I've got a '97 F150 with a 5.4.

The truck started throwing a lean code. Checked the fuel pressure and it was low so I replaced the filter and got 2# back. Not enough so I put a new fuel pump in her.

Now she's throwing lean codes on both banks. Clear the codes, drive the truck for 20 to 30 minutes and the codes return. Run diagnostics while driving and the short and long trim voltages on both banks look normal.

So what's next?


Thanks,
Bass

 

Vacuum leaks. Check/clean MAF.

If the fuel trims were normal, it wouldn't be setting fault codes for the mixture.

 

Thanks. Already checked for vacuum leaks and found none. MAF was next on my list so glad to hear someone back that up....

 

Mine threw codes saying it was running lean Nd looked all over for a vacuum leak. Someone on here told mme to clean the MAF sensor and that's all it was. They make a spray for cleaning it. Have been told only to use that and not cleaners such as brake cleaner.

 

Haven't had a chance to pull the MAF sensor yet. Probably this weekend.

The sensor's pretty delicate and costic cleaners would likely damage it, or even leave a deposit on it.

 

Brake cleaner and MAF cleaners work good. Carb cleaner leaves a film. Just spray the filaments, don't touch. Also check the PCV hose elbows front and rear. The rear one tends to get overly soft and cracks.

 

I've always heard to stay away from brake cleaner. No matter though as I've got MAF cleaner and electrical component cleaner on the shelf.

I'm thinking that this won't solve it though. The truck also is a bit hard to start. When the truck is cold, you have to engage the starter for 1.5 - 2 seconds.

 

Just asking a question here...............

Assuming the new pump gives acceptable pressure readings at the test point could this condition be related to worn injectors?

I don't know enough about these systems so forgive me if this is a foolish question!

 

Did cleaning it help?

 

It rained all weekend so I didn't get a chance to do it. Covered space at the house is at a premium.

Still on the radar for ASAP.

 

Have you cleaned the MAF sensor yet?

 

Sorry for not getting back. The truck's been parked while I worked on other stuff.

Cleaned the MAF sensor, no change. After clearing the codes, the truck runs for about 20 minutes before the Check Engine light comes back on. 20 minutes continuous, two ten-minute trips, with or without complete cooling between trips. 20 minutes.

Both left bank lean and right bank lean are being thrown. Both of the O2 sensor's voltages/patterns look normal and regular on the graph.


~Bass

 

hey folks, i have a 1998 f150 4x4 with a 5.4l, since i bought it it has been running lean. (p0171, p0174) i have done everything i can think of. i have replaced the fuel filter, maf, spark plugs and coils, egr, egr sensor, pcv valve, pcv hose, intake vacuum lines. i cannot think of anything else that i can replace. if you know somthing i dont please let me know. thanks fellas.

 

Well, I would definitely check the O2 sensors since they are what guides the ecm in regards to fuel air mix..... then I would run a smoke test to look for leaks!

 

Stop thinking about things to replace, start thinking about what is needed to accurately diagnose the fault.

Start by pulling the freeze frame data and posting it. The conditions under which the code(s) set is important to know.

O2 sensor very rarely cause "lean" codes. Don't shoot the messenger(s).