po 171 and 174 stumped

[michaelwilson98]

Alright quick update finally got around to that fuel filter change. When I drove it felt a little different so I'm keeping my fingers crossed. I also replaced the alternator because it was staring to make that "something got stuck in the fan" sound. I get stuff like that from a shop in salem oregon they rebuild and sell starters and alternators in there shop instead of sending them to somewhere outside the country. Awsome guys

 

[michaelwilson98]

Finally got around to changing the filter a few days ago. I drove for a few days and that light is back on. So going to take it to a shop for diagnosing. I'll let you guys know what the diagnosis is.

 

[AppleWood]

Maybe time for a smoke test? Sounds like a very good diagnostic tool when all else fails.

 

[koda2000]

Have you checked your fuel pressure? As far as getting an exact diagnosis/cure, there are several reasons that can trigger those lean codes. No one can tell you exactly how to fix yours w/o you going through the process of elimination.

Possible reasons for P0171/P0174 include:
- upper/lower intake gasket leaks
- vacuum leaks anywhere after the MAF
- clogged fuel filter
- low fuel pressure
- MAF sensor issue

 

[joe doe]

on the 2000 4.0 ohv engine all you need do is take the upper air intake off and replace the oring seals that mate it to the lower intake . thats your issue .been there done that .
no need to remove the lower ,unless while your in there you wanna do the whole thing .but 9 out of 10 its just the upper .

 

[Turdle]

Replacing both lower and upper intake gaskets is not that hard. You'll find your problem when you do.

 

[Dirt n Oil]

I have a question that includes these codes, but may be more related to OBD2 or PCM...
So, for several months up to the present, I've had to prime the fuel pressure by turning the key forward a few times before attempting to start. Recently, i changed the fuel filter, after depressurizing by pulling the fuel pump relay fuse(and a different black 3 pronged square fuse that i thought was it at first) while running. Then, came these codes after a couple days. A few days later, i reset the codes by disconnecting the battery, and they haven't been back after several hundred miles, even after depressurizeing again (this time by pulling the fuse first, then cranking it a few times).
Did i get the codes simply because i pulled the fuel pump relay fuse(and a different black 3 pronged square fuse that i thought was it at first) while it was running?

 

[koda2000]

I have a question that includes these codes, but may be more related to OBD2 or PCM...
So, for several months up to the present, I've had to prime the fuel pressure by turning the key forward a few times before attempting to start. Recently, i changed the fuel filter, after depressurizing by pulling the fuel pump relay fuse(and a different black 3 pronged square fuse that i thought was it at first) while running. Then, came these codes after a couple days. A few days later, i reset the codes by disconnecting the battery, and they haven't been back after several hundred miles, even after depressurizeing again (this time by pulling the fuse first, then cranking it a few times).
Did i get the codes simply because i pulled the fuel pump relay fuse(and a different black 3 pronged square fuse that i thought was it at first) while it was running?

my guess is that you have a fuel pump which is on it's last legs. by pulling the fuel pump relay/fuse while the engine is running, you starve the engine of fuel. that causes it to run lean (P0171/P0174 codes, too much air/not enough fuel). the only time you should need to prime the system (turning the key ON/OFF) multiple times is if you've gotten air in the fuel line, like after changing the fuel pump. if you have to do this regularly to get your engine started, you have a fuel pump or regulator problem.

 

[JB3]

For me i threw parts at it for a while. Everyone thought it was the intake gaskets, even the shop. Well 30 miles later aftrr doing uppers and lowers the codes were back.

Ultimately the problem turned out to be the fuel pump, and more accurately, the lines right above the tank were cracked and fuel was leaking there, but not noticably with the tank up.

Replaced the fuel pump at the same time. Codes have not come back

 

[MtrJunkie]

I had the codes last week. Replaced upper and lower intake gaskets and they went away.

 

[MuddinMounty]

It's running lean regardless, could be intake gaskets, could be fuel filter, could be fuel pump. All scenarios should be checked and tested. Mine was a combination of both intake gaskets and fuel filter. My pump is up next on the replacement list just as preventative maintenance. Best of luck!

 

[Dirt n Oil]

It's running lean regardless, could be intake gaskets, could be fuel filter, could be fuel pump. All scenarios should be checked and tested. Mine was a combination of both intake gaskets and fuel filter. My pump is up next on the replacement list just as preventative maintenance. Best of luck!

Could be a vacuum hose, especially the one that dives under the battery to the vmv. The battery acid leaks onto and corrodes it.
Or a dirty MAF sensor, etc.
I think somebody already posted a pretty thorough list of things to check for, concerning these codes.