Excessive fuel pressure with rebuilt fuel pumps?

[lancemb]

I have now had this problem twice and wondering if anyone else has and/or what can be done about it?

Twice now (once on a 58 and now a 57 - same pump number) I have installed a newly rebuilt pump with the new type of diaphragm that is supposedly impervious to newer fuel, only to have it cause fuel to gush out of every orifice. Both cars ran well on with old pump (being replaced for good measure and to have original style). Neither had any issue with carburetor, just too much fuel pressure.

On the 58 I put a regulator on but after a short while the pent up pressure in the pump caused the seal to blow out the top. Plus the regulator looked terrible. I put an NOS AC pump on and the car ran perfectly. Now, I have the same problem; I bought a newly rebuilt pump thinking the other one was some fluke or I had somehow messed something up (although don't know how that would be possible).

I already ordered an NOS pump but this does not seem like a good long term solution. Eventually I will need another one and there are more of these cars on the road than there are NOS pumps.

Any solution to this? What is it about these new diaphragms that cause excessive pressure? Is there a way to mitigate this?

[old-tank]

It would be nice to know the actual pressures of the two pumps....

[lancemb]

It would be nice to know the actual pressures of the two pumps....

I agree that would be nice but I don't have a gauge. Plus I don't want to spend the extra time and money unless there was some solution that could come from it. If there was a way to adjust the pump then I would certainly do that! One thing is for certain though; it's too high on the rebuild.

[JohnD1956]

Isn't there an adjustment when assembling the pump?  I remember there being some adjustment in the dual pump for the 56 but honestly can't remember if the adjustment was on the fuel side or the vacuum side, or both.

[buick5563]

I don't think there is an adjustment, but I also don't think it is the material of the diaphragm.

These are just feelings of mine. I can't back them up.

Was anything else done that was fuel related?

Sounds more like a stuck float or bad needle and seat assembly.

[95Cardinal]

I had the same issue on a (new) 73 Chev fuel pump.

Output pressure was about 7 psi. I was enough to cause flooding issues.

This was in my hot rod, so adding a regulator was not an issue.

Set the pressure at 5.5 psi; problem solved.

[lancemb]

I don't think there is an adjustment, but I also don't think it is the material of the diaphragm.

These are just feelings of mine. I can't back them up.

Was anything else done that was fuel related?

Sounds more like a stuck float or bad needle and seat assembly.

The carburetor was not touched (R&R ONLY) and the car ran fine on it just 2 months ago. Replaced the fuel line because it was brittle; that's it.

I just can't think of anything else besides the diaphragm. There aren't too many variables. I wish there was an adjustment built into the pump!

[Caballero2]

Fuel pressure regulators, after market, are available at your Napa store and are manufactured by Holley and others.  I use one on my 1999 Kawasaki mule with a racing electric fuel pump.  Works great.  I think it is more important that your fuel pump and fuel lines be ethanol compatible.

 

Dan

[lancemb]

Fuel pressure regulators, after market, are available at your Napa store and are manufactured by Holley and others. I use one on my 1999 Kawasaki mule with a racing electric fuel pump. Works great. I think it is more important that your fuel pump and fuel lines be ethanol compatible.

Dan

Dan, I tried this tbe first time I had this problem on my 58, and the pressure was so great that after a couple hundred miles the pent up pressure blew the seal out from the top of the pump, sending gas pouring everywhere!

[old-tank]

I agree that would be nice but I don't have a gauge. Plus I don't want to spend the extra time and money unless there was some solution that could come from it. If there was a way to adjust the pump then I would certainly do that! One thing is for certain though; it's too high on the rebuild.

http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html  ...handy tool everyone should have.

Even I can afford this one.  Numbers are important if only to tell the fuel pump rebuilder that the pump has too much pressure and how much.  In a mechanical pump the pressure is controlled by the valves.  As noted some float valves in the carburetor are more sensitive to just slightly higher pressures and in this case yours may be marginal and about to fail with any pressure.

Like troubleshooting computer problems:  don't "skip this step and try something else"

[Beemon]

When I rebuilt my fuel pump, the shop manual makes it clear not to stretch the diaphragm on assembly or else your fuel psi goes up towards 11. Could have just been a bad rebuilder, too.

[Joseph P. Indusi]

I agree with Beemon. The older shop manuals said to be sure to not stretch the diaphragm during assembly. If it is too tight the pressure will be high and the volume somewhat lower. I seem to recall putting a slight pull on the center post of the diaphragm and then tightening the screws holding the gas pump chamber to the body of the pump.

Joe, BCA 33493

[NTX5467]

To me, this sounds highly unusual!  I can't envision too much fuel pressure causing pressure regulators to fail or a needle/seat assembly "holding" that much pressure by themselves.

 

What I CAN envision is a rubber-tipped float needle failing from ethanol'd fuel and then allowing a very compromised control situation, which can also be similar to a float level that was very much "too high", resulting in the "leak" situation.

 

I believe the Holley "higher performance" mechanical (rebuildable) fuel pumps have a spec pressure range from 5.5-7psi.  I can't see why any other pumps would have a different operating pressure range.

 

The OTHER thing I can envision is a new fuel pump having some "trash" internally which is flushed out during use, resulting in it getting to the needle/seat and not letting them seat correctly.  But this would have to get through a filter to get there, so that might be "out".

 

One possible "fix" would be an inline fuel filter with a "return line" on it.  Chrysler had some on their higher-performance engines in the early 1970s or so.  This would allow any excess fuel "not needed" to be returned to the fuel tank, just as a "three-line" fuel pump would (one line being a return line).

 

I strongly concur on the ethanol-resistant diaphragm material.  I just haven't seen the situation you mention in my own experiences.  Sorry.

 

NTX5467 

[lancemb]

To me, this sounds highly unusual! I can't envision too much fuel pressure causing pressure regulators to fail or a needle/seat assembly "holding" that much pressure by themselves.

What I CAN envision is a rubber-tipped float needle failing from ethanol'd fuel and then allowing a very compromised control situation, which can also be similar to a float level that was very much "too high", resulting in the "leak" situation.

I believe the Holley "higher performance" mechanical (rebuildable) fuel pumps have a spec pressure range from 5.5-7psi. I can't see why any other pumps would have a different operating pressure range.

The OTHER thing I can envision is a new fuel pump having some "trash" internally which is flushed out during use, resulting in it getting to the needle/seat and not letting them seat correctly. But this would have to get through a filter to get there, so that might be "out".

One possible "fix" would be an inline fuel filter with a "return line" on it. Chrysler had some on their higher-performance engines in the early 1970s or so. This would allow any excess fuel "not needed" to be returned to the fuel tank, just as a "three-line" fuel pump would (one line being a return line).

I strongly concur on the ethanol-resistant diaphragm material. I just haven't seen the situation you mention in my own experiences. Sorry.

NTX5467

It seems strange, I agree. But I'll see how it runs on the NOS pump and report back. I've had the same situation twice though on two different cars.

Also, after thinking about it and seeing the previous posts the diaphragm being the issue makes sense. If it stretches more than the OEM material (which I believe it does after handling both) it seems likely that it could then displace more volume on each stroke, thereby increasing pressure.

I am returning the pump that just caused this issue, but still have the other one if I want to experiment in the future, perhaps with my other car. I would have bought the pressure gauge and done it now if not for the fact that I am moving in two weeks and literally every hour counts as I start packing up the garage!

[Alfa]

Hi Lance

 

Not wanting to get in the way of house moving (!) but if your rebuilt pump blew the seal out, there is something fundamentally wrong. Either the diaphragm material is inappropriate, as mentioned above, or the travel on the pump is too great (ie the wrong cam follower or something similar).

 

I think it needs another look when you have time.

 

Adam.. 

[60FlatTop]

Fuel pump pressure on mechanical pumps has generally been controlled by the slotted rod on the diaphragm and the pump arm spring. Back pressure slips it to a neutral position. The pumps producing high pressure are probably binding and assembled wrong. Fuel pressure regulators are for electric pumps.

 

I am reminded of a 1932 Hudson Greater Eight that I did a whole bunch of work on to make it capable of going to the corner store for a gallon of milk. One of the tasks was to remove the fuel pressure regulator between the carb and the fuel vacuum tank. (You should have a big grin.)

 

I just looked up at the set of mechanics text books my Mother helped me buy in 1959. They are on the shelf over my computer. Don't they make books like that anymore. I'll have to Google and see.

Bernie

[carbking]

Fuel pump pressure on mechanical pumps has generally been controlled by the slotted rod on the diaphragm and the pump arm spring. Back pressure slips it to a neutral position. The pumps producing high pressure are probably binding and assembled wrong. Fuel pressure regulators are for electric pumps.

 

Bernie

 

Also, the use of the incorrect return spring will effect the pressure.

 

Being in the carburetor business, we have chased our share of wild geese created by improper rebuilds. Most enthusiasts don't think about fuel pressure if their carburetor is leaking. There is a company out there (I cannot mention their name on these forums) rebuilding pumps that has no idea what they are doing. 

 

I CAN mention the fact that this company is NOT Then and Now Automotive, who also rebuild fuel pumps. We have had no issues with pumps rebuilt by T & N.

 

Jon,

Edited October 14, 2015 by carbking (see edit history)

[NTX5467]

Bernie, the situation you describe (on the variable-position pump arm) sounds like a train wreck-in-waiting.  Variable pump stroke?  Well before we had "variable retard valve timing" circa 1968?  I've not known of a variable-pivot fuel pump arm, but then there are things I've never seen, too.

 

I would think that a "stretchy" fuel pump diaphragm would make less rather than more fuel pressure, due to the variability of its "compression" shape (where it would stretch and not push as much through the valve). 

 

NTX5467

[Joseph P. Indusi]

I agree with NTX5467 in Post 18. A diaphragm that is stretched tight will pump at a higher pressure than a loose® diaphragm and that is what the old shop manuals were warning against in their instructions on rebuilding fuel pumps.

Joe

[lancemb]

I agree with NTX5467 in Post 18. A diaphragm that is stretched tight will pump at a higher pressure than a loose® diaphragm and that is what the old shop manuals were warning against in their instructions on rebuilding fuel pumps.

Joe

[lancemb]

I agree, if it is loose. The new diaphragm material (that I have seen) is much more flexible than the original though; a very different elasticity. This could allow more stretching per stroke while not being loose. That's my theory at this point.

Gonna put the NOS pump in my car tomorrow and see how it goes!

[60FlatTop]

Fuel pump operation is described on pages 47 & 48 of the 1959 version of Automotive Fuel, Lubricating, and Cooling Systems by William Crouse; published by McGraw- Hill Book Company. I just pulled it down off the shelf and checked. I was 12 when I bought them. My Mom helped, I think there were four installment payments. Prior to reading the books, my knowledge was limited to one year working in the tire shop and the sharp kick start rap the doctor gave me in September, '48 while he was holding me up by the ankles. It hasn't always been easy.

 

Think about it, what happens when the needle vale on the carburetor closes and the diaphragm is still pulsing.

Bernie

[NTX5467]

The whole issue with fuel "supply" is that it's dynamic.  With the engine running, fuel is leaving the float bowl as more is desiring to enter after the fuel pump moves it in that direction.  The float bowl "float" and "needle/seat" modulate it at THAT location to maintain a reasonably-steady level in the float bowl.  This is where pump capacity and fuel line sizing comes into the mix, which can also relate to the stroke of the fuel pump's push rod.  Pump capacity and the engine's needs are coordinated in the original design phase of the fuel system.  Should something change, which can increase the engine's need for more fuel pump capacity, then line sizing and/or fuel pump capacity (gallons/hour @ a specified pressure) will need some upgrades.  Another pair of items to consider in this mix include the "lobe lift" on the cam lobe or bolt-on eccentric which pushes the fuel pump's push rod and how that relates to the "pump stroke" of the pump itself.

 

Bernie, I did something similar in 1966 for a Motor Repair Manual (1959-1966).  It came while I was home sick with an almost week-long illness (freshman year).  I read that book cover-to-cover!  That was in 1966.  I've still got that book, too!

 

NTX5467

[lancemb]

OK I will stop being hard headed and consider almost anything at this point! Perhaps I do have a carb issue that was not manifesting with the old pump.

So I installed the NOS pump and it was totally dead - no pressure whatsoever so it was probably and old defect put back in the box. Coincidentally I was looking in the trunk of my other 57 and found that I had a spare NOS aftermarket brand in the original style, so I tried putting that one on. Lots of pressure and also fuel gushing out of carburetor again!

Since I am moving and have little time left to pack, I was out of time or would risk not being out of the house in time. Since I won't be able to work on the car in my temporary living location I decided to have it towed over to a shop I've had do work in the past. This gets the car out of my way, and they can rebuild carburetor if needed.

I left them a detailed history of the situation so I am anxious to see what they say. I am guessing carburetor rebuild will be standard as that is the one thing that was not yet done as part of my mega tune up!

[Ttotired]

You would have to say the needle and seat (or float) after so many pumps

 

I am watching this with interest as I need a new fuel pump for my Buick (its spraying onto the block a bit)

 

Mick

[60FlatTop]

Remove the airhorn from the carb and turn it upside down with the needle and float still in place. Blow into the fuel supply fitting. See what happens.

Bernie

[buick5563]

It took me a long time to figure that trick out on my own, Bernie.

Definitely take the top off first though. It tastes funny and makes your tummy hurt if you don't.

[old-tank]

Ok, Bernie I'll bite.  What does the "book" say and what point are you trying to make blowing into an upside down airhorn section other than demonstrate the integrity of the float valve?? 

Two years ago I was troubleshooting a fuel delivery problem I had in 95* + and elevation of 6,000 ft + (it was vapor lock that was not resolved by my electric pump after extended use).  Anyhow pressure tests showed:

1) electric pump only before the mechanical pump = 9 psi (Airtex 5-9psi pump)

2) mechanical pump only at the carb = 5psi

3)electric pump only (but pumping through the mechanical pump) at the carb, engine not running = 5psi

4)electric pump with mechanical and engine running =5 psi

So the mechanical pump will regulate pressure with the valves and the diaphragm with the spring under it.

1955 had two pumps with the later rated at a higher pressure and the only internal difference is the size of the valves and a different spring assembly under the diaphragm (same diaphragm used)

The stroke volume is limited by the cam that the pump rides on.

The pressure would be regulated by the valves and the spring under the diaphragm.

More to  come after I test an upside down airhorn with a pressure gauge (where I have we heard that before  )

Willie

[60FlatTop]

The needle valve should make a nice tight seal. Most have a Viton tip, but even the brass seals well.

I read the book in 1959 and maybe three times since, not counting a couple of days ago. The basics plus the intervening years of actually working on the stuff kind of develops an intuitiveness. 20 years ago, when I did the AFB on my Riviera I had a bunch of parts from a 1958 Lincoln AFB in the pie tin. They were a little different but if they looked bigger or better I put those in. Wait until the next owner finds those!

 

I don't do any of the things "real" hobbyists do; lay the cars up in winter, stabilize the fuel, fight the dreaded vapor lock, switch to radial tires, use zinc additive oil, search for boat gas pumps, or run a degausing line stem to stern. Yeah, I blow in carburetor passages and cut the tags off mattresses, but the stuff works (and you know I wrote "stuff" but wasn't thinking it.).

 

All you need is a few special tools and a good helper.

[lancemb]

So they took the carb apart and said it looked pretty varnished. Not too surprising. I'll probably know more next week!

[60FlatTop]

I wear Diesel jeans when I blow in carburetor air horns, not those little shorts.

 

Bernie

[NTX5467]

{Remove air horn, intact. Invert and pressurize fuel feed passage in carb orally.  Breathe through nose ONLY!}

 

Even with a good lever arm for mechanical advantage, I don't really see the float (in the above scenario) being heavy enouth to keep the needle in place when the passage is orally pressurized more than a "sigh".

 

The Carter AFB and AVS Strip Kits had a few different needle/seat assemblies, with different orifice sizes.  An "oversize" needle/seat orifice would slow down the fuel's speed in the line, allowing it to accumulate more under hood heat, which might cause other issues of vehicle performance at lower rpms and fuel needs.

 

Hope y'all weren't doing that with leaded fuel!

 

NTX5467

[TexasJohn55]

Maximum fuel pressure is determined by the diaphram SPRING, the other components only determine flow rates.

[buick5563]

{Remove air horn, intact. Invert and pressurize fuel feed passage in carb orally. Breathe through nose ONLY!}

Even with a good lever arm for mechanical advantage, I don't really see the float (in the above scenario) being heavy enouth to keep the needle in place when the passage is orally pressurized more than a "sigh".

The Carter AFB and AVS Strip Kits had a few different needle/seat assemblies, with different orifice sizes. An "oversize" needle/seat orifice would slow down the fuel's speed in the line, allowing it to accumulate more under hood heat, which might cause other issues of vehicle performance at lower rpms and fuel needs.

Hope y'all weren't doing that with leaded fuel!

NTX5467

It actually does work, Willis.

Think about it. It only has to resist to less than 9 lbs. max.

Realistically more like 4-9 like my electric.

Edited October 24, 2015 by buick5563 (see edit history)

[lancemb]

I wear Diesel jeans when I blow in carburetor air horns, not those little shorts.

Bernie

That's good. You probably wouldn't look as good in them.

[MrEarl]

Dang it, had pinned this one for What's Happening on the Forum but the word count got exceeded about 10 posts ago....

Looking forward to the outcome though...

[60FlatTop]

I'm wondering how many have flipped and air horn over and blew into the fuel fitting. They'd get a pretty good lesson in spirometry.

Bernie

[NTX5467]

5563, to me, I can do what I feel is a good check of how the needle/seat might be by actually looking at the contact pattern on the needle's "tapered area" and then where it touches the "seat".  Looking for consistency of sealing area and integrigy thereof.  Works for the Viton-tips, too.  Of course, the float level adjustment would need to be correct, too.

 

I don't recall any of my automotive "mentors" EVER advocating doing what Y'all are allegedly doing with a carburetor!!  Even the "older-timers" with a strong shade tree!

 

(Learn something new every day!!)

 

NTX5467

[TexasJohn55]

 

5563, to me, I can do what I feel is a good check of how the needle/seat might be by actually looking at the contact pattern on the needle's "tapered area" and then where it touches the "seat".  Looking for consistency of sealing area and integrigy thereof.  Works for the Viton-tips, too.  Of course, the float level adjustment would need to be correct, too.

 

 

(Learn something new every day!!)

 

NTX5467

Willis, good theorizing but not very useful on new needle and seat.

[lancemb]

Well it's official! A good cleaning and rebuild of the carburetor and the fuel pump works fine. It was reading just under 7 pounds. Well I grew up working on fuel injection systems of the 1980's and early 90's so carburetors are something I am not well informed on yet I guess as I have never seen this where a car runs seemingly okay on one fuel pump and then needs a carb rebuild on another, but I guess the other one was just weak. It's crazy to me that I had this experience before and had a different outcome, and that threw me off. I hope this thread helps somebody else or there!