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Excellent thread. I've almost solved a ten year problem. Car is a 66' mustang with an EFI 5.0 w/an AOD out of an 89 foxbody. Many years ago I got a harness that was told it was out of a 90' 5.0 AOD stang. It has the light blue jumper wire along the bottom row of pins.

I also purchased an ecu from someone at the time who told me it was out of a stang, years ago I had no idea I needed an A9P. After pulling the ecu which I had buried up inside the dash, to my amazement it was not an A9P, it was a truck ecu! The car always ran rich, idled sloppy, I tried many things over the years.

I just pulled the ecu and did a test of pin 46 during crank and there is zero voltage. I'm going to get an A9P ecu. HERE IS MY QUESTION:

Upon inspecting the wiring and the light blue looped wire, the opposing connector has NO wires in either pin location, meaning, the looped wire is doing nothing. I do not see anywhere where this harness has been cut or modified at all. I'm going to track down a diagram but has anyone seen this? Wires missing in those pin locations?
 

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Excellent thread. I've almost solved a ten year problem. Car is a 66' mustang with an EFI 5.0 w/an AOD out of an 89 foxbody. Many years ago I got a harness that was told it was out of a 90' 5.0 AOD stang. It has the light blue jumper wire along the bottom row of pins.

I also purchased an ecu from someone at the time who told me it was out of a stang, years ago I had no idea I needed an A9P. After pulling the ecu which I had buried up inside the dash, to my amazement it was not an A9P, it was a truck ecu! The car always ran rich, idled sloppy, I tried many things over the years.

I just pulled the ecu and did a test of pin 46 during crank and there is zero voltage. I'm going to get an A9P ecu. HERE IS MY QUESTION:

Upon inspecting the wiring and the light blue looped wire, the opposing connector has NO wires in either pin location, meaning, the looped wire is doing nothing. I do not see anywhere where this harness has been cut or modified at all. I'm going to track down a diagram but has anyone seen this? Wires missing in those pin locations?

It’s up to you to verify the pins in the connectors are in the correct spot

This loop talk is not needed

Just I’d the circuits on the pins, no one can tell you your 30 year used harness is the correct one
 

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Upon inspecting the wiring and the light blue looped wire, the opposing connector has NO wires in either pin location, meaning, the looped wire is doing nothing. I do not see anywhere where this harness has been cut or modified at all. I'm going to track down a diagram but has anyone seen this? Wires missing in those pin locations?

Reading your post, i don't think the o2 harness wiring has any bearing on your issue. Sounds to me like you have an early Mustang speed density engine harness which had a 5-wire connector at the o2 harness, vs the later 1989+ (Mustang) engine harnesses which had a 7-wire connector.

Now, that mismatch isn't an issue as the early cars did not use the jumper and routed the wires elsewhere.

I think your issue is more or less the truck ECU and engine harness combo. I beleive the trucks went MAF in 1993, so it's possible the 1990 "mustang" harness you bought was really a 1990 F150 5.0 harness which is provisioned for speed density. I don't know as i haven't examined many f150 wiring harnesses. But the fact that you have 5 wires on that harness at the o2 connector suggests it's a speed density harness. Before you slap the A9P on, you want to verify the harness is set up for MAF. On the speed density mustangs, that involves changing a few wiring pins around on the ecu and running 7 more wires. You might have to check wire colors on the ECU and compare them to SD or MAF mustang wiring to see what you have exactly.

Do you have a MAF on your car? What's the ECU number on the computer?
 

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The car does have a MAF on it and the wiring appears to be factory. I don't ever call modifying it to MAF. I installed this harness over ten years ago. The car fire up and ran, but it always ran rich. I went though everything you can think of to fix the rich condition but nijing worked. That's why I think this thread is a God send!

The part number on the ecu is E9AF-14624-aa (GTE).
 

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WHAT did you do to try to fix the rich condition?

How do you know you have a rich condition? Smell?

Using an excuse that it has run for ten years, so you think all is okay, is a result of any imperial measurements, that is what i think....
 

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The car does have a MAF on it and the wiring appears to be factory. I don't ever call modifying it to MAF. I installed this harness over ten years ago. The car fire up and ran, but it always ran rich. I went though everything you can think of to fix the rich condition but nijing worked. That's why I think this thread is a God send!

The part number on the ecu is E9AF-14624-aa (GTE).
How do you know that it’s rich?
Is there a CEL and fault codes for a rich condition?
Do you have a wideband AFR gauge on it?

It’s possible that you aren’t going into closed loop, you need the O2’s operating correctly for that. Easy check though.

Don’t say “it smells rich”, you can’t diagnose a rich condition by smell.
 

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We hooked it up to a four-gas analyzer and it had high CO levels at idle (Hc was fine). So it's not just "smelling rich". I have tried swapping MAFs, replacing O2's, new 195 degree thermostat, coolant temp sensor, all things that would "contribute" to a rich condition.

That's why I said this thread is a God send because I believe it's the incorrect ECU. I'm going to check the pinouts at the ECM to make sure it's a MAF and not a hacked SD.
 

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Just look up the 3 digit code.
There are many other MAF EEC’s out there beyond A9P, A9L.

And if you think it’s rich, pull the fault codes.
 

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Should have mentioned, no fault codes KOEO or KOER (11's) only codes are EGR codes because I have the EGR disconnected.

I also checked the MAF pins at the ECM and the numbers and color codes are correct. It's definitely a MAF harness. I will get an A9P computer and install it. At least I'll know I have the correct ECM.
 

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The part number on the ecu is E9AF-14624-aa (GTE).

Can you post a pic. I don't get any returns when i search those numbers.

Edit:

Yeah, thats not the ECU box code. I beleive that's the connector part number

Check out this overpriced auction for an A9L. The white label states A9L, where the reverse side has a printed p/n and the GTE tag. This isn't the code. You want the 3 or 4 digit box code on the label side

https://www.ebay.com/itm/A9l-Factor...h=item2f24947dbd:g:-ecAAOSwPrtbzJyo:rk:1:pf:0
 

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We hooked it up to a four-gas analyzer and it had high CO levels at idle (Hc was fine). So it's not just "smelling rich". I have tried swapping MAFs, replacing O2's, new 195 degree thermostat, coolant temp sensor, all things that would "contribute" to a rich condition.

That's why I said this thread is a God send because I believe it's the incorrect ECU. I'm going to check the pinouts at the ECM to make sure it's a MAF and not a hacked SD.
You have cats on the exaust??

You hooked up a gas analyzer,,,,that was great....then you failed the rest of the way to diagnose

You shot the parts cannon at it, that rarely works

It should take 30 mins to diagnose this, first thing you do is measure the 02 signal, are they lying?

That is why you verify wiring........
 

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Not sure if I need a pic hosting website to post this, so I copied and pasted the pic. Hopefully it comes through.

This is the only markings on the entire ECU.
That's not the ECU code. I have several ECUs and they all have that marking.

You are missing the label, so basically you have an unknown ECU

Here's the labels on some ECUs I have for example. A9L and B9M1 (89 t bird 3.8) are the box codes
 

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