89 Fox Problems

Rob88

Member
Nov 8, 2020
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I have a 89 Coupe I just did a V8 swap on but I'm having some problem getting the fuel pump to prime. I also noticed Im not getting any power to my fuel injectors. So the fuel pump is good, I tested it before installing it. The ECU has had the capacitors replaced, I know the ECU works, I tested it on my other Fox and the fuel pump primed and the car started. The ignition is new and turns the car over but no start. I've tested the four fusible links by the starter solenoid, they're all getting 12volts. The ECC relay by the ECU is clicking. The red wire and the red wire with the black stripe that goes to the inertia switch in the trunk is not getting any power. The orange wire with the blue strip under the driver seat is getting power. The pink wire and red wire under the driver seat isn't. I was starting to think that the harness that runs under the carpet to the trunk, maybe a wire had corroded. But I noticed when I took a small jumper wire and jumped it from the orange wire to the pink wire on the fuel relay connector the fuel pump primed. I was told the car will start like this this but I don't want to run it that way..."rigged". I want it to run the correct way. With the fuel pump running 2-3 seconds etc etc. I picked up another fuel today and I'm going to give it that a shot tomorrow. But just in case it's not the fuel relay, what could it be and why isn't my fuel injector harness getting a pulse? I need help and I don't know what else to do or where else to look.
 
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Blown88GT

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Nov 13, 1999
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4 cyl & 8 cyl engine harnesses are not identical.
Anyway, diagnose voltages with this wiring diagram. Don't just throw parts at it.
With ignition off, see if you have continuity from ECU pins 37 & 57 to fuel pump relay red wire.
I can't remember if 57/37 are hot all the time with ignition on. It is power to the injectors & the fuel pump relay control side.
I know that pin 1 (KAPWR) Keep Alive power is hot all the time, ignition on or off.
 

Foxslider

im not that much of a idiot
Oct 25, 2019
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I lost the fuel pump and spark a whileback. It was the relay for the ECU for me. You are getting spark at the plug? Just to be certain its only a fuel pump power problem?

No way its the ignition switch?
 

Rob88

Member
Nov 8, 2020
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Richmond V.A
I lost the fuel pump and spark a whileback. It was the relay for the ECU for me. You are getting spark at the plug? Just to be certain its only a fuel pump power problem?

No way its the ignition switch?
Yes, I'm getting spark. The ignition switch is brand new. It turns over the car.
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Is the computer giving you codes?
Here, go through this checklist:
 

Mustang5L5

Put lubricant all over the balls
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The only wiring swap I did was the V8 engine harness and headlight harness from a 89 LX.


Verify the O2 sensor harnss jumper is pinned correctly for the ECU you are using. If it's a manual ECU, you need to pin it as a 88-90 Manual trans car.

Having this jumper wrong can fry the ECU
 

Rob88

Member
Nov 8, 2020
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Richmond V.A
Verify the O2 sensor harnss jumper is pinned correctly for the ECU you are using. If it's a manual ECU, you need to pin it as a 88-90 Manual trans car.

Having this jumper wrong can fry the ECU
Just asking, but what does the O2 sensor harness have to do with the fuel pump not priming?
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Just asking, but what does the O2 sensor harness have to do with the fuel pump not priming?

if it’s wired incorrectly it can fry the ECU which can cause the no fuel pump prime issue you are having.

not saying this is the cause, but something to check, especially if you try another ECU or have to repair yours.
 

jrichker

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Verify the O2 sensor harnss jumper is pinned correctly for the ECU you are using. If it's a manual ECU, you need to pin it as a 88-90 Manual trans car.

Having this jumper wrong can fry the ECU
O2 Sensor harness interchange and modification

Revised 24-Oct-2020 to add O2 sensor harness connector pin layout diagram
Originally Posted by 302EFI

The wires for the 02's and low oil did not change throughout the years, they are all in the same place.
The main ones you need to worry about are (on the harness end (ECU) that plugs into the 02 plug) is:
\- 1. Lightblue / yellow
- 2. White / Purple
- 3. Purple / Yellow
The White/Purple & Purple/Yellow gets looped for a automatic ECU
The Purple/Yellow & Lightblue/Yellow for a manual ECU

End of 302EFI’s comments.

O2 sensor harness pin layout, transmission side wiring connector.

Not all wires are shown for clarity and simplicity
Thanks to Mustang5L5 for help with the drawing…

attachments\664193\


See http://forums.corral.net/forums/gen...manual-auto-differences-year-differences.html for more O2 sensor wiring harness info

Basic premise to use with transmission swaps:
Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L. Doing so will damage the computer’s internal signal ground.
Only run an Auto trans O2 sensor harness with an A9P in a car that has an Auto trans. Using a 5 speed trans O2 sensor harness with an Auto trans will cause no crank problems.
See the pictures below for help finding and fixing the burnt computer trace.
hash-146a243133771eeba54f17b17d721b1f-jpg.jpg

The fix is some careful soldering of a small jumper wire across the burnt section of copper trace.
20160325_234845-jpg.553347

The 4 cylinder O2 harness uses 4 wire O2 sensors. It probably won’t work correctly without modifying it.