Afternoon chaps,

New Jaguar owner and this is the first time Ive done any ODB diagnostics, so I'm a little confused about how to interpret the results. The Trim levels seem to be fluctuating quite a lot - is this normal? What could be going wrong (if anything)?

Symptoms: Its fine sometimes, but other its lacking a huge amount of power. When it lacks power it makes a bit of a noise (raspy, almost sounds like exhaust blowing, but Ive checked it and its intact).

Ive uploaded a video of the results, it was mostly behaving itself when I did the video:

ST-FTRM1, LT-FTRM1, ST-FTRM2

LT-FTRM2

Any help with this would be appreciated! Thanks in advance.

 

Just drove her, shes running low power again. Did the code scanner, trim levels seem to be a lot worse (fluctuating to +/- 20).


Any clues anyone? Am I looking at the right thing?

Thanks in advance!

 

No codes at all?
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Thanks JagV8. From what I can gather from my newly acquired knowledge about fuel trims, I am guessing that I have a vacuum leak. Is this a correct diagnosis?

From what I have read, this may be caused by the following

1) Airbox leak
2) Hose from air intake to drivers cam cover
3) crankcase ventilation line from passenger cam cover to drivers side (close to brake booster)
4) Hose from brake booster to intake manifold near throttle body
5) Leaking intake manifold gasket
6) leaking EGR hose/Exhaust manifold tube.

Are there any more usual sources?

Are there any nice ways to guess or whittle down which one is causing it? Can I get away with spraying with carb cleaner and waiting for a rise in engine revs (would this work on a supercharged engine?)

Sorry if these sound simple questions, I've been reading for hours and am getting a bit lost!

 

Well, what LTFT values do you have (in P) at idle & 2500-ish rpm?

You can hope for a rev change but depends on the above and also on whether the leak is where you can spray.

 

8.5 idle (tested twice now) and 15-18 at ~2500RPM.

(Higher numbers mean more fuel being added because of more unmetered air, right?)

Thanks

 

Both banks exactly the same?

Not an air leak if LTFT goes UP with revs.

Might be an underreading MAF but other things are possible.
Definitely running CL (closed loop), both banks?

Worth reading engine sensors to see if any looks to have an implausible value.
Kinds of things are in JTIS but here's a pic to give clues OnBoardDiagnostics.com - Engine Basics

(MAT is IAT in our cars)

The O2 sensors are 2 kinds so ignore them for now. No reason to think they're bad.

 

Double checked the results this morning after confusing myself over yesterdays results. Definitely closed loop.

The LTFT oscillates between 17.9 and around 9 while at 2500rpm. Stays on 17.9 for a good 30 seconds, then climbs down to 9ish, stays there, then shoots back up again.

Bank 2 is about 0.7 higher than bank 1 at idle.

Does this help?

IAT is around 93F (42c constant)
Maf 0.713 (idle) 8.6 (2500rpm), fuel pressure is 55 +/-1
IGN ADV (DEG) is 5.0 (idle) 42.5 (2500rpm)
MAP 11.2 (idle) 8.3(2500rpm)

O2S12/O2S22 seem to oscillate upwards and down, im guessing thats because of the varying trims. Highest I've seen it is 0.8, lowest is 0.035.

Any further advise deeply appreciated - Thank you

 

I don't really know what's wrong but not an air leak into a vacuum line. But maybe something like EVAP purge valve or the like not doing what it should. Have a good look at JTIS e.g. Electrical Guide to understand all the many actuators & sensors and think hard how anything could cause what you see. E.g. it can't be a bad MAF as it wouldn't cycle would it? (Well, it could be underreading all the time as well as whatever is wrong, but chase the weirdness first.) Switch a/c off as it would just be another thing messing around.

Oh - JTIS etc use several names for some sensors (and some are non-standard names anyway). Written by different authors or something.

 

Ive done an unhealthy amount of reading the past few days, but still trying to get my head around the trim results I've got.

Im leaning towards the EGR valve - could this create the creeping values or is it more likely to be electrical/sensor? Can it self detect that its failing?

By having a high base trim value of 8.5 can I assume I also have a vacuum leak as well as another issue?

Would the purge valve not create a negative value?

Thanks

 

If the EGR is involved I would expect a code for something concerning the EGR?

With no codes I am puzzled too??
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The jag diagnostic tools can watch as actuators are commanded so could make it easy to figure. Find someone with one (IDS/SDD/etc), maybe. Or wire into the circuit and see what's happening - but tough to do as many are PWM (if that's a new term, don't DIY any such wire!).

 

Taken her into a jag specialist. Annoyingly the fuel trims were fine on the day & the engineers havent been able to fault them since having the car. I think the tool they used is auto-logic.

They did say one of my catalysts were breaking up (had a rattle), so I've got a new one on order. (She has covered 128k miles). Is this likely to be the cause of my problems, or merely a long term symptom?



Ive had no fault codes for the last 3 weeks, however when I bought the car there was a big vacuum leak (one of the pipes had popped off). This originally caused the following codes: P0171 - Generic System too lean (Bank 1), P0174 - Generic System too lean (Bank 2), P0102 - Maf or Vaf A Circuit low input, P0112 - IAT Sensor 1 Circuit Low Input And a P1111 (Jaguar system pass). Im not sure if this will have anything to do with it?

 

Depends how long it was off. May have been causing damage all along.

You can be down on power with a blocked cat.

 

Did you reset the ECU when the air leak was fixed? I don't mean just clearing the codes, but the fuel trims too?

If not, then your strange fuel trims and even the poor performance in certain situations could just be a left over.

Would need one of the S-type experts to chime in if the procedure is the same, but on an XKR you simply disconnect the negative battery cable and touch it to the positive terminal for 15sec.

From there, you can get a clean start and see if the very high fuel trims come back.

 

Best - and quicker - to clear them but it relearns anyway and the weird behaviour (or low power) isn't going to be caused by not clearing them. Yes it's enough to disconnect battery but no point at this stage.

 

Let us know if the new cat changes anything. If it's blocking the exhaust it would reduce power a good bit.

Still surprised that with all the problems you have no codes?
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+1 but maybe it's so confused it can't figure what to flag.

 

I had an air leak for the longest time (both banks indicated lean via OBD2) and it turned out to be the long plastic PVC hose that runs from the back on the intake elbow to the ufo on the left side of the motor (when you are looking at it).