Engine EEC-IV Problems

EDDIEM75 · Jun 17, 2025

nickyb said:
You know when the ignition. Module gets hot it usually craps out,you can pull it off the dist. And put some heat sink grease on it.

The entire ignition is suspect at this point. Have to get the ecm repaired or replaced before I dive back in. But yes the ignition module would be a thing but it doesn't have to get hot. Let sit for awhile. Start it up. Immediately turn off. Won't restart.

I might need to start new thread...Any suggestions for ecm rebuild or replacement? It has an a9p which from my understanding is technically for auto but should work fine. Need to look into the O2 situation that blows pin 46 though.

gkomo · Jun 17, 2025

ECUExchange but may be worth buying an A9L and then having that one repaired? Not sure how far along with wiring changes you are with the A9P

EDDIEM75 · Jun 17, 2025

gkomo said:
ECUExchange but may be worth buying an A9L and then having that one repaired? Not sure how far along with wiring changes you are with the A9P

As far as how far along with wire changes I am goes I haven't made any changes so far. The car's been up and running since a rebuild five or six years ago. It's not mine but I've driven it quite a bit during that time and it runs really well. Always had idle/surge issues but the owner didn't really mind for the most part. I'm the dummy that went down this rabbit hole. Can't say yet what's exactly going on with the open pins 46 40 60 in the ECM. Meaning pin 46 wouldn't ground even before I plugged up the cig powered scanner. At the time it really just had the idle issues though. Once i plugged up the cig powered scanner the hard start/no start issue started. Obviously the ECM was having issues prior to plugging in scanner being there was no ground in pin 46. I'm just wondering if when I plugged the scanner up it did more damage to the ecm due to there being no ground with a cig-powered scanner. I don't know. What I do know is diag-ing it with a faulty ecm is pointless. Now hopefully I put a new ecm in and everything's addressed.

But finally to your point on the wiring changes. I just today came across the thread mentioning the 02 wiring situation damaging the ECM. It's absolutely something that has to be looked at before installing new ecm. I haven't gotten into the details in that thread about what exactly to look for with what setup etc. But i will of course. I am concerned that the 02 wiring issue mentioned in that thread might be what damaged the ecm even before i plugged up the scanner. Any input regarding the 02 wiring deal is certainly welcome. Not asking for a complete breakdown of that entire thread just your experience with that wiring situation. Sorry post got so long.

GOvert · Jun 18, 2025

If you haven't, it may be a good time to take out the ecm and inspect it. It's easy for humans to make procedural mistakes and I am human and constantly reminding myself to disconnect the vehicle battery before R&Ring eecs, ecms, pcms etc. Removing it and remove its cover; and giving it a good inspection might give you some extra insight as to what is going on with the ecm and to see if there is a programmed J3 chip attached to the J3 port. If it has a J3 chip, it is movable from ecm to ecm. During the inspection, look for burnt components, particularly little "can" shaped capacitors that could be bad. The top of them will bulge.
Here is a Stangnet link to a discussion about pin #46 which is signal return:
EEC Capacitor Replacement, Pin 46 Jumper to Ground, & General EEC Work Question
Resist the urge to throw parts at it in search of a problem. Parts cost money and unless you have disposable income for parts that you may not need... If it were me and I had access to a Fox body of the same year, I would install the suspected ecm into a different vehicle. I would think that for a vehicle sitting still test, KOER, it wouldn't matter if the 2nd car had a T-5 or AOD. You're just wanting to hear the engine run.
Where in TN are you?
ADDED: I read that you might start a new thread. I'm not here often but I bet some of the veteran Forum members would say, that by doing such, it would only confuse the situation. It's best to just keep going on the thread that you started in the first place. Users in agreement, give a thumbs up!

General karthief · Jun 18, 2025

EDDIEM75 · Jun 18, 2025

GOvert said:
ADDED: I read that you might start a new thread. I'm not here often but I bet some of the veteran Forum members would say, that by doing such, it would only confuse the situation. It's best to just keep going on the thread that you started in the first place. Users in agreement, give a thumbs up!

Just for clarity I was referring to who to use for ecm rebuild when I mentioned a new thread. But someone already gave me an answer I feel would be a good choice after researching. But yes I gotcha. And I appreciate the original reply.

GOvert · Jun 18, 2025

@EDDIEM75 Ok, on your thoughts about the ecm, post etc. I'm curious how close you might be to my location. I'm near the AL/TN line. Do you have a friend or associate that has the same year Fox body that you are dealing with? I have to leave the house again today to go back to my Shop but while I'm out, I'm going by another Mech/Tech Mustang friend's shop about an EEC-V situation. I'll see what he might have there that he is working on at the moment. I'll be back here ~5:30 to 6:00 pm central time. I was wondering if you were in our region or too far out. Tennessee is a long spread-out state. I'm 4.5 hrs to Memphis and 4.5 hrs to Knoxville. Nashville is not too far away.

Blown88GT · Jun 21, 2025

The Snap-On MT2500 is an OBDI scanner. Don't know how Snap-On connected or worked. The connection should be at the diagnostic port under the hood, not directly to the EEC-IV ECU. Ford, GM, & Chrysler have different connections & pinouts. BTW, OBDII was not mandated until 1996. You can still buy the Innova Ford Code Reader for $26 at AutoZone.

EDDIEM75 · Jun 23, 2025

GOvert said:
@EDDIEM75 Ok, on your thoughts about the ecm, post etc. I'm curious how close you might be to my location. I'm near the AL/TN line. Do you have a friend or associate that has the same year Fox body that you are dealing with? I have to leave the house again today to go back to my Shop but while I'm out, I'm going by another Mech/Tech Mustang friend's shop about an EEC-V situation. I'll see what he might have there that he is working on at the moment. I'll be back here ~5:30 to 6:00 pm central time. I was wondering if you were in our region or too far out. Tennessee is a long spread-out state. I'm 4.5 hrs to Memphis and 4.5 hrs to Knoxville. Nashville is not too far away.

Sorry my world got busy. Thank you for the offer but I'm not sure at this point how someone or something could help. My main concern at this point is the ecm and why or what is fried. I can see where two capacitors have lost contact with the board. It's an a9p with a 5 speed. Don't know if the car was originally an aod or not. I ran across a thread related to certain o2 wiring harness whether aod or 5sp will fry ecm. I'm needing to read that thread thoroughly to determine if I just need an ecm rebuild or address an o2 harness issue first then have ecm rebuilt. Fyi I'm in the North Nashville area. Again thanks for the offer.

Blown88GT said:
The Snap-On MT2500 is an OBDI scanner. Don't know how Snap-On connected or worked. The connection should be at the diagnostic port under the hood, not directly to the EEC-IV ECU. Ford, GM, & Chrysler have different connections & pinouts. BTW, OBDII was not mandated until 1996. You can still buy the Innova Ford Code Reader for $26 at AutoZone.

Yes plugged in at diagnostic port behind driver side strut tower. Snap-on gets ground from Port. I believe it won't power up due to a ground issue in ecm possibly. The diagram i have has pin 46 at port as computer test ground. It is ground with key off but with key on it had signal voltage 4-5v. I've got to get a better understanding of wiring in this circuit and the o2 before continuing. Thanks

General karthief · Jun 23, 2025

First....determine if the car was originally a stick or auto
Second....send that computer in to get repaired, most here use the ECUExhange
Third....check and adjust the 02 pins for the computer
An inexperienced opinion based on hang'n here, the pins on the 02 need to match the computer before you turn the key on, some have gone for a while and never had a problem, sometimes it take many miles to effect the computer and it eventually will.
a computer that does not communicate with a scanner, void of human error, has issues, think about it, how many 30-35 year old desktop or laptop computers are in use today?

FastDriver · Jun 23, 2025

Never had a fancy Snap-On scanner, just the little Actron scanner, and all it really does is send the signal to a bulb that flashes. The actron is powered by a 9v battery, and doesn't depend on the diagnostic port for power or ground, other than to read the code.

There's an old thread around here somewhere on how to use jumpers to send the signal to the check engine light, in order to count the flashes and retrieve the codes.

In any case, it's kinda crazy that you've done all this thinking and talking without pulling a screw & push-plug and pulling out the passenger kick panel. With it removed, you'd know immediately if there's a piggyback chip sticking out of the J3 port. Given that you've talked about dead pins, I don't see how you haven't already been in there. To answer an earlier question, the stock EEC-IVs do not take a tune via a flash. The J3 piggyback chip carry any adjustments to the tune, and when removed, the EEC reverts back to its stock tune. This can be useful for diagnosis, so long as you have an MAF 'calibrated' to your injectors. You should really run through Jrichker's cranks but no start checklist. Failing to crank when hot can be your TFI module, a faulty fuel pump, a failing MSD box, and several other things.

The fuel smell is pretty typical of cars with a 'calibrated' MAF, because the MAF can't change injection duty cycle while cranking. In fact, what size injectors are you running? 24s and 30s shouldn't cause a failure to crank, but the bigger the injector, the harder the car will be to crank. I don't really suspect this is your problem since flooring the throttle & cranking should clear the fuel out. However, with what you've said to this point, I wouldn't be surprised if you have several factors contributing to the problem you're experiencing.

EDDIEM75 · Jun 23, 2025

FastDriver said:
Never had a fancy Snap-On scanner, just the little Actron scanner, and all it really does is send the signal to a bulb that flashes. The actron is powered by a 9v battery, and doesn't depend on the diagnostic port for power or ground, other than to read the code.

There's an old thread around here somewhere on how to use jumpers to send the signal to the check engine light, in order to count the flashes and retrieve the codes.

In any case, it's kinda crazy that you've done all this thinking and talking without pulling a screw & push-plug and pulling out the passenger kick panel. With it removed, you'd know immediately if there's a piggyback chip sticking out of the J3 port. Given that you've talked about dead pins, I don't see how you haven't already been in there. To answer an earlier question, the stock EEC-IVs do not take a tune via a flash. The J3 piggyback chip carry any adjustments to the tune, and when removed, the EEC reverts back to its stock tune. This can be useful for diagnosis, so long as you have an MAF 'calibrated' to your injectors. You should really run through Jrichker's cranks but no start checklist. Failing to crank when hot can be your TFI module, a faulty fuel pump, a failing MSD box, and several other things.

The fuel smell is pretty typical of cars with a 'calibrated' MAF, because the MAF can't change injection duty cycle while cranking. In fact, what size injectors are you running? 24s and 30s shouldn't cause a failure to crank, but the bigger the injector, the harder the car will be to crank. I don't really suspect this is your problem since flooring the throttle & cranking should clear the fuel out. However, with what you've said to this point, I wouldn't be surprised if you have several factors contributing to the problem you're experiencing.

I believe I've touched on everything you've mentioned...

1. Actron runs off cig lighter.

2. Jumper wire does not flash codes{1993}.

3. Have removed ecm. Capacitors bad. No chip

4. It's not failing to start when hot. Start cold, immediately turn off and will not recrank.

5 And agreed several factors contributing. Fried ecm and possible o2 harness issue for starters. 24lb with pro m. I'm not really concerned about that injectors, ignition etc. Its without a doubt ecm and possibly wiring issues. Needing to determine o2 harness situation. Thanks

Mustang5L5 · Jun 25, 2025

I had the Actron. It's nice but it doesn't do much more than a simple Innova 3145 or paper clip method can do.

Regarding the ECU, this vid has some things you can check. Right off the top of my head checking continuity from pin 46 to pin 40/60 will give you a big clue to if the ECU is burned

View: https://youtu.be/p73aWm9OXbU?si=LLO7buRQ2d6DB82x

EDDIEM75 · Jun 25, 2025

Mustang5L5 said:
I had the Actron. It's nice but it doesn't do much more than a simple Innova 3145 or paper clip method can do.

Regarding the ECU, this vid has some things you can check. Right off the top of my head checking continuity from pin 46 to pin 40/60 will give you a big clue to if the ECU is burned
View: https://youtu.be/p73aWm9OXbU?si=LLO7buRQ2d6DB82x

Yeah the Actron is fine. I really just use it for my 93 k1500. It's as valuable as any with that ecm. Was hoping to get some pids from TPS, map etc. when this whole thing was just an idle issue. Never used it in an eec4.

Havnt watched video yet but have checked those circuits and OL. Will check video out shortly. Thanks

I'm still working my way through the o2 harness situation and at this point it doesn't appear to be the reason ecm fried. Vehicle has a wide band and an additional o2 harness. Then there's the fact I'm not the one who put this engine trans harness etc together. Everything could very well have been done properly but without verifying everything I won't know. Not really a situation where I look up wiring diagram on Mitchell alldata and start working circuits. This is why I don't take modified custom whatever vehicles in on flat rate. Not only can't make money you lose money. I'm just looking at it when I have free time. Anyway all good.

I am curious about something. The ECT sensor and tps sensor possibly more have two pigtails in this harness. Any idea why?

Mustang5L5 · Jun 25, 2025

EDDIEM75 said:
Yeah the Actron is fine. I really just use it for my 93 k1500. It's as valuable as any with that ecm. Was hoping to get some pids from TPS, map etc. when this whole thing was just an idle issue. Never used it in an eec4.

I don't think you can get PIDs. Or at least I couldn't on the Actron I had. Reason why i ended up selling it.

EDDIEM75 said:
I am curious about something. The ECT sensor and tps sensor possibly more have two pigtails in this harness. Any idea why?

Not sure what you mean here. ECT, ACT, EGR PV, TPS, BP sensor all share a common sensor ground. Pin 46 from wire 349 That's why when pin 46 fries, the engine doesn't run well, if at all since it takes out a lot of sensors.

As for O2 sensor harness jumper, for a 1993 with a manual trans ECU ( i assume it's a stick) it should be pinned same as bottom left

EDDIEM75 · Jun 25, 2025

Mustang5L5 said:
I don't think you can get PIDs. Or at least I couldn't on the Actron I had. Reason why i ended up selling it.

Not sure what you mean here. ECT, ACT, EGR PV, TPS, BP sensor all share a common sensor ground. Pin 46 from wire 349 That's why when pin 46 fries, the engine doesn't run well, if at all since it takes out a lot of sensors.

As for O2 sensor harness jumper, for a 1993 with a manual trans ECU ( i assume it's a stick) it should be pinned same as bottom left

Related to the Actron...is there anyway to read sensor voltage on these engines/ecms other than with multimeter. There's gotta be some device capable of that?

Two pigtails meaning two connectors. Of course one connector is plugged into the sensor and then there's another connector for that component that could also be used coming out of the main wiring harness. Also when looking up some parts there are two options for same vehicle/engine.

On the o2 harness situation since I do not know the history of the vehicle or did the engine trans harness install myself Im working on determining which harness o2 is currently in this vehicle to prevent frying the rebuilt ecm. It has a9p ecm so i should be ok from what I've read but will still need to double check. There's been a lot of hands in these 30+year old vehicles at this point and who knows who's done what. Most diy'ers make a complete mess of things. Some of the crap I've seen over the past 30 years in absolutely cringe worthy by any standards. So there's that.

Thanks for the response

Mustang5L5 · Jun 25, 2025

EDDIEM75 said:
Related to the Actron...is there anyway to read sensor voltage on these engines/ecms other than with multimeter. There's gotta be some device capable of that?

I don't really know. I'm sure there is a way as i imagine Ford had a method to do it. Now that I think back to it, i didn't have an Actron unit, but instead had a Rotunda diagnostic unit. It still didn't do anything beyond the basic code reader which is why i sold it off.

A lot of guys use breakout boxes which connect in series between the 60-pin harness and the ECU allowing you to probe the individual pins through the breakout box while the engine runs.

A9P would be the auto ECU, so actually the pinout for the o2 harness jumper would need to match the bottom right position in the above diagram

FastDriver · Jun 25, 2025

Moates quarter horse is going to give you all of the voltages or sensor readings that anything sends to the computer.

Kind of pricey, just for that, unless you're also going to tune.

General karthief · Jun 25, 2025

Sensors, senders.......
Sensors have two or more wires and communicates with the computer
Senders generally have one wire and communicates with the gauges
Now on the injector harness the ECT and IAT have similar connectors and if the injector harness is flipped right to left the sensors could be on the wrong wires. Or if the harness was taken apart things could get confused.

EDDIEM75 said:
Two pigtails meaning two connectors. Of course one connector is plugged into the sensor and then there's another connector for that component that could also be used coming out of the main wiring harness. Also when looking up some parts there are two options for same vehicle/engine.

What intake you gots? (Don't remember if it was mentioned) I ask because some explorer intakes don't have the hole for the IAT sensor.
That may be the connector you're referring to.

gkomo · Jun 25, 2025

Mustang5L5 said:
A9P would be the auto ECU, so actually the pinout for the o2 harness jumper would need to match the bottom right position in the above diagram

If i'm not mistaken he has a A9P but a manual conversion.

Engine EEC-IV Problems

EDDIEM75

New Member

gkomo

now i can hopefully expect to receive the shaft

EDDIEM75

New Member

GOvert

General karthief

wonder how much it would cost to ship you a pair

EDDIEM75

New Member

GOvert

Blown88GT

EDDIEM75

New Member

General karthief

wonder how much it would cost to ship you a pair

FastDriver

I was uncomfortably high & wearing a helmet

EDDIEM75

New Member

Mustang5L5

That is…until I whipped out my Bissell

EDDIEM75

New Member

Mustang5L5

That is…until I whipped out my Bissell

EDDIEM75

New Member

Mustang5L5

That is…until I whipped out my Bissell

FastDriver

I was uncomfortably high & wearing a helmet

General karthief

wonder how much it would cost to ship you a pair

gkomo

now i can hopefully expect to receive the shaft

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Engine EEC-IV Problems

New Member

now i can hopefully expect to receive the shaft

New Member

wonder how much it would cost to ship you a pair

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New Member

wonder how much it would cost to ship you a pair

I was uncomfortably high & wearing a helmet

New Member

That is…until I whipped out my Bissell

New Member

That is…until I whipped out my Bissell

New Member

That is…until I whipped out my Bissell

I was uncomfortably high & wearing a helmet

wonder how much it would cost to ship you a pair

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