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Discussion Starter · #1 ·
Here's the whole story. It's it a little long so please bear with me.

I been recently having an engine problem with my 93 MX6 LS which I've owned since new. Seemingly like clockwork after the engine has warmed up, the engine will either suddenly die and then just as suddenly come back to life or just cut off forcing a restart. In either case, the engine check light will come on and stay on. However, the engine will run fine thereafter until I shut it off and let it cool down again.

I took it in the dealer to have it checked out. Yeah, I know it was my first bad move, but I'm not a gearhead by any measure so forgive me. The service people came back to me and told me that they couldn't even get any diagnostics from the computer and that they recommended first replacing the computer. At first I wasn't surprised until they told me that the replacement part costs ~$1300USD and was a special order. Reluctantly, I agreed to have it replaced (yeah another bad move). The part will be in tomorrow and I'll be taking my car in the following day to have the computer replaced.

Dissatisfied about the cost, today I did what any geek would do and jumped online and started price searching on the web. One of the sites that popped up was this one (great bbs btw) which lead me to the Mike's and Julian's wonderful faq sites and in turn lead me to the diagnostics information. I followed the instructions, shorted TEN to GND, turned the key to ignition, watched the CEL turn on then off and but then no codes where displayed. Hmmm. So either the computer is faulty like the service center said or it's working as it should and there are no stored codes to display (and the service people are horribly incompetent).

Is there any easy way to induce an error that will confirm that the diagnostics are working? Like I said, I'm not knowledgeable when it comes to car engines so looking at the list of fault codes didn't give me any easy answers to this question. Perhaps there something like pulling a particular fuse which will make a sensor not function and cause an error to be displayed by diagnostics? Any suggestions?

P.S. I believe my original problem (engine dying after warm up) is probably the failing ignitor problem that is described at the above mentioned faq sites. Anyone concur?

Thanks for reading my long story.

Regards,

greenMX6
 

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When the engine dies and comes back to life and "the engine check light will come on and stay on", do you mean that the light is on while the engine is actually running? Or just when the engine is dead or the RPM is below 500?

To check the PCM, go under the hood and disconnect the TPS sensor on the throttle body, or the VAF sensor or the ECT sensor over by the rad cap near the front of the engine. Then turn the ignition on and wait 10 or 20 seconds. Turn it off, ground TEN and try to run the diagnostics again. You should get codes flashing then.

When you've proven the PCM can display codes, remember to plug everything back in. The codes in memory won't matter once everything is plugged back in.

It's remotely possible that the PCM is faulty and has a bad or cracked solder joint; it happens, not very often, but it can. Sometimes vibration or a rough road can cause the joint connection to become momentary and cause running problems. Given how well made the PCM is, I doubt that's the problem... But like I say, it's possible.

It could be the igniter, though it usually fails when the engine is under load (like when merging on a highway): the engine stalls and after a minute it will re-start. Your cutting-out and coming back to life doesn't sound typical of a igniter. It may be a bad connection to a crankshaft position sensor but if that were failing, I'd expect a code.
 
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Discussion Starter · #3 ·
Mike, thanks for the reply.

The CEL does stay on while the engine is running.

I've more to report. This morning I drove the car and reproduced the problem. I shut the engine off grounded TEN and then checked for codes again. What I got was two quick flashes, then pause, then two long flashes, then pause again, and then 4 quick flashes. The sequence then repeats itself. I interprete this to be '02' followed by '24'. Am I right?

According to the list of codes, '02' means there was a loss of signal from the NE2 crankshaft position sensor which is something you mentioned specifically Mike. And '24' means there was an RH02S inversion error. Are they both the cause or is one or the other the result of the problem?

Back to the problem of the suspected bad PCM. Is it possible that the Service Tech using his diagnostic tools wasn't able to get any codes and simply assumed there should be codes which then lead him to believe that the PCM was bad? Quoting from the repair estimate, "Tech noted "PTCM"<sic> will not communicate w/ testing unit". However when I checked things out using just a piece of wire and watching the CEL, it appeared to be working fine. Maybe there's a problem with the Tech's tools? Should I go ahead with the PCM replacment (~$1300!! +labor) even though I believe it's working properly (or at least well enough)? If not, I might be stuck with the bill anyway since it was a special order part and I had to prepay for it. It's probably going to a tough battle to convince them to refund my money. Either I pay for it or they do, but one way or the other, someone is going to be stuck with that big bill. Sigh.

Thanks again.
 

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greenMX6 said:
Mike, thanks for the reply.

The CEL does stay on while the engine is running.

I've more to report. This morning I drove the car and reproduced the problem. I shut the engine off grounded TEN and then checked for codes again. What I got was two quick flashes, then pause, then two long flashes, then pause again, and then 4 quick flashes. The sequence then repeats itself. I interprete this to be '02' followed by '24'. Am I right?
Yes. You've read out a code 02 and a code 24. The 02 is the NE2 crank position sensor (the one down by the crankshaft pulley) and the 24 is the right O2 sensor (the one by the firewall.)

According to the list of codes, '02' means there was a loss of signal from the NE2 crankshaft position sensor which is something you mentioned specifically Mike. And '24' means there was an RH02S inversion error. Are they both the cause or is one or the other the result of the problem?
I'm going to venture they are independent of one another. O2 sensors are common problems on the V6 and are considered maintenance items IMHO.

The NE2 CKP is a bit more troubling. If the car cuts out momentarily then comes back to life, what you've seen is the PCM stop getting pulses from the NE2 (engine dies), the PCM requiring a few turns of the crankshaft to verify it (by counting G pulses from the distributor CID sensor and not seeing NE2 pulses) and then switching to the NE1 sensor in the distributor as a back-up. Another possible cause is that the NE2 sensor is momentary and comes and goes periodically. The outright dying problem may be yet another problem, possibly related to the igniter if that has not yet been replaced.

Try this: get the car idling and pop the hood. Locate the NE2 connector. It's near the "front" (pulley-side) of the engine, near the rad cap there. Try wiggling that connector and the wires going to it, being careful to avoid spinning parts and belts etc. If there's a flakey connection there, you may be able to cause a stall or a miss or something.

Back to the problem of the suspected bad PCM. Is it possible that the Service Tech using his diagnostic tools wasn't able to get any codes and simply assumed there should be codes which then lead him to believe that the PCM was bad?
This is very possible. It's hard to say of the tech really knows what he's doing.

Quoting from the repair estimate, "Tech noted "PTCM"<sic> will not communicate w/ testing unit".
He may be calling it a "power train control module" or PTCM. Regardless, as you note, it's wrong. There's a PCME (engine controller) and, on ATX cars, a separate PCMT (transmission controller.)

Should I go ahead with the PCM replacment (~$1300!! +labor) even though I believe it's working properly (or at least well enough)? If not, I might be stuck with the bill anyway since it was a special order part and I had to prepay for it. It's probably going to a tough battle to convince them to refund my money. Either I pay for it or they do, but one way or the other, someone is going to be stuck with that big bill. Sigh.

Thanks again.
IMHO, no, you should not install the new PCME until all possible problems with the NE2 sensor are ruled completely out. If the new PCME is still in the box, never been connected to the car, there's no reason it cannot be returned for refund. Once connected to the car though, they most likely will not take it back.

FWIW, I'm not satisfied the problem has been traced to the PCME given what you've said has been done. If they refuse to consider further diagnostics (i.e. NE2) and want to plug that new PCME in, have them put in writing that, if the car still exhibits the problem with the new PCME, that the old PCME will be re-installed and the the new one returned for full refund, signed by the manager. It's still remotely possible that the PCME is bad (bad solder joint etc) but it sounds like there's other more likely possible solutions first. Remind them of Occam's Razor: "Of all possible solutions to a problem, the simplest one is almost always the best and correct one" (or something like that.)
 
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Discussion Starter · #5 ·
I tried what you suggested and wiggled the sensor when the engine was idling. Nothing. I also tried wiggling everything else wires, plugs, etc. around the radiator cap but again nothing happened.

Whatever it is, it only seems to happen about when the engine gets up to normal operating temperatures from a cold start.

As for the ignitor. Your remark about "if that has not been replaced" got me thinking. I dug through all my old service records and found that it indeed was replaced along with the whole distributer assembly, plugs, and wires in October of 98. It totally slipped my mind. Damn.

So if it's probably not the ignitor. Then what? Hmmm. I'm going to take my car back into the dealer tomorrow, get my refund for the PCME which I don't need, and have them take a look at it again. Now that I can show them how to properly pull diagnostics from the PCME :), maybe they'll be able to figure out exactly what's wrong now.

Thanks for your help Mike!

greenMX6
 
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