Langdon HEI problem, I think

[martybose]

The vehicle:

1947 Plymouth Business Coupe

230 ci flat head 6 from a 1950 Dodge; about 5K miles on a complete rebuild

9 to 1 compression with Edmunds aluminum head

Dual Carter-Weber carbs on an Edmunds manifold

cast iron dual 3-into-1 headers, dual 2 inch exhaust pipes

very mild aftermarket cam

No engine-driven fan, dual electric pusher fans in front of the radiator

The ignition:

HEI ignition from Langdon's Stovebolts, modified for a Mopar flathead

original application 1984 Chevy 2.8L V-6; internal module, external coil

MSD 8.5mm plug wires

Autolite AP 425 platinum plugs, gapped at .060" (had to use 0.043" indexing washers, as the exhaust valves were closing the plug gap!)

The problem:

I have been having what I believe is a heat-soak problem. I can drive all day around town with no problems, but if I go on the freeway, drive a few miles, then pull off and stop at a stoplight idling, when I take off I'm missing a few cylinders. My supposition; the ignition heats up from lack of air flow (remember, no engine driven fan). I can usually spot it starting, because instead of heating up at the light it cools off; apparently an unfired air/fuel mix pulls heat out of an aluminum head real well. If I let it sit overnight it starts up and runs just fine.

My first thought was either the coil or the ignition module. I replaced the coil first, no improvement. Last weekend I replaced the ignition module in the distributor using thermal paste. Started fine, ran around town fine, made two freeway runs with no issues. I was coming home to celebrate, hit a stoplight just half a mile from my house. Noticed the water temp dropping, and bigger than life it dropped some cylinders as soon as the light changed. Wasn't as bad as before, almost cleared up when the revs got above 2500, but definitely not right.

Questions:

1. Should I try another ignition module?

2. Could the ignition pickup be bad? I've got another one of those if it makes sense.

3. Am I missing something else that I should be looking at? The car has an alternator and holds 13.7 volts, so I think I'm okay there.

Marty, a bit frustrated .........

Edited May 19, 2011 by martybose
why can't you see typos until after you've posted them?

[Plymouthy Adams]

replace the high tension coil wire from the coil to the distributor tower..

[faucet47custom]

We have a 96 Honda Del Sol that started running rough about 20,000 miles after a full tune up. When we took it to the dealership for a check up, the service manager told me that the older motors don't like the Platinum plugs. They put in old style plugs and replaced one plug wire and it runs like a dream. I would try a different set of traditional plugs. Under ten bucks and quick to change

[Don Coatney]

Interesting that your temperature gauge shows your engine cooling off at a stop light after a freeway run. My engine does just the opposite. My temperature is around 170 when I am on the freeway irrevelent of ambient. As soon as I stop after a freeway run my temperature gauge shoots up to 200 or higher. If I am stopped for an extended period of time the temperature continues to climb even with the electric fan running. So if I sit for an extended period of time I have found that if I increase my idle speed up to 1500 or so by use of the throttle cable my temperature will stabilize and drop. I see this as a circulation issue where the water pump does not move sufficent volume at low RPM's.

Having said all of this I wonder if you have the same issue and your gauge may be lying to you due to low circulation. Try increasing your engine RPM's at the stop light and see if your problem gets any better.

[martybose]

Interesting that your temperature gauge shows your engine cooling off at a stop light after a freeway run. My engine does just the opposite. My temperature is around 170 when I am on the freeway irrevelent of ambient. As soon as I stop after a freeway run my temperature gauge shoots up to 200 or higher. If I am stopped for an extended period of time the temperature continues to climb even with the electric fan running. So if I sit for an extended period of time I have found that if I increase my idle speed up to 1500 or so by use of the throttle cable my temperature will stabilize and drop. I see this as a circulation issue where the water pump does not move sufficent volume at low RPM's.

Having said all of this I wonder if you have the same issue and your gauge may be lying to you due to low circulation. Try increasing your engine RPM's at the stop light and see if your problem gets any better.

When mine is working right it is the same as yours. Typically 160-170 while driving, gets up to about 190 after coming off the freeway, but cools off pretty quickly when the fans come on. The cooling off after the freeway only happens if it is dropping cylinders.

One person has suggested that this particular ignition was designed for 0.050" gap, not 0.060". I suppose the module could be getting a bit overworked by too large a gap, so I will be closing the gap a bit in the next day or so.

Marty

[martybose]

Well, changing the coil and the ignition module didn't improve the situation, so I decided to replace the pickup coil (since it is the last electric part in the distributor). Took the distributor out, took it apart, installed the new pickup. Unfortunately it is a chinese-built piece that was slightly bent, so the reluctor was hitting one of the poles. Loosening the screws didn't do it, so I was trying to support the stamped steel part while "persuading" it with a small hammer. I guess I didn't support it right, as part of the distributor casting broke off. So now I will be ordering another distributor and starting over again.

At least now I have quite a collection of spare parts for the next one!

Marty, sorta bummed out .................

[oldodge41]

Since it happens when your engine temp is dropping, could it be related to your fans coming on and running? Maybe dropping voltage on the ignition circuit or possibly creating some type of electrical interference on the circuit. Just a thought.......Tim

[martybose]

Since it happens when your engine temp is dropping, could it be related to your fans coming on and running? Maybe dropping voltage on the ignition circuit or possibly creating some type of electrical interference on the circuit. Just a thought.......Tim

No, the problem doesn't manifest that way. This morning it started misfiring within 30 seconds of starting the engine; the temp gauge needle hadn't even started to move yet.

I'm starting to wonder if I'm missing something else; I might pull the tops off of the carbs and look around tomorrow.

Marty

[martybose]

I tried an experiment yesterday. I dug out the box that contained my original points ignition system. It had the distributor, the coil, the ballast resistor, and it's own set of sparkplug wires; the only part in common with the HEI system was the wire coming from the ignition switch. I closed the sparkplug gaps down to 0.035", got it all installed, got it timed, and it was running well. Went for a ride, got one block from my house, and it started misfiring, just like before.

So apparently it isn't an ignition problem after all, it's something else. The week before I had opened up both of my Carter-Weber carbs to see if maybe there was some crud in them, or maybe some evidence of float level problems, but they were clean as a whistle and the float levels were fine.

I called my mechanic, who unfortunately is retired and 1000 miles away now, and ran it down for him. He asked if their was a heat riser that could be screwed up (No, because neither my Edmunds intake manifold nor my Phillips cast iron headers have provisions for one; the Edmunds is water heated). He asked if I was losing any coolant, thinking about an internal leak in the Edmunds, but I said I only had a very small external leak that I hadn't fixed yet, no significant loss of coolant. His closing thought was that it might be something that is introducing a vacuum leak after the engine heats up.

This problem has been with me for two years now, and I still don't have a clue about the cause, and I'm getting a little depressed about it.

Marty

[greg g]

What fuel pump are you using??? Is it puttin out enough quantity and or pressure???

I found my stock pump has an internal screen. It was clogged with debris. It would start and idle all day but wouldn't drive more than 30 MPH without bucking.

My pump also has a hollow bolt that holds the base onto the lower chamber. The gas flows through thie bolt. It had a chunk of stuff stuck in it. It was acting like a flapper valve. It must have been closig down with increased flow, and relaxing as rpms diminished. I know I have rust it he gas tank, I am running 3 in line filters. they are the first things I check when driveability problems appear. Also every spring I blow air from the pump back to the tank to clear the itank pickup filter.

You seem to heve eliminated ign problems, but just for yucks, try runing it with a jumper wire to by pass the ign. Perhaps it is the wire or even the switch itself.

I was talking a mechanic at the dealership I worked at about a pickup truck that was intermittantly running rough and cutting out. He had checked everythig and found no problems. the tech was talking to the owner as he was picking it up. When he dropped it off, he used the key drop envelope and only put the ign key in for service to use. As he was picking up the truck he reattached his igh key to his "WORK KEY RING" which must have weighed 3 to 4 lbs. I mentioned that the weight of the keys might be puttig a strain on the ign switch and pulling the key out of the run position enough to cause problems. They looked at me like I was nuts, but he decided to remove his work keys from this truck keys. He drove off. Came back about 3 weeks later and said he had not had a problem since lightening the load. He decided to change the switch any way just to make sure that was the deal, Apparently it was.

So check your switch and wiring to the coil.

[martybose]

I'm using a Facet electric fuel pump, located next to the fuel tank. Although I can't check it while I'm driving, the fuel pressure gauge on my distribution block shows a constant 3 pounds, just like it always has. Since I've got a new plastic tank, new fuel lines and 2 inline filters that look fine, I think I'm okay there.

Funny you should mention the ignition switch; as I was typing my entry this morning I was thinking about how many wires are on the switch and was wondering about installing a relay to power the ignition directly from the battery; might try that.

Marty

[Don Coatney]

When he dropped it off, he used the key drop envelope and only put the ign key in for service to use. As he was picking up the truck he reattached his igh key to his "WORK KEY RING" which must have weighed 3 to 4 lbs.

Greg;

Not the first time I have heard of a weighted key fob causing problems. But the problem is more likely with the fair sex using there 25 pound purse as the key fob on newer vehicles.

Marty;

Sounds like you have covered the electrical and fuel potential issues by the process of elimination. So time to think about the mechanical possible issues. Couple of thoughts. Could you have one or more cracked or broken valve springs? Could you have a carbon build up in the combustion chambers that breaks up releasing chunks that hold the valves open? You might try bringing the engine up to full operating temperature and introducing small ammounts of water down the carburetors to steam clean the combustion chambers and boil off any carbon build up.

[greg g]

compression check would be the first step.

[martybose]

Don,

I doubt that I have any of the issues you mentioned, because I had the top end of the motor apart and cleaned everything while I was replacing all of the valves. Having dealt with broken valvesprings with a prior set of plated springs, I haven't heard anything that makes me think that is an issue. Add to that the fact that the symptoms don't immediately appear, then suddenly they are affecting multiple cylinders. Something else is at work here.

Marty

[Andydodge]

Marty, how old are the plug leads?........just curious......do you have another set that you could swap to check?........andyd

[martybose]

Marty, how old are the plug leads?........just curious......do you have another set that you could swap to check?........andyd

When I installed my old points distributor it had its own set of plug leads; same results.

Tomorrow I'm going to make up a jumper cable (with a switch) to connect the ignition directly to the battery and try that.

Marty

[Don Coatney]

In 1971 I had a Plymouth Duster. It started misfiring so I replaced the sparkplugs and inspected points. This did not fix the problem. I went to the dealer and had there mechanic check it and he could not figure out the problem. So I drove it 40 miles to the next town where the dealer had an occiliscope. Five minutes later the problem was found. It was a couple of bad sparkplugs. And this was the new sparkplugs I had just installed.

In reading your posts I do not see where you have replaced the sparkplugs. It appears you are still using the Autolite AP 425 platinum plugs. I see where you re-gapped them when you installed the original distributor but you did not replace them and they are common to your problem from the beginning. You might try replaceing them.

[james49ply]

have you thought about carbuerater icing? high humidity, air going through a restriction (throttlr plate) and the air will cool to the point of freezing. I have this problem here in Florida, effects my motorcycle too. when it happens again, feel the lower section of the carbs, I have seen ice form on the out side also. just a thought for you:)

[greg g]

I just read somewhere that platinum plugs do not work well in old engines.

have you tried the old standby of pulling one plug wire at a time to see if anything changes?

[martybose]

Well, I tried 3 different things this afternoon that were suggested by various people.

The first was to make a jumper to run the ignition directly from the battery, bypassing the ignition switch. I actually cut up an AC extension cord, terminated one end appropriately, and put a toggle switch I had on the other end and ran it though the vent window. The car started but ran like crap.

So I put in a brand new set of sparkplugs after resetting the gaps to 0.035" Still starts but run like .......

So I pulled out the plugs (which all looked fine, BTW) and did a quick compression test (with the short adapter this time!). With the hand throttle pulled all the way out so the carbs were open, I had 140-145 across the board.

So nothing gained by any of these exercises.

My next move will probably be to take the spare electric pump, which I've never run, put the quick connect plug on it, then substitute it and its new filter for the one in the car. If I'm right it won't make a difference, but I'll have a known good spare properly configured and ready to go. if I'm wrong, maybe it will have something to do with this dilemma ........

Marty, in frustration

PS on the platinum plug issue, I was never able to find an 18mm 1/2" reach conventional plug for my head. The OEM head uses a 3/8" reach plug, but the Edmunds head should have a 1/2" reach plug. Granted, I ran a 3/8" Autolite 306 plug for a long time until I noticed my error, might try it again just because.

Edited May 31, 2011 by martybose
typo

[martybose]

The frustration continues. This weekend I pulled out the Facet electric fuel pump and its filter and replaced them. Started the engine up and it sounded fine, let it warm up and it still sounded fine. Went for a ride, made it about 6 blocks, was at about 2500 RPM in second gear and felt something as I was pushing in the clutch to shift to third; and it was on maybe 3 cylinders again.

Limped back to my place, listening to occasional popping in the exhaust system. Pulled into my garage, jumped out and pulled the plugs, did a compression check; 145-150 on all cylinders with the throttle open.

There are no vintage rubber pieces anywhere in the fuel system, and the only thing I haven't tried replacing is the rather large Fram fuel filter. There is no evidence of anything in the carbs. and the fuel level looked okay.

Talked to my mechanic, he has suggested pulling the carbs apart and try blowing out all of the fuel passages to see if there is a fleck of junk that is floating around and randomly plugging something up. Maybe next weekend; right now I don't even want to look at the car.

Marty

[Don Coatney]

If you have not done so try going back to the "short reach" sparkplugs to see if it makes a difference.

[martybose]

If you have not done so try going back to the "short reach" sparkplugs to see if it makes a difference.

I put in a set of new 306's, and it started screwing up about 4 blocks from my house.

I may have picked up a new clue or two, however.

1. It was idling real slow, so I had to add another quarter turn to the idle screws. Maybe my mechanic is right that I need to go into the carbs?

2. After I got back into the garage I was holding the idle at 1500 RPM, and twice while I was watching the tach it seemed like the ignition cut for a short interval, and the tach needle dipped at the same time. This is a mystery, because the old points ignition is running on a bypass switch connected directly to the battery terminal of the starter solenoid; have to think about this a little.

Marty

[Don Coatney]

I put in a set of new 306's, and it started screwing up about 4 blocks from my house.

I may have picked up a new clue or two, however.

1. It was idling real slow, so I had to add another quarter turn to the idle screws. Maybe my mechanic is right that I need to go into the carbs?

2. After I got back into the garage I was holding the idle at 1500 RPM, and twice while I was watching the tach it seemed like the ignition cut for a short interval, and the tach needle dipped at the same time. This is a mystery, because the old points ignition is running on a bypass switch connected directly to the battery terminal of the starter solenoid; have to think about this a little.

Marty

Are all your electrical terminals tight and secure? I had an issue once with a loose lug on the back of my amp gauge. I also had an issue once with a loose screw on my ballast resistor. In both cases the engine stumbled same as you describe.

[martybose]

Are all your electrical terminals tight and secure? I had an issue once with a loose lug on the back of my amp gauge. I also had an issue once with a loose screw on my ballast resistor. In both cases the engine stumbled same as you describe.

All of the electrical connections under the hood are on a terminal strip that I know is tight; I'll get under the dash and check everything else next weekend. Thanks for the thought.

Marty