The Stovebolt Site Forums The Shop Area The HiPo Shop Need help sorting out distributor on my 261....HEI

Hello everyone,

I bought a converted Chevy S-10 HEI distributor from Langdon when I started this project long ago, which I finished last summer. I have always had a subtle, strange, irregular "miss or skip" at idle and at higher RPM's. Originally, I attributed it to the cam I have, but I have since changed my mind about that- It is definitely ignition-related, as the ignition simply skips a beat irregularly. I have an old Heathkit Oscilloscope, and was looking at the screen- when the ignition skips, the image on the screen disappears for a split second, then re-appears.

Anyway, I checked the resistance of the plug wires (they are good) and changed the plugs to 3332 NGK XR5, and it runs better, but still has the "skip".

I opened up the distributor, and blew out any debris that might be in the coil pickup/trigger.

I removed the module, only to discover that it looks like it was run over- cracked, maybe even a little melted, and generally very derelict, as though it had come out of a scrapyard engine with 200k miles... a little bit disappointed by this. I am going to replace the module, simply based upon the physical damage that I see (cracks go all the way through it).

My question is this: I have searched high and low for the correct wiring of the 4 pin ignition module and coil pickup. After finding that module in there, I do not trust that the coil pickup was plugged in properly.

The coil pickup has two wires coming out of it- GREEN and LIGHT YELLOW (See pics below). The modular plug coming from the coil pickup can be flipped over (if necessary) to reverse the wires.

This S-10 ignition module is supposed to come out of a 1982-1984 S-10, and is not your run-of-the-mill GM 4 pin module with different pin markings and does not have the large spades angled outwards at each end, like the common 4 pin HEI module (see pics). I have located a replacement, which I am sure is made and China will fail next week, but I would like to get it wired up correctly, regardless....

Where the Coil pickup connects to the module, there is a Pin "P" and a Pin "N". The other side of the module has Pin "C" and Pin "+", but I am familiar with those codes "+" goes to batt/+ coil, "C" goes to trigger/negative side of the coil.

In the pics below, is the coil pickup plugged into the the ignition module correctly? Green wire is plugged into Pin "P", and light yellow (white?) wire is plugged into Pin "N"

I had the same issue locating a module for the HEI on my 235. I crossed the AC Delco number and found it was an 2.8L V6 distributor. I found the correct AC Delco/Delphi module on Rockauto.

Craig- yes, it took a while to find the right one.... do you remember which order your coil pickup wires were plugged into the module??

GREEN wire and YELLOW (white?) wire

Attached is a picture of the module wire on my distributor.

Thanks Craig! Well, I’ll be danged᠁your wires are opposite.

I have read that different coil pickups will have different polarities᠁ and that the wires will have to be reversed sometimes, depending upon the application.

The mystery deepens᠁..

The pickup-to-module wiring only works one way- - - - -don't ask me how I discovered that! If you get a "no spark" condition when you spin the shaft, reverse the wires. You can test a HEI distributor by spinning the shaft with a cordless drill motor with the housing clamped into a vise- - - -no need to install it in the engine.

Jerry

Thanks Jerry- That’s what I needed to know. I was afraid of frying the new module by wiring it backwards. I hooked it up like it was, and it’s running again.

The very slight miss at idle and at higher rpm’s is still there.

I tested the coil with a multimeter and everything appears to be normal- have you ever had a coil that drops out momentarily while idling, but otherwise performs well?

You probably already checked but you might make sure you don't have any plug wires laying on top of each other. You can get induction firing and that can cause this.

Years ago a friend used zip ties to get his plug wires all together neatly and his engine didn't like it at all. Not realizing what he had done, he tossed a lot of money at solutions before he learned he had caused the trouble trying to make everything look all special.

Heat can cause coils to act oddly, too. Not uncommon to see this.

Have you checked with your oscilloscope again? Usually those control modules either work or they don't (make sure you use thermal grease to mount them). I haven't seen too many work only occasionally. I have seen some Fords go through lots of them before somebody shows up and cleans the mounting area really, really well with acetone and a razor blade. Otherwise they'll sit cocked by about half a mm and if that happens they will get too hot and that will kill them dead.

And finally please be certain you have a really good ground to your engine. HEI requires a good solid connection with ground and if it doesn't get it, you can have intermittent results. I don't think you can have too many ground connections, actually and the old braided cable doesn't really do it for me.

Good luck!

The final years of the Ford 302 changed the firing order and this resulted in increased likelihood of inductive misfire. Spark plug wires are routed in very specific ways and held in clips to keep certain wires from being anywhere near other wires due to causing serious misfires.

High resistance plug "wires" can be a source for an intermittent miss. The carbon impregnated string conductors that most ignition systems run instead of metal core wire can break down and fail to flow enough current for a good spark. Use an ohmmeter to check each plug wire, and replace them if you find more than 1 K-ohm per inch. For instance, a 12" long plug wire can have up to a maximum of 12K ohms, etc. Most wires will have less than half that much resistance, but don't get tempted to run metal core wires- - - -they can cause rapid erosion of distributor cap terminals and rotor tips. A yellow or orange looking spark is OK- - - -the "hot blue spark" we're used to looking for hasn't been there for a few decades, even on very high voltage ignition systems.
Jerry

And here is one other thing if you get to the end of the list and you haven't sorted it.

Even if your 261 was rebuilt and got a new camshaft and cam gear, remove the timing gear cover (not fun if you didn't change things so it can be removed without removing the oil pan) and gently tap your camshaft toward the back of the engine. If you are careful you might also be able to do this by removing the distributor and trying to move the camshaft using the distributor driving gear.

Then using a flat bladed screwdriver gently try to move the camshaft forward toward the radiator. There should be .001" to about .004" of clearance between the cam and the retaining plate...or thrust plate, call it what you wish.

If you can visibly see the camshaft move, that should not occur and it might be your problem or it might be adding to it. Your cam lobes are made so there is an angle to the rear of the lobe. That makes the camshaft push back toward the rear of the engine...but not always as efficiently at low speed idle it seems.

Twice over the last 60 years I've seen it happen where there is a lot more clearance between the cam and the retaining plate and both times it has made idle wonky. As the cam moves in/out it can change ignition timing and also to some extent valve timing.

I don't believe it takes as much as you might think. About 30 years ago I owned a 235 with a camshaft that had over .020" clearance between the plate and camshaft and it was to the point where idle had to be set up to nearly 1000 rpm to make it run. At higher speed the cam would move toward the rear but at 500 rpm it would bounce back and forth altering the timing constantly.

Good luck.

Jon, if there is movement as you describe, what is the fix? Do you shim it with a thicker thrust plate or something?

There is only one good way and that is to remove the gear, machine, file or sand down the spacer ring so that the spacer is just .001" thicker than the retainer plate and reinstall it.

You can try using a press to push the gear down further but I've never seen that work. Ideally if you use the metal cam gear you can put it in the oven at about 350 degrees and the cam in the freezer for about 3 hours and then install the gear.

Some people will tell you that if you just press the aluminum gear on to the camshaft at the same temperature it won't work as well, but I've never received any instructions with any of the gears I've bought and I know back many years ago when we actually had machine shops in Dallas the folks just pressed them on at the same temperature.

If you use the fiber gear, I would not heat it up...I think it used a steel center and not aluminum so it may be different. I have also seen people machine the front part of the cam completely level with the gear, drill a hole, thread it and use a screw and a large fender washer to keep the gear from moving outward and I've seen people drill two holes in the slot between the cam and the gear, thread those and use set screws to keep things from moving.

A few weeks ago Jerry mentioned he was planning on reaming the inside of the gear (to make it a tight but moveable fit) and using a retaining screw so he could move the gear advanced/retarded to adjust his valve timing. I don't know if he did that yet, though. I don't know if wear causes these to develop a greater tolerance or if they just never were installed right or if heating/cooling causes them to move. But I do like the idea of using some sort of mechanical means to keep them in place.

Some engines use spring loaded rotating buttons to force the camshaft back toward the rear of the block and I suppose somebody could do the same with the stovebolt engine. All the manuals I have say .001" to .005" max.

Below is a camshaft I bought around 1997. All I know is that it is a hydraulic lifter Sealed Power cam. I also got a new set of Sealed Power lifters with it, but I'v never used it. As you can see, the gap is .005" which is right at the outside edge.

How can the cam move back and forth when the angle on the timing gears pushes it back against the thrust plate when the engine is running? If the cam and crank had straight cut gears, or a sloppy chain drive, "cam walk" could be a problem. That's why we put a "thrust button" on the small block Chevy race engines when we ran a double roller timing chain, and reinforced the timing cover by brazing a heavy flat washer in the middle of it. Cam walk on a stovebolt six is impossible.
Jerry

Jerry, I understand that...what you said is logical, sensible and I thought the same thing looking at the gears. In fact the first time this happened to me (around 1976) this would have been the last thing I would have thought possible. But the man who owned Cylinder Head Sales Co said he had seen this happen several times and the way to fix it was to take away the excessive clearance. Which he did in a few minutes when I brought the cam to him.

I know I've seen this happen twice, it happens at low rpm and the people who designed the engines and wrote the shop manuals must have put those clearance numbers in there for a reason. In fact in the 48 to 51 shop manual it is mentioned 4 times, and in the 1957 manual those numbers are mentioned 3 times. I also know somebody started adding the spacer to the thrust plate to make it easier to install the gear and hit the proper clearance. And in my case once the thrust plate was brought back to specs the idle problem was resolved. Over the years I've seen this mentioned on the VCCA, ChevyTalk and other forums, so I have to think maybe a few others have had the same issue and came to the same conclusion. I will say the two times I witnessed this the cam gear was the fiber style. Whether that made a difference I don't know.

Sounds like a lot of work to cure an idle stumble, and if the gear is installed correctly the first time, it's a moot point. I believe the modification to make the gear a slip fit and bolt it on is probably a better way to solve the problem. Some of the nitpicking we hobbyists do these days would have caused a flat rate mechanic to get fired back when these engines were in daily drivers. Changing a timing gear was a 3 to 4 hour job when I was doing flat rate work, and that included dropping the oil pan to get to those two bottom timing cover bolts. If a line mechanic couldn't change a timing gear before lunch, he probably wouldn't have a job the next day. I seriously doubt that those guys got picky about the end play on the cam.
Jerry

Good point. Keep your toe on the pedal at stoplights if the stumble bothers you and forget about it. It isn't a Formula 1 racer.

Excess vertical and/or horizontal movement of the distributor shaft probably has more of an effect on ignition timing than cam end play, and correcting that is a pretty simple fix that doesn't involve major engine disassembly. I like to put a Torrington needle bearing at the top of the housing to correct shaft wobble on a point type distributor, which can also make a big difference in spark timing between cylinders.
Jerry

I would bet on high resistance plug wires. One can also check for high voltage leakage by looking the the running engine in total darkness. That's particularly effective if it damp out.

Lots of good information here- thank you.

I tested the plug wires and two of them were about 1.5k ohms per inch. I will replace the wire set. I have one on order now.

Immediately after all my testing, I did a hot valve lash adjustment and a dynamic compression test for the heck of it- 120-130 psi on all cylinders, there weren’t any bent pushrods, so I am hoping this means it is unlikely that I have a sticking valve.

Went to drive the truck, and my idle drops to near stall when I depress the brake (I have vacuum booster under the floor). Time for a new booster, I think.

I’ll post again when the new wires arrive on Monday.

Oh, and yes, I modified my front bearing cap to be able to remove the timing cover from the outside᠁..hopefully it won’t come to that!

261 running with valve cover removed

Hopefully you won't have to remove it, Dave. As I was careful to say in my first sentence "if you get to the end of the list and you haven't sorted it..." So it is a last resort check, but as I also said it is generously mentioned in shop manuals through the years so somebody had learned something about that very narrow clearance and wanted to pass it along. Or I suppose somebody could argue they just owned stock in ink and paper companies and wanted to be certain they made the manuals as verbose as possible.

One other thing to mention: When you check the resistance of plug wires I've decided it is worth the time to check them at the inside of the distributor...once the wires are installed you can just tip up the distributor cap and go from there. My mini-Hei from Tom had a defective distributor cap. Tom wouldn't have ever seen it and I never told him because he's a gentleman and there was no reason to ask him to send me another but one of the little nipples on the top was loose and didn't make good connection with the spade piece on the inside. Played havoc with resistance checking and as you'd expect didn't help the engine run, either. Sort of like having two spark plugs on that one wire to be honest. The way I noticed it was when I removed the plug wire (to check resistance, actually), the nipple piece followed it. Even jamming it back in didn't help. It was okay for a while but once the engine warmed up, it would separate again and start missing. I JB-Welded it in place and saved the cap for reasons that probably only make sense to me, but again it may be worth checking. The Made in USA Delco distributor cap if you need it is GM#1979208 and they show up on eBay from time to time. Good luck.

Distributor caps can do strange things that make diagnosing an intermittemt miss a nightmare. The old "odd-fire" Buick/Olds 3.8 L V6 from the early 1980s had a chronic problem that could make a mechanic want to invent phrases that would make a sailor blush. One of the screws that held the HEI coil into the cap was right above the connector for a plug wire, and the insulation was a bit weak on some caps. A high resistance plug wire could cause the voltage from the rotor to drill a hole in the cap material and jump to the end of the screw- - - -causing a nasty miss, but only during a hard uphill pull, trailer towing, etc. Until GM increased the thickness of the plastic in that area, it was a pretty common problem, but one that was incredibly difficult to find.
Jerry

Make sure that all of your spade connectors inside of the distributor are not made with too soft of brass. If any of the connections are loose and you find that you can easily mash the female spade connector tighter, you may find that to be your problem.
I ran into that scenario with a Accel HEI distributor. Those slightly loose connections will wreak havoc on an HEI. They seem not to like stray electrons randomly milling about.
Another thing to check is the tachometer wire (if your distributor has one). If this wire even comes close to a ground it will cause a random misfire. If it finds a good ground, it will completely disable the distributor. Hotrodders are known to utilize this wire with a kill switch to prevent theft.

And all this᠁because I wanted something “better” than a points ignition.

I checked all of my spade connections, ran a temporary extra ground, but no change. I also bypassed the ignition switch, thinking it might be intermittently grounding out, but that didn’t remedy the problem either.

New plug wires show up tomorrow.

I also pulled my 7inch dual diaphragm brake booster, and it is leaking very badly. New one on order. That sucker was in service for only 7 months before it failed. Now it’s got me wondering if it’s been leaking since day one᠁

Well, probably an obvious thing but a leaking diaphragm would make you run a bit leaner (maybe notably if it is leaking enough) but it wouldn't cause a spark event to be missed. We'll be curious to see if the new wires help.

Checked the distributor cap for defects, cracks, loose terminals and checked ohms from inside the cap to the end of the wires- everything was good there.

When I had it on the oscilloscope, and the display set to “parade” (all ignition events in a row, end to end, as opposed to being overlayed), I could hear the engine miss, and at the same time the parade line would shorten by about one cylinder/ignition event. This is the primary reason I keep going back to the ignition.

If the plug wires don’t fix it, then the only things I haven’t replaced are the pickup coil/trigger and the ignition coil. But the ign coil has passed all ohm checks, so I am hesitant to throw more money at a new coil.

I agree that having the booster leak would cause a lean condition (and when it got really bad, the engine would barely idle). New booster will be here Tuesday evening, hopefully.

By Wednesday I should know more.

Because the engine has had this miss for so long, I would expect to see some evidence of cross-firing on the outside of the plug wire if that was the cause, right? Regardless, I will also install wire separators with the new wires.

Make sure that both the ignition module and the pickup coil are original equipment GM parts- - - -not some offshore knockoff. The module in particular has some dedicated circuitry to limit current flow when the coil primary reaches 100% maqgnetic saturation. Aftermarket modules eliminate that feature because of the cost of manufacture. If I 'm forced to use one of the offshore clones of the HEI distributor for some reason, I trash the electronics and replace them with OEM components.
Jerry

It hasn't been mentioned but your spark plugs...what gap are you using, Dave?

Did brake fluid get sucked out of the master cylinder though the booster and into the engine intake? That could cause a miss.

Jon, plug gap is presently 0.045”. I have tried 0.055” with no improvement.

Carl,
Now that is something I have never heard of, but understand how it could happen. The vacuum line was dry, and there was no evidence of any fluid where the master cyl mates to the booster, so no.


Jerry,
I didn’t know that. I have an “Echlin” module now, made in China I am sure. There was no change after I swapped it out with the GM OEM module. I had a lot of trouble finding a FLAPS that could get a hold of any module for me. I guess now I know why Langdon preferred to use a used GM module over a new Chinese one᠁ if I can find a GM module at a reasonable price, I’ll get it on order. I sure don’t need a dead module stranding me far from home᠁.


The New wires showed up today, so I checked them with he ohm meter and installed them with wire separators. Truck actually runs a bit better, but the miss is still there, just not as bad as it was. I have it up on jacks with the brake booster out, so I plugged the vacuum fitting at the intake manifold to run the engine

I took the tops off the carbs a couple of weeks ago, to make sure the bowls were clean, jets and all passages were clean. Both carbs respond appropriately to idle mixture and idle speed adjustments. I synched them as well.

The slight miss is still there.

When I was a kid, we had a'54 IHC truck what has a leaking hydro vac, every time you hit the brake pedal it would get a little shot of brake fluid into the intake, engine would speed up.

Even a little brake fluid in an intake produces a huge cloud of choking white smoke and a terrible odor from the tailpipe. If you've ever experienced that happening, you'll never forget it. The engine speeding up from a leaky brake booster is simply a vacuum leak- - - -there's no brake fluid involved.
Jerry

I have found GM modules on eBay. The GM part number is 10482423 from what I've written down here. You know looking at the oscilloscope shot again the spark happened but it wasn't strong. Is there a way you can check each cylinder to see what is happening?

One other heads-up- - - -a coil can pass all the resistance tests and still have problems. An open circuited (or very high resistance) plug wire can make the coil fire through the insulation between the primary and secondary windings, and create a path for a future miss. Eventually, it will develop a carbon track through that hole and the miss will happen more frequently. Ohm checks of both windings WILL NOT show up the problem. I have taken more than one problem coil apart and found those holes and carbon tracks, so I'm not just spitballing that theory. A HEI coil can develop in excess of 50K volts on open cirtcuit, and that kind of voltagbe can make its own pathway to complete a circuit.
Jerry

Late to this conversation᠁.
Delco d1959 is the module part number in my Langdon.
When I bought my dizzy from Tom in 2021? ( it was very near the last he made) and installed it I had a hard stumble during acceleration, I chased my tail checking and rechecking everything again and again for weeks including reinstalling the orig points dizzy to confirm it ran as before (with the new wires and plugs).
For lack of ideas (and desperation) I bought and installed a new OEM Delco D 1959 module. The stumble was GONE, truck ran and has run better than it ever had since.
I immediately looked to buy another OEM module but could not find another. From time to time I search for that part and have yet to find a real one ᠁.just other brands᠁ didn’t realize how lucky that purchase was᠁..

I bought but have not tried an off brand module, might be worth testing᠁ if I had time᠁.
And I keep that points dizzy on the shelf᠁..

Chuck

How about this one? 2 minute search on Ebay:

www.ebay.com/itm/275890554376?

Also fits Opel and Vauxhall:

www.kakapart.com/parts/delco-remy-d1959.html

"No-name" aftermarket equivalent:

www.aliexpress.com/i/3256805013782179.html?

Jerry

Spot on Jerry,
had not seen one (and hadn’t looked in a while), but being reminded went onto eBay right after I posted that and bought the OEM one with box and in the wrapper, the other unwrapped one looked pretty weathered for being NOS, almost looked like someone saved their old part after a change out"..

Wondered about all those Opel 1.3 ones, you think they are the same?

A word from a man who has dealt with China...please avoid TEMU and AliExpress. Alibaba is better. I've dealt with some companies affiliated as sellers through Alibaba and have not had any problems.

The child slaves at TEMU did a good job making my kitchen sponges. I got so many emails from them after that one purchase I had to block them.

You aren't the first person I've heard that warning from, though.

The module doesn't care what engine it happens to work with, or how many cylinders it's firing- - - -it's just an electronic on/off switch that interrupts the primary coil winding current flow. The Delco-Remy OEM units have all the fancy control circuits for monitoring coil magnetic saturation, and a trigger circuit that doesn't start primary current flow until it senses distributor rotation. That's important to prevent coil burnout from an accidental "switch on- - - -engine stopped" situation. That's what causes a total meltdoen of Pertronix systems pretty often. Most HEI coils have a primary resistance of only 1/2 Ohm- - - -that's a surge current of 24 amps of primary current flow or more, at least until the inductive reactance of the primary windings kicks in.
Jerry