hi all,

my 1988 f150 supercab 351w auto trans ... anyway i was driving today went from about 40mph had ludge ludge ludge speed went down to 30-20 - 15 -10-5 mph before i got to a parking lot to chek it out. it also was backfireing a bunch as well .... i was told it could be the gas filter or mabe the gas pump i do have 2 tanks ... am gonna try putting some gas in the frount tank in the am and see if the truck runs ok... any ideas tonight would be helpful and thanks in advance...
James

 

Its probably not the filter, a plugged filter usually doesn't cause backfire, but if its older than 12k miles than go ahead and replace it anyways. Cheap insurance....

It could be too much water in the gas. Were you unusually low on gas or had just filled up?

Backfire is typically caused by unburnt fuel being dumped into the exhaust. Typcally caused by poor timing, firing, or valve issues. It could also be a bad injector flooding the cyclinder but this is a lower probability, as also could be caused by high fuel pressure flooding all the cylinders.

I would check spark, spark plugs, wires, cap, rotor, and coil first.

I would check timing next. Pull the SPOUT connector and then start the truck if you can. Timing should be set at 10 deg.btdc. Dont forget to put the spout back in when you're done.

The 351's fuel pressure should be about about 40 primed with engine off and around 32psi running. Pull off the vacuum line from the FPR (fuel pressure regulator) while running;you should not see any gas at the vacuum port or in the line (replace FPR if you do) and the pressure should jump up to around 40 again. Replace FPR if pressures are too high. Check high pressure pump if they are too low.

I hope this is a good start.
Popa Tim

 

Hi All got the truck going this morning i put gas in the frount tank truck runs normal now... so unless i miss my guess i need to put a gas pump on the rear tank...
to do that do i need to drop the tank or can i just get a pump i can mount under there some where?
Thanks for all the help!
James

by the way popa tim i checked those things you told me about all seem ok to me...

 

if the rear pump is bad you'd see it in the fuel pressure test when on that pump.
If pressure is ok, I'd dump that gas.

Theres a low pressure pump in the tank. You can drop the tank or left the bed and do it from on top. Many prefer to left the bed for what its worth.