Your location would be a good start!
Jus say'in
6sally6

Good to see that you are still around, Lance.  Still got that beautiful Vert?  Why haven't we seen you since the Vandalia Bash?  Just wondering.

1.   Was it running with this PCM and then it quit?
2.  The label that matters are the big leters on the main connector.  Should be A9P or A9M or even A9L if someone has mixed things up.  Butt (TS&T), the '92 Stang with AOD should have come with an A9P EEc-IV PCM.
3.  If this is the initial fire-up attempt, what harness are you using and are you sure the main EEC relay (hopefully installed) is working.  That relay delivers v-power (12 volt) to the PCM and all the injectors and other goodies.
4.  The best way to troubleshoot is to try a "known good" PCM.  Any of those I listed above will do if you can borrow one.
5 Again, if this is the first go you definitely should run a KOEO (Key On, Engine Off) test first.  That will tell you if the PCM is happy with all it's little buddies in the system and that it is talking to them properly.
6.  OBD 1 code readers should still be available and not too ridiculous in price.  My friend bought one when we EFI'd their Falcon on ebay.
7.  You can read the codes without a reader if you have a "Check Engine" light properly wired in and I'm sure you could find the instructions on Gargle or I could email them too you.  If there is no check engine light then  wire one in.  IT'S ELECTRONIC FUEL INJECTION.  You need to know when it's not happy.

Last edited by Bullet Bob (1/25/2021 10:07 PM)

Its largely impossible to test the PCM out of the vehicle.  The shops that rebuild them have specialized equipment that can simulate the PCM being in a car.  Typically local places just sell a reman PCM. 

If the injectors are not firing I would suspect the PCM absolutely last.  I've yet to see a bad Ford PCM.  Never seen a bad GM one either.  Most times they get replaced because its something the guy trying to diagnose a problem suspects due to a lack of understanding of how it works.

How do you know the injectors aren't firing?
 

Ok, I have the Ford cable.  I put in fresh batteries it still fires up.  If you want to try to use this you can borrow it.  If you think it could help. I will even make a road trip to Ofallon, I need outta this house!  Lol.   Hopes this helps.

Greg B wrote:

TKOPerformance wrote:

Its largely impossible to test the PCM out of the vehicle.  The shops that rebuild them have specialized equipment that can simulate the PCM being in a car.  Typically local places just sell a reman PCM. 

If the injectors are not firing I would suspect the PCM absolutely last.  I've yet to see a bad Ford PCM.  Never seen a bad GM one either.  Most times they get replaced because its something the guy trying to diagnose a problem suspects due to a lack of understanding of how it works.

How do you know the injectors aren't firing?
 

 
My Jeeps alternator went out. More like the voltage regulator. It took the battery and the ecm with it. When I replaced the alternator and battery, afterwards I had the dreaded p0606 code. (Faulty ecm checksum error). This is one of the few codes no one can reset. It still ran fine, but here in Missouri they will not let a vehicle with the check engine light pass emmisions. They no longer check the actual emissions it puts out on obd2 cars. Just the codes. Anyways I had zero choice but to replace the ecm. I searched around the area for someone other than the dealer to try to reflash it, because that was all I believed it needed. No dice. That's when I found the online ecm exchange services. With the new "refurbished" ecm, I now have p0300, p0302, p0304, and p0308 codes. It ran great for a little while until it got cold, so I know it isn't an installation issue, like a bent prong. Nor do I believe that 3 cop's suddenly went out at once. I think it's a moisture issue. It was raining cats and dogs the day it started misfiring. I think the company did open up the replacement ecm to inspect it, but didn't reseal it well. Right now, I'm kind of caught between a rock and a hard place with this thing. But I wanted to make the point, sometimes you DO have to replace a computer. I

Lance, ima head downstairs and see if I have a Ford cable for the auto xray code reader. If I do, you can use it if you like.

I wouldn't say they NEVER go bad, but three thoughts about your situation:

1.) I had a P0606 code in my F250.  It was a faulty FICM, not the ECU, and after considerable research and understanding of the electric/engine management system it became clear that the FICM failed because I continued to crutch bad batteries.  There are some parts in modern electronic engine management systems that require proper battery voltage to operate, and if the voltage is too low they use step up circuitry that can overheat and fail if it isn't addressed in short order.  Interestingly, just like my situation this occurred in your Jeep after a battery and alternator went bad. 

2.) Jeeps are notorious for coils going bad.  Its entirely possible that you have several that are bad.  My cousin keeps spares in his glove box the failures are so common.  Also, when was the last time you put a set of plugs in it?  Its common for bad plugs to throw missfire codes. 

3.) Newer computers are also considerably more complicated that the ECU in a '92 Mustang.  The simpler an electronic device is the less likely it is to fail.  Even given that they are still fairly robust.  My main point is that I've seen a lot of ECUs replaced that did not fix the issue.  Typically because the ECU is the least understood part of an electrical system that is already the least understood system in a vehicle.  When frustration and confusion set in people tend to make up their minds that it must be the black box they don't understand.  This leads me to exhaust all other possible causes in a situation like the OP's before concluding that replacing the ECU would fix the issue. 
 

TKO,
I believe we have verified that the relays are functioning. I can hear the pump running. I am able to measure rail pressure at 45 PSI. I can see fire from coil, as well as a timing light sensing all 8 plug wires, so the juice is getting beyond the distributor. The injectors have 12v to them, but while cranking the engine over, the voltage doesn't flinch. If I pour fuel in the intake, the car runs. Checked all the grounds I know to check. The PCM has power because the pump runs with the key. This is what has us wondering whether the PCM could be bad. It is a remanufactured PCM already, so someone else apparently had one go bad, or thought they had anyway. I couldn't have gotten this far without help from someone who is pretty car sharp, but I'm eager for your insight. Does what I describe make you wonder about the PCM?

L

Lance wrote:

TKO,
I believe we have verified that the relays are functioning. I can hear the pump running. I am able to measure rail pressure at 45 PSI. I can see fire from coil, as well as a timing light sensing all 8 plug wires, so the juice is getting beyond the distributor. The injectors have 12v to them, but while cranking the engine over, the voltage doesn't flinch. If I pour fuel in the intake, the car runs. Checked all the grounds I know to check. The PCM has power because the pump runs with the key. This is what has us wondering whether the PCM could be bad. It is a remanufactured PCM already, so someone else apparently had one go bad, or thought they had anyway. I couldn't have gotten this far without help from someone who is pretty car sharp, but I'm eager for your insight. Does what I describe make you wonder about the PCM?

L

No, not yet.  Have you verified that you are getting a PIP signal from the distributor to the PCM?  Just because it has fire doesn't mean there's a PIP coming from it.  This could be a bad TFI module that is throwing spark, but not letting the PCM know its throwing spark.  If you have a known good TFI I would change this first.

I would also check the TPS.  It sounds crazy, but if the PCM thinks the accelerator is floored it won't command the injectors to fire on start up. 

If neither of those work I would get a set of noid lights and check for injector pulse.  If it sat for a long time it could be several injectors being clogged and failing to spray fuel.  One or two far enough apart in the firing order would still allow it to run, but two right next to each other will not.  I had this happen before and after going crazy and trying all kinds of stuff I had the injectors cleaned and the car started right up afterwards. 
 

Greg B wrote:

TKOPerformance wrote:

Greg B wrote:

 
My Jeeps alternator went out. More like the voltage regulator. It took the battery and the ecm with it. When I replaced the alternator and battery, afterwards I had the dreaded p0606 code. (Faulty ecm checksum error). This is one of the few codes no one can reset. It still ran fine, but here in Missouri they will not let a vehicle with the check engine light pass emmisions. They no longer check the actual emissions it puts out on obd2 cars. Just the codes. Anyways I had zero choice but to replace the ecm. I searched around the area for someone other than the dealer to try to reflash it, because that was all I believed it needed. No dice. That's when I found the online ecm exchange services. With the new "refurbished" ecm, I now have p0300, p0302, p0304, and p0308 codes. It ran great for a little while until it got cold, so I know it isn't an installation issue, like a bent prong. Nor do I believe that 3 cop's suddenly went out at once. I think it's a moisture issue. It was raining cats and dogs the day it started misfiring. I think the company did open up the replacement ecm to inspect it, but didn't reseal it well. Right now, I'm kind of caught between a rock and a hard place with this thing. But I wanted to make the point, sometimes you DO have to replace a computer. I

Lance, ima head downstairs and see if I have a Ford cable for the auto xray code reader. If I do, you can use it if you like.

I wouldn't say they NEVER go bad, but three thoughts about your situation:

1.) I had a P0606 code in my F250.  It was a faulty FICM, not the ECU, and after considerable research and understanding of the electric/engine management system it became clear that the FICM failed because I continued to crutch bad batteries.  There are some parts in modern electronic engine management systems that require proper battery voltage to operate, and if the voltage is too low they use step up circuitry that can overheat and fail if it isn't addressed in short order.  Interestingly, just like my situation this occurred in your Jeep after a battery and alternator went bad. 

2.) Jeeps are notorious for coils going bad.  Its entirely possible that you have several that are bad.  My cousin keeps spares in his glove box the failures are so common.  Also, when was the last time you put a set of plugs in it?  Its common for bad plugs to throw missfire codes. 

3.) Newer computers are also considerably more complicated that the ECU in a '92 Mustang.  The simpler an electronic device is the less likely it is to fail.  Even given that they are still fairly robust.  My main point is that I've seen a lot of ECUs replaced that did not fix the issue.  Typically because the ECU is the least understood part of an electrical system that is already the least understood system in a vehicle.  When frustration and confusion set in people tend to make up their minds that it must be the black box they don't understand.  This leads me to exhaust all other possible causes in a situation like the OP's before concluding that replacing the ECU would fix the issue. 
 

 
I have traced and prodded all the wiring, I am satisfied that isn't the problem. With the replacement pcm, it passed inspection, and ran fine for a while with no problem. The new codes started on a super rainy day driving, right after I got gas. I suspected it was the fuel pump first impression, but that was the first thing I checked and I have a solid 50lbs. I admit I haven't checked each coil yet, but it seems very unlikely to me three going out at once. I'm down to, cam sensor or crank sensor with it throwing no code, or back to the pcm. My Scooby sense tells me that is wherein the problem lies.

Plugs?  I've had bad plugs throw multiple misfire codes before.  Nothing wrong with the coils or the PCM, just worn out plugs.

Possibly the company formerly known as Chrysler builds bad PCMs,  I confess to not having a ton of experience with them.  Most of the stuff I work on is Ford, GM, Subaru, and Toyota.  They all have their own quirks, but with OBDII diagnostics are largely diagnostics. 

https://www.youtube.com/watch?v=e5-dpLpi_10
https://www.foxresto.com/
$25 to test. But like others, I wouldn't jump to the conclusion that the ECU is bad. Visually, about the only thing you can look for is the condition of the capacitors.
I use the code reader that BB linked to, does everything you need an OBD1 reader to do.
All good info and questions from BB as well. Regarding the harness, if using a modified Fox harness, the salt and pepper shaker connectors are known to be problematic.
A dead TPS with a reading near 5V will make the ECU assume a flooded start attempt, and shut down the injectors. Have you verified no injector pulse with a noid light?
Dan's questions and suggestions are also good. As BB asked, has it ever run in its current configuration?
What exactly have you done to diagnose the problem?

Resolution! All the above advise considered, we had delivered the PCM that came with the 92 GT to SIA electronics. We knew ahead of time their workforce was temporarily demolished by mandated quarantines, so instead of their usual 1-3 day turnaround, we would be without for over a week. Without the PCM, I couldn't really check any of the above items. Yesterday morning, I caught wind of a PCM out of a 93 GT AOD and was able to acquire it for $50. I plugged it in, fully expecting that it couldn't possibly be the PCM. But what the heck! Decided to bump the key and check, just for giggles.

To my great surprise, it instantly started! Stunk up the garage because I didn't expect exhaust. Wouldn't stay running without goosing the throttle because I had all the mass airflow stuff disconnected. But once I stuck that back together... voila! I have a running beast once again. Drove it right onto the trailer and took it home.

Just figured you all would enjoy hearing a success story after all of your investment of advice. Thanks, as always. Super helpful group of guys! Love it.

Lance

P.S. If any of your are curious to see what we were playing with, you can find pics here:

https://www.svdg-ofallon.com/mustang-fastback

Last edited by Lance (1/31/2021 9:22 AM)

Awesome!

Nice car😎

Always a fan when someone posts a resolution to their problem.  Strange it was the PCM, but I long ago learned to never say never.