First post here and new to Ford trucks thanks in advance for your help. I have a 91 F150 with the 5.8L with 65,000 miles. I just bought it after the truck had sat up for some time. I just replaced both fuel tanks and fuel pumps. The front fuel pump constantly runs and doesn’t turn back off after it should have primed the system. The rear pump doesn’t turn on at all but the fuel gauge indicates correctly for both tanks. Also, the check engine light is on, there is no clicking when I turn on the key and I bought an OBD1 code reader and plugged in but it doesn’t connect to anything. Lastly, the truck does start and run off the front tank/pump but it misfires, runs rich and shoots flames out of the tailpipe. It does drive but if you put more than 1/8 throttle the engine starts to choke out and misfire. Is this a multitude of problems or an ecm issue? Where should I start?

 

The fuel pump running constantly is indicative of a bad PCM, probably leaking capacitors.

 

thanks for the reply, forgive me for my ignorance but is PCM the same as the ECM (ie the computer located on the firewall)?

 

Yes, PCM is the same as the ECM, just different different terminology.

 

Great thanks, any guess on where to start on the backfire / sputtering? Could that also be linked to the PCM?

 

Your symptoms point to a bad computer. You need to send yours in for repair or purchase a rebuilt one.

 

Yes, both problems and a few others
Get another processor in it quick
Processor, ECM,ECU yes, yes, yes
Mine had no visibly leaking caps, but missed miserably (like hell all over the place), I could only drive it with a chase car following me

 

I got one ordered. I will install it Saturday and report back. Thanks

 

It is kind of a crap shoot with the reman ones
Some are not well
Have fun
I joke with people about WWIII and an EMP blast.
We all will need a spare (in a lead box) and a few ignition modules etc.
The part about your truck starts and runs on the front tank, but does not run on the rear tank, will be a different problem

 

Where would one send one to be repaired?

 

This name popped up in another thread. I have no info on his work and no affiliation to him. There are other repair service outfits, but the names escape me at this time.

https://www.tylerwolski.com/
edit: This is another that I have seen mentioned in forums.
https://siaelec.com/product/ford-ecm...repair-return/

 

Another recommendation from the the folks at Fullsize Bronco: https://modulemechanics.com/

 

+1 to the ECM/ECU/PCM being the problem. I went through this exact issue recently and picked up a reman unit from O'Reily. Resolved my issue and fixed some of my weird shifting issues as well.

 

The pcm did fix the issue. No check engine light and cranks right up. I do think now the alternator is going bad. Battery is constantly getting weak and eventually the truck will sputter and stall when I put it in gear. Having changed all the fuel pumps and the plugs, wires, ignition coil, cap and rotor in fairly confident that is the issue. No check engine light when it does this and when I press the throttle the needle in the voltage gauge has a pretty big fluctuation. Any other suggestions this could be before I throw $100 on a new alternator?

 

Monitor the voltage to help test the alternator
Use a DVOM and see i the voltage jumps up to 13 or 14 when you start the vehicle