I have a 87 Bronco II with a 2.9
The problem I'm having is the fuel pump relay will not energize unless I put ground to the tan wire. Then it will pull in and the fuel pump's run.
Also I'm not getting a pulse at the injectors when I spin the motor over. But I am getting spark at the plugs.
I had a buddy of mine scan the computer but he could'nt get anything out of it. His scanner could'nt find the computer.
I have replaced the staitor & module in the distributor, The computer and totally unrapped the wiring harness and tested all the wires and found nothing wrong. It's like the computer is shut down.
I have been working on this for 3 weeks and have'nt gotten anywhere. ANY HELP WILL BE GREATLY APPRECIATED !!!!!!!!!!!

 

The PCM controls the grounding of the fuel pump relay, as well as code output and fuel injector firing. Have you checked for battery voltage at the PCM power pins (red wire at pins 37 and 57)? How about a good connection for the PCM grounds (black/ltgreen wires at pins 40 and 60). The PCM is grounded directly to the battery (small wire that connects to the battery cable). Any problems with this ground connection can create problems for the PCM. Check power and ground for the PCM and see what that looks like.

 

Thanks for the help mrshorty.

I checked the pins you suggested last night and I'm getting 12 volt at pins 37 & 57 and a good ground at pins 40 & 60

Anything else you can think of that might cause this.
I'm starting to think that I got a bad computer from the part supplier. It was a remanufactured one as ford has discontinued making it.

 

Does it have a waranty? It might be bad. Just a thought.

 

The PCM should also get "switched" 12V. This is done via a
relay, check to see if this relay is being "picked" when you turn
the ignition switch on....

 

I got my hands on a wiring diagram & checked cont. from every wire that runs to the computer to the end connection. All tested good. MAN that was a job.
It has to be the computer.
Now to fight with the part supplier for warranty on the new computer.

Unless there is a sensor that will shut the computer down????

ANYONE....

 

OK.
So today I got a new computer from the part supplier and a new O2 senser. Installed them turned the key and...... NO FUEL PUMP RELAY.
I am about to give up!
Does Anyone Have any idea what might cause this????????????

 

I have to thinkg that there is an electrical problem between the fuel pump relay and the PCM. When you replaced the PCM, did it replace everything from the connector up, or was it a module that plugged into the existing "connector" and housing (I don't know. never had to replace a Ford PCM)? Does the new PCM give you trouble codes yet? A signal at the injectors? Will the engine run if you ground the fuel pump relay?

 

Hope it's not what happened to mine that I had. The tailpipe busted so all the exhaust was blowing out right on to my fuel tank. It ended up melting the wires to the fuel pump and parts of the fuel pump (inside the tank,) all with more than 3/4 of a tank of gas left. Mechanic thought I was lucky it didn't explode. Just thought I'd share a story. That was an 89 that it happened to. Good luck getting it figured out.

 

Hay! mrshorty good to here from you. And thanks AG4.0 for your warning.
I have tested the tan wire that runs from the fuel pump relay to the PCM by appling ground to the tan wire at the PCM plug and the relay pulls in and the pumps run.
The new PCM was the complete computer,Without the harnis plug. I also replaced the staitor and module in the distibutor.The fule tank and tank pump is less than a year old. the exhaust is stainless steel. The O2 sencer was replaced because the cap on it that the wires go into was loose. And I also tested all of the wires from the PCM plug to there end terminaition "as per the 87 Ford Bronco II 2.9L V6 Fig 3 Engine Compartment diagram" And found nothing.

Maybe if I tell you how it quit it may help.
My daughter had the truck. She said that she felt a cupple of surges and it died. When she tried to restart it, it fired up and than quit within 2or 3 seconds. This repeded 2 or 3 times.
She did say she got it to start once but it would only run above 3000 rpm. and than quit as soon as she took her foot off of the peddle. After that it never started again.

Dose this give you any ideas?

 

The last thing left is the fuel pump.
Do the fuel pumps ground affect the PCM in any way?

 

A bad or shorted out EEC relay will cause the fuel pump relay to not work or work off & on. I would check that one out.

 

I've Replaced both the fuel pump & EEC relays And tested the wires. The EEC relay pulls in with the key on and sends power to the PCM and the fuel pump relay. But the problem I'm having is the PCM won't send a ground to the fuel pump relay via the tan wire. if I apply ground to the tan wire the relay pulls in and the pumps run.

 

SInce you have no ground to the fuel pump relay AND no injector pulse, it sounds like the PCM itelf might not be grounded. Reading these wiring diagrams makes me crazy sometimes, but if i'm reading it correctly, pin 60 on the PCM and the battery are both grounded to the engine. Pin 49 is grounded to G-306, which I cat find a location listed. Pin 20 is grounded to G-110 (body). Cant find the location for this one either. Not sure why it would require 3 grounds, but thats what the wiring diagram "seems" to indicate.

 

Thanks for the reply 87 XLT

Pin #60 splices 4 times to the neg. bat. term. (Tested good )
Pin #49 is the ho2 sencor ground, grounds to the block. (tested good)
pin #20 Splices to #60 neg. to neg bat. term. (tested good)

Just a thought, Does this truck have a speed limiter? And does it run from the speed sencor and if so how does it work?
It is just a thought. Because you would think that it would shut off the fuel pump & the injectors if you passed the programed speed.
Could this be shorted out?