CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

1990 Chrysler LeBaron 3.0L V-6 dies in heat

I’m beginning to think that this issue is heat related. It’s been over 100F for the last week.

This car has not been driven much in the last five years, maybe once a month. It belongs to a friend whose son has come back home for an extended stay. (I think we can safely say he’s moved back in.) It is her second car, so her carless son started driving it every day. Unfortunately they look to me for all things automotive. I’m looking to you.

The car was towed to me the other evening. Yesterday I let it run and get warmed up, and then I successfully drove it about a mile. Later I let it idle for twenty minutes and attempted another short trip. It died before I got out of my driveway. It’s never shown HOT since the headgaskets were replaced five years ago. I checked for spark at the coil, and found a spark that would easily jump 1/4" or more, but it was yellow, not blue. It would not start at that point. It did start after sitting for a couple of hours. I did not attempt to drive it. I don’t see a shrader valve to check for fuel pressure. Is there one? It is throttle body injected.

I would test the primary and the secondary resistance of the coil while heating it up with a hair drier/heat gun to see if the resistance goes out of spec.

Tester

Check the fuel pressure, it is common for those pumps to quit when they get hot.
You will need a “T” to connect to the fuel rail on the Mitsubishi engine. (See photo)

I waited until it died again, and checked the impedence of the coil. According to the website I looked at, it should be under 1.0 ohms on the primary. It showed 2.0. The primary to secondary should be between 10 and 11K ohms. This coil showed over 16,000. I figured it was bad, so I snagged one off of a running car and installed it. It did the same thing, died after things got all warmed up. I checked the used coil, and it had readings less than the one I removed, but still not at the “rule of thumb” specs I found.

Tomorrow, if I have time, I’ll make up the T fitting Nevada_545 suggested.

Then the next thing to check is the ignition module. Remember, the spark should be a bright blue color. Not a yellow color.

Tester

@Tester, by ignition module are you referring to the hall effect pick-up module inside the distributor? I had one of those flake out on a LeBaron my wife drove 20 years ago.

Checking the resistance of a coil can be tricky. Coils have impedance, which consists of resistance and reactance. You can’t check reactance without an instrument called an “octopus”. A VOM only checks resistance, but because of the reactance, the resistance changes with time. The general rule is to measure the resistance for 17 seconds before recording the value.

The 17 seconds is to allow all the reactances to settle out so they no longer affect the resistance. They never totally settle out, but after 17 seconds, they are so small that they cannot be measured. An AC powered VOM is more accurate as well, some battery powered VOMs have trouble measuring coil resistance.

BTW, the 17 seconds is for small coils/transformers. Big commercial 3 phase transformers can take hours to get a stable reading using a larger AC powered (5-10 amp) Ohmmeter. A specially programmed 50 amp ohmmeter can cut the time to 30-45 seconds.

OK, I think I figured it out. I went to my friend with the running LeBaron to see if I could borrow the ignitition module from his to check mine out. It pays to have friends in low places. He at least knew what module it was. He showed it to me on his car. BONG! The bell rang in my head. There is about a 3" diameter outlet for the air to travel from the ignition module to the air filter through a 3" plastic corregated hose. It draws air through the ignition module which contains some sensors and a large finned heat sink. The 3" hose was almost completely disconneted from the air cleaner end. Therefor there was little if any air being drawn past the ignition module to keep it cool as well as any other air sensors inside that black plastic box. It’s a wonder the car ran as well as it did. It’s sittinig outside idling as I type. I’ll take it for a drive in a little bit as see what happens.

That is the Powertrain control module. The engine induction tube is connected to the PCM to cool the inside components but I have seen a number of cars over the years with missing tubes and it won’t kill the car. The PCM may not last as long but I have never had to replace one because of a missing induction tube.

So, that’s not the ignition module in question? I guess my friend DIDN’T know which module it was. Which one is the ignition module then? There is another module on the passenger fender.

Will a hot or bad PCM cause the engine to die?

MG. The component you see on the air cleaner is the ECU/ignition module. Or the Lean Burn System

I always hated this Chrysler ignition system. The last one I worked on for this problem was a a late 70’s early 80’s Magnum. What a piece of crap.

Tester

What I’m speaking of is not ON the aircleaner. It is screwed to the driver’s side fender, near the front. There is a 3" diameter duct about two feet long between it and the aircleaner. Is THAT the ignition module? If so, MIGHT the fact that the duct was not pulling air through it have been causing the LeBaron’s stalling Issue?

The ignition module is inside the PCM on these vehicles and usually reliable. This is refered to as a SBEC module (single board engine controler) much different than the electronic spark control modules used on the V-8s.

Put a tube on it if you want to but if the computer is failing it won’t restore it.

If it was my car I would replace the fuel pump as a blind folded guess (I worked at a Chrysler dealer 1989-1998).

On GM’s the ignition module is mounted under the coil. Its the thing with a bunch of wires going to it.

@Bing But were talking Chrysler.

It did die again late yesterday, but with the gas gage pointing below empty I just put a gallon of gas in it. It started back up, but it was time to go home by then. I have not had a minute to mess with it today.

@Nevada_545 Sorry I didn’t get back to you sooner. As usual it turns out you were spot on with your blindfolded guess. It was indeed the fuel pump, apparently in intermittent mode. I fabricated the “T” fitting and installed it. The car played right along, dying after about 20 minutes with zero fuel pressure. The pump I removed looked new, nice and white with no discoloration from years dipped in fuel. Extremely deceptive. The car’s owner didn’t want to spend the money. She had replaced it before, and driven it very little. You’ll love this… I told her it HAD to be the Fuel pump. The internet said so.

That’s good to hear. How about the fuel filter? Good circulation is important for these pumps.
BTW are you the fellow in Great Britain?

I could blow through the filter with no effort. I’m sure it’s fine. It may have been replaced with the pump the last time.
Nope, although some of my ancestors were. I think Joseph E Meehan is a true Brit. He spells tires as tyres, and once owned a Sunbeam Imp. I have not seen him around for a while.