Bad idle when warm

[THE EVIL TW1N 12]

My car has recently developed a bad idle when warm. When the engine is cold, it runs ok, but the closer it gets to operating temp (160-180), the rpm's start dropping to where it barely idles and has turned off a few times. It does this in park/nuetral and in gear, doesn't matter. Worse when it's in gear tho. I am running a Holley 4150 HP 950 carb, no choke. I've done the following with no improvement whatsoever:

 

*checked for vacuum leaks

*verified fuel pressure

*completely disassembled carb twice and cleaned it

*checked voltage

*ran the car with and without crane ignition hooked up

*ran with completely different dizzy and ignition module

*tried two different coils

*ran with alt belt removed (to check if alt was freezing up)

*no unusual noises from valve train

*ran two different power valves in carb

 

What could it be? Torque converter? A lifter? I haven't fully tested this engine/tranny set up since I've been working out gremlins here and there. The engine has been tuned with a a/f gauge. The car tach'd up to about 4000-4500 when I punched it on the freeway once in 3rd gear. It's supposed to stall at 3000.

 

I'm running out of ideas here.

Edited June 3, 2014 by THE EVIL TW1N

[Stock 87 12]

Running no choke. To compensate for this are you running it slightly fat? As it warms up the engine requires less fuel. Did you try leaning out the pilot circuit a touch?

[Max Power 74]

I was thinking along the same lines. Other than heat induced/related failures like vacuum leaks or wires behaving badly intermittently, the car demands more fuel when cold, which is apparently provided. When warm, it needs far less, so maybe you are far too rich. You mentioned you did AF ratio stuff, but didn't mention if you did it over the heat cycle or when the car was acting up.

 

Your list of diagnostic attempts is pretty thorough, so I am not sure what else to suggest. I can tell you that in spite of making many Holleys run well over the years, sometimes you get one that is just possessed.

[THE EVIL TW1N 12]

Running no choke. To compensate for this are you running it slightly fat? As it warms up the engine requires less fuel. Did you try leaning out the pilot circuit a touch?

 

I was thinking along the same lines. Other than heat induced/related failures like vacuum leaks or wires behaving badly intermittently, the car demands more fuel when cold, which is apparently provided. When warm, it needs far less, so maybe you are far too rich. You mentioned you did AF ratio stuff, but didn't mention if you did it over the heat cycle or when the car was acting up.

 

Your list of diagnostic attempts is pretty thorough, so I am not sure what else to suggest. I can tell you that in spite of making many Holleys run well over the years, sometimes you get one that is just possessed.

Yes it was tuned when warm. The car ran great for a couple weeks, but then out of nowehere it started with this problem. It's very frustrating.

[THE EVIL TW1N 12]

Alright, update... I checked the a/f ratio, everything was good at idle.

 

It was idleing pretty bad, so I checked timing and it was at 6-8*.... I revved it to about 3500 and when the idle came back down, it was perfect. Checked the timing and it was at 20* at idle. Then after a couple minutes, it was idle'ing pretty bad again and timing was at 6-8* again.

 

What would cause this? The two coils I tested were both the canister type (Blaster 2). Do you think it starts to run hot and starts to fail? You think I should test a newer better style one? Like I stated before, it did this with my Mallory Unilite distributor, and my Pertronix distributor. I have another spare ignition module for the Petronix too if I needed to test that, I just don't see how realistically it can be that tho.

[SA69mach 39]

So your timing is dropping 12-14 degrees after warming up.

What distributor are you using? Does it have vacuum and mechanical advance?

 

Strange to see that happen. Could be the gear ring on the shaft has slipped the pin?

[THE EVIL TW1N 12]

So your timing is dropping 12-14 degrees after warming up.

What distributor are you using? Does it have vacuum and mechanical advance?

 

Strange to see that happen. Could be the gear ring on the shaft has slipped the pin?

That's part of the problem, it does it most times but then seems to correct itself and run fine. Or maybe the low timing is where the correct setting is, and the more advanced setting happens when it sticks or something. Either way, not sure what's really happening.

 

It did this with two different distributors/ignition modules. Both distributors are vacuum advance btw.

[SA69mach 39]

OK. 12 degrees variance is a LOT. If the timing is retarding by 12 degrees without you physically moving the distributor, and it does this with two different distributors, then that leaves the drive teeth of the cam, or the timing set. I can see you have a built engine, and this is not what you want to hear. But if your electrics are eliminated, then it is mechanical. 12 degrees variance at idle is pretty significant.

 

I am not the big expert on engines by any means, but for what it is worth, I think a front tear down is in your future. it would pay to take it to a very competent mechanic who can verify the timing variance and check the evidence.

 

You may be lucky and just have a slipping lock-down ring on your distributor.

 

Your timing set may be slipping on the cam end, or the end may have worn. It happens, but it should not with quality cams.

 

You have done a lot of testing and elimination to trace the problem, and it would be worth re-creating the timing variance with vacuum lines off and maybe even mechanical advance weights removed, or locked down with a real heavy spring, to be sure it is not either of those adjustments. Like you said, you may have set initial timing with a stuck open vacuum shaft, or a stuck open weight, but...realistically that is very unlikely with TWO different distributors. Worth trying before opening the front of the engine though....

 

Please let us know of your progress.

[THE EVIL TW1N 12]

I sanded down the ground the contacts to the ground straps (I probably should run more) from the engine to the firewall, and from the engine to the ground on the battery. I found that the negative to the battery wasn't tightened down all the way. I started the car up and idled fine.

 

I drove it some and couldn't get it to run like crap, and the timing never changed. The last time I removed the negative from the battery was just before the car started to run with this idleing issue when I straightened the steering wheel out.

 

The cam is a Crane Cam. I did inspect the timing chain prior to putting together the engine, so it's possible something happened afterwards. I've never seen a double roller break a tooth and skip, but I guess it's possible.

 

Hopefully it was just the electrical (ignition) system acting funky from having a poor connection to ground. I won't be able to drive the car again until thursday at the earliest. I'll post a future update to see if there was any change.

[SA69mach 39]

Good work. I am hoping for you that this is an electrical gremlin caused by the bad ground. That would be a great result and an easy fix.

 

I have found my lighting is the first thing to suffer with bad grounds. But you have a hefty engine, so it might be the biggest drain and the first thing to go bad.

 

Good luck. I recommend ground from engine to firewall, negative battery to engine PLUS negative battery to body (I use the solenoid mounting bolt) That grounds the engine bay and should be sufficient for engine electrics. Instruments is another matter...

[THE EVIL TW1N 12]

Good work. I am hoping for you that this is an electrical gremlin caused by the bad ground. That would be a great result and an easy fix.

 

I have found my lighting is the first thing to suffer with bad grounds. But you have a hefty engine, so it might be the biggest drain and the first thing to go bad.

 

Good luck. I recommend ground from engine to firewall, negative battery to engine PLUS negative battery to body (I use the solenoid mounting bolt) That grounds the engine bay and should be sufficient for engine electrics. Instruments is another matter...

I may put a ground in a similar area. I agree that in the past with similar grounding issues that lighting is usually the first to show, but I've almost never driven this car at night. So I didn't get that clue. It's still a little early on declaring this was the issue, but I really really hope it was this. No fun at all chasing gremlins.

[SA69mach 39]

Yes, that is the truth. Chasing problems is part of the "joy" of these old cars.

 

I am very keen to know how that engine runs for you. I have a mind to build a stout 351 W into a 427 and would be obliged if you would post the driving experience and characteristics of that car and engine when you get it running.

Can I ask why you chose a automatic transmission for your car?

[THE EVIL TW1N 12]

Drove it last night and today, everything still good. =)

[THE EVIL TW1N 12]

Alright, another update.

 

Driving it last night, it started doing the wandering timing at idle again. So I took out the distributor and found that the magnetic sleeve had a good amount of wiggle. The sleeve is supposed to be on there tight and be locked into the top base where the mechanical advance is. So I spun it as much as I could (I guess 1/16 of a spin) and it's on there tight now. I put it back in the car and now the timing holds at idle at where it should. I really think this was the problem from the get go where the sleeve would spin slightly, giving me that wandering timing. I may take out the distributor again and epoxy the magnetic sleeve onto the top base to ensure it wont come loose. It's a Pertronix brand distributor BTW.

[SA69mach 39]

Hmm, wandering timing is not a small problem. In my earlier posts I had a lot of work lined up for you to check the mechanicals of the timing. All that for a loose component in a Pertronix distributor?

I say that is not good enough from Pertronix. One of the fundamentals of a distributor is to maintain settings. Since Pertronix is a dedicated ignition system manufacturer, I expect their designs to be foolproof and a big step above OEM units.

Would you be willing to post some pics of the parts that came loose? It might help a lot of other owners who are experiencing poor timing and performance.

Pertronix needs a letter of complaint too, in my opinion, and take it from there depending on what they say.

Glad you found the gremlin!

[THE EVIL TW1N 12]

Hmm, wandering timing is not a small problem. In my earlier posts I had a lot of work lined up for you to check the mechanicals of the timing. All that for a loose component in a Pertronix distributor?

I say that is not good enough from Pertronix. One of the fundamentals of a distributor is to maintain settings. Since Pertronix is a dedicated ignition system manufacturer, I expect their designs to be foolproof and a big step above OEM units.

Would you be willing to post some pics of the parts that came loose? It might help a lot of other owners who are experiencing poor timing and performance.

Pertronix needs a letter of complaint too, in my opinion, and take it from there depending on what they say.

Glad you found the gremlin!

I did find some similar posts from a few other people on different forums where they said the car would randomly run like crap, but they never posted if they found a solution. Believe me, I been chasing this gremlin for 2 - 2.5 weeks. I thought it was my idle circuits in the carb with something lodged in there. I must have taken the carb off 6 or 7 times and completely disassembled it and cleaned it out 3 times. I ended up stripping one of the fuel bowl threads on the body of the carb. Set me back 2 days alone to order the HeliCoil kit to fix it.

 

I'll post pictures soon. I had to partially take apart the distributor to get a good look at what was going on. Under the sleeve with the magnets is another round metal sleeve that goes over the inner distributor shaft. This metal sleeve is pressed into the top mechanical advance base plate. Basically, that metal sleeve had a good wiggle to it. I used vice grips and spun that sleeve and it tightened it up really well against the mechanical advance base plate. I dont believe it'll loosen up anymore. Before using vice grips to tighten up, I had just tightened it by hand, but it would dislodge fairly easily. We'll see what happens.

[THE EVIL TW1N 12]

Ok, another update.

 

The wandering timing at idle is fixed. But now the mechanical advance was sticking at whatever timing the springs would stretch to (silver springs). Example: if I revved it to where it would advance from 18* to 24*, it would get stuck at 24* at idle. Same if I would take it to the full 34* max. It would just not come down to the 18* initial.

 

To correct it, I used one silver and one brass (heavy) spring. The timing did slowly come back down to the initial 18* after a few seconds. I couldnt tell what RPM the timing was maxxing at (34*) due to doing this alone, but I would guess somewhere around 3200-3500rpm based on ear. I will have to double check when I get someone to help me out.

 

So, as of now, all timing issues are resolved. I'm not sure if the silver springs (and copper springs) got stretched out at the eyelids throughout all this in removing and reinstalling them a bunch of times and that's why I had to use the stronger springs. Either way, based on my experience, I can say overall I am not very happy with the PerTronix distributor.

Edited June 9, 2014 by THE EVIL TW1N

[SA69mach 39]

I agree - I am not happy with your Pertronix distributor either. Even with double springs your weights are hanging and slow to return? Something not right there...

 

My concern for you is you have a great engine, built nicely. Now , you get your engine spinning hard and then back it off, if your advance is held high by the sticky weights, you risk detonation.

 

You now have had two major faults in that one distributor. Sloppy magnetic ring retention, and now sticking weights.

 

Time for a re-think on the distributor choice. I know Glazier Nolan can do recurves on stock distributors, to suit your engine and cam. So that is a fall-back option - give them a call and see about having them make a distributor for you.

 

But first order would be to contact Pertronix direct and tell them of the two faults in your unit. They would want to work with you to identify the problem and treat you right for a replacement or full refurbishment of your unit.

What is the part number of the dist?

[THE EVIL TW1N 12]

I agree - I am not happy with your Pertronix distributor either. Even with double springs your weights are hanging and slow to return? Something not right there...

 

My concern for you is you have a great engine, built nicely. Now , you get your engine spinning hard and then back it off, if your advance is held high by the sticky weights, you risk detonation.

 

You now have had two major faults in that one distributor. Sloppy magnetic ring retention, and now sticking weights.

 

Time for a re-think on the distributor choice. I know Glazier Nolan can do recurves on stock distributors, to suit your engine and cam. So that is a fall-back option - give them a call and see about having them make a distributor for you.

 

But first order would be to contact Pertronix direct and tell them of the two faults in your unit. They would want to work with you to identify the problem and treat you right for a replacement or full refurbishment of your unit.

What is the part number of the dist?

I bought it from Summit. Part #PNX-D131701... I'm on the fence on contacting PerTronix. If I do, I believe they will want me to send out the distributor to them for inspection and verification before receiving an answer. And I can't stand the car just sitting there for weeks while I get a run around, even if ultimately I do get a new unit, refund, or whatever.

 

I had a similar set back with my brakes where it took about a month to get them back from SSBC. They did me right by fixing the issue, but my time is worth more than that. I'd rather put in some extra time at work and move past it.

[SA69mach 39]

Cant hurt to call and see what they actually say.

Summit may also have a solution that will suit you.

 

I understand you not wanting to lose the use of your car, and if neither company will play fair, then report your problem in a new post, titled "Problem with Pertronix distributor model XXXX" It will get picked up by web searches. Post exactly what went wrong and how Pertronix and Summit responded. No one wants bad press unless they are stupid.

 

I think you are going to need a new distributor in any case. You cant just sell your current one, at least I would not do that. And you cant trust the one you own now. It is faulty.

 

Couple phone calls, see what happens. You already spent more time discussing it on here than it would take to try.... just saying bro..