Got a vacuum leak that is causing LTFT's of 18.9 % on Bank 1 and 17.6% on Bank 2, and occasionally throwing a P0171 code. The only other code I'm getting is P0420 which is associated with one of the catalytic converters and the P1111 code signifying that all of the monitors are working. The car runs very well otherwise; smooth idle, good throttle response and power. Also, the LTFT's drop to near zero over 2,000 rpm. Here's what I've changed so far in looking to solve this:
-Upper and lower intake manifold gaskets
-The line with the check valve running from the intake manifold to the brake booster including a new O-ring
-The line running from the intake manifold to the purge solenoid in the engine compartment including a new O-ring
-The PCV valve and hose
-The VVT grommets/seals on the valve covers
-Checked the intake manifold bellows and they're fine

Aftrer all that the LTFT's dropped about 5% each for about a day or two, then went back what they were before. What have I missed here?

Thanks.

 

The problem may be the air sensor just before the bellows on the intake air filter assembly. You might want to remove it and clean it with maf cleaner and see if you get a change. You may also try unplugging it and see if it changes running conditions.

 

Also could be the o2 sensors are getting old and not reading correctly

 

Thanks for the suggestions. Had previously cleaned the MAF sensor, but did it again anyway. No change in the readings and the car barely ran it all with it disconnected. The O2 sensors for Bank 1 (the one with the highest readings) were changed within the last two months. The MAF flow is 3.9 - 4.4 g/s which a mechanic friend said was too high (should be 3.0 to 3.5 g/s). I've checked everything with two different scanners and they both read the same, so it's not that. While researching this in the Forums I came across a post that suggested that perhaps the bolts holding down the manifold were placed incorrectly (there are two different sizes, three each for specific locations) and that that could cause a vacuum leak. Going to check that this afternoon. After that, out of ideas.

 

The bolt lengths are 47 MM for the rear of the manifold and 94 MM at the front of the manifold. This is looking at the engine facing from the radiator. You might also want to check the isolators for any damage. They are the same front or back.

 

Jags can sometimes pull vacuum thru the brake booster. Maybe just for a test unhook it from the booster and plug the line and see if the readings change. If they go back to being in range then your problem is in the booster. It’s something easy to try and eliminate the possibility

 

Do the IMTs have the later GREEN 'O'ring seals?

 

I disconnected and plugged both vacuum line from the intake manifold and nothing seemed to change. I also loosened and re-torqued the intake manifold bolts according to the pattern shown in my Haynes manual (see attachments) thinking that they were probably accurate. Actually, avern, your suggestion makes more sense, so I'm going to re-arrange them with the longer bolts in the back and see if that makes a difference. One of the IMT's has a black seal and the other one a green seal (don't know how or why), but they're cheap enough so I'll order some more and replace them.

After I finished re-torqueing the intake manifold bolts, both LTFT's dropped about 5%, but after letting it idle for awhile, they went back to where they were; no idea why.

 

You misunderstood my orientation facing the engine. In your picture bolts 3 and 4 are the 47MM

 

With all you have tried and all the work you have done, I would recommend getting a smoke test done to resolve locating a leak. It just needs to be a shop that has the smoke machine. You can remove the PCV hose from the cam cover and input the smoke thru the hose.

 

Thanks for the clarification Vern, I made the change although it made no difference. It's not currently throwing any P0171 or P0420 (lean bank and catalyst) codes, so that's good. I'm going to try to borrow my mechanic friend's smoke machine this weekend and see if I can track down the remaining leak(s). My 2006 X-type wagon has near-zero LTFT's, but has a lot less miles on it, if that matters. Per Motorcarman's suggestion I ordered the green IMT O-rings to replace the black ones currently on there. Not sure what the difference (if any) there might be between the black vs. green O-rings, but leaving no stone unturned.

 

When you replaced the lower and upper intake manifolds gaskets did you inspect the lower plastic intake manifold for any cracks?

 

The fuel trims tell you whether it's good or bad. A code just says it's terrible. Yes the O rings matter because you need vacuum-tight seals everywhere, no exceptions. Again, the fuel trims show you.

 

After re-torquing the intake manifold, replacing various O-rings (again!), the bank 1 LTFTs are continuing to drop from a high of 18.53% down to 14.23 with bank 2 now under 10% and the car is running about as well as any other car with 152,000 miles. Many thanks to all the Forum members that stuck with me with suggestions and ideas. Much appreciated and look forward to being able to reciprocate.

Max

 

You can speed up the 0.0% start up by removing power to the ECM.
Clearing DTCs with a diagnostic device will NOT start all from zero.
The STFT and LTFT start at the last reading.
Removing power AND clearing the DTCs will start ALL from ZERO.

Repairing the issue will take time to get the real STFT and LTFT to normal.

Just a 'heads-up'.

 

Thanks Motorcarman,

A great suggestion, but after driving myself crazy finding the vacuum leaks I'm enjoying driving the car around and using the Torque app on my phone to watch the numbers come down. Kind of like stretching out the satisfaction of finding the solution (with help from you and this forum, of course). Back in the 70's I owned a foreign car repair shop in New Jersey. We had a sub-specialty in Jaguars, so you know we didn't lack for business! Rebuilt my share of the 6-cylinders and one or two 12's. Our computer diagnostic equipment consisted of a Sun (remember them) console with gauges for vacuum, dwell, and RPM. No emission issues to worry about and setting and syncing the SU's was about as challenging as it got, with the exception of adjusting the valves with an assortment of shims. The hard physical work mostly involved changing components the front suspension where all of the rubber in the suspension components seemed to fail with great regularity. And don't get me started on Lucas...... Anyway, just the musings of an old motorhead.

Thanks again for your help.

Max

 

Did you finally solve the problem?

 

SEE POST #14

Default FINALLY SOLVED! - No Longer Singing The Vacuum Leak BluesAfter re-torquing the intake manifold, replacing various O-rings (again!), the bank 1 LTFTs are continuing to drop from a high of 18.53% down to 14.23 with bank 2 now under 10% and the car is running about as well as any other car with 152,000 miles. Many thanks to all the Forum members that stuck with me with suggestions and ideas. Much appreciated and look forward to being able to reciprocate.

Max

 

Glad you got your problem fixed useful info for the future. I too worked for a Jaguar dealer 40 yrs ago and remember SU carbs and straight 6’s and V12’s. Then some years later I had a very good career as a salesman for Sun Electric selling engine testers and diagnostic equipment. And now 40 yrs on I have a little sideline overhauling SU carbs and doing tuneups on classic cars here in Norway as nonone here knows how to balance carbs or tune by ear.