Engine EEC-IV Problems

Jarhead67 · Jun 25, 2025

GOvert said:
Did you look at the spark plugs today?
I didn't catch the shop slang "brick". When I purchased my scanner, The Snan-On guy referred to it as the Snap-on MT2500. A Mech/Tech friend called his, a Snap-on Scanner. I'm in a partnership (very small) garage and there is already something else in the shop that we call "the brick". I'm sure that in the big garages/shops and dealerships, a lot of slang is thrown around.
Where in TN are you?

Jarhead67 · Jun 25, 2025

EDDIEM75 said:
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.

I suggest you get an A9L ECU and have it rebuilt by ECUEXCHANGE. Then you’ll be working with the correct ECU designed for the car.
And, the OHM ECU can’t be tuned without adding a chip.

Mustang5L5 · Jun 26, 2025

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

Right, but A9P is an AOD ECU. So the O2 harness jumper needs to be pinned to match the ECU. Automatic in this case.

If it is pinned for a manual trans, it will burn up the trace on pin 46.

GOvert · Jun 26, 2025

@Mustang5L5 Interesting information about the Fox body, auto, T-5 ecm differences. Direct me towards some wiring diagrams for 1988 and 1989 5.0s.
Now I'm wanting to avoid making a mistake with these two different pcms while working on brother's '88 converted to mass air and a factory AOD.
ADDED 10 mins later: Maybe that is the diagrams in post #35?

Mustang5L5 · Jun 26, 2025

GOvert said:
@Mustang5L5 Interesting information about the Fox body, auto, T-5 ecm differences. Direct me towards some wiring diagrams for 1988 and 1989 5.0s.
Now I'm wanting to avoid making a mistake with these two different pcms while working on brother's '88 converted to mass air and a factory AOD.
ADDED 10 mins later: Maybe that is the diagrams in post #35?

Full 1988 EVTM here. Hit download top right once you click on the page.

Resource icon

1988 Mustang EVTM

Jan 18, 2024

Electrical and vacuum troubleshooting manual

gkomo · Jun 26, 2025

Mustang5L5 said:
Right, but A9P is an AOD ECU. So the O2 harness jumper needs to be pinned to match the ECU. Automatic in this case.

If it is pinned for a manual trans, it will burn up the trace on pin 46.

My original suggestion (some post above i believe) was to buy a A9L and have ECUExchange go through it, but i caveated that with asking how far along was the wiring updated already to account for the A9P. If none, then a no brainer to buy a A9L.

Mustang5L5 · Jun 26, 2025

The jumper can be easily changed. Not a hard procedure.

My default advice has always been to setup the car for one specific transmission. By that, i mean if the car is automatic, then setup all the wiring for auto along with grabbing an auto ECU.

Electrical Thread 'O2 harness repin'

Jan 27, 2019

This thread is a HOW-TO for the process of repining the o2 sensor harness to match ECU/Trans, in the event the car is swapped. See post 15 as to what the jumper should be repinned to.

Step one. Remove the o2 sensor harness from vehicle. I find it easier to do on a bench plus it allowed me to degrease and reloom the harness. You can do this in the car if you want...it's that easy.

Here's the default loop setup in my 1988 AOD car

First you need to remove the red clip. Lightly pry up with a small pick

Next, look down inside with a light and you'll see small...

AeroCoupe · Jun 26, 2025

Buy a $200 ECU and send it to get repaired for another $150 or just repin the O2 harness....yeah I am repinning that mofo.

General karthief · Jun 26, 2025

I am not paying 200 bucks for a unkown computer.......ah, cause I already have one
Or two.......
I won't sell a computer unless it's been to the ECUexchange,

GOvert · Jun 27, 2025

@Mustang5L5 @EDDIEM75 My apologies to the OP for getting off of the original issue at hand but these discussions can turn into learning experiences for others too. When I turned 14 and quit working on bicycles to work on cars and trucks, I knew already knew several important things, three of the most important is righty tighty, lefty loosy (spelling), don't let out the "magic smoke" and mechanical devices with moving parts have to have oil or grease. What I'm getting at a short 50 years later is there is always more to learn.
Yesterday after some research here reading what Mike (Mustang5L5) shared, and going by the local Fox body guy's shop, I think I have a better understanding of what is going on with the A9L, A9P ecms and the way that the o2 harness is wired differently year to year and T-5s vs AODs. Tell me if I'm correct.
The ecm pinouts are the same, just the year to year and transmission options are different. A9P ecms "tune" bin file is a little different than the A9L tune and according to my local Fox body friend, the A9P pcm works well with the T-5 for a bit of better performance. Just the o2 wiring configuration needs to be correct for your original configuration.
I'm about to have a hands-on learning experience with a Foxbody 5.0. A person close to me has upgraded his '88 to Mass air and at the same time added Explorer/Mountaineer GT-40 style lower intake and upper plenum, larger throttle body along with an EGR delete. We still need to add a bung to install an AEM AFR gauge kit to the vehicle which will give real time AFR readings. Also, this signal from the AFR gauge will be split to feedback through the old EGR circuit to get RT, real time feedback to the ecm with a Moates QuarterHorse device. As I think and type this, we will have to look at what to do with the EGR wiring that is about to get or not, the tri resistor circuit to make the ecm think that the EGR is in place.
See, I've again found out something that I don't know.

FastDriver · Jun 27, 2025

GOvert, no need for the 'tri-resistor circuit' as you call it. Just snip the EGR-to-A9L (I assume you're switching to A9L) wire, and splice in the WB O2 signal. I can't name it off of the top of my head, but there's a boolean Scalar (0 or 1 value only) input in the Stock Tables that will disable all EGR functionality. This will ensure that the A9L isn't looking for it, at all. The resistor circuit is only meant for cars that are left on the stock tune. They will eventually kick the check engine light without it.

General karthief · Jun 27, 2025

I'm gonna ask,
can you take the EGR valve off the intake, block off the opening leaving the valve plugged in and hide it someplace so the computer thinks it's working?

Mustang5L5 · Jun 27, 2025

General karthief said:
I'm gonna ask,
can you take the EGR valve off the intake, block off the opening leaving the valve plugged in and hide it someplace so the computer thinks it's working?

Not desirable. Will run a little lean at part throttle cruising because the ECU thinks that inert gas is being injected

Really, just unplug it. The ECU will disable its function.

If you don’t want the check engine light, there are resistor tricks to make the ECU think the egr is stuck open/closed (I forget which) which triggers a different code. That code doesn’t display the cel and still disabled the function in the ECU.

General karthief · Jun 27, 2025

Mustang5L5 said:
Not desirable. Will run a little lean at part throttle cruising because the ECU thinks that inert gas is being injected

Really, just unplug it. The ECU will disable its function.

If you don’t want the check engine light, there are resistor tricks to make the ECU think the egr is stuck open/closed (I forget which) which triggers a different code. That code doesn’t display the cel and still disabled the function in the ECU.

Damn....more useless ideas from the guy in the back row

GOvert · Jun 28, 2025

@FastDriver I'm just now looking in the GUFX related file/s and haven't yet gone through and identified the "switch" per say. I'm looking for the 0 or 1 value in the parameters.

GOvert · Jun 28, 2025

@FastDriver This might be it.

FastDriver · Jun 28, 2025

There ya go. Set that to 2. I just looked in my own tune and it's disabled.

GOvert · Jun 28, 2025

@FastDriver
Are you using the 'decipha' files and TunerPro RT, Quarterhorse etc?
I'm just getting familiar with the equipment and getting to know my way around some different bin files.

FastDriver · Jun 28, 2025

I got my QH with a license dongle for BE & EA used on FB marketplace for $250. So, that's what I use. If they weren't already free to me, I'd've tried tuner rt.

I did not use decipha's tune (A9L2.bin) as a base, and instead stuck with the stocker (A9L.bin). I was most comfortable starting from a known point and tweaking from there. I think the A9L2 shuts down some of the timing tables, which is good for simplicity & probably perfectly fine, but I wanted to try to keep the elevation adjustments & WOT table. That said, if it's ever a problem, I'd be willing to kill the other tables and go down to a single table, as I'm pretty sure that's the only way to tune on my standalones in my other cars.

The car I'm tuning is a simple H/C/I car that was running well around town, but had minor surging. So, my intent was to only makes small changes from stock to clean up idle. That led to quite a bit more.

I followed the 'Leech Motorsports' videos on youtube, and searches on eectuning.org with an occasional post for a special exception or two.

GOvert · Jun 28, 2025

When I purchased my Quarterhorse, at the time it was only available to purchase with BE. I already had TunerPro RT installed on my laptop and had gotten familiar with the way that it works. I'm using it in an EEC-V situation. I would like to use BE on the Fox body Mustang but I haven't yet determined if I install it on my laptop with TunerPro RT, will there be conflicts? But I suppose that if only one of the two different programs were in use, it shouldn't be a problem? I don't want to mess up my TunerPro RT stuff that is logging properly with my 1999 Crown Vic pcm controlling a 5.0 c-n-p project.
If I can get near the Fox body vehicle with my Quarterhorse, can I simply copy the existing bin file? I know that the owner would want to keep the A9P and only make the few necessary changes before programming a chip.

Engine EEC-IV Problems

Jarhead67

Jarhead67

Mustang5L5

That is…until I whipped out my Bissell

GOvert

Mustang5L5

That is…until I whipped out my Bissell

1988 Mustang EVTM

gkomo

now i can hopefully expect to receive the shaft

Mustang5L5

That is…until I whipped out my Bissell

Electrical Thread 'O2 harness repin'

AeroCoupe

lube between the nut and the face. I know my lubes

General karthief

wonder how much it would cost to ship you a pair

GOvert

FastDriver

I was uncomfortably high & wearing a helmet

General karthief

wonder how much it would cost to ship you a pair

Mustang5L5

That is…until I whipped out my Bissell

General karthief

wonder how much it would cost to ship you a pair

GOvert

GOvert

FastDriver

I was uncomfortably high & wearing a helmet

GOvert

FastDriver

I was uncomfortably high & wearing a helmet

GOvert

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Engine EEC-IV Problems

That is…until I whipped out my Bissell

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now i can hopefully expect to receive the shaft

That is…until I whipped out my Bissell

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lube between the nut and the face. I know my lubes

wonder how much it would cost to ship you a pair

I was uncomfortably high & wearing a helmet

wonder how much it would cost to ship you a pair

That is…until I whipped out my Bissell

wonder how much it would cost to ship you a pair

I was uncomfortably high & wearing a helmet

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