91 Talon Won't start, ECM toast??

[rednesss]

So I have a 91 Talon turbo. Recently I have been having problems with the CAS so I bought a used one from one of the members here and installed it. Now I had to modify it slightly due to the fact that my 91 has a molex plug right on the CAS and the one that I bought had a short wiring harness with a plug on the end of it, approx. 12 in. I connected the 4 wires to their corresponding pins, turned the key and it ran great. Drove around for a week until today, when I got into it at work, drove home 30 miles and stopped at the bank to throw a check into the ATM. When I got back into it, turned the key and it won't start. It cranks over just fine, but doesn't even sound like it is going to even remotely start. Hmmmmm, I say. So after a bit of trouble I tow it home. I pull out the test light and multi-meter and start checking things. Now first thing I notice when I turn the key on is a sickly buzzing noise coming from the area of the intake. I track that down by pulling the plug on the ISC motor. Next I plug in my Palm w/MMCD and I can't get anything out of the ECM, it keeps saying Serial Comm Error or something when I try and read any codes. This drives me nuts. Just for kicks I get the old ECM out that I had replaced some 2 1/2 yrs ago and throw that in the car. Turn the key on, power up the Palm and it has no problem reading the ECM and says no coded stored. Now I plug the ISC motor back in and theres no more buzzing noise, I'm thinking this is good so far. Now I go to start the car, and it turns over and over. Nothing. Try it again and it starts to catch, it sounds like it is really flooded so I let it sit for a minute. Try it one more time and this time it starts but it's running like crap, really rough and sporadic. I turn it off to think for a moment and turn the key back on and now the CEL doesn't come on. I turn the Palm on and now it says ECU COMM Error and now I'm thinking that my old ECM is now a paperweight. Could a bad ISC motor cause the whole ECM to go belly up??? It's a relatively new ISC as I replaced it when I replaced the ECM about 2 1/2 yrs ago. At this point the car ain't movin. I don't want to start throwing a bunch of money at it so I'm hoping that someone can lend me some wisdom here. Thanks in advance.

 

[playitlouddsm]

Are both of your ecm's stock, not chipped or anything? Did you check to make sure your getting spark and fuel?

 

[rednesss]

Yeah stock ECM, and I'm getting spark and by the smell of my exhaust there was plenty of fuel there. I tested the fuel pump in MMCD and it kicked on. I'm not thinking it's fuel related as I'm a little perplexed as to why an ECM that was alive and putting out a signal all of a sudden starts acting like it's completely dead.?????????

 

[AWDPetmitsu]

If your ISC was faulty, it can very well take out the drivers for it in the ECU and render it useless.

When you turn the key on, does the boost gauge needle rise to zero? If not, that's a sure sign your ECU is dead.

Before you do anything else, test your ISC. The instructions are here:

http://dmtalon.v8eaters.com/ISC.html

Make sure you do both the resistance test and the function check test. If it passes both, it's ok to reuse it after you install a repaired ECU; assuming your ECU was blown in the first place.

 

[rednesss]

The ECM that I took out, when I turned the key the turbo boost guage would go to zero, the CEL did come on but it never would go off. I know that after about 4-5 seconds the CEL is supposed to turn off if you don't crank the engine over. It just stayed on and if you watched it closely (the CEL light) it would flicker just slightly like there was a little voltage draw on it, but it looked like it was trying morse code. I'm going to test the ISC today and see if it's fried. I definitely don't want to put another ECM in it if it's just going to fry it in a minute.

 

[rednesss]

Well I tested the ISC just for Ohm resistance and I got values of about 34-35 ohms between pins 1 & 2, 2 & 3, 4 & 5, and 5 & 6, however I had no continuity between pins 3 & 4, basically infinite resistance. I haven't tried the 6 volt battery yet, should I even bother????

 

[rednesss]

So I took the cover off of the ECM and noticed an area where it appears that there has been quite a bit of heat, it's discolored not quite dark brown but definitely on the scorched side. The numbers next to it are: R112, R113, R114, R115 and R101. This entire area appears to have been quite hot at some time. Anybody know if these resistors?? are related to the ISC circuitry??? They are barrel-shaped, light blue, and have "270J" printed on them. ??????????

 

[steve]

Those are part (27Ohm 1W resistors) of the flyback circuit for the fuel injectors. I can't remember seeing those overheated on anything others than some of the '90 ECUs. What's the part number on the ECU in question?

Steve

 

[rednesss]

Md166262
E2t36578
1806

 

[steve]

I saw from your email that the board is marked 6578M as well. That means that it matches the case and together they would be the right ECU for a '91-92 AWD.

Double check to make sure that the injector resistor pack on the firewall is good and check the electrical system voltage when the car is running to make sure it doesn't go over 14.7v. This may have happened some time in the past.

From the measurements you gave us it sounds like your ISC is OK electricly. Pins 3 and 4 are on different coils inside and I wouldn't expect you to measure anything. When the ECU is first turned on it homes the ISC and if you were to pull it and watch you would see it move in and out when you turn the ignition on and again a short set of steps then you turn the key off.

Your getting both types of comunications errors from MMCd. They mean two different things. The Serial Communications Error means the cable is disconnected or something is holding the dataline. ECU Communications Error means the ECU didn't respond to the commands from the datalogger and that the datalogger did see the command it send echo back to it.

Any signs of capacitor leakage or corrosion on either ECU?

Steve

 

[rednesss]

Where would you find the injector resistor pack??? I'll need to read up on the testing procedure for that. The car won't start right now, but when it was running before, from MMCD the voltage was usually right around 14.2-14.4 volts. Well I guess that might rule out the ISC, I didn't take it off and do the 6 volt battery part of the test, just tested the ohm readings between the pins. I'm getting the Serial Comm error from ECU #1, the one that was in it when it went from running just fine, to won't start. I'm getting ECU comm error from ECU #2 the old one that I took out 2 1/2 yrs ago. ECU #1 was rebuilt by ZDR 8/2003, the board looks like it did have leaking caps but they replaced them and ran some jenny wires to bridge the crappy traces. ECU #2 smells like a cheap hooker and has all kinds of corrosion around the original caps.

 

[rednesss]

You know the other odd thing I noticed was that when I had ECU #2 plugged in, when I turned the key on, the MPI relay would click on, stay on for about 3-5 seconds and then would click off, and then the ECU #2 would quit communicating with my Palm. I would then get the ECU comm error. However when I had ECU #1 plugged in, the MPI relay would come on, and stay on and only turns off when the key is turned off. I thought that was weird.

 

[steve]

It sounds like you have two bad ECUs at this point. I'd get them fixed or replaced before chasing anything else.

http://members.shaw.ca/dsm.1000q/Engineprimer/
http://members.shaw.ca/dsm.1000q/Engineprimer/1G/respack.htm

The

 

[rednesss]

Yeah I think so too. Can I send you the ECU and have you take a look at it?? Maybe you can tell me what went wrong??? I'd hate to put a new one in only to have it go belly up because of a bad electrical problem.

 

[steve]

Sure. Send me an email and we can discuss it.

Steve

 

[rednesss]

Will do, now I have a used ECU coming and want to make sure that I'm not going to plug it in and just pop it like the old one. Is there anything in particular that I should test prior to plugging in the new ECU so that I don't end up with an expensive paperweight??? I tested the ISC for resistance, am going to pull it out this weekend and do the battery part of the test to it to insure that the pintle is moving in and out, assuming that it's good, other than that I don't know??? There were no codes being thrown prior to this episode other than 23 I think which is the CAS and I replaced it with a working used one. The car ran fine for about a week and a half with the used CAS in it without throwing any codes. I was just wondering if you had a list of "usual suspects"????? Thanks.