96 F-150 P0174/P0171 Codes

[Eelpout08]

1996 Ford F-150 205,000 miles. Head Gaskets done last fall, no other major engine work since I bought it with 87,000 miles. Has always had a bit of a rough idle when warm, and runs rough for a few seconds when started warm for the last few years, no cel until now. Cel came on a week or so ago with no noticable difference in performance, until i decided to take it into town to get it checked out the other day. made it half a mile or so and it cut out/lost power under any kind of load. It died completly on the way back home, then started right back up and ran fine the rest of the way. Starts just fine and idles great in the driveway.

Diagnostic tool shows 6 codes:

P0174(System too lean-Bank2)

P1131 (Lack of HO2S11 switches-sensor indicates lean)

P1151(Lack of HO2S21 switches-sensor indicates lean)

P0171 (System too lean bank 1)

P1130 (Lack of HO2S11 switches-fuel trim at limit) (Pending)

P1150 (Lack of HO2S21 switches-fuel trim at limit) (Pending)

Any ideas?

I am assuming its not a bad vacuum hose or leak since both banks are lean and it gets worse with more throttle

Also assuming the only sensor it could be is Mass Airflow Sensor since both sides are affected

One thing i thought of is low fuel pressure/fuel pump going? Forgot to try the back tank while driving to rule out the fuel pump

Any thoughts are appreciated

[Jeremy airjer W]

I think your on the right track.

It wouldn't hurt to pull the MAF and make sure it's clean.

Plenum gaskets are pretty common on the 5.4 but there shouldn't be an issue since they where done with the head gasket repair. There is a vacuum hose on the very backside of the intake plenum on the passenger side that likes to rot out. It's al out impossible to see but it can be felt/heard with the engine running and it ca be seen when you smoke check them.

4WS will chime in with some thoughts when he sees this I'm sure.

[Eelpout08]

Im sorry i failed to mention it is a 351/5.9 Sorry about that!

[1968]

Can't remember if those still had a 3 pump system. If so, switching tanks won't make a difference if the high pressure pump by the filter is failing. Hopefully it is that, it's very easy to replace. Replace the filter too if it's been a while or the pump is bad.

Checking sensor/computer grounds is always a good idea on an older truck too. Especially if it's had a major service. Back of the cylinder heads are frequently used for grounds.

[Eelpout08]

No extra pump by the fuel filter. went and checked for obvious vac leak noises and all the grounds i could see/feel. nothing jumped out at me. took it for a drive on the rear tank(was on the front tank when problems were going on) it ran fine, plenty of power. switched to the front tank to see if i could get it to act up but it still ran just fine the mile or two back home. going to clean the MAF sensor just for the heck of it.

[Eelpout08]

Drove it a few times and it has run just fine. I did clean the MAF but i dont know if that was the cause or not, i kind of doubt it was. I think i will clear the codes and see if the CEL comes on again. Could it be something as simple as bad gas or water in the gas? It doesn't seem very likely to me but who knows. It would be nice to know what was/is causing the problem to avoid getting stranded somewhere when it decides to act up again

[Jeremy airjer W]

Is this the old body style with the 5.0 or 5.8 liter?

[JOHNBIGDOG]

Im sorry i failed to mention it is a 351/5.9 Sorry about that!

[Jeremy airjer W]

On yeah, never mind then!

[Eelpout08]

Well im 99% sure it is the fuel pump going in the front tank. runs fine on the rear tank, as soon as i switch to the front tank it loses all power above idle. now i wish i hadnt filled that tank the other day