I have a 1995 F-150 with the 5.8L engine and E4OD tranny. Often during the first 4 or 5 miles of driving the truck tends to bog down or almost stall and then finally catch itself when i step on the gas pedal. After a few minutes of this it seems to smooth out and runs good, finally the check engine light comes on but no further symptoms come about. Also I'm not positive yet but i think my gas mileage has been decreasing. I was thinking it could be the oxygen sensor causing the engine to run too rich, and when i step on the pedal the extra air leans it out. Anyone have any ideas?

 

If the gas mileage IS getting worse, I would guess a clogged or dirty fuel injector. If it isn't, then I would guess a clogged fuel filter or weak pump.

I would put in some fuel injector cleaner and watch the gas mileage.

 

I'll try that injector cleaner... its only a few bucks so its worth it. I know the filter is good that was just recently replaced. If it was a fuel pump wouldnt it continually bog? After the truck warms up good and the check engine light comes on it stops bogging and runs good.

 

Pull the codes to see what that CEL was about. AutoZone or you can do it yourself. http://fordfuelinjection.com

If you suspect the fuel pump, switch to the other tank and see if that happens on that tank.

 

The truck only has one tank so i cant switch to another one, but i dont think the fuel pump is bad. When i first got the truck i had a problem with the engine not revving up and it turned out to be a clogged cat, cutting the cat off and having duals put on solved that problem, but in the midst of having the problem diagnosed i had the pressure checked and it was good. Im leaning toward a sensor becuase stepping on the gas peddle immediately makes the engine rev back up to normal but as soon as i let off and start coasting it bogs again. I might have to take it to the shop to get the codes pulled since no auto parts stores near me can do it. If anyone has more suggestions let me know. Thanks!

 

I am not a computer expert, so take this for what its worth.

QUOTE:
"After the truck warms up good and the check engine light comes on it stops bogging and runs good."

I believe that when the check engine light comes on, the computer reverts back to a set of pre-determined tables of what the fuel, timing, etc requirements should be. It will no longer look at the sensors since one or more of them is showing a value outside of the established limits.

So yes, it very well could be a sensor. The only way to tell for sure is to have the codes pulled like "93greenf150" said.

 

Yes, the no cat could be causing a problem too. Autozone sells universal replacements. I'd put new cat on and a new o2 sensor in and see what happens.

 

There is no cat but there is an oxygen sensor in a cross pipe right after the downpipes from the manifolds. The truck ran flawlessly for four months so i dont think the problem is not having a cat. I pulled codes and found several codes or the ECT sensor, ACT sensor, and TPS sensor. If the ECT sensor was bad wouldnt my temp gauge read incorrectly?

 

No the ECT and the dash gauge use different sensors.

 

The truck has to be warmed up for the ECT and ACT to pass the test. So maybe, those two sensors are good (they rarely go bad anyway).

The TPS can definetly cause those symptoms you describe. Try replacing it, it's cheaper than an O2 sensor.

 

I pulled the codes again and found this:
ECT sensor
2 codes for HEGO sensor

Should I just replace both? Which one would be most likely to cause hesitation and bogging. Which one would be most likely to cause bad gas mileage?

 

Remember, the truck has to be at operating temperature for the ECT to pass.

An old O2 sensor can cause bad gas mileage.