I recently bought a 1997 F250HD 4x4 w/5.8L. The truck has 144,000 original miles. PCM went out about 2 months after I bought truck. It went into Failure Management Mode and wouldn't clear.One code only code shown was IAT sensor.But,after replacing it,still didn't clear.Did pin test and PCM showed bad.
Well,now truck seems sluggish with new PCM.Checked timing,it's dead on 10* base,air filter is new,I did a vaccuum check to see if any backpressure problems with exhaust and everything checked out fine.
Truck seems to have power when cold,but,after reaching normal temp,it's a slug.Lugging up hills.I pulled out the new IAT as it was an Autozone unit. I put the factory IAT back in.Haven't had a chance to drive it yet with old IAT.
I do know my fuel economy has dropped from 16MPG to about 10MPG.
Also,when I leave truck idling for about 5-10 minutes,it will idle up,sputter and shut off.Turn key and it will spin over but not start up.After sitting for about 15 minutes,it will start up just fine.
Anyone have any clues? Suggestions?

Thanks

 

Bad coil, and/or tfi module on the distributor.

Adrianspeeder

 

Alright,replaced IAT with a new factory Ford unit,replaced TFI with factory Ford unit also,TFI unit was factory remote mounted on drivers side fender to help reduce heat.New MSD Blaster coil,New Motorcraft Platinum plugs and Motorcraft wires.Replaced standard air filter with a new K&N unit. Only thing I haven't changed yet is the fuel filter.
Also,as far as the sputtering and stalling after idling for several minutes,I connected a spark tester to plug wire and have plenty of spark.So,I'm leaning more toward fuel system.Fuel reg issue? Any info would be greatly appreciated.

Thanks

 

confirm fuel pressure with a pressure guage on the fuel rail.
sounds like your pump is going bad or you are vapor locking

 

Got dual tanks and does it with either tank.Any cure for vapor lock?

 

I'd change the fuel filter, and if the problem persists, check the fuel pressure when it dies and see what happens.

 

Well,got fuel filter changed (still had factory one installed), also checked fuel pressure.I've got 32psi at idle,38psi at cruise speed and 40psi under load.The more I have thought about it,it doesn't have the power it had even cold since replacing the ECM. I pulled plugs as well today and they look new,no tan or carbon coloring at all , they are bright white like out the box so, I'm thinking I've got a lean-run condition. Going to try to get by dealer and have friend run a scan and see if anything shows. What's chances of the ECM bought from Ford being bad?

 

somethings wrong there. your pressure should go down as your rpms go up.
32psi is borderline at idle.

 

Actually, it's the other way around. The pressure increases when the vacuum is reduced or removed from the regulator, and opening the throttle reduces manifold vacuum. Thus, when you "give it gas", you are causing the fuel pressure to rise.

 

really? huh, ok well, just dont mind me. i cant think worth a damn this week.