Slant 6 wont idle after warm

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DM7969

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Thousand Oaks, California
Car ran fine for a couple of months. Now after I travel for about 5-10 miles it will not idle when I pull to a stop. If I am on the freeway it runs like a champ. Once it cools I can restart it and it idles. I was told possible vacuum leak. I checked the intake/carb bolts and they appear all tight. Also I was told to check/replace the points and coil. Any suggestions?

Thanks in Advance, Darryl
 
I'd start by swapping the ballast resistor. Cheap, easy and a common problem. Does it start, and then die when you left off the key? I think they usually fail open, but could be getting hot and changing resistance/opening up. Next would probably be the coil for similar reasons. I would think the points are OK at the moment, but I forget what happens if the condensor fails. Oops! Misread question, thought it died after getting warm and wouldn't start until cooled down. Advice still might apply though.
 
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No, it's probably not the ballast resistor. With a faulty ballast resistor, the car won't start (most often it'll start but immediately die when the key is released from "start" to "run"). That "heat up and increase resistance" thing happens about once every two or three nevers. If the engine runs at all after the key's released, the problem's not the ballast resistor. The coil is probably not the problem, either -- they can fail, but they seldom do.

Heat-related quality-of-running problems are almost always carburetor/fuel related. If this were a heat-related ignition/electrical problem, the engine wouldn't run (or would run very poorly at all speeds) once it got hot. If the condenser fails, the engine runs poorly (at all speeds) or not at all.

So, while the ignition-related tune-up replaceables (points, condenser, spark plugs and wires, cap and rotor) ought to be kept in good condition -- Tune-up parts and technique suggestions in this thread -- focus on the carburetor first to fix this specific won't-idle problem. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Problem or no problem with it, the carburetor's idle mixture and speed must be adjusted correctly (info at same link).

The PCV valve also affects the idle more than higher engine speeds; if it (or its hose) is faulty or clogged it can cause a no-idle condition. Moving further down the list of things to check: if the valve adjustment is too tight, it can cause a cold-idle-hot-run-but-not-high-idle problem.
 
slantsixdan said:
No, it's probably not the ballast resistor. With a faulty ballast resistor, the car won't start (most often it'll start but immediately die when the key is released from "start" to "run"). That "heat up and increase resistance" thing happens about once every two or three nevers. If the engine runs at all after the key's released, the problem's not the ballast resistor. The coil is probably not the problem, either -- they can fail, but they seldom do.

Heat-related quality-of-running problems are almost always carburetor/fuel related. If this were a heat-related ignition/electrical problem, the engine wouldn't run (or would run very poorly at all speeds) once it got hot. If the condenser fails, the engine runs poorly (at all speeds) or not at all.

So, while the ignition-related tune-up replaceables (points, condenser, spark plugs and wires, cap and rotor) ought to be kept in good condition -- Tune-up parts and technique suggestions in this thread -- focus on the carburetor first to fix this specific won't-idle problem. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Problem or no problem with it, the carburetor's idle mixture and speed must be adjusted correctly (info at same link).

The PCV valve also affects the idle more than higher engine speeds; if it (or its hose) is faulty or clogged it can cause a no-idle condition. Moving further down the list of things to check: if the valve adjustment is too tight, it can cause a cold-idle-hot-run-but-not-high-idle problem.
Click to expand...

I had thought a possible fuel problem. But it seems strange the idle difficulty is only when it is warm. When the problem originally started I removed the air filter and the car idled better. So I thought it was a clogged filter although it looked fine. Then it was all down hill, the first time I was stranded was on the freeway and the car was running perfect till I stopped in traffic. The car died and I could not keep it running enough to get in gear to exit the freeway. When it cooled down it started and idled fine. Thanks for the help SIX225 and slantsixdan.
 
DM7969 said:
I had thought a possible fuel problem. But it seems strange the idle difficulty is only when it is warm.
Click to expand...

Not strange at all.

When the problem originally started I removed the air filter and the car idled better.
Click to expand...

This suggests the curb (hot) idle mixture is too rich.

You will want to get the three books described in this thread as quickly as you can, otherwise you'll be shooting in the dark every time something doesn't work right on your car.
 
I have had small blocks with too much wear, slack in timing chain. ran fine at start up, drove to city and stop for light, would not idle right. this case was timing chain. but I bet Dan is right about fuel mix too. woreout parts cause lots of malfunction.
 
Idle/low speed circuit is clogged or blocked.
It runs as long as the choke is partially closed because it is forced to pull fuel through the booster. Choke opens, and now it can only pull fuel from below the throttle plate.
The fact that when your car died on the freeway, you couldn't get it to drive off tells me the transfer slot is dry.
That is controlled by the idle/low speed circuit
That is most likely.
If your engine is later model and has an EGR valve, it could be hung open causing an internal vacuum leak
 
Stuck heat riser valve? I noticed mine was stuck after I first got it. Ran OK, but as it got warmer it just didn't feel as responsive. Loosening it up seemed to help.
 
Here again, the heat riser valve needs to be kept in good working order, but no, a stuck one isn't causing a no-hot-idle condition.

Match the suggested fixes to the described symptoms. Guessing games and calling out random part names don't really help the OP get his car fixed.
 
A condensor usually results in loss of ign., many times intermittently resulting in dying/restarting & pleasantly awaking the entire neighborhood with a bang! Not that.
A heat riser stuck closed could do something like this, esp w/current fuel, if it overheated the intake enough to cause percolation in the carb. bowl.
Hit Dan's links and read, there is always something to be learned no matter how much You've read/done/heard, follow through.
 
Read posts 3 & 5 over and over. Doesn't get any clearer.
 
Suggestion for a new section on FABO
We call it, "Troubleshooting Lottery"
Here's how it works. We set up a PayPal account.
Someone with a problem that needs sorting kicks $5 bucks into it.
Everybody who wants to take a crack at fixing it, also throws in $5.
You get one post in the thread to state your case.
The OP has one week to fix his problem.
At the end of that week, if anybody got the fix right, they get all the money in the pot.
If nobody gets it, it rolls over to the next problem, and the OP gets his $5 back.
Who's ready to play
 
whitepunkonnitro said:
Suggestion for a new section on FABO
We call it, "Troubleshooting Lottery"
Here's how it works. We set up a PayPal account.
Someone with a problem that needs sorting kicks $5 bucks into it.
Everybody who wants to take a crack at fixing it, also throws in $5.
You get one post in the thread to state your case.
The OP has one week to fix his problem.
At the end of that week, if anybody got the fix right, they get all the money in the pot.
If nobody gets it, it rolls over to the next problem, and the OP gets his $5 back.
Who's ready to play
Click to expand...
I like it, but if we fail to solve his problem then IMO the money should go to the OP, cuz he's gonna need it!lol
And, the OP has to fill out a forum provided questionnaire, in which he tells us #1; what we're working on, for crying out loud. And then detailing the issue most specifically . None of this; "my car won't idle, what could be wrong", crap!
 
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Love the idea in spirit, in practice could get messy,lol! I can see "My car suddenly started running like s**t!" , followed by 20 postulations, ending with "Oops, accidentally filled
up w/E85 at a station i'm not familiar with".............where does THAT money go?
I love that You're tryin' to spice it up here tho' Tony:thumbsup: !!
 
Thanks everyone for all the replies and help. I changed the fuel pump and the fuel filter. There was no change in poor performance. Cap, rotor and points were in very worn condition. Replaced the cap and rotor and switched the car over to electronic ignition while I was at it. Car instantly started and idled very well. I was probably running on 3 or 4 cylinders in the past. It was if I put a turbo on it, it had a ton of power. Cold and hot start was instant. Started the car the next morning after sitting over night and it started right up.

Thanks again, Darryl
 
Great result. A few details would make this thread more useful to others. We now guess a slant-six engine, before ~1971 (points). Most likely, it needed new points or timing/dwell adjusted (i.e. routine "tune-up" back in the day). But, e-ignition is smarter. What system did you convert to - Mopar, Pertronix, GM HEI module?
 
Lottory is a grand idea, too bad 3 guys will chime in with the same diagnosis worded differently 15 seconds apart or the guy with the best explanation will get scooped by "check carb" and there will be a big stink on who should get it, or it was 'part this and that so well split the pot'...if someone wants to manage that mess, be my guest. But best of luck on us helping. Its nice to read 8 different POV's for 'no spark'...re-attach coil wire.
PS>>> I was going to mention those pesky vacuum thermo-valves<<<<
 
I used the Pertronix, it was very easy to install. I don't know if I was lucky but I didn't have to adjust the timing. I bought the car used, 1969 Dart convertible. I believe the ignition parts were pretty worn when I bought the car and became considerably worse the few times I drove the car. The slant six make decent power and is very fun to drive now. I have a engine swap planned but I am not in a rush now. Thanks again for all of the input, this site is great!
 
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