Advice needed : GM HEI Distributor Failure

[Electra63]

Hello folks.  I need some help/advice about the GM HEI ignition distributors

 

I purchased a 63 Buick Electra about 18 months ago.  The previous owner upgraded the ignition system by installing the black cap HEI type distributor.

It has run fine since I've owned it.  It always fires up first time (except when its been sat for a bit and needs a few cranks to get the fuel moving).

So last week it was too wet to drive it so I left it idling with the garage doors open.  I was busy with another job in the house and when I returned 10-15 minutes later the car had stopped running.  I tried to re-start it and nothing.

So after some investigation I verified the fuel system was OK and determined that it was an ignition problem.

After removing the distributor cover and doing some further research about these HEI units I noticed that the black carbon button in the cover has burned/eroded away and there is a corresponding burned/etched area on the pickup tab on the rotor arm.  See photos

The main coil checks out and at this stage I don't think its the pickup module.  I believe the carbon button eroded away and lost contact with the rotor arm.  I can also see some slight rubbing/heat marks around the hole in the cap where the button pokes through (photo).

The cap/rotor on the original do look a bit cheap so I have purchased a MSD replacement cap and rotor which are a direct fit and look to be of better quality.  The kit also came with two new carbon buttons - one regular and one low resistance.  The low resistance one is  supposedly to be used with the high output MSD coil.

 

So I have two questions before I install the replacement parts:

 

1.  Based on this information does it make sense that the carbon button could just wear out and cause this failure?  I read that the rotor and button should be considered wear items....or could there be another underlying cause of this failure that I haven't seen (yet)

 

2.  Bearing in mind that I'm not replacing the original coil with a high output coil at this point, I'm considering installing the low resistance carbon button anyway as I don't think it can hurt?   Or should I stay with the regular button?  They are the exact same size just different material composition.

 

An other recommendations ?

 

thanks !

 

 

[old-tank]

That is not the problem,  Even with no button the spark would jump that distance.  Most often it is the module.

[Oldtech]

Module or Rotor.  The Rotor can Puncture through under the tab effectively grounding out the spark.  Early white ones probably the worst.

It can also be a broken wire from the pickup unit. They flex with the vacuum advance and will break inside the insulation. 

Edited January 21 by Oldtech (see edit history)

[Electra63]

13 minutes ago, old-tank said:

That is not the problem,  Even with no button the spark would jump that distance.  Most often it is the module.

OK thanks.  I'm going to check the module too

[Electra63]

6 minutes ago, Oldtech said:

Module or Rotor.  The Rotor can Puncture through under the tab effectively grounding out the spark.  Early white ones probably the worst.

thanks.  Yes I saw another forum about the White units....  No idea where this one was purchased from. 

Previous owner had a friend with a shop and they seem to have done a decent job from other work I saw but I'm pretty sure on this HEI unit they just bought a cheap one that was suitable.

I'm going to fit the new cap and rotor and give it a go.  If, as old-tank says, its the module, then I'm sure I'll know pretty quickly...

the carbon button is shot and I dont like the look of the burned area on the arm so I'm replacing those anyway.

Edited January 21 by Electra63 (see edit history)

[Electra63]

Update

Well it looks like old-tank was right.  I fitted the new rotor and cap, tested the ground of the distributor etc and all ok. 

Fired up the starter and... nothing.

Off to buy a new module now. 

Someone ex GM on YouTube recommended getting a NOS Delco module as the older versions seem to be more reliable than the new no-brand/imported units.

Anyone else agree with that ? 

 

Thanks for reading!

[TexRiv_63]

Buy two modules and keep the spare in your glovebox.

[Electra63]

9 minutes ago, TexRiv_63 said:

Buy two modules and keep the spare in your glovebox.

Right thanks.....plus the tools to change it roadside in an emergency if needed I guess 🙄

[NTX5467]

One winter when the weather was very cold, a C-30 with a utility bed was towed in.  Complaint was "No start".  Our tune-up tech got the job and started investigating.  He found a completely missing carbon contact between the coil and the rotor.  Yet it ran when it was parked, when it was warmer.  Replaced the cap, button, and rotor with OEM GM items, considering it was at the dealership.  Plugs were also checked and they were wide-gap too.  New ACDelco spark plugs.  THEN it started and ran as it should.  The GM HEI, with the standard coil, is designed to fire spark plugs with a .100" plug gap, but it was also noted that plug wire condition became an issue past about .080" plug gap.  Some mid-'80s Olds engines had a .060" to .080" plug gap OEM.  THESE things prove the power of the standard coil!

 

Perhaps MSD's quality is better now that the Holley group owns it?  After a multitude of ownership changes over the past 20 years.

 

The electronics of the GM HEI module are supposed to be pretty trick, from what I've read.  Some replacement companies talk about them in the dialogue for THEIR products, neglecting to say the stock GM HEI module has the same attributes.

 

Be SURE to use the heat sink paste with the module, between the module and the distributor housing!  PLUS that the coil is grounded too!  Those two areas, other than the noted wear areas, are the "common" things about HEIs not working as designed.

 

IF you buy quality parts, should be no worries about having to change them on the side of the road.  Which is why making sure the coil is grounded and the heat sink paste is under the module.

 

Enjoy!

NTX5467

Edited January 21 by NTX5467 (see edit history)

[EmTee]

Be sure to smear a thin coating of the thermal grease on the underside of the new module and ensure the mating surface on the distributor is clean.  Heat generated within the module is supposed to be transferred to the distributor housing.  If this isn't done the module will run hot and fail prematurely.  A small capsule of thermal grease should come packed with the new module.

 

Edited January 22 by EmTee (see edit history)

[Electra63]

Thanks emtee

Yes I have specifically ordered a module that comes with the thermal grease packet. 

I'll probably be fitting it later this week and then hopefully I'll be back on the road 

[EmTee]

When HEI became standard equipment in GM cars for 1975 I remember a period of a few months where it seemed that a new GM (mostly Pontiacs for some reason) would be towed-in for a 'no-start' condition.  After diagnosing the first two or three we simply came out with a rotor and screwdriver right off the bat.  The early rotors would be burned-through and ground the spark to the distributor shaft.

[60FlatTop]

I agree with the heat sink grease comments. It is an over the counter thing that comes in a tube, used to be at Radio Shack as well. Some of the 50 year old cars with HEI may be running with dried out grease. Taking a look should be on the service checklist.

 

In recent years I have started buying off the shelf computers. I used to have them custom built and they had a 12-14 year life span. Twice I had to replace the dried heat sink grease om processors at about 10 years. It is the same stuff. So if you do have an HEI unit it is something to be aware of.

 

 

[Oldtech]

19 hours ago, TexRiv_63 said:

Buy two modules and keep the spare in your glovebox.

If you do that the one in the distributor will last forever!

[Electra63]

1 hour ago, Oldtech said:

If you do that the one in the distributor will last forever!

😂...of course

[Electra63]

2 hours ago, 60FlatTop said:

I agree with the heat sink grease comments. It is an over the counter thing that comes in a tube, used to be at Radio Shack as well. Some of the 50 year old cars with HEI may be running with dried out grease. Taking a look should be on the service checklist.

 

In recent years I have started buying off the shelf computers. I used to have them custom built and they had a 12-14 year life span. Twice I had to replace the dried heat sink grease om processors at about 10 years. It is the same stuff. So if you do have an HEI unit it is something to be aware of.

 

 

Right.  I had a similar experience with a TV.   An original Sony flat screen lasted me 15 years and was still working fine when I donated it to Goodwill.  The replacement lasted 5 years....and when I did some in depth research it seems the some of the electronics are now designed to be at or close to the limit in certain components that are heat sensitive so they're effectively wear parts.  From what I've read over the last few days I've learned to consider these ignition modules to be similar - i.e. wear items that will eventually give up due to heat cycling.  Not if, but when....

I will certainly be paying attention to getting an even film of grease on the whole back surface of the module.

Its unfortunate that the failure on this module seems to have also cost me a new distributor cap and rotor arm, but that's the way the cookie crumbles sometimes I guess.

I'm just thankful that it happened when it was idling in front of my house and not on a busy 5-lane LA highway !

[Electra63]

Update. I received and fitted the new module.  It was running rough so I had to tweak the timing. 

After removing the vacuum advance connection I set the timing at the 12 degrees advance mark and it now idles nicely but a slight misfire when I jab the throttle.  

I had to go out of town for 10 days but when I'm back I'll try to fine tune the timing. Any hints on this ?  Does a misfire on acceleration usually mean too much or too little advance?  Just so I know which direction I should try to finesse it. 

It was running great under all conditions before the module failed.

Oh and just to confirm I tested the ground and it's 100% and also made sure I have a full 12v to the distributor 

 

Thanks 

[NTX5467]

Initial timing should NOT affect misfires happening.  Although it there it too much initial timing, it can cause pinging on acceleration.

 

Where did you get the module from?  Just curious.  Seems to be many issues, of late, with ignition components from Asia failing right out of the new box or causing other ignition issues.  From condensers to control modules, etc.

 

NTX5467

[EmTee]

There may be one or more fouled spark plugs caused just before the old module quit.  Try a cylinder balance test - ground each spark plug one at a time and note the RPM drop.  Check the plug and wire associated with a cylinder that doesn't cause an idle speed drop similar to the others.

[Bloo]

Module replacement should have NO effect on needed timing. If it were me, I would set it where it was before, when the car ran correctly. Otherwise you are just adding complication. Experiment with timing after it is fixed. Some thoughts about HEI problems:

 

Where did you get that black HEI rotor? Those were a KNOWN PROBLEM GM part from circa 1975. They can burn through and cause the car to stop running. It was common knowledge to replace any black HEI rotors that you find on sight in the 80s. I believe I have also seen a GM TSB of some sort to that effect, but long ago. I haven't even seen one of those black HEI rotors since the 80s. The replacements are white. They can burn through too somewhat, or at least lose energy through the plastic. Energy lost down through there will cause extreme rapid wear of the mechanical advance mechanism, so white ones shouldn't be left in forever either, but at least the car probably wont stop running and need a tow. Aftermarket rotors in other colors like white, blue, grey, red, etc. are generally fine.

 

I see you replaced the cap and rotor with new aftermarket (MSD). Good. For others reading this later, the cap really did need to be replaced too. That was arcing just above the rotor because of the bad carbon, and that raises the spark voltage. It will try to blow out of the insulation everywhere. HEI caps have places where spark energy can blow through to ground at the coil or coil screws. It is much more of a problem on 6 cylinders that eights because of the contact locations in the cap, but eights fail too and no way would I trust that cap after seeing that button, even if the cap looked fine. To answer your question though, carbon buttons are not a common failure, more like an occasional failure. It's always something that should be looked at.

 

Plug wires should be tested. Assuming you don't have an automotive scope laying around, just ohm test them with a multimeter. It doesn't necessarily prove them good, but it would prove they weren't the source of the failure. Resistor wires should be in the kilo-ohms, probably somewhere between 2k and 8k, but the main thing is the resistance values (Kohm) should go up with length. If you find one radically different, much higher than the rest, or if one is much higher than the others but in the middle somewhere for length, get new wires.

 

In my opinion run your spark gap at .045" .

 

In an HEI there is a ground for the coil. It might be a strap or a wire, and on anything old enough to have a black rotor in it, it is a wire unless someone replaced it. There are 5 pins on an HEI cap, and if you have four, the strap or wire is missing. The car will sort of run for a while, and it is super common to find them missing. The spark energy will damage the coil, usually blowing a hole from a wire to ground that you can see but not always. Sometimes it ruins the module. The strap version goes in under the coil before you put it in. The wire version goes on a coil mounting screw up on top. If you find the strap or wire missing, just get a new coil.

 

Regarding a stumble, sometimes the wires on the pickup in the base of the distributor can fatigue and break. The vacuum advance is constantly moving those wires. To check for this, and also to check for a bad vacuum advance, (a 2-for-1 check!) do the following. Retard the timing quite a bit, but so the car will still run. Hook a Mityvac (hand vacuum pump) to the vacuum advance and pump it up. The vacuum advance should hold vacuum. If it doesn't it's bad. If the engine cuts out when the vacuum advance moves, those wires on the pickup are probably fatigued and broken, and you need a new pickup (or distributor,). The retarded timing is just to make sure that excessive timing from vacuum causing the engine to try to kick back on itself does not fool you. Put timing back.

 

One more thing, your vacuum advance may (probably) have too much advance. The aftermarket makes vacuum advances with stop kits, and also stop kits separately. Whether you need it or not is anyone's guess, but HEI was introduced in about 1975(?) and I think nearly everything had EGR by then. An engine with EGR needs more vacuum advance than one without. Vacuum advance cans with too much advance are laying everywhere. This often isn't noticed on HEI, but I think the reason is that most old HEIs didn't have their rotor changed very often and the centrifugal advance barely works due to extreme wear. This is not good for best performance, but masks an over-aggressive vacuum advance, so often goes un-noticed.

 

Make sure the vacuum hose doesn't leak. If this is a stock engine, or close, be sure to connect it where Buick connected it, most likely ported vacuum.

 

[NTX5467]

Over the years, I have heard about HEIs having the propensity for the mechanical advance mechanism to stick.  In my case, on my '77 Camaro 305 I bought new, the mechanical advance has never stuck.  A quick twist of the rotor tests that.  It's not got over 700K on that same distributor with no issues.

 

When I did the cam and carb upgrade at 92K miles, I pulled the HEI apart to check and clean it.  Some "soft varnish" prevented an easy removal of the distributor shaft, but a quick dose of carb cleaner fixed that.  No bushing wear.  Everything worked freely, so ai cleaned and lubed it before it went back in.

 

After about 22 years, I had the cap off looking at things.  I touched the center of the HEI module and it moved.  It was the original.  It was basically sitting there until I touched it  When I got ready to go to work, the car would not start.  IF I'd hit a bump enough to jar the module, the car would have died immediately.  A new module fixed it.

 

In earlier times, FEW people knew about the carbon button and that it was the wear interface between the coil and rotor.  Some cars came in, running flaky, and the button was gone from wear.  It was available separately from GM Parts, but came with all new coils.  The coil ground is often overlooked.

 

Enjoy!

NTX5467

[Electra63]

19 hours ago, NTX5467 said:

Initial timing should NOT affect misfires happening.  Although it there it too much initial timing, it can cause pinging on acceleration.

 

Where did you get the module from?  Just curious.  Seems to be many issues, of late, with ignition components from Asia failing right out of the new box or causing other ignition issues.  From condensers to control modules, etc.

 

NTX5467

Module was from eBay from a US seller and it's a genuine Delphi part.  I tried to find a genuine brand name to avoid any quality problems.....open to feedback on that 

[Electra63]

Thanks for all the replies!  Plenty to digest.

I'll be digging into this again at the end of this coming week when I'm back home. 

I appreciate you all taking the time to share your experience and advice 

[NTX5467]

"Delphi" was what happened when GM spun-off their OEM radio (Delco), steering gear (Saginaw), and a few other sections which they used for OEM GM items, but they were also doing work for other OEMs by contract.  It might now be as close to an ACDelco part as it can be, but now being a private entity, no real way to know.  FWIW

 

Just some thoughts,

NTX5467

[XframeFX]

On 1/21/2024 at 10:31 AM, Electra63 said:

The previous owner upgraded the ignition system by installing the black cap HEI type distributor.

Some great advise from experts here. But much talk on the evolution of the HEI system. Obviously, Nailheads never had this unit installed. Electra63 even indicated so.

Instead of aftermarket parts on an OE system, were looking to source and install OE grade components on an aftermarket system.

If this is a Davis distributor, I'd replace with a cap and rotor (blue) from DUI. Much of their components are Made-in-USA.

If indeed a DUI distributor, that black rotor is likely not original

From: https://performancedistributors.com/product/gm-heidui-v8-cap-rotor-kit/?attribute_pa_color-choice=black

 

 https://performancedistributors.com/product/buick-nailhead-dui-distributor/

 

[NTX5467]

The DUI ignition is a good upgrade from the basic HEI system, which Davis has expanded to many other non-GM engines.  Even with the HEI module attached outside of the normal OEM distributor cap of many vehicle brands.

 

To muddy the waters a bit on ignitions, check out all of the information and videos at www. progressionignition.com.  A bit pricey, but with many features of a "computer-controlled" distributor, including an anti-theft feature.  With using a modern cell phone to control and adjust it.  Quite neat stuff, for a price.  I found this from a mention in another GM vehicle forum.  I don't recall a Nailhead application, though, BUT it looks like the guts that run the system would fit inside of a GM points-style distributor, just from what I can see in their videos.

 

Enjoy!

NTX5467

[Electra63]

On 2/2/2024 at 8:24 PM, NTX5467 said:

"Delphi" was what happened when GM spun-off their OEM radio (Delco), steering gear (Saginaw), and a few other sections which they used for OEM GM items, but they were also doing work for other OEMs by contract.  It might now be as close to an ACDelco part as it can be, but now being a private entity, no real way to know.  FWIW

 

Just some thoughts,

NTX5467

Thanks.  This makes me more confident in the (Delphi) module I purchased....although these days you never know 100% if its a knock-off or the real thing.

I went to the official Delphi website and the photos look the same as what I received form the ebay vendor so fingers crossed....

I'll be doing some more investigation into the misfire over the weekend.

[XframeFX]

6 hours ago, Electra63 said:

I'll be doing some more investigation into the misfire over the weekend.

Misfire? Please keep us posted on progress and nature of misfire.

[Electra63]

One other question....

What should the spark plug gap be with the HEI distributor? 

Does everyone agree with the .045 advised by Bloo earlier in this thread ?

Thanks 

Edited February 10 by Electra63 (see edit history)

[old-tank]

Check the spark plug wires with your ohm meter.  If carbon core wires, all that manipulation may have damaged them internally.  Also if you have platinum or other exotic electrode plugs ( these plugs if fouled do not recover well), replace with common resistor plugs.

[Bloo]

3 hours ago, old-tank said:

Check the spark plug wires with your ohm meter.  If carbon core wires, all that manipulation may have damaged them internally.  Also if you have platinum or other exotic electrode plugs ( these plugs if fouled do not recover well), replace with common resistor plugs.

 

THIS^^^ Resistor wires should measure a few Kohm and get progressively higher in resistance proportional to length. Bad ones overstress the new ignition parts.

 

Always troubleshoot with standard issue plugs if you can. It can't be repeated enough. Platinum plugs of the sort used back in the 1990s can look perfect in a visual inspection, give a perfect pattern on a scope, and still be misfiring. It probably still holds with modern versions. I'm not going to throw shade if anyone wants to try it, after all modern cars use platinum and similar exotic plugs. Nevertheless, get them out of any older engine that doesn't require them while you are trying to solve a problem.

 

[Electra63]

thanks Bloo & OldTank.  I'm pretty sure mine has 'conventional' plugs but I'm going to double check and I'll certainly check the leads.

The car ran great prior to the distributor failure - fired up first time etc

I finally have a couple hours free this afternoon so its off to the garage I go.

[NTX5467]

Spark plug gap can be whatever you want, past .035" gap, up to about .060" gap, with an HEI.  Many small block Chevy V-8s were spec'd at .045". which coincides with the point where the advantages of the wider gap start to diminish.  Normal points would tolerate .040", from my experiences (for normal driving).

 

NTX5467

[Electra63]

Update

so...after a few hours working on this yesterday, I found the following:

- removed and inspected all the plugs.  5 or 6 of them were sooty.  Cleaned them all and checked the gaps which were all around 0.35-0.40

- checked the plug leads and all were OK - from 2-4k ohm depending on the lengths

- after completing all that, I started the car again and the same result - idles OK but misfires on increasing revs.    More noticeable when I jab the gas pedal and less so when slowly increasing the revs.

- the engine also idles uneven - like its firing on 7 out of 8 cylinders or something...

 

My thoughts then went to the fact that perhaps the new module was bad out of the box so I went down to Autozone and bought their version.  Installed it and....the same result.  So I have ruled out a bad module.

- so then I wondered if the new carbon button that came with the cap was too high a resistance v the previous one so I installed the low resistance one that is meant for a high output MSD coil, thinking that if I had a weak spark that would help.  But still no change to the engine behavior....

 

I also noticed what seems to be a shiny deposit on the driveway under the tail pipes.  It's not oil but I think it could be unburned gas...😐

 

So I'm now wondering if I should suspect the coil ?  I did check it with an ohm meter and the two windings checked out within the range that I found online....but I also saw an article saying that the coils can fail gradually - I think the writer called it 'layered failure' or something similar whereby a coil can break down gradually before failing completely.

 

I'm now unsure whether :

a) buy a replacement coil, or

b) trash the whole distributor and get a 100% new unit or

c) could I have a mechanical problem that is giving me the symptoms I'm seeing.  

 

I have had the timing light on it quite a bit, trying different degrees of advance between about 8-12 (made no difference to misfire) and the flash from the timing light seems consistent.

 

Anyone had experience of a 'gradually failing' coil ?

any other ideas?

 

thanks for reading

 

[Bloo]

Carbon button resistance is window dressing. Was the coil ever run without a ground wire? Did you look it over for cracks, marks from arcing, or holes blown in the coil leads? They do fail, but my guess from hunderds of miles away without enough information is that it is fine.

 

Double check your firing order.

 

15 minutes ago, Electra63 said:

I'm now unsure whether :

a) buy a replacement coil, or

b) trash the whole distributor and get a 100% new unit or

c) could I have a mechanical problem that is giving me the symptoms I'm seeing.  

I sure wouldn't go for a or b yet.... not until the cause is nailed down.

c) I'm starting to think so. In any event I can't rule it out.

 

What happens when you put vacuum on the hose to the distributor? Broken wires inside the insulation on the pickup? That would have been the only thing you touched except the module. I'm not going to say it is impossible for the module to cause this, but it is almost impossible. It would be an edge case.

 

Is there any tendency to backfire?

 

What does it sound like revved up to maybe 2500 or 3000 rpm at a constant speed? Is there a steady rhythmic snapping noise in the carburetor?

 

Is there any possibility a vacuum hose could have got broken while you were working on the distributor? The fact that some plugs look different suggests this might be. All vacuum lines matter, but look especially around any vacuum fitting located out on an intake runner. Got power brakes?

 

If there is no tendency to backfire, put your safety glasses on, get it warm and on low idle with the choke open, and look down the carburetor barrels. At a steady low idle state the only fuel should be coming from the idle jets which are under the throttle plates where you can't see them. You should not be able to see any fuel coming out of the discharge tubes in the middle of the venturis. In fact, you should see no fuel anywhere. If there is fuel running out, something is definitely wrong and it is probably the carburetor float.

 

Check the firing order again. I know I keep harping on it. Sorry about that. It is so easy to swap the two adjacent cylinders that follow each other in the firing order. I can't remember nailhead firing order offhand, but it would be 5 and 7 if it were a Chrysler or a Chevy with 18436572. Most of us have done this at some point whether we will admit it or not.

 

 

[EmTee]

Do you have a vacuum gauge?  I'd be interested in what it says at idle, ~2000 RPM and when you 'jab' the throttle...

 

Edited February 12 by EmTee
typo (see edit history)

[JohnS25]

I think I would do a compression check and see if it has even compression on all cylinders 

 

 

 

[Electra63]

Thanks guys

The coil looks good. No burned smell and no obvious damage.  It looks pretty much brand new.  The distributor was not that old either.  I'd say probably 3 years max. 

When it was running it did have a noise like a stuck lifter but it never got any worse in the 18 months I've owned the vehicle.

I'll check the easy stuff first like firing order. I did tag the leads before removing them from the cap and took a photo to be sure not to mix them up but  not saying it's impossible....

I'll also do Bloo's carburetor inspection.  When it was not running there was a strong-ish smell of gas around the carburetor area but I assumed it had just got flooded when I was cranking it with no spark. 

I'll post an update in a few days when I've had a chance to work on it some more. 

I appreciate all the advice !

 

 

[JohnS25]

27 minutes ago, Electra63 said:

When it was running it did have a noise like a stuck lifter but it never got any worse

I would do a compression check

[Bloo]

I second that.