No Fp Prime/no Koeo Light

[jrichker]

That stock battery cable is not existent on my Stang. Never had one.
However, there is a ground attached to the sheet metal right by the computer under the kick panel.

That is not the computer power ground. That is the shield ground for the TFI wiring.

The computer power ground is 2 each 14 gauge wires that connect to the body up near the windshield washer filler neck.

Karthief gave you the text from my ground tech note, but did ' get the diagrams, so here they are...



Rear mounted battery ground wiring. Follow this plan and you will have zero
ground problems.

One 1 gauge or 1/0 gauge wire from battery negative post to a clean shiny spot on the chassis near the battery. Use a 5/16” bolt and bolt it down to make the rear ground. Use a 1 gauge or 1/0 gauge wire from the rear ground bolt to a clean shiny spot on the block.

One 4 gauge wire from the block where you connected the battery ground wire to the chassis ground where the battery was mounted up front. Use a 5/16” bolt and bolt down the 4 gauge engine to chassis ground, make sure that it the metal around the bolt is clean & shiny. This is the alternator power ground.

The computer has a dedicated power ground wire with a cylindrical quick connect (about 2 ½”long by 1” diameter. It comes out of the wiring harness near the ignition coil & starter solenoid (or relay). Be sure to bolt it to the chassis ground in the same place as you bolted the alternator power ground. This is an
absolute don’t overlook it item for EFI cars
The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it 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.

Note: The quick disconnect may have fallen victim to damage or removal by a previous owner. However, it is still of utmost importance that the black/green wires have a high quality ground..

Picture courtesy timewarped1972

Crimp or even better, solder the lugs on the all the wire. The local auto stereo shop will have them if the auto parts store doesn't. Use some heat shrink tubing to cover the lugs and make things look nice.

 

[General karthief]

Thanks, I work better with visuals.
Cartoons, get it? Car-toons

Nevermind.

 

[Dane Brahler]

Okay so even after triple checking all my grounds AND resoldering the fried trace I still have no fuel pump when I turn the key!!! This has turned into one heck of a nightmare!

I have no ohm reading from pin 46 on ecc connector to pin on ecc.

To restate:
-battery grounded to seat belt studs(4ga)
-block grounded to chassis(4ga)
-computer "dedicated" pigtail grounded to alternator ground on block
-hego grounded to intake bolt

I have good ohm readings from pin 46 on the computer to pins 40/60 on the computer. I know that issue is resolved.

-Ecc relay is clicking when I turn the key
-With key on, I have 12.4 volts at fp signal wire(tan/green) from ecc connector to ground
-i have 12.4 volts at fp relay at fp signal(tan/green)
-fuel pump runs when I jumper yellow wire and pink/black wire at fp relay.
-i still have good fuel pressure 40psi at Schrader valve.

EEC TESTER:
-no fuel pump on when jumpered signal wire to ground.
-no code dump when I connect black/white to test input

I'm at the point where I believe the computer is just fried simply because I did have the tester working prior to pulling engine.
Thoughts? Opinions?

 

[General karthief]

Pull the computer and see if it has a burnt trace

 

[Dane Brahler]

Pull the computer and see if it has a burnt trace

Burnt trace in two different locations. Checked for continuity once I soldered the connections and they all checked.. just doesn't make sense. If I jumper the fp relay the car runs fine!

 

[General karthief]

Will the computer give you codes? Not that your looking for a specific code, just to see if it's functional.

 

[Dane Brahler]

Will the computer give you codes? Not that your looking for a specific code, just to see if it's functional.

Nope. It won't give me any codes from the eec tester. Is there any way to pull codes with the engine running? Am I even doing the koeo correctly?
Jumper the black /white wire to the diagnostic port then turn the key to "on"?

 

[Dane Brahler]

New discovery:
Before I soldered the signal ground trace this did not work. Just tested it again and when I turned the ignition key to on the fuel pump came on!

 

[General karthief]

Nope. It won't give me any codes from the eec tester. Is there any way to pull codes with the engine running? Am I even doing the koeo correctly?
Jumper the black /white wire to the diagnostic port then turn the key to "on"?

This will tell you how to pull codes
https://www.stangnet.com/mustang-fo...codes-from-eec4-in-86-95-5-0-mustangs.889006/

 

[Dane Brahler]

I just picked up a different ecu today
It is an 88 mustang gt speed density computer model DA1
i have the maf conversion harness already and it was hooked up to the old ecu.
with the key on, the fuel pump kicks on for 2-5 seconds as it should! (HOORAYY)
engine will crank but now it wont fire up like it would with old ecu and fp relay jumpered. Am i missing something now sense this is a "speed density" computer? this MAF conversion harness is made by FMS. Is there additional changes that need to be addressed now?

 

[Deleted member 215073]

I thought you needed to replace the computer as well when you convert to mass air? If that's the case, a speed density computer won't work.