2007 LR3 SE 4.4L

150,000 miles

Feels like he's running perfect, Check Engine light came on.

Mechanic said the code was for "running lean".

Possible culprit(s)?

Semper Fi!

 

For the CEL, I always think to start with the MAF Sensor and throttle body.

 

I think the OP needs to know what the actual CEL is first - a lean code should be specific for a certain bank AND should honestly carry with it some other codes as well, perhaps AFR-related codes for o2's etc.

There's lots of mental diagnostics and process of elimination to do though - for example if both banks are lean, it could be the MAF, BUT if only ONE is lean and the other is perfect, it's almost impossible as the metered fuel would be identical to both banks.

If it's an injector it should give you a specific misfire, however most CEL's are generally rich codes, so this is kinda strange.

Throttle body gum-up would be insignificant for anything except idle, and in that case it usually doesn't change the AFR (because the MAF sees the reduction as well, hence stoich AFR) but the flow is reduced to the point where it's rough.

I mean lean has to be caused by (lack of) fuel generally - as it's difficult to get an EXCESS of air into an engine. Unless of course the MAF is metering incorrectly or is dirty.

The other elements restricting fuel would be some kind of regulator issue, clog, fuel pump, etc - however I think the engine can monitor fuel pressure? maybe not.

I think the rest of the issues would be bank-specific or cylinder-specific, which would throw codes as such.

Gotta get hold of the entire error code info for the ECM.

 

Blah blah blah....clean/change the MAF and throttle body and you're done. That's what history tells us.

 

Thanks for the suggestions.

Mechanic cleaned the MAF sensor and throttle body, sounds like that did the trick.

 

Nah, lean codes are pretty rare - never seen one myself.

 

Well it seemed to work...

 

Yeah but why? How? which part, and what was altered to eliminate the codes?

Saying "clear some stuff and check some sensors" isn't exactly diagnostically sound.

Clogged TB = less flow = rich, not really significant.

I like to aim my diagnosis based on what the customer gives me, not just generalizations on the good-old TB etc.

You haven't really addressed the initial lean code so - I hope he's right, but I've seen this happen a million times before (code inexplicably fixed).

Even if you're right, you wouldn't know why - which kinda defeats the point from my perspective (which has served me very well in the past).

 

So...what you're saying is that the MAF isn't the root cause of the lean code because that's not a usual symptom for a bad MAF Sensor? (honest question, not matter-of-fact).

If so, I can see what you're getting at.

 

I had the lean codes(both banks) on my 06 4.4 LR3 with 253k miles.
I performed a smoke test, with a cigar.
Turned out the intake gaskets were no good.
After replacement, I was still getting bank 2 lean code.
I then replaced all of the original o2 sensors purchased from AB....
That fixed it for me.
Good luck