Running Lean

[tigerhawk]

Hello all, first time poster here.

Here is the guts of my problem. I have a 99 mountaineer 4wd with 105k on it. The CEL came on and I took it in for a diag at a dealer. The error code they got was that it was running lean. They spent about 4 hours troubleshooting it and couldn't find anything. I told them to replace the fuel filter since it needed it anyway. They didn't charge me for the diag and just turned off the light. Now the next day I get it again. I had driven it home without any problem (45 min drive) and now I got the same problem this morning after driving it about 7 minutes on the road at about 60mph. At idle I am at about 500rpms (it was starting to idle down furthur at stops but now seems ok probably thanks to fuel filter). I changed my plugs at 70k. Here is what I think (and I'm no expert):

Could I have gotten "bad gasoline"?
Do the injectors need cleaned?
Is my dealer unqualified?
Simple air filter maybe?
Does the timing need adjusted? (tune up)

Please help, I love my truck and it feels like I'm not taking care of her when that light is on. I appreciate any help

 

[Turdle]

It could be an intermittent fuel pump relay.
It is easy to diagnose, just switch it with another one in the power distribution box. disconnect the battery for a few minutes to clear the code, and post back if it works or not.

 

[Papa]

Wouldn't a fuel pressure gauge help verify that?

 

[mrboyle]

First thing I would do is clean the Mass Air Flow Sensor (try searching for MAF Cleaning).

 

[jp450]

If all the vac lines are attached and in good shape then I would suspect that it would be the intake gaskets if you have the SOHC. They are a known problem on the SOHC. Easy to replace and cheap at the dealer.

 

[tigerhawk]

Problem solved!! It ended up being a bad O2 sensor, so after about 3 hours of digging and replacing the engine runs fine now. I'm just curious why it didnt come up that to begin with and only said that it was running lean in both banks. The engine would only act up when I came to a stop and then it would try and choke itself out two or three times and then go back to normal. Thanks for all your help although guys. I appreciate it being not uber-mechanically inclined.

 

[jp450]

Thats strange that you got both banks lean with just one bad O2 sensor. Keep an eye on it and should you get the P0171 & P0174 again then do the intake gaskets.