I haven't posted a question in quite some time, I have just been DRIVING a lot! So great to just enjoy the car after a busy Summer last year of maintenance and upgrades. I would however like reactions from some seasoned members (or anyone really) regarding a fuel trim/MAF issue.

A few months ago I replaced my MAF with one from a salvage yard car. The old one was giving me high positive readings (+15 to +25) on acceleration while fuel trims at idle were near perfect. The new one gives me slightly high fuel trims at idle (+5 to +12) and near perfect fuel trims at speed and during acceleration. Car runs and idles fine with either MAF. What should I make of this? The fuel trims I am referring to are all short term. The long term with either MAF seem to stay between 0 and +5.

I am revisiting this issue because of a small issue with a noise at certain RPM. It may be nothing but I am in the mood for a little "car repair therapy", as my wife calls it.

Thanks

 

Sounds like the old MAF is spot on.

I see Short term trim sitting at zero and bouncing +/- a few percent, Long term sitting at near zero or +1.6 - +4.7, but both sides the same. Depending on temperature, short term will move rich under acceleration and drop back to near zero at idle. At constant 2500 RPM, on the road, Long terms close to zero, or slightly rich (+), short terms slightly lean (-).

 

Thanks. I'm going to switch back to the old one for a few days and see if I notice any changes. It seems to me I had trouble with all of the readiness codes clearing with the old one, whereas when I installed the newer one I got P1111 very quickly.

I really want to perform a smoke test to be sure there are not significant leaks. While this seems simple in theory, I have not yet found a practical approach. The only local mechanic I go to (which is rare) will NOT do anything to a Jaguar, not even a smoke test. He performed the test on my BMW without complaint, but won't touch the Jag.

P.S. -- Just ordered new rotors and pads yesterday; very excited about doing that work next week. Unrelated, I know....

 

It is possible the old MAF may have other issues. Maybe, try cleaning the new one, tighten up all connections along the air tube and see how it runs. Torque the bolts on the cam cover, as well. Check the seal on the dip stick if the left bank is running rich.

One of the guys also recommended using carburetor cleaner along any possible source of air ingestion (along the intake manifold, etc). When the idle stumbles, you found your weak point. But if the long term trim is just slightly positive, you may not have a problem.

Best of luck in getting the old rotors off: worked my *** off until my 265 # son shows up with a BFH, slowly turning the rotor and hitting it hard enough to break the rust seal. Left side came off much quicker, went to the big hammer sooner.

 

Well, even though I cleaned the MAF from the salvage yard before I installed it a few months ago, I cleaned it again today and re-installed it. The fuel trims seemed much improved with all four hovering within 2 or 3 of zero. When I let off the gas and coast the short term fuel trims go briefly to between -5 and -18, but settle quickly back to around zero. I will keep an eye on the fuel trims for a few days, but it seems that Jim's simple recommendation to clean the MAF may have been timely advice.

I will keep a large hammer available during the brake job (maybe I'll borrow Thor's?). The last time the brakes were done was by the Jaguar dealer, but I think that was at least 5 years ago because the previous owner did not drive the car very much. We'll see soon enough whether or not the rotors put up a fight. I ordered Akebono ceramic pads and Centric (preferred?) rotors. I'm going to bleed new fluid throughout the system also. Off topic again.... oh well.

 

You do not need "significant" leaks to muck up the idle fuel trim!

 

True about small leaks causing issues...

That's why I would love to find a local shop/friend to smoke test my car; OR - find a good used/homemade unit fairly cheap that I can add to my tool collection.

 

I had a small leak where the intake tube connects to the MAF housing (the place with the large clamp).

I took the cover of the intake housing loose, then first fitted the intake tube well onto the MAF, tightened the clamp, then lowered the cover and closed it.

My LTFT's now hoover around zero after cleaning the MAF, and refitting the intake as described.

 

Or drive down to Atlanta and use mine!

 

On cars (but never had an XJ) I've found tiny sprays near a leaking hose have made short trims go crazy thus identifying the leak.

There may be hoses you can't get to, though.