1990 Bronco Fuel pump doesnt run unless jumped

[marketgy]

Hopefully somebody can help im stumped. My 1990 Bronco just up and quit in mid stream. I've replaced plugs, wires, cap, rotor, coil, tci module, eec relay and finally the fuel pump relay as well as reset the inertia switch, no luck. Now when I take the fuel pump relay off and run a small wire into the hot port and another port on the harness housing, the fuel pump turns on and the truck starts, basically I created a small jumper. Logically we thought it ultimately ended up being the relay since we got it to run right at the point of entry where the relay goes but no go. Any ideas at this point what it could be I'm lost?

 

[miesk5]

yo M,

WELCOME!

Check for;

Socket Corrosion

power from Fusible Links W & N using:

Wiring Diagram in a 90



Source: by Seattle FSB (SeattleFSB) at SuperMotors.net

A, J, L, M, G, W, N, G & P Location in Wiring Diagram in a 90; Fusible Link A-Brown 18ga to Rear Window Defroster; L-Brown 18ga to C202; M-Blue 20g to C202; G-Blue 20g to Exterior Lamps; W-Blue 20g to Fuel Pump Relay; N-Blue 20g to EEC Power Relay; G-Blue 20ga to Trailer Adapter; P-Blue 20ga to Splice 115 to Connector 202 & Exterior Lamps & Daytime Running Lamp (DRL); J-Green 14ga to Alternator



Source: by Seattle FSB (SeattleFSB) at SuperMotors.net

Location pic; EEC Power Relay (BROWN Connector) next to the FP Relay (GREEN Connector), Trailer Tow Relay (Grey Connector) & EEC Test Connector pic in a 90; on driver's side fender apron to the rear of the Airbox

Source: by Seattle FSB (SeattleFSB) at http://www.supermotors.net/registry/media/844464

I need to try another ISP soon; Comcast has decided to slow down speeds again

 

[marketgy]

Thanks so much for the reply, I'm kinda following you here. Based on the 2nd diagram it looks like the wires for the fusable links are near the battery. Now, I'm not quite sure how to trace to corrosion issue based on the symptoms I mentioned. Is it something near the relay harnesses, are more on the battery side? Now once I trace the corrosion how do you recommend the best way to clean up. Thanks for the help.

 

[BroncoJoe19]

Here is another angle of attack.

If you look at the diagram, you are jumpering the relay out of the picture and the engine is starting. FOr that to be the case you jumpered the Yellow to Brown wires within the fuel pump relay socket.

Since you are sure that the relay is good, then there is a problem in the other... two smaller pins. The RED one brings power to it. You can check for power there with a test light, with the ignition key turned ON/RUN. If no power, then you have to look back... why not?

What completes, the other side of the circuit is that the PCM grounds the Tan/LightGreen wire, if not... then we need to find out, why not?

In the middle of the Tan/Green wire (between the relay and the PCM) is the SELFTEST connector, the one you use for pulling diagnostic codes. It is right next to the fuel pump relay. If you replace the relay into its socket, and ground out the fuel pump test pin of the self test connector, the fuel pump should kick on continuously (with the key ON/RUN) That is of course provided that the Red one has power as we discussed above. IF the fuel pump kicks on, then the problem is that the PCM is not sending a ground.

If the PCM is not sending a good ground, the first thing to check is the PCM ground. Located at the driver's side hood hinge.

Here is a picture of the sleft test connector labled so you can determine the fuel pump self test pin.

http://broncozone.co...&attach_id=6766