Lean conditions, confused, help?

[iaresev]

Hi,

So I took my 99 4.0 in for an inspection and it threw three codes. Left bank lean, right bank lean, and P1151 which is something about the upstream o2 sensors.

There are two sensors, and both sides are being read as lean. Can anyone use their experience to help me target the problem? The shop gave me a damned laundry list of things to fix for it so I will not be returning there for the work. I have a set of o2 sensors already just haven't put them on yet.




PS, if you suggest putting on these o2 sensors, tell me how the hell you get to them!

 

[DennisF]

I had the lean codes on my '98 about 3 years ago and found the intake manifold was leaking. I could actually see water getting sucked in between the plastic riser and the manifold while washing the engine, while it was running. It was fairly easy to replace the upper manifold gasket. The CEL was reset, and the problem hasn't recurred.

The 1151 code may go away when you eliminate the lean bank codes, since they're related.

Good luck!

 

[Sasquatch_Ryda]

Both banks being lean is usually a vacuum leak, and the lower in take is a well known point of leakage on the 4.0L's.

 

[Mutant Pony]

Plugged fuel filter is also a common cause of these codes. Probably not the o2 sensors.