1985 Automatic Mustang 5.0L fueling issue

livinnstix

New Member
Oct 2, 2011
10
0
1
Hinesville, GA, US
Hey guys,

Have the car listed in the title. chasing a fueling issue, I found the relay under the seat and the inertia switch in the trunk. I tracked down a wiring diagram and this is what Ive come up with at the relay under the seat. (used a multimeter and these are the readings)

Red/Black - 12V - turns relay on and off

Tan/Light Green - 12V - should ground relay? (attempted to force a ground and made the dash go crazy)

Yellow - 12V - power wire

Pink/Black - dead - fuel pump
(fuse has power in and out)

If someone can tell me which wire is supposed to be the ground.

I jumped the yellow wire to the pink/black wire and makes the fuel pump turn on but still no fuel to the injectors (throttle body injection).

First post and Ive tried doing searches and can't find what I need so I was hoping someone could help me out and point me in the right direction. The wiring diagram I have doesn't show much just components and there wires but doesn't show where the power comes and goes.

Today I chased my fueling issue to the injectors at the CFI. I rented a noid test set and no lights at all. Broke out the multimeter and I have 12V to all 4 wires at the injectors (white/orange, Red, Red, White/Green). I disconnected the injectors and checked them with positive and negative test leads and they clicked. I took the distributor module off and had that checked and it was good. At this point Im looking really hard at the ECC.

I can get the car to run on starter fluid/gas in a cup but the injectors are not firing.

Issue: Injectors not firing, fuel pump not kicking on without jumper wire.

Any help would be greatly appreciated. Thanks in advance.
 
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jrichker

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The ground for the fuel pump relay is provided by the computer. The computer also provides the ground for the injectors, causing them to fire.

There is very little documentation or help with the 85 CFI system, most of the cars are either full EFI or carb.


The following is from the 86-93 EFI electical system troubleshooting, your 85 may be the same.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972
ground.jpg


Correct negative battery ground cable.
56567d1230679358-positive-negative-battery-cable-questions-86-93-mustang-oem-style-ground-cable.gif


3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.
 

jrichker

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The photo shows evidence of either corrosion or overheating or both. Figure out what pin number it is and then check out a Chilton shop manual for your car. Your public library may be able to borrow a copy, or you can buy one at the auto parts store. If you are going to keep the car, spend the $20-$30 for a manual. It will pay for itself it time and sweat saved.

0900c1528004e2a2.gif
 
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