FINALLY found a major problem with my car - HELP!!! - TCCoA Forums
 
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post #1 of 8 (permalink) Old 04-14-2008, 04:39 PM Thread Starter
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FINALLY found a major problem with my car - HELP!!!

ok since I have been baffled by what is wrong I took it to a knowledgable ford mechanic. He just called me back and this is the problem he found (he said there may be other problems, but this needs addressed first):

Whenever the car starts up, it is going into self-test mode. He checked the STI and STO circuts (for the wiring harness) and they are ok. But he thinks there is a problem with the PCM. He had it hooked up to the monitor and can see that the O2 sensors won't even switch on. So I guess I need a 91 SC or XR7 PCM (from a 5 speed). Anyone here have issues like this before? Lol - no wonder why the car drove like crap and missed and loped when it got warm! Also, anyone with ANY information where to get a 91 PCM, PLEASE either PM me or e-mail me ([email protected]). I told him I would call him tomorrow and let him know if I could find any. I also have a paypal account if anyone is willing to part with one they know is a good part (I don't want to buy a PCM that may not work right)
Thanks guys for any help here!

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #2 of 8 (permalink) Old 04-14-2008, 10:15 PM
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I had the exact same problem. What I did was run a new ground from the engine to the chassis on the passenger side of the car and from the battery to the chassis on the drivers side.

It was caused by a ground loop in the system.
What I did to diagnose the system was check for voltage differences at the sensor grounds. I found allot of fluctuation and the ecm only needs a 5 volt signal to go into self test mode.

I've come into this world with nothing and still manage to have some of it left.

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post #3 of 8 (permalink) Old 04-15-2008, 07:18 PM Thread Starter
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this was from the sccoa:
"For some reason people (DIYers and mechanics alike) seem to gravitate towards the "ECU/EEC/PCM is fried" conclusion. Sometimes they are right, but most of the time, it's another problem. The biggest thing to remember is that the EEC is just a computer: it does what it's told. If one or more of your key sensors are giving false readings, there's not much the EEC can do. Don't take this as a knock on your mechanic, but here are a few things I would check/clarify before replacing the EEC:

Find out if the car "stuck" in limp / failure mode or self test mode. There is a big difference. Limp mode is designed to get you off the road or to the shop. The EEC has detected a pretty major problem and is "limping" along. I don't know exact details but limp usually runs a very conservative timing map, lots of fuel and a very low rev limiter. A function of limp mode is that the car runs like crap! Self test mode is something entirely different. It is initiated by jumpering wires in the diagnostic connector (can't remember Fords' real name for it) and meant to test the function of the EEC and associated sensors. In self-test mode, the computer runs a series of tests and then spits out any resulting codes. If your car is really stuck in self test mode, then it is an easy diagnosis: either there are wiring problems or the EEC is fried. If the computer is in limp mode, then it's a little harder. I've seen bad computers stuck in limp mode, but that is pretty rare. It's much more likely that sensor / wiring problems are giving the computer bad info which is in turn putting it into limp mode. In that case, changing the computer won't do a thing.

The posts about grounds are on the money. Have your mechanic check / add grounds. A missing or bad ground will really screw things up.

Since your mechanic has a scanner, he should be able to easily see most sensor values. It should be pretty obvious if a bunch are way out of range. It is interesting that he mentioned the o2 sensors. I'm guessing that he means the sensors aren't switching (like they normally do). Did you by chance have you head gasket(s) go? Coolant kills the o2 sensors.

If you can get a known good EEC for $40, then it's a cheap thing to rule out. On the other hand, don't expect it to fix your problems.

Vince"

Now its just an issue of finding the right PCM for my car. I was told by the mechanic (as well as another member) that 89-95 PCM's will "work" in my 91 car (as long as it is a 5-spd), but they wouldn't be right. Is this true as far as needing the right year/calibration for my car? (I can only use a 91 pcm?) This is what my mechanic gave me:

Calibration # 1 15 A RO

Engineering # F1WF 12A650 AA

Part # F1W8 (or y but it looks like an 8) 12A650 AB

Now this is what a guy with a 91 5-spd SC PCM sent me:
"my code on my 91 sc.....fosf-12a650-l2b..................LOE1 is the 4 code in caps that u also need" I assume LOE1 was what he thought the calibration code is/was, or did the mechanic give me the wrong one??? Are these interchangable? Is there a way to tell or find out what PCM's I can use?!?
ANY help here would be appriciated! Thanks guys!

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #4 of 8 (permalink) Old 04-15-2008, 07:47 PM
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It is sometimes helpful to have a picture to know what you are looking for:

http://forums.tccoa.com/showpost.php...52&postcount=9

Maybe this will help you explain it to your mechanic so you know what to look for.
I hope this help.

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post #5 of 8 (permalink) Old 04-15-2008, 09:06 PM Thread Starter
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I see these before and so has he, but I am just confused what numbers are what, and if my mechanic has the right calibration # or the other people do - and what can be used with my 91 SC - I am so frusterated. The car is sitting at beasley ford untill I can get a PCM - ARRGH

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #6 of 8 (permalink) Old 04-15-2008, 09:28 PM
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If all else fails, you might want to check www.car-part.com. A quick search shows 6 (if I used
the correct catch code).

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post #7 of 8 (permalink) Old 04-16-2008, 04:40 PM Thread Starter
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ok, first off, I can't do anything (like with grounds, etc.) because the car is and has been in the shop for about a week now. But I did show the mechanis a printout of this post, and he has been looking into the grounding issues. He didn't want to take the SC off, but he told me he "wasn't convinced there isn't a wiring problem". The more I think about it, the more I DON'T remember if I grounded the heads. He has tons of books open and was looking at all the wiring diagrams - do all SC's have BOTH the heads grounded, or did some just have one (pass. side)?

on to the EEC - still havent found one yet - I fount out for calibration codes
1-15a-ro
1-16a-ro

15 designates manual, 16 is auto... Anyone know about part number suffixes? Because mine is # F1WF 12A650 AA
I actually found (in Kansas of all places) a F1WF 12A650 AC

Will this work? From what my mechanic told me the part # for all the pcm's is the 12A650 but the suffixes before and after are what designate the different models. He wants me to stay away from the 89-90, and auto PCM'S, as they are different values. BUT what he said is the AA AB AC BA, etc at the end are different sowtware revisions. Can anyone verify this? I mean I assume its true - and if it is, the "F1WF 12A650 AC" SHOULD work in my car.... right? I know that is from a 1992 5-spd SC... OH WHAT A HEADACHE

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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post #8 of 8 (permalink) Old 04-23-2008, 03:45 PM Thread Starter
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ok I ordered a PCM for $85 from a 92 5-speed, but I also found out aomething else that was wrong... The one (I bought 2 new o2 sensors) must have been bad from the box, because it was shorting everything out. He replaced it with a new one, and he says the car runs ALOT better (he still hasen't driven it), but there is still a problem with the sti (self test input) circuit. He wants to make sure its not the pcm, since the voltage is still fluctuating on the circuit (I keep asking him about the grounds and I forgot to ask him the last time, so I dunno about that but he is definatly aware of that). I didn't know whis, but he said the O2 sensors are actually tied into the PCM, and with the sensor shorted out, could have damaged the PCM by either the short itself, or even by voltage bleeding back into the pcm through the sensor. Well at least my car is getting fixed!

Anyone know where to get a pair of cheap used (blown out, or I can clear them out) aftermarket cats that will fit 2 1/4" exhaust? my zip is 17356 - I prefer aftermarket ones, as my exhaust is custom... Thanks guys! Hopefully I will get my car back soon, and this wouldn't cost me tons of $$$

91 sc - put the stockgears back on, underdrive pullyes, rear air hydraulics, headers, no cats or resonator, lowered 1 1/2", 10% pulley, cam, 70k, rebuilt engine bored .30 over, finally fixed!
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