These are coming up together pretty regularly.

JTIS points to:

Blocked Air Filter (New one is on order)
Fuel System Return Blockage (How is this checked?)
Leaking Injector(s) (How to test?)
FPR Pressure too high (replaced it last summer)
ECM Signal error from:
ECTS (Whats this? How to check?)
MAFS (Checked - OK)
IATS (Whats this? How to check?)
TPS

The filter/plenum/hose is airtight and I sprayed it down looking for leaks - None. Besides, that wouldn't enrich the system anyway.

Short term fuel trim bounces between +2 and -2 but the LTFT is in the +5 to +6 range; again not reflecting a Rich situation but a Lean one.

Thoughts?

Thanks!
I'm sure this

 

Most every rich xk/xj ive ever had over the years that wasnt a bad fuel pressure reg/useally broken or bad vacuum line. Was a bad amss air flow, and forget the readings at idle and differant rpm. Im not talking stumbles or erratic idles, those are easy to read when monitoring the mafs flow readings. Im talking about rich engine codes. I keep a few to swap in as a fast diagnostic tool and every time change the issue once i believe its the mafs. My money is still on the mafs, just due to experiance still may not be YOUR issue in the end, but then I have the sensors to swap, got anyone you know with another jag? They dont have to be identicle, and swap theirs out, its only 2 screws and 30 seconds to change

 

I don't have a MAF to swap so I just bought one.

I'll do some comparisons between old and new against the baseline post them here for future reference. Thanks, Steve in Indy, for the MAF data...

 

Way to pay attention Scott. I'll be anxious to see the comparison. Many times the MAF is erroneous only at certain flow rates. That's why the grid is so helpful. There is more to the fuel trim story yet involving load range mapping. At some point I'll get a Fuel Trim Primer Part two put together.

Standing by for your results.

Cheers,

 

I'll look forward to that!

I suspected that the MAF problem might be erratic or momentary. So I watched the values last night as I drove around local and highway. Casual observation didn't yield anything useful of course, other than a string of numbers roughly corresponding to engine speed and a lot of poor driving. (I guess if there was some big flat spot in output you'd see that...)

I also watched the LTFT and STFT values and here's what I noticed. The STFT values seem to be relatively small for the most part, +/- 2 or so. The LTFT values are typically much greater in value, +/- 11, 15, 18 or so. I recall that LTFT's are dervied from stored STFT values but I wonder how, exactly, they are derived.

If the LTFT value was just an average of the STFT readings over time, the LTFT values would be at about the same range. Clearly they are not, but are much larger. One answer might be that the LTFT accumulates the STFT readings over a static time period rather than averaging them. Or maybe it just averages peak values or accumulates values that are over some threshold.

Much to learn. My MAF shipped today USPS, so it will be a few days yet...

The new air filter just arrived. I'll replace that first, just to eliminate that as an issue.

 

Well you have found your problem, those Long Term fuel trims well above positive 10% are the reason for the Rich Faults. Now you just need to find the cause. I believe the MAF sensor will do it.

I had thought maybe you had seen the other thread on fuel trims, possibly not. Read through this:

https://www.jaguarforums.com/forum/s...ad.php?t=49317

That should help you get your first grasp on what the numbers mean.

Cheers,

Edit: When you are through this, I DO expect your signature to change from Math Book to Lovely Mistress!

 

While waiting for my MAFS to arrive I changed the Air Filter just to clear that issue from possible causes. It wasn't particularly dirty.

However, since then, the codes haven't come up - and from recent experience they should have by now, several times. I'm going to check the status of the LTFT next time I get it out for a run.

 

Just so we can quantify exactly what's going on here, I'd urge you to use my Mass Air Flow chart you have, and record your readings at the same four points. Now that is all done at a stop, holding the brakes firmly, preferably in an open parking lot. Do that with your original air filter, and the new one, and again if you get a new MAF Sensor. That way you can see what's doing what.

This will be interesting.

Cheers,

 

Sure. A little 4-way test with the new vs. old MAFS and the new vs. old Filter. I have everything at hand, I can get to it when I'm back with the car early next week.

 

The testing was interesting but sort of inconclusive.

There was no clear failure of the MAFS in my case as there might be on other instances.

Looking for live, intermittent, failures was not conclusive either - the LTFT readings jump around a lot and there was no clear flat spot.

Still, the codes kept popping up and the LTFT generally negative teen values.

I ended up installing a new rebuilt MAFS and after a bit (90 miles) the LTFT levels moved into positive ranges all of a sudden.

I guess what I learned is that LTFT and STFT analysis is a great diagnostic tool but a failing MAFS won't reveal itself this way until it totally fails.