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Lean, Leaner, and Leanest

RªMB°

NAXJA Forum User
Location
Yucaipa
Over the last week my XJ started to run lean. I replaced the fuel filter, coolant temp sensor, and TPS( Throttle positioning sensor).
After all this I still am running lean.:puke:
Anyone have any ideas?
 
*Post year/engine for the best advice
*What causes you to think you're running lean? Devil is in the details here....
*Any check engine light? If so, have you pulled the codes?
 
Its a 95 4x4 with a 4.0 I6

The check engine light only tells me a code 51 which means it runs lean.
 
Fuel filter, dirty/clogged injectors, fuel pump, ie: not enough fuel perhaps. Check fuel pressure at rail to determine the fuel line, filter, and pump are up to spec(iirc it's low 30's psi and 39psi when return is disco'd). It could also be a leak in the exhaust, a cracked header, thus the o2 sensor reads lean(and then dumps more fuel).
 
Vacuum leak, check all the vacuum hoses, and manifold bolts.
 
Fuel filter, dirty/clogged injectors, fuel pump, ie: not enough fuel perhaps. Check fuel pressure at rail to determine the fuel line, filter, and pump are up to spec(iirc it's low 30's psi and 39psi when return is disco'd). It could also be a leak in the exhaust, a cracked header, thus the o2 sensor reads lean(and then dumps more fuel).

Vacuum leak, check all the vacuum hoses, and manifold bolts.

Question for the experts????????????? Could it be the O2 sensors?

Yup, Yup, Yup

I'd say in reverse order they were posted, they are the usual suspects. You can often determine if the O2 sensor has failed with a DVOM. You will look for a change in output when you artificially introduce excess air into the intake (create a vacuum leak.)

If the above don't yield any better results, you may want to look into cleaning/ replacing the injectors and inspecting/ testing the pressure regulator (if it fails, it can reduce pressure and create a vacuum leak)
 
Ha ha Ha . Are we talking about sensors? Dont forget the MAT (manifold Air Temp. Sensor).:yap:
Low resistance or a short, ECU thinks,the engine is hot. The fuel mix is lean.
 
Last edited:
I worked on it all day today and this is what I found:
The muffler was so banged up from me wheeling rocks in the river that was half the problem.
Now I have a code 13 which you can find here http://www.geocities.com/JeepI6Power/obd1.html
Thanks 5-90 for providing the info.
 
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