<TABLE border=0 width="100%"><TBODY><TR><TD vAlign=top width="100%">Hello. first of all excuse me my bad english

I have a 199 F-250 XL superduty long bed 122000 miles on it. 5.4 Liters v8 gasoline with automatic transmission and 38 US gallons fuel tank capacity.

When the truck is cold, idles and runs fine (transmision in parking or neutral and i cant get 5000-6000 rpm easily)

After 20-25 minutes i get the highway the truck has loss of power on heavy acelleration and starts to hesitate, but if i only push the pedal a little the truck acellerates normal but i cant get more than 2000 rpm because the trucks hesitate again. I parked the truck near an store. I put on parking and neutral the tranismission and the same problem (i can get more than 2000). But if i turn off the engine and start it inmediatly in neutral or parking i cant get 5000-6000 rpm again without no problem and for a long time. I run again on the highway and becomes the same problem after a minutes. I you let the truck overnight and start it in the morning idles and run fine (until it fails in 15-20 minutes again)

I replace the fuel filter and fuel pump (when i remove the fuel pump, i noticed that the gasoline was very hot and i dont know if is this normal) but the problem remains. I also changed the TPS sensor, clean canister and hose relief valves and nothing.

Only if you push the acelerattor pedal for a long time (after 5 minutes of hesitation) the service engine light came on and it shows p1150 p1151 and the o/d lights starts to came on and off (i think because the transmision wants to change to a overdrive because receives a signal from TPS and there is no enough fuel or somtehing). If you turn off the engine and restart it the o/d transmision light came off and if you drive for a minutes at low speed and acelerration (in the downton for example) the service engine soon lights come off.

When the truck was fine, i get about 15 mpg but now 7-8 mpg.

Please i need some advice i am a biotech enginerring and sometimes i need to carry refrigerated reactives quickly so i cant let my truck fails again

 

Almost sounds like you have a clogged at converter or two.

 

I removed the exahust line and problem continues :/

 

What about MAF sensor or oxygen sensors?

 

Could be the MAF. Have you tried cleaning it?

 

I clean the maf and oxygen sensors and nothing. Also i disconnect the MAF because its suppossed that if you disconnect one sensor the PCM gives default values.

what about a bad fuel pressure regulator?

 

Yea i clean it also i disconnect it but problem remains.

what about a bad fuel pressure regulator?

 

It is possible. Look for fuel in the vacuum line going to it. They will often suck fuel thru them when the diaphragm goes bad. I have also seen the check ball in them go bad and cause fuel to return to the tank when not running and taking a lot of cranking to get the pressure back up again.

 

Thanks i will check it.

Recently i noticed that the fuel pump relay its a little bit hotter than the others

could a bad fuel pump relay cause the symptoms?

 

Maybe if the contacts are burnt and it isn't getting full and constant voltage to the pump.

 

Mine started out as a loud knock that was thought to be timing chains slapping by the previous owner. I heard the noise and knew it wasn’t. So I bought it. Checked compression and I’ve got 180 ish psi on all the cylinders. But I have a backfire coming through the intake with fuel pump relay disconnected so it couldn’t start. I determined I had a miss in #3. I checked the air filter and found the center cone was gone so the engine had been sucking unfiltered air, bugs, dirt and everything in between. So I replaced the air filter, all injectors, coil packs and plugs and fuel filter. Problem went away and came back way way worse but not it’s not a miss on #3. It’s the engine bogs down and won’t run. I can get 4K rpm and it sounds like a race car going 200mph but I’m barely moving. Then it will “cough” and sling you back in the seat then back to bogging down. I cut the cats out and tried that. Same thing. Put a new flow master cat in each side. No change. When it was running with no cats it was throwing a code for ho2 sensor. I’m seriously at a loss and I don’t have the money to keep throwing parts at it. I have a few videos that you can hear the backfire through the intake I was talking about.

 

I’ll say it sounds to me you have a mass air flow sensor not reading like it should. Fuel pump relay will not cause this. If you have access to a code reader.clear all codes and go back and drive it until it messes up. Scan it and see what codes come back. Also check antifreeze level just curious if you are having to add any? Be sure that exhaust is ruled out. And also check the air filter I’ve seen a clogged one cause this same problem. So do a quick check of these things but the maf voltage should be monitored at idle and with a load if these other quick checks don’t reveal anything. Thanks

 

Did you ever figure out what was wrong?