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Eagle Talon No Longer Likes the Heat

Still driving my '90 Eagle Talon TSi with all wheel drive with 185k on the clock. Runs fine cold. If it has been running in the high heat (95 degrees F or higher) or has been running then turned off and sits a while (~ 40 minutes or so), it runs like it only has 3 cylinders firing. Actually, it may really have only 3 cylinders firing because the plug on cylinder # 1 looks quite different from the other 3 (I checked after driving a couple hundred miles like this in the summer heat, didn’t have much choice - had to get home). No change with new plugs and wires. Could be the ignition coil or the Ignition control module, but maybe something else? Any suggestions on what to look at next?

When you change the ignition coil pack, you also replace the ignition module.

And that’s where I’d start.


Hmm. I was thinking I might be able to swap the two coils out with each other to see if the problem migrated to a different cylinder. Not sure that is really an option, though, looking at the part. The ignition control module is a separate part.
Sorry if this is a basic question, but why would both the ignition coils and the ICM need to be replaced, rather than one or the other?

Exactly how did the #3 plug look different? Can you Google a chart for “reading” plugs and post what you find? There are lots of charts with photos that offer excellent comparisons with explanations. I’ve linked one in,

No check engine light, then?

[quote=“4carseats, post:3, topic:94814”] why would both the ignition coils and the ICM need to be replaced, rather than one or the other?

A faulty coil could damage the ICM perhaps, and a faulty ICM could damage a coil maybe too. Without the proper diagnostic equipment, it probably makes sense to replace both while you are at it. Heat adversely affecting coils and ICMs are both a common thing reported here. Crank position sensors too.

If you are the scientific type and are experienced enough to work under the hood safely, depending on how your ignition system is configured, it might be possible to disable the cylinders one at a time. I do this w/my 43 year old truck sometimes by just pulling a plug wire from the plug. If you find where disabling a certain cylinder doesn’t affect the engine performance, that would be a clue that cylinder isn’t working for some reason.

The plugs for cylinders 2, 3, and 4 look they have normal wear, almost exactly like the photo shown. The plug from cylinder 1 looks a little like the wet fouled plug on the left, but not as bad as that. (Kind of amber/tan in color, damp looking.) These plugs only have about 18k on them, and this problem wasn’t occurring on short drives, or even longer drives unless the car was stopped for about 40 minutes and driven again until the summer months this year, when it started happening after about 40 minutes of driving in the heat.

Sounds like you’ve lost the reliability of your spark.
George posted a good method of checking for this. I’d suggest leather work gloves to do so. It prevents getting shocked and impaling the back of your head on the hood latch.

Yours would not be the first 26 year old vehicle to have had its ignition coils become heat sensitive. Over time, the coating used to insulate the coil windings can fracture due to thermal expansion and contraction of the copper windings within and short out when hot, recovering once cooled. These coils have served you well. If it were mine, I’d just change them and see if the problem disappears. It’d cost you more for an engine analyzer to do a formal diagnosis that to just replace the coils.

Ok, I understand that coil and ICM can affect/damage each other now. (I did some quick research on the ICM and coil and saw the same recommendation to replace both on almost all of the sites I looked at.) I’ll be replacing the coil pack, ICM, plug wires and plugs this weekend.

The check engine light would come on after the problem had been happening for a while when the car was hot, but because the car requires an ODB 1 code reader, none of the local car parts shops had a reader that would work for it, and the error code would reset each time after the car cooled down. (For a short time, when the weather was cool, the problem could be induced by driving at highway speeds, parking and shutting off the car for about 40 minutes, then restarting the car. The car would sound and feel like it was only running on three cylinders and the check engine light would come on a few minutes after the car was running like that, so I tried to only drive it where I knew I would not have it stopped for more than 15 minutes or it would be stopped for more than 4 hours. However, I discovered that if the car was run at highway speeds for about 15 minutes at 60 MPH or higher, the problem would go away and the car would run normally again then the check engine light would go off - which convinced me it was some kind of heat soak problem - the temp gauge never went above normal.)

I probably should have checked the code, but the 12 volt test light I had didn’t register anything. I now know the output is only a 5 volt signal, but I don’t have a scope, or a light or buzzer for that value.

This car has 4 overhead valves per cylinder, and the way the spark plugs are deep in between the valves it would be a little tricky to test the spark for each cylinder, but it could be done with some effort and a modified plug wire. But it would have to be done with the car engine hot, since the problem does not exist when the engine is cold or warm. I’m kind of relying on the engine performance, sound, and appearance of the spark plug from the number 1 cylinder being different in appearance from the other three that the cause is either the coil or the Ignition Control Module. I can’t think of what else it could be and hope I didn’t miss something.

I did have the intake manifold cleaned, as well as the fuel injectors and fuel filter replaced just last year due to a clogged injector problem, and that had no affect on this heat related issue at all.

I keep a spare spark plug on hand for checking spark. I just remove the wire from the cylinder under test (leaving the plug installed), attach the wire to the spare plug, and hold the base of the plug against a good ground. I can see the spark between the plug electrodes during cranking. This method may not work on certain engine configurations. In any event, best to leave this task to a pro unless someone who knows has shown you how to do it safely.

The thing about OBD I, you don’t really need a code reader. The engine computer – once you figure out how to get it to do so – usually just blinks the code out. The factory service manual will have a chart what to do for each code. The same manual also explains how to get the computer to cough the code out for you.

I think you’re on the right track. If that doesn’t pan out, other common heat related problems that cause missing or stalls reported here seem to be

  • crank position sensor (your engine may not have this part)
  • cam position sensor
  • fuel pump
  • fuel pump relay

Thanks, this has been very helpful. The spark plug test using a spare plug makes sense and doesn’t seem too difficult, even with the engine hot.

The ODB 1 connector is near the dead pedal on the driver’s side, pins 12 and 1. Just need to have the problem induced to the point the check engine light comes one and a light to read the 5 Volt pulse for the code. There are multiple books for the factory manual for this car; I have two of them, but neither of the ones I have list the codes. I probably can find the codes on the net, though.

This car does have a crank position sensor. I hope it isn’t that - I’m not sure it’s a part I can get to - but that would be the next thing I’ll look for if the ICM and coil doesn’t eliminate the problem. As you said, this is a 26 year old car, and the coil pack and ICM sit on top of the engine. That’s a lot of thermal cycles over the years…

Installed the new ignition coil, ICM, plug wires and spark plugs. The car drove great in the 100 degree heat for about 15 minutes or so in traffic with top speeds up to only 45 MPH, then the rough running with no power problem (like it was running on three cylinders) came back again, just like before with the engine light coming on quickly. However, after another 5 minutes of driving, the problem went away, and the light went out almost immediately. After another 5 minutes, the problem came back again. I parked the car for about 20-30 minutes to run my errand and it started up with the engine light on and acting like it was back to running on three cylinders again. On the return trip the problem went away yet again (and check engine light went out) for a couple of minutes, then came back yet again. I hooked up a 6 volt light bulb between pins 1 and 12 of the diagnostics connector and nothing - the bulb did not light up once. (Even if the check engine light is out, there should be a regular pulse of “1’s” coming out, but the check engine light remained lit.)

The part that is labeled as the crank position sensor actually gets its information off of the cam, and it located at one end of the top of the engine. I’m a little concerned about replacing that due to the need to have it aligned with TDC and not having a timing light of my own to adjust it. Also, I hate to throw more parts at it without knowing what the actual cause of the problem is. I’m starting to worry it may be the ECM, although that is located in the passenger compartment and was replaced less than ten years ago due to a capacitor shorting out (and was very expensive then).

Any ideas on what to do next?

There’s a number of possibilities. I think you’ll get to the bottom of it faster by having an experienced shop help you from here. You can run out of money guessing pretty fast by parts swapping on problems like this.

I guess if I had this problem on my Corolla I’d bring out my o’scope and look at the ignition pulses in the spark plug wires when this is happening. If I didn’t see anything wrong there , either with the waveforms or the timing, I’d test the EGR valve. It may be sticking open occasionally.

I’m probably going to have to bring it in to my mechanic, as much as I hoped to avoid doing that this time. At least the problem isn’t as intermittent as it had been in the past and it can be induced fairly quickly now. For troubleshooting purposes, that should help the shop out.