuel line toward the carburetor. That fuel is under much more pressure than the float valve in the carburetor is designed to hold back, and it blows right through, overflowing the carburetor and flooding the engine. With a return line, that pressure would have escaped back to the gas tank. You'd still have an empty fuel pump but the engine, being not flooded, might start right away and refill the fuel pump.

 

Edited February 12 by Bloo (see edit history)

[NTX5467]

To be clear, the carb jet our tech inserted was into the rubber return line going to the tank from the fuel pump.  For some reason, apparently the orifice in the fuel pump return line fitting was too big or whatever.  This moved the location of the orifice restriction to the return line from the pump.  NOT a factory issue.

 

In some vehicles, I suspect their fuel system was not fully-evolved when produced, so rather than change all sorts of production specs, it was easy to configure an inline fuel filter with a 2nd output fitting for a return line, then just add the metal lines to the tank to the car.  These items were usually termed "vapor separators".  Of course, the additional fitting would need to be positioned pointing upward so any vapors might collect there rather than being forced into the carburetor float bowl area and then into the atmosphere via the bowl vent valve.

 

At times of low rpm and low fuel demand (when mechanical fuel pump efficiency is allegedly at its highest), that "vapor line" could also serve as a normal fuel return line to keep fuel moving in the lines, with less time to absorb heat radiated from the roadway in the summer months, decreasing the possibility of vapor lock, hopefully.

[60FlatTop]

Going back to the fuel starvation thing, if the feeling is frequent over time the tops of the pistons might already be showing signs of burning through.

 

It is a known issue with V12 Jaguars and some replace the pistons without addressing the fuel problem. I am back to minutely studying the secondary spark signatures.

[NTX5467]

On ignition coils, I'll admit that I fully do not understand all of the dialogue around certain coils having different resistances and such.  Every time I have tried to verify those resistance numbers, what I got was nothing like the specs.  I could verify conductivity, but little else.  When I did replace an older coil with a new one, thinking the old one was not as good as it should have been, in the 1990s, even the ACDelco coil had no numbers on it, only a small elliptical gold tag with the "C" word on it.  The engine ran no better with it, so I put the OEM coil back on.

 

In the middle 1980s, Chevrolet released a different HEI coil for the Camaro L69 4bbl V-8.  Had different color codes on the wires.  I ended up with one of them and put it in my '77LT 305.  The car ran no different at any operational situation.  Yet, Chevy apparently felt it was needed in that application.  BTAIM

 

I remember when the first 50KV coils came out in the 1970s.  Usually bigger with heat sink ribs on them, many times.  The gave the engine that "performance" look of power, which could be important back then, to compliment and aftermarket carb, intake, and headers.  The general perception was that EVERY spark was 50KV, which had to be better for just driving around, with sparks that would start a forest fire.

 

Then, it was mentioned at a Holley Carb seminar, by the engineer-presenter, that a coil would only produce enough spark to fire the plug each time it fired.  If all it needed was 10KV, that's what it produced.  Which kind of blew holes in the earlier perception!  Which also made the comments I read in the earlier 1970s about wider gaps between the rotor tips and the spark plug wire contacts in the distributor caps, as to the wider gaps being "performance-robbing", inaccurate, too.  Just made the coil build up a bit more juice to fire the plug, just like the wider plug gaps the HEI coil could potentially fire.

 

The main advantage of an electronic ign system is higher rpm spark accuracy.  In some dyno tests in the later 1960s, the elec ign systems would produce another 10 or so horsepower just because the sparks were consistent and accurate, although "point bounce" was not detected.  All with stock OEM or replacement stock coils of the time.

 

As things have evolved, with respect to stock replacement coils for 1960s ign systems, to me, OEM stock is best, even if it might be OLD.  As long as it works, it's good, AFAICD.  Now, it can be easier to procure high KV aftermarket ign system coils, which can be a consideration.  Pertronix and others have such coils they sell to go with their ign kits, which is fine and good.  Also taking the coil out of the conversation should things not work!  Just like camshaft companies not wanting to warranty their camshaft if you didn't buy the lifters from them too.  From experiences with up to 11.0+CR 7000+rpm Z/28s in the late 1960s, those 30KV coils will work with other high compression motors, too.  Remember, that's all we had back then and they worked fine.

 

Over the years, I've come to realize that for a reasonably stock motor, factory specs are only a starting point, of sorts.  Meaning that if the specs are deviated from a bit, things will still work pretty well.  Depends upon what the perceived issue might be and how close to the desired specs things might be.  To me, having a float setting a 1/32" lower than spec will not cause the engine to run badly, for example, as long as the fuel pump supplies fuel sufficiently to keep the main jets in the bottom of the fuel bowl covered.

 

My possible obsession is with ignition distributors to fire the spark plugs accurately.  Meaning that every cylinder gets fired at the exact time in relation to TDC.  Which is one item that should contribute to engine idle smoothness.  Wear on the distributor breaker cam becomes the issue here as the wear appears to be inconsistent between the breaker cam lobes.  Which means the point gap will not be the same on each cylinder.  Which then relates to the dwell not being the same, when then affect when the plug fires in each cylinder.  Which then builds the case for a "non-wearing switch mechanism" to trigger firing the coil.  Whether from a magnetic-impulse mechanism or an LED/shutter drum situation.

 

I saw an illustration of how "sizing" of the condenser related to which part of the ignition point contact pair the "peaks and valleys" accumulate on.  If the condenser was under-capacity, the erosion was oriented toward one contact, if it was over-capacity, it was oriented toward the other contact.  Which meant that having one which was "more/just right" would mean lessened erosion in either direction.

 

I remember the original Ford TFI module debacle.  Never did follow it to see what was changed.  If it was a "heat" issue, then moving the module to a cooler locale and a better heat sink, that's good as long as using it in that same orientation in its "new home" is followed.  BTAIM

 

Enjoy!

NTX5467

[60FlatTop]

40 minutes ago, NTX5467 said:

n some vehicles, I suspect their fuel system was not fully-evolved when produced, so rather than change all sorts of production specs, it was easy to configure an inline fuel filter with a 2nd output fitting for a return line, then just add the metal lines to the tank to the car.  These items were usually termed "vapor separators".  Of course, the additional fitting would need to be positioned pointing upward so any vapors might collect there rather than being forced into the carburetor float bowl area and then into the atmosphere via the bowl vent valve.

Here is an interesting excerpt from the Jaguar XJS Handbook https://www.jag-lovers.org/xj-s/book/Jaguar.html  :

 

SURGE TANK VENTING: The vent line from the surge tank doesn’t go to the vapor separator, as one might expect.
Instead, it connects back into the main tank about 2” above the bottom. However, this is not a simple opening into the
tank. Inside the tank, this fitting continues as a tube that makes a couple of bends and terminates with an open end
pointing upward a couple of inches from the top of the tank.
Meanwhile, the fitting for the return line from the engine compartment is at the bottom left rear corner of the tank.
Inside the tank, this fitting continues as a tube that runs across the rear of the tank -- there are actually a couple of clips
brazed to the inner surface of the tank to hold the tube in place -- and then bends upward and terminates with a 180º
hook that pokes its end down into the opening of the pipe from the surge tank fitting described above. The connection
of the two pipes is not liquid-tight; if you tip the tank over and pour a liquid into one of the fittings, it will leak out of the
connection within the tank. But it doesn’t appear to be a very loose fit; the tube from the return line appears to nearly
fill the opening in the end of the tube from the surge tank vent.
In other words: the fuel returning from the engine compartment passes through the main tank but really goes directly
back to the surge tank, with a leaky connection inside the main tank to allow air to bleed out or somethin

[NTX5467]

8 minutes ago, 60FlatTop said:

Going back to the fuel starvation thing, if the feeling is frequent over time the tops of the pistons might already be showing signs of burning through.

 

It is a known issue with V12 Jaguars and some replace the pistons without addressing the fuel problem. I am back to minutely studying the secondary spark signatures.

As always, using a borescope to inspect the top of each piston/combustion chamber might be needed before tearing things apart.  Borescopes are relatively inexpensive, depending upon quality and resolution.

 

NTX5467

[RivNut]

Any chance the vent hose (loops over the filler neck) is clogged?  At speed, there’s not enough fresh air replacing fuel in the tank causing a vacuum in the supply line / fuel pump. 

[XframeFX]

On 2/3/2024 at 7:01 PM, Cornpanzers Riv said:

after I bought a brand new pump from Napa.

Wow, a lot to digest here. A great round table on a multitude of possibilities. However, the fuel starvation under load can eliminate ignition with the pinching-off of the 1/4" return line. 50% towards a resolution!

 

However, to follow-up on what has been discussed here. Common theme is that Jobber replacement parts are not what they used to be and muddied with "aftermarket performance" parts. The line between them has faded away. One-size-fits-all and manufactured over-seas. Some are even reverse engineered:

 

1) From other posts, the only GOOD mechanical fuel pump is a rebuilt unit But if DIY with a kit, beware of substandard components in some of these Kits. One kit instructs the purchaser to scavenge parts off the old diaphragm! For a new replacement, Local NAPA Canada stocked a Nailhead Pump. It was not an Echlin. Instead, a cheap Spectra-Premium, so was the heater-core, both NAPA.

 

2) Comparison of ignition coils still seem to be rated by max secondary voltage by some. With all the specs out there, turns ratio, milli-henry and primary resistance. The latter is best for application. Basically any coil greater than 1.5 ohms (w/ballast resistor) up to 3 ohms is for old style breaker points using coil saturation method. For current limiting method, primary coil resistance of .7 ohms  or less (no ballast resistor or breaker points).

Interesting to note that aftermarket is packaging <.7 ohm coils in traditional "cans" for retro-fit and claiming "High Performance". OE had transitioned to E-Core coils long before abandoning distributor ignitions. No doubt aftermarket offerings are confusing. They target the plug 'n play crowd.

 

3) When researching those aftermarket offerings, I resorted back to Ford's TFI and GM's HEI. Dave R's small body cast iron conversion uses HEI but best to use a coil not hotter than .7 ohms because of the small 4" diameter cap. The DUI 5.25" cap Nailhead HEI is slick. For one, No cast iron body! Also, it comes with a hot E-Core HEI coil and optimal advance curve.

For now, I have the Ford TFI working great. $9 for junkyard TFI, $16 thermal paste and $89 for new MSD Blaster II .7 ohm coil. This is like Pertronix customer testimonials, too easy, points are gone, don't look back! But I still use points to trigger the TFI but will not degrade and last forever.

An interesting rant on TFI ignition: https://www.promracing.com/tfi-distributor-shutter-wheel.html

 

4) Analysis of secondary Voltage patterns as Bernie eluded to, very useful. A Pico-Scope (has the best SW) should be 2nd to a good dial-back timing light with tachometer as must-have tools. I have neither, forever prioritization on project expenses. I continue struggling with what I have, analysis tools from the 80s. If unlimited resources, a third item would be a wideband air/fuel instrument. Interesting how many do not analyze, preferring plug 'n play. Aftermarket loves those guys.

 

Would like to learn what final fix on the original issue will be.

 

 

 

 

 

 

Edited February 12 by XframeFX (see edit history)

[NTX5467]

On 2/5/2024 at 1:00 AM, XframeFX said:

TFIs were relocated from the distributor to a heat sink mounted on a fender well because the engine would die when too hot. Most recovered when cooled. I believe a class action law suit was registered.

 

They have a direct path to the coil bypassing the electronic timing module for "Start". It can be enabled by opening a connector in the harness near the TFI module to set base timing. This path is primarily used for "Start" but is also a backup, limp mode and sends a diagnostic signal.

 

I am using only the "Run" path, no backup. Again, I keep a spare module in the glovebox.

 

If TFIs were bad back in the 90s, there are QC issues with new replacements today, even Motorcraft brand.

 

So far, I'm impressed. Operates as low as 9 Vdc (ballast resistor), will fire any coil (current limiting trigger), will power down if no pulse is present (key left ON) and rock solid dwell. Above all, a simple install. The 2 holes in the heat sink line up with two of the three holes on the fender where the Voltage Regulator was.

 

An interesting read/rant for a Ford Shutter Wheel:

https://www.promracing.com/tfi-distributor-shutter-wheel.html

Here's the address for a "Dead Dodge Garage" YouTube video on how to use a GM HEI module in anything with your choice of ign coils.  Just be sure to remove the locating nubs on the back of the module, plus apply the heat sink material.    www.youtube.com/watch?v=Avp0Lzw83e4   or just Google "Dead Dodge Garage HEI module" and it'll probably get to the same location.

 

NTX5467