1990 Bronco Fuel system electrical issues


New member
Dec 18, 2019
Orlando Fl
I wanna start by saying thanks to all who have posted about these fuel system electrical issues. I have read many threads in this forum. They have gotten me to where I stand with my truck today. My issue seems to be typical to these trucks. I turn my key on. No prime at the Fuel pump. Unplug the fuel pump, check voltage, meter shows around 4.5 volts. Same 4.5 volt reading at inertia switch. Same 4.5 reading at fuel pump relay on the red wire. 12v at the yellow wires. Same 4.5 reading at the EEC relay red wire. 12v at the yellow wire. So where do I go from here? Any more help is greatly appreciated!!
Last edited:


Active member
Staff member
Nov 25, 2012
2 thoughts for ya,
Have you pulled the EEC and checked for Damage, And have you probed the Fuel relay to make sure its working properly?


96 Bronco 5.0
Staff member
Oct 18, 2005
Coronado, CA
Yo Geo,
As Skittrer advised.
EEC IV PCM Removal in 87- 91:
To remove it first disconnect battery & use a 10 mm socket to unbolt the wiring harness connector from inside the engine bay. Then pull plastic kick panel from inside cab & remove the retainer clip.
The firewall rubber gasket will have a pretty good grip on the connector so it will take some persuasion to free.
Remove it by lifting rear slightly & wiggling it out of driver's inside kick panel adjacent to pedals.
"Should be one small metal screw holding it. Just slide it out, but be careful w/ gasket for firewall. Don't mess it up, you can reuse it." by Darth_ted_82

EEC IV Capacitor Replacement in a 90 by seedpress @ https://www.broncozone.com/threads/fuel-delivery-problem.20788/
Also inspect resistors.
Although relatively inexpensive, I would avoid Cardone reman PCMs.
AES Modules @ AES Modules | Rebuilt & Reman Control Modules

ProTech Auto Systems @ Ford Car Computer Repairs for ECU, PCU & TCU
jermil01 wrote, "In the past I've bought an EEC from these guys before. Good service and fast turn around. Plug in your info and you'll quickly find what you're looking for: Price is pretty reasonable.."
G7 Computers @ https://www.g7computers.com/pages/how-does-this-work
...gedebohls wrote, " i went with sending my ecu to G7 computers in Canandaigua, NY, the reason i went this way is because i send them my unit, i get my unit checked out 100% and they will then fix as needed. I like this bc I will know for sure if my ECU is or was bad, etc, and I get my ECU back fixed. the cost is $225 plus shipping one way, if nothing is wrong with my ECU i get 100% refund. Once i get my ECU back or get an update from G7 I will update."
Update; "I sent the EEC to be rebuilt by G7 computer and they quickly sent the EEC back saying they replaced a faulty resistor. When the EEC came back I still had the same issues with the bronco , and we spent a lot of time re testing and checking things to only determine that the only possible issue was a bad EEC, so back to G7 Computer. This time they determined a faulty Main processing chip, and stated that the damage was to extensive to replace the main chip, I get it; it is a computer sometimes it is hard to pin point an issue when it is intermittent. My question is; is it just not cost smart for a company like G7 to not want to replace the main chip, or can you just not replace the main chip? So in short G7 sent the EEC back to me and will credit $225 of the $250 saying they get a diagnostic fee of $25, which I also get , "Well sort of get". "
@ https://www.fullsizebronco.com/foru...-free-zone/500174-94-gremlin.html#post7155426

A long time Ford mechanic wrote, "The main causes of failure is water in the PCM plug or cap failure inside of the PCM. Make sure you have enough Di-Electric Grease in the plug to waterproof it."

Ryan M wrote in his "install a chip" article @ Fuel Injection Technical Library » install a chip
"DO NOT USE EXCESSIVE TAPE TO SEAL THE COMPUTER. TOO MUCH TAPE WILL CAUSE THE COMPTUER TO OVERHEAT!" The tape and a piece of foam was to be places around the chip J3 port, but can be applied to the case itself.

I recall that someone here that their PCM died due to a bad weatherstrip. No further details were provided.

In an old ford truck forum that is now off line. "The water leakage may be due to the PCM connector cover not seating completely and water leaking down from the cowl panel grille (cowl top vent panel) area."

Here are the 1990 Bronco Pre-Delivery Shop & Electrical & Vacuum Troubleshooting Manuals (EVTM), Partial by my buddy Kingfish999 in Google Drive @ https://drive.google.com/drive/mobi...?usp=sharing&tid=0BzRTW4yeT2u4NXB6NW5neFRoZGc
Find page # of item desired in contents, then flip screen down like spinning a thumbwheel, then stopping periodically to see what page you are on.
Suggest you download for faster scrolling and to use the table of contents index.

1990 Ford Bronco Brochure, partial by El Kabong @ 1990 Ford Bronco Brochure pictures, videos, and sounds | SuperMotors.net

Free registration for some wiring diagrams (86 through 96) and Technical Service Bulletins, (80 through 96), same as by Ford @ BBB Industries- Premium Alternators, Starters, Power Steering Products and Turbochargers | TSB and Wiring Diagrams Database End-User License Agreement

Good fortune!


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