Hi all, I have been chasing a lean reading on both banks for a few months now. It has beaten me into submission. I can't seem to fix the problem. This started after I replaced all the coolant hoses, timing chain and all tensioners. I have a check engine light P0171/4 with the occasional air intake temp reading code. I had checked for vacuum leaks using MAF cleaner while checking fuel trims with my reader. I found leaks on 2 fuel injectors, two intake ports, the brake booster connected to the throttle body, the accordion air intake and the part load breather hose. A lot of leaks. This is what I've done so far:

1. New Air intake
2. New part load breather hose
3. fixed the brake vacuum hose leak with new o ring (from kit which includes the brass sleeve and plastic holder
4. New intake manifold gaskets
5. New throttle body gasket
6. Fuel injectors sent to "Fuel Injector RX" for cleaning and new seals
7. New MAF sensor (purchased at NAPA)

Here's the problem. After all of this, the car runs great but I still have the check engine light and occasional Restricted Performance. I have sprayed all the air intake paths with throttle body cleaner while checking the fuel trims and everything seams tight with no leaks. I need help figuring out the next plan of attack.

 

What are all the trims with hot engine, parked, at idle & rev to about 2500?

 

At idle STFT is at 25 and LTFT is 19

At 2500rpm STFT is bouncing around 4 and LTFT around 10.

 

I had this problem with my XJ8. The other possibility is a clogged fuel filter or a weak fuel pump. I replaced the intake manifold after a smoke test showed a slight leak, but every few months I would still get the same lean codes. It was worst when the weather was cold. There are utube videos for a smoke test, or you could get a pro to do one.

 

I did a smoke test which is how I found the brake booster vacuum leak. I replace the fuel filter last year and the old one looked good with no blockage.

I did a ride today with live data to see where things are. I was getting STFT at around 2,000rpm on the highway bouncing around between -4 and +4. LTFT was around -5. My MAF reading at 2,000rpm on the highway was around 55. At idle the MAF was around 3.8. When I leave the highway and come to a stop, the STFT goes to around +20 and the LTFT pegs at +19.

 

This sounds as a typical air leak after the TB (so between TB and engine). At idle the vacuum is much higher there as with normal driving, so more false air can be sucked in explaining the fuel trims and low maf reading.

 

I think you're right, the problem is I can't find it. I replaced the intake manifold gaskets and checked them. No leaks there. The part and full breather hoses have no leaks. I can't figure out where else it might be leaking.

 

I expected more trims as I believe you have 2 banks - are both banks similar? If they are then yes sounds like an air leak.

 

Don't forget to check the EGR valve under the TB and your vent tube leading from the valve cover back to the valve.

I feel your pain, finding those air leaks are frustrating, but when you've solved them all eventually, you'll be elated with yourself.

I also assume you did a hard reset to clear the ECU trims after your initial barrage of repairs?

 

I know you said you replaced the intake manifold and TB gaskets, but by chance did you replace the oring between the TB elbow and the intake manifold??

The EGR (if you have one) pipe going to bank one exhaust manifold is also a good idea (that has already been mentioned), but would only make it leaner on that one bank if the bellows was cracked because the pipe doesn't go to both exhaust manifolds. Unless there was a gasket leaking between the EGR and TB elbow.

 

I don't think I replaced an o ring at the TB elbow. Where is that? My car is a 2000 XK8. Do I have an EGR pipe?

 

I forgot this little update. Yesterday, I was frustrated with getting RP messages twice while driving. I decided to clear the codes and see what happens. I have driven about 150 miles on the highway and side streets since. No codes yet. I have not checked the fuel trims since resetting the codes and yes both banks were reading very similar trims.

I did not do a hard reset after the work.

 

Well this is interesting. I had to make a 30 mile round trip tonight. 15 miles to destination, no problems. Half way back home, check engine light came on. I checked it when I got home. Surprisingly, it's not a lean code. It's P0101. Air leak in the main intake or a MAF problem.

 

Better to double check that you got an true Jaguar MAF, I don't know napa and if they sell the stock part or aftermarket. You could try to put your original one on again to start with.

 

The MAF I got from NAPA was rebuild and of course I had to give them the original one as a core. Could this problem be the NAPA MAF?

 

There have been reports of aftermarket parts being a problem.

 

+1 on aftermarket/rebuilt MAF sensors being an issue. On two seperate Jags we put in 2 rebuilt MAF sensors in each car and one time the car wouldn't start. The other time the engine ran poorly. As far as the other car is concerned, both times it did have lean codes with no actual vacuum leaks present. I think it may have been a calibration issue with the rebuilt MAF is why it thru a lean code. I insisted we put in Denso/OEM MAF sensors in both cars an they have been fine ever since. I'm not saying this is what's causing your cars issue, however, if you plan on keeping this car I'd pony up for the Denso/OEM sensor and have the piece of mind. In my experience every time a car becomes old and factory sensors slowly become hard to find, I have had way better luck obtaining a good used one when a new one isn't available.

Btw, this oring I spoke of is between the plastic intake manifold and the aluminum throttle body elbow. With the little straw on a can of brake cleaner I'd spray around that area first and see if the idle goes up alittle. I must admit that I never had a vacuum leak there, but anytime plastic and heat is involved, anything is possible. I was just merely trying to throw out areas of possible concerns. Everytime I have fixed a vacuum leak somewhere, I always perform a hard reset to zero out the fuel trim tables and then go from there. With LT numbers as high as yours, I suspect that performing a hard reset won't fix your problem. But I'd do it anyways just to see.