bought a used 1991 f150.the owner claimed he put in new fuel pump,patched hole in rear tank and add power to the fuelpump.turns out he put used pump and spliced power to the pump. it died on the way home so i towed it. replace the junk battery,fuel tank,fuel pump relay and pump.started right up. drove it 2 days but noticed it was hard starting.also with key on the pumps run non-stop.it died on the way home started to lose power backfired once and died no restart.towed home again put scanner on it. it's f150 5 speed manual 4.9 300.received the following codes:
keep alive codes 18 loss of idm input to pcm spout circuit grounded.
56 MAF circuit higher than max. volt
57 neutral position switch circuit open.
on demand codes
57 octane adjustment servo pin in use
18 see service manual.
i do have spark.it tried running one time put sputtered and died.it turns over but no start.the fuel filter looks new,not brand new.he had receipts showing maf cleaned and recommend new pump.any help or ideas? thanks.

 

Your truck doesn't have a MAF and 57 doesn't apply to our trucks. I think you may have counted wrong, 56 is an automatic transmission code. You might want to check the fuel pressure.

 

ok i am using a matco md1000 and thats what im getting.i figured the 57 was null.and i have checked it several times guess i will try again

 

If you're using a scanner then they must be right, but you're still getting an automatic transmission code for a manual truck. Maybe it has the wrong computer in it.

 

well sean the fuel pressure thing was a good start.line appears plugged.i can only assume the ecm is correct.doing parts checks i came up with the same number.idiot i bought it from pulled the cel light and jerry rigged the fuel pump power.

 

That would also lead me to believe there was a computer problem.

 

any idea where the power comes from to feed the fuel pumps??

 

Yellow at the fuel pump relay is hot at all times and power comes from a fusible link attached to the solenoid. Red is hot with the key on and comes from the EEC relay.

 

so the red wire off the ecc relay goes directly to the fuel pumps??if so than i have an open.

 

The red wire on the EEC relay goes to the red wire on the fuel pump relay.