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Old 04-23-2011, 05:11 PM
Alterado Alterado is offline
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5.4 fuel system problem...

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
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Old 04-23-2011, 06:59 PM
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LxMan1 LxMan1 is offline
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Almost sounds like you have a clogged at converter or two.
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Old 05-01-2011, 08:53 PM
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Almost sounds like you have a clogged at converter or two.
I removed the exahust line and problem continues :/
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Old 05-01-2011, 09:00 PM
pidaster pidaster is offline
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What about MAF sensor or oxygen sensors?
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Old 05-02-2011, 07:03 PM
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Could be the MAF. Have you tried cleaning it?
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Old 05-02-2011, 10:07 PM
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What about MAF sensor or oxygen sensors?
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?
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Old 05-02-2011, 10:09 PM
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Could be the MAF. Have you tried cleaning it?
Yea i clean it also i disconnect it but problem remains.

what about a bad fuel pressure regulator?
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Old 05-07-2011, 11:25 PM
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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.
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Old 05-08-2011, 12:07 AM
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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?
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Old 05-08-2011, 05:34 PM
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Maybe if the contacts are burnt and it isn't getting full and constant voltage to the pump.
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Old 05-08-2011, 05:34 PM
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