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Discussion Starter · #1 ·
For starters, my car isn't a mustang, but an old f100. However, I swapped the engine and 5 speed trans from a 91 mustang gt. I rebuilt the whole engine, put in an E303 cam, GT40 heads and intake, the heads have a performance valve job and are midly ported. I have 1.6 roller rockers and hardened pushrods. Stock everything else.
So, my problems start here. I have always had a check engine light on, and I have never been able to get codes, so I just figured something was wrong but didn't think anything of it.
Just a couple of weeks ago, I noticed that it was running like crap. I would drive, let off the gas and it would die. When it wasn't dying, the rpms were all over the place. 900-0-800-1000-10-900. It would run like that for about 30 seconds at most and die. I checked the base timing and it was at two. Two? Yes, two. So I timed it up to 11 and it ran a lot better for about...10 minutes. then it went back to how it was, rpms up and down and dying.

I was thinking bad ECM or something along those lines because the computer wouldn't communicate with the scanner, or the paperclip/jumper wire method.

Does anyone have any idea what it could be?

Thank you, Corey
 

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well..........

you have a engine and trans from a '91 mustang.

Are you using the entire engine and trans harness from the '91?

or are the harnesses pieced to together from different years?

You need to be accurate, 87-93 harnesses are different and are not compatible with each other.
 

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91 has air bags. I believe the harness you are using if the ford engine swap harness. its meant to swap carb to efi. so you are using the correct harness. check you dist gear. it only held in by a roll pin. make sure you are using a STEEL GEAR! NOT IRON!

what dizzy are you using?
what ecm are you using?
 

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just to make sure,

you have the correct engine, inj, O2, and trans harness?

If you do, there is an issue with it, or an issue with the ecm.

You need to produce codes, even a 11 system pass.

If you have somebody that can try your ECM on their mustang, manual if that is what you have, verify the ecm is good.
 

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Discussion Starter · #9 ·
There is no trans harness, it's a manual.
Is there any other way to find out if the ECM is bad? I don't know of anyone who has a foxbody.
I can't produce codes, the computer won't communicate. I've tried many different ways.
 

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a9l is the man trans. go over your grounds first. those a9ls are getting harder and harder to come by. if you can't find one and suspect your ecm, there is service on ebay that is only $100. just type in a9l and it will pop up. you send them your ecm and the repair it and send it back to you. I have used this service a few times and on my own person stang. never had a problem. worth a shot.

try a junkyard but its probably not there. no return on electrical is the policy most of the time.
 

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There is no trans harness, it's a manual.
Is there any other way to find out if the ECM is bad? I don't know of anyone who has a foxbody.
I can't produce codes, the computer won't communicate. I've tried many different ways.
Maf cars require VSS input,,,,,,its the trans harness.

As I suspect, this conversion was not done right.

Without looking at it, I couldn't tell you exactly whats wrong.
 

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vss is the speed sensor on the back of the transmission. a PROPER maf conversion incorporates the signal from the sensor to the computer. but since you are using a harness for the carb to efi conversion, I doubt these wires are included.

not hooking these wire up would cause a stalling problem. not a communication problem.
 

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I have the aftermarket ford racing harness, but it requires egr. It even states in the instructions that it requires egr. Not sure how that would affect how truck runs though. Unless yours is different from mine or you used a tuning program to disable egr.
 

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Discussion Starter · #17 ·
What would the communication problem be then? It won't give any codes, the CEL just stays on all the time.
Does the VSS part of the speedometer cable? I'm using the original speedometer cable from my truck. I might be able to use the mustang one, but i'd have to figure out how to wire in the vss. Where do the wires go?
 

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Unless I missed something you say that there is no EGR connector on your new harness, so are the EGR pins tied together with a resistor in the harness? IF you are running a stock A9L out of a '91 Mustang-which had an EGR valve and you aren't running a chip or tuner on the J3 port that turns off the EGR the EEC want's to see the EGR. So, no signal (wires in the harness connected to the EGR pins and an EGR emulator would do the trick for you) means total EGR failure which means a CEL on all of the time.
Ford Racing Fuel Injection Retrofit Harness M-12071-A50 - LatemodelRestoration.com
doesn't mention not having an EGR by the way.
 
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