I have a 2000 XJ8L 4.0L looking for the MAP sensor. I dont see it on the bracket on the fire wall, I dont see any hoses not attached to anything nor electrical connections missing a sensor. Car is throwing lean codes, I cleaned the MAF sensor and want to do the same to the MAP but can't find it

 

MAP isn’t used an XJ8, on XJR it’s only for EGR monitoring

 

Thanks, this was driving me nuts. Any thoughts on codes. I P0171, P0174, P1111.it shows both banks running lean. Cleaned the MAF, might replace it. I dont see any broken air/vacuum lines. Possibly injector but that's pretty rare for both banks right?

 

I have chased these codes on all my cars and it's always some vacuum leak. Could be the oil stick O-ring is missing, the oil cap O-ring is leaking, that plastic hose from the valve cover has a crack, the little rubber vacuum hose under the TB is leaking, or the air intake is not attached fully to the throttle body, or the manifold gaskets are bad among the possible causes. Maybe even the throttle body is loose? (Don't over tighten it though!) If any reason the car is sensing the vacuum is not up to par the codes will appear and there are a lot of places to check. If you have a smoke generator you can force smoke into the intake and see where it comes out. I do not but a number of guys on this forum do and may point you into that direction. I could definitely use one on my XJR as it's showing the same codes!

If you have a DTC code reader you can check the long and short term fuel trims to verify the problem. The numbers should be rather low. (A few % high and low) If it's in the 20% area you will defiantly get the codes.
Always a real issue with these cars and not easy to spot.

 

I second the motion to check for vacuum leaks with a smoke machine. If its lean on both banks, that usually means its getting extra unmetered air in somewhere after the MAF, probably quite a lot of it, and there's tons of places that it could be leaking. One of the more common things is an old vacuum hose gets loose and a little starter hiccup blows it off its nipple. You can look and look and look among the rats nest of wires and hoses in most any emissions era car and not spot it with the naked eye. Its not that you didn't see it but that the brain didn't register it. It's the same syndrome as losing a tool you had in your hand just moments ago, looking all over the garage for it for half an hour and then realizing it was in the first place you looked the whole time. Smoke machine is the vacuum system equivalent of having a buddy dial your number after you misplaced your cell phone somewhere in the garage. Its hell getting old.

 

One of the old school ways to find a vacuum leak is by using a spray can
of carb cleaner. The engine picks up when you spray an area where the
leak occurs and you find it much quicker.

 

If you're going to look for leaks that way be sure not to rely on hearing anything.

Use OBD and watch the STFTs. They swing a lot if you spray in the right place.

But first watch the fuel trims at idle and then rev to about 2500. If the trims were not near zero and drop to near zero then you do have an air leak. Otherwise you're looking for something else.