My '07 XJR runs beautifully, but has a subtle cold start misfire which bothers me. It disappears after a few minutes.
I'm about to replace the infamous Valley Hose (occasional hot coolant smell), and would like to know if there are known startup misfire causes to check while I'm in there.
The car doesn't seem to be throwing any codes (per my Foxwell scanner). I did just install a new battery (Exide Sprinter L5/H8 lead calcium); no joy. I've searched the forum; found several seemingly related threads, but they don't seem to have resolved the problem. I do recall an experienced jag pro mentioning various items that could give slight vacuum leak upon cold start, but can't seem to find the thread. Car has ~130K miles, and is a peach in general
Any thoughts?

 

When’s the last time you changed the spark plugs? I had that happen before when my plugs were starting to get fouled. If they have carbon build up on them, they might misfire just a bit until you get some heat in the engine to assist with the combustion process.

 

Thanks Jazz!
(The plugs were replaced about 28K miles ago)

 

Once hot, what are the 4 fuel trims at idle?

 

Probably a coil pack on its way out don't worry it'll throw a code eventually and if it has a vacuum leak you'll get a p0171 or p0174 or misfire code which will vary depending on which cylinder is misfiring

 

+1 on the coil pack,
The ones from China have been a good investment
Eight delivered for less than $100.
Two years plus since they were installed in both of the Jaguars.

 

Which is OK-ish, except that damage to the cat(s) can be occurring gradually. Better to check the trims, pending codes etc.

 

Thanks All! (What a great forum...)
- Yeah; coil packs was my first thought as well, just v surprised that no codes seem to be showing
- Fuel trims: Now, first I need to learn how to monitor these. Assume it is in the "Dynamic" (engine running) aspect of my OBDll Foxwell scanner? (I'll work to figure this out and then post results here)

 

Your Foxwell reader, will show you all four of your trim numbers.

 

With a defective coil pack, I would think that the misfire would occur at all times, and not just when the engine is cold. In any case, you will be getting a code soon enough. Let us not overlook poor compression as a possible cause, but I think something like that would be a rare event in a Jaguar.

 

Thanks, jagv8 and Wing, for nudging me into Fuel Trims*

OK, with the car warmed up and idling for 30 minutes (in the garage):

Time 30 min 20 min 10 min 2,500 RPM (steady engine speed, car stopped in park; 30 min warm up)
LTFT Bank 1 +9,38% +7.03% +5.47% +7.03%
LTFT Bank 2 +11.72% +9.38% +8.59% +9.38%

As a fuel trim newbie, not sure what all this means, though guess that the ECM is adding fuel. If it matters, I watched the LTFT values increase during warm up, as shown
Other notes:
- The STFT values bobbled around between -2 and zero (bank 1) and +1.5 and zero (bank 2)
- Driven a couple of times (50 miles) since new battery swap; no PCM (powertrain module) codes set
- When starting in garage, I distinctly felt the startup miss. I can hear it as well outside the car; sounds like a dud cylinder. Smooths out at startup idle in about 3 minutes
- While scrolling through "Live Data" parameters (there's dozens of 'em), came across "Misfires Since Last Reset", shown by cylinder #. Not a single misfire logged...

* Note: A fellow forum member - XJRguy (Steve) - has posted a great primer on fuel trims: https://www.jaguarforums.com/forum/g...ed-quiz-49317/ This helped my understanding of things a bit

 

- (Sorry the Fuel Trim Table (above) is smushed together. It apparently got truncated by the forum text autoeditor)

- Two more driving cycles, yet still no CEL or codes. Believe the (double digit) LTFT numbers indicate a significant problem, so not sure why this would be (??)

 

The idea is to go for a drive to get the engine hot then park. Get the trims at idle and then rev to about 2500 and get trims again.

If the STFTs are small no need to post them as the LTFTs will be most useful.

 

The plot thickens...

- Two more drive cycles, and have a code: P0442-00T Evap System Leak (small leak)
- Assume "00T" Temporary as it hasn't happened enough to become permanent yet?
- Gas cap is new and tight (original broke last year)
- Only conclusive forum thread I could find involved "purge valve" (believe its under LH wheel well liner): Do these create P0442 ??
- (The plastic air filter box, lid, and large plastic air tube to the intake plenum were brutalized on this car when I bought it ~ 4yrs and 48K miles ago. I've JB welded etc back into function, but could some small leak here be causing a P0442 code? Ask because of some ramblings in the P0442 thread I studied)

Fuel Trim Update (tks jagV8)

- Roughly same idle LTFT values after driving cycle; hot, in Park: (Bank 1) 9.38 (Bank 2) 10.94
- Ditto 2500 RPM hot Park: (B1) 7.03 (B2) 9.38

 

You're getting there

Search on here may get you ideas/fixes for the P0442.

That the trims do not drop near 0 means you're not fundamentally looking at an air leak (other than the P0442 issue) - so rules out a ton of work & hunting. You can live with those trims if needs be.

In case you need "smog" I think just the P0442 needs fixing.

You could also look at the individual OBD monitor statuses to see if any is unhappy. (Ever code clear or battery disconnect also clears them so avoid both.)

I wonder if the "misfire" could relate to the P0442 - I'm not figuring how but can't say either way, sorry.

hmm... wonder if it could be fuel-related. Changed the fuel filter?

 

Thanks, jagV8!

- Is there a good reference source for expected "OBD Values"? (I assume these are the many live data parameters eg, MAF output, which accompany LTFT, etc?)
- P0442: Assume this is a small vac leak in fuel tank/charcoal cannister vacuum circuit controlled by the purge valve. Other than outright failure (eg, stuck open), do these solenoid valves sometimes leak a bit due to dirt or wear?
- Thanks for the insight: ("...You're not fundamentally looking for an air leak..."). I interpret that a small (eg, P0442) vac leak would be relatively insignificant at 2,500 rpm, causing LTFT to drop toward zero. Whereas, a misfire would be adding (unburned) oxygen at all speeds; ditto a faulty, say, MAF?
- Believe this car has original MAF, which I cleaned four yrs ago. I did read a couple of (wandering) threads about "lazy" or aftermarket MAF's causing similar problems (ie, double digit LTFT values; no CEL or code. Don B (bless him) wrote an excellent one, which involved meticulously chasing down miniscule vac leaks before finally replacing a seemingly good MAF
- Fuel filter (replaced 4 yrs ago): Do I follow that a clogging filter might cause a lean misfire at all speeds, giving these LTFT values? (BTW, this car runs liked a scalded cat uphill at full throttle, from which my old school brain has heretofore deduced that fuel supply and ignition integrity are OK)

This IS a bit like reading a whodunnit. Clues everywhere. Trying hard to finger the real culprit before ending up on the side of the road...

 

You don't necessarily have a "lean misfire".

If the fuel/air mix doesn't ignite properly there's air left so the O2 sensor causes the PCM to adjust and add yet more fuel. It looks lean but actually isn't.

OTOH, if it burnt OK but there's O2 left then it's also seen as lean (well, it is in this case!) so again the PCM adds fuel.

It would be great if the car had foolproof fuel sensors (as well as the O2s) but they're REALLY expensive and do not like 600C exhaust gas so no-one fits any.

Generally, actual misfires trigger P030x / P0171 / P0174 codes and they do that long before you can feel them. You don't have these and your trims pretty much rule them out.

That makes me think you probably do not have misfires but instead something else that you feel. Bad motor mount, or ... (something).

 

Once again, many thanks, jagV8!

"That makes me think you probably do not have misfires but instead something else that you feel. Bad motor mount, or ... (something)"
Funny, this is about the only car I've had in years (all German) in which I HAVEN'T replaced the motor mounts (others liquid filled, split, leak etc)
The engine definitely feels a little rough at start up, just like a duff cylinder, smooths at ~3 minutes or so. Engine is v smooth hot in drive stopped in traffic

Assuming it ain't actually misfiring, any more insights as to what is pushing those LTFT values up? (I assume there not normal??). Gas mileage on trips is ~ 23mpg (US Gallons)
(I'm going to replace valley hose (and everything around it, waterpump, belts, etc) and leave on trip to Montana at end of month. Love to not meet the LTFT culprit on a lonely highway somewhere...)

PS: My Dad's a Yorkshireman; my mother from Chesterfield, I was born in St Albans...

 

Mystery of the Missing Cat

Chapter 3: The Culprit Leaves His Card...

Ran a couple of errands today in the Jag, and - bingo - on comes the CEL. P0442 INT is the code: Intermittent evaporative system leak; small
- I've checked the (newish) gas cap and filler neck; all looks well
- LTFT values same as previously reported
- Any typical XJR issues which might cause this?
- As its "intermittent", and I'm having startup miss or roughness, is there a startup evap evacuation mode which might be involved?
- (Looking for an X356 - '07 H VIN - service manual and / or OBD code troubleshooting guide. The service manual pdf link in the stickies is for the early x350 cars; up to G VIN)

 

I'm better at air leaks! Also, they're far more common.

Any sensor the PCM needs (for closed loop) and which is a bit out of spec but not enough to flag a code would be a suspect. I suppose that includes fuel pressure, MAP, er, not sure what else. Or something causing such (that's why I asked about the fuel filter).

In theory, also any actuator that isn't quite right but with both banks hih all the time that rules out everything I think (you don't get 8 bad injectors all at once, etc) unless I've overlooked something. I may have - stare at the car info in Jag doc thinking how closed loop works. Here's a generic 2-bank car: OnBoardDiagnostics.com - Engine Basics

I don't know if a pesky evap valve or the like could do it and yet report just that code.

EGR valve? As I say, stare at car info and think hard.

Lazy IAT or ECT? Dunno.

In CL (closed loop) the PCM software is looking at the sensors lots of times per second and adjusting the actuators. It can detect SOME anomalies and post codes but not all and anyway some are just a bit out of spec as is to be expected with age & mileage.