Pending meens there is an issue detected, the ecm has not been hard set yet.
When I bought my XKR, I scraped the aftermarket intake fast. The stock set up works as good as it gets. An after market intake did not improve performance, and caused more problems then good. I'm happy to report that since I have, I haven't had any issues with my car. And what you describe is the same problems I was having. Put the stock set up back on and see if that fixes it.

 

It may be time to find a shop with a smoke machine. It would be able to identify a tiny crack in a gasket or a small split in a hose.

 

Good point on the potential problem with an aftermarket intake system (the car also has a Mina cat-back exhaust system). The car (subjectively) seemed to run really well with these components installed; better throttle response from rest being the most noticeable improvement. These components were on the car for a few months with none of the current problems, so I'm thinking more along the lines of smoke-testing all of the connections as a means of locating the problem. My (inadequate) understanding of the system is that the ECM sets the fuel mixture based on the airflow through the MAF sensor, so a smoother path for intake air shouldn't trigger any codes, nor should a more free-flowing exhaust system.

All that said, I still have the factory setup, so I may give re-installing that a try if no other problem can be found.

 

Sorry to make this thread one of the living dead, but with the advent of additional testing and information I'm sorely in need of some help. After diligently finding and sealing some small vacuum leaks, and extensive road testing, here's what I've got:

At idle, the short-term fuel trims hover around .8, and the long terms are 5.5 and 7.1 respectively.

At a 2,500 rpm, the short-terms hover around 2.9 and long-terms drop slightly to 3.9 and 5.

When I accelerate past 2,000 rpm the short-terms spike up to 25 and the long-terms to around 19 and above. I then get pending faults of P0171 and P0174.

The car idles perfectly and has great throttle response off the line. It also pulls very smoothly when GENTLY accelerating at highway speeds. No pending faults, no codes. It does, however, take a lot of gas pedal travel to get the transmission to downshift, after which it seems to hold back a bit and I get the pending faults and the P0171 and P0174 codes or, worse yet, a brief period of Restricted Performance.

I'm using the Torque app to get these readings, which are consistent. Given these symptoms, I'm wondering if it could it be the throttle body or MAF sensor, or another hidden vacuum leak. In the case of the throttle body, how would I test it? It appears that the previous owner replaced the throttle body with a used unit, for what that's worth. The fuel pump pressure is 35 psi at idle and jumps to 38 psi at higher rpm's, which sounds like it should be adequate.

I want to find the problem without just throwing parts at it, but I'm running out of ideas.

Max

 

Not a typical air leak - LTFTs drop a lot when you rev (parked - keep it simple).

That doesn't rule out a leak at speed when some valve/etc might be operating and the cause.

MAF/TB look rather unlikely!

 

Have you replaced both VVT solenoid O-ring seals? They were the culprits causing the P0171/P0174 codes on my wife's 2006 XK8 back in February....

 

If your LTFT are low at idle, there should not be much in terms of basic air leaks. I suppose there could be other air leaks that come into play when the computer engages some subsystem, like the evap. I would recommend you go around the engine heads and throttle body area, and replace all o-rings in all those Norma hoses. Remember, if you see oil, there is likely an air leak, too. For these codes, all air leaks are cumulative. In other words, there can be multiple sources to this problem, all contributing to the code.

More likely though, the next logical step is to focus on the air flow meter. I would recommend you find out the correct DENSO number for it, and search eBay and Amazon. Some can be downright cheap. I had bad luck with an eBay sensor listed as compatible with my XK8 (in retrospect, with the wrong DENSO number), but good luck with a Toyota part that carried the right DENSO number, at $22. And yes, to the untrained eye, they all look exactly the same.

I also hear the car can run with the air flow meter disconnected. Maybe you can test this, and see if the ECM is better able to manage the fuel trims without the input of the air flow meter. If so, the meter is obviously the culprit.

Best of luck, keep us posted.

 

Replaced the VVT o-rings already, which improved the situation some. As fmertz stated, that with fuel trim shown, there's likely no single, basic air leak. Since this occurs regularly when accelerating past 2,000 rpm, and involves both banks, the air flow meter might be the culprit. I'm going to try disconnecting the air flow meter as fmertz has suggested and see what effect, if any, it has on engine performance.

Thanks everyone for the suggestions.

 

That's almost as if it's fuel-starved at higher revs. Wondering if a faulty 2nd pump could do that. Maybe watch fuel pressure as it acts up (may already be in the freeze frame data).

 

I agree with you that it sounds like fuel starvation at higher revs. Not sure why it seems to be reluctant to downshift unless you really put your foot down almost to the floor. It's an XK8, so there is no second fuel pump to deal with. Not sure how I can set it up with a pressure gauge that can be read while driving down the road (pressure gauge hooked up to the fuel rail, hood not latched, hard acceleration? What could possibly go wrong?). Too bad the Torque app can't read fuel pressure.

 

I have fuel pressure readings on my TorquePro app.

Sorry just found this:

 

Here's an update. I could not find any more obvious vacuum leaks and decided to check the O-ring on the oil dipstick. It was there, but the dipstick seemed to have some lateral play when it was all the way in. On a hunch, I sealed the dipstick tube with a piece of saran wrap around the dipstick with the result was that the short-term full trims stayed near "0" (-.8 to +.8) and the long-term trims dropped below 5%. Best of all, after flogging the car up and down the highway, no codes were tripped.

I've not been able to find a listing for the O-ring without the dipstick, nor do I know what the size of the 0-ring should is and will have to either go trial-and-error, or remove the dipstick and plug the dipstick tube and remove it to check the oil.

Has anyone found a place to purchase the O-ring without the dipstick?

 

Good work finding that!

It is always a painful Easter egg hunt finding simple things like special fasteners or o rings that only cost pennies but involve too much time and driving around to source. But if you have an industrial or hydraulic supply like Graingers near, that is probably your best bet. I believe just a basic buna-n nitrile o ring is suitable for oil exposure and if you bring your dipstick in, they can find a size to fit.


Andy

 

FWIW, I have the Harbor Freight O-ring kit, with hundreds of them, and I was able to find a suitable replacement for the dip stick o-ring in the collection. It is inexpensive and nice to have on hand, in cases like this and so many others.

Best of luck. Keep us posted.

 

Great idea! Forgot about Harbor Freight; the savior of every shade tree mechanic. I'll run by there today.

 

Harbor Freight has the O ring kits for several different types of O ring material, depending on your need.

 

I struggled for a long time with all the same symptions, cleaned the MAF sensor three times, checked fuel pump pressure, cleaned the throttle body, changed the air filter, ran the cleaner through the gas tank, bought the VVT seals, checked all the hoses for air leaks, changed the fuel filter.

But it was that damn MAF sensor all the time. I bought one from walker on Amazon for $34 and change and the problem was solved and has been for many weeks.

That MAF is a sneaky little item that can talk crap to your ECM and mess with your fuel mix big time. You don't have to buy the big money parts to find a fix, the made in China one works fine.

If I find I have to invest in a name part and spend 10 times my cost down the road I will do it but for now I am a happy Jag owner.

 

Great to hear that you found the problem. I just bought the very same MAF sensor from Amazon, and am keeping it in reserve in case the current fix doesn't hold. Went to Harbor Freight to check out the O-ring kits. They have several in both SAE and Metric sizes, and different rubber compounds. I bought the Nitrile in Metric sizes and hope I can find one that fits and seals the dipstick tube. My last resort is to purchase a new dipstick for around $ 35 (ripoff) because the O-ring isn't sold separately.

 

I bought the metric O-ring kit with Nitrile rubber and was able to find one that was a very snug fit in the dipstick tube. Car seems to be running (never say gre-t or even o-ay; the Jaguar gods monitor this site). Hope everyone has a terrific 4th, and thanks again for sticking with this thread. I'll provide a (hopefully) final update to close it out.

 

UPDATE: Car running really well, STFT's near 0 at idle, LTFT's +7.8 and +5.5 respectively. At high rpm's however, the LTFT's spike up to 20 and higher, and often above the 25% threshold, tripping the dreaded Pending Fault and Restricted Performance.

Since I had already purchased the Walker MAF, I decided to install it and see what effect it had. The LTFT's went to around 17% at idle, STFT's are around 10%, the air/fuel ratio went from 14.7 to 13.6. The car runs well, but those fuel trims concern me, so I re-installed the original MAF and will try to replace the Walker with an OEM Denso LNE1620CA unit. Unfortunately, it appears that no one carries that in the Denso brand, just aftermarket ones that claim to fit perfectly.

Anyone ever find a place to purchase the OEM Denso unit?