Hello All. My '04 XJR has two issues that may be unrelated:

1) When warmed up on hard acceleration/high rpm I get misfires. I can hear more than feel them. And they are uneven. In other words, not a steady misfire like one particular coil. The car keeps pulling ahead. If the car was 50 years older I would think it was something like mildly floating ignition points.

2) When cold the car vibrates under any acceleration. Even mild. Not a bad vibration. Just like the timing is not optimal. Once it begins to warm up it smooths right out.

Other than that, the car runs smooth and quiet. Seems to perform well up to the high end. 114,000 miles. Passed roadside emissions about a year ago. No codes are thrown. Good quality premium gas. New OEM spark plugs at about 100k. It's probably been going on for 10,000 miles and hasn't gotten any better or worse. And I couldn't swear that the two issues started at about the same time. Just about everything that I can think of would probably throw a code, except maybe catalytic converter? Injectors?

Thanks for your insight.

Mike

 

My 05 Super V/8 did that but much worse. Turned out to be driver side cat. converter restricted. I paid a dealership $108 to diagnose it (one hours time)

 

I'm surprised it's not flashing the MIL to show misfires, but if it's not then I too would suspect a cat.

You could look carefully at fuel trims for clues as they're usually thrown all over the place by a bad cat.

 

"When cold the car vibrates under any acceleration. Even mild. Not a bad vibration. Just like the timing is not

optimal. Once it begins to warm up it smooths right out."


Is it vibrating or hunting?

Many of these cars,including mine, hunt a bit when cold and at small throttle openings which disappears when

the tranny warms up.

I believe it is a 'feature' not a fault assoc. with a redesign of the torque converter blades.

 

With your given mileage and recent plug change i would day is time to also look at the coils. I had the same symptoms but worse. Worse enough it was confusing the transmission. The car would get better once it would warm up. It finally gave a code a couple after weeks of this. Misfire cylinder 6. Got new plus and replaced coil #6. Problem solved. Will look at replacing rest of coils soon.

 

I would second the coils (perhaps one wasn't seated completely when you did plugs?)

Ours had a plug go bad and the only time it showed the code for the bad one was after I replaced all of them (at 128 K I thought they were all due).

I verified the suspect coil by clearing the codes and installing it in the opposite bank. Sure enough it ran rough but did not throw any codes. These coils must have a way of going bad that the computer can't sense easily.

Be sure to check the spark plug gap, if you put them in out of the box I think ou will have coil issues.

 

Sadly the dealer tool can see the misfires building up per coil but not the ordinary diagnostic (OBD etc) tools.

 

Thank you all for your contributions. I think I would be able to tell if it was a coil issue. I assume the misfire would be a steady miss, even if it didn't kick in until higher rpm/loads and I think I would detect the symmetry. My miss is more hectic or random in nature. And more subtle.

As for the vibration, it is definitely engine, not the transmission 'searching'. And that is not a misfire but just a roughness.

JagV8 said "You could look carefully at fuel trims for clues as they're usually thrown all over the place by a bad cat." I don't understand what you mean by looking at fuel trims. Can you explain?

 

Misfires commonly are NOT a steady miss and the car will usually detect them long before you do. It's very common to have people with misfire codes in denial because they can't feel the misfire at all. (BTW the typical cause is a bad coil. And you will not be able to tell by past experience if it's a coil. You'll need to DO something like buy a tester, a definitely good OE coil or whatever.)

What you describe may be something else. Or possibly it occurs sufficiently randomly that the PCM can't see a pattern - but you'd be in a rare case if so.

OBD tool with live data, such as an elm327.

If you think of your car as a network of computers with an engine etc controlled by them you'll not go far wrong.

 

I have an older OBD2 that does not display real time data. Following your advice I looked at OBD2 on Amazon and can't believe the technology you can buy for $20. I ordered one and can't wait to get my hands on it. Will post my results here if I figure out the problem. Thanks

 

Try it when parked to get used to it.

 

Which OBDII reader did you end up with?

I also have an old reader which doesn't show live data. I also have a cold misfire, and no misfire codes. I DO have a bad RH cat code (P0420, IRRC)

I looked on Amazon, and see that there are lots of Chinese? bluetooth dongles (eg ELM 327), but reviews say they're dodgy (problems connecting to ECU, issues with required cell phone app downloads)

I'd like to but something as compatible as possible with the Jag (07 XJR) OBD system, if any suggestions

 

I ordered this one:
http://smile.amazon.com/BAFX-Product...ilpage_o00_s00
because of the guaranteed compatibility, great reviews and 2 year warranty. It is due to arrive today. I will post my results when I have had a chance to play with it.

Ps. Their specs say it doesn't work with iOS.

 

For iOS get a wifi elm327
For Andriod get a BT one

 

I received my BAFX and it looks great. The problem when I went online was that there were dozens of OBDII that said they were ELM327 and it took some digging to figure out that most were knockoffs. Anyway, the BAFX works with the 2004 XJR and coupled with the Torque Android app (free lite version, I paid $4.95 for the full version) provides a ton of great information.

I got pending P0101 Mass air flow circuit code several times, then a full fault that never showed on the car's fault system. I checked the wiring and I am getting good vacuum (19 in at 5000 ft altitude at idle) and see no loose or cracked hoses, so I am going to invest $110 in a MAFS and see what happens.

 

Update - I replaced the MAFS and the rough acceleration has smoothed out, but still have the misfire at hard acceleration at high RPM. I am now suspecting coils since the other problems have been eliminated. I'm not sure if there is a way to determine for sure if it is a coil problem or which one(s) using the OBD2. I'll have to learn more (Unless JagV8 or someone can provide some guidance? I would like to learn.). If not, I can always buy a couple and switch out them in and out until I find the offending ones. And if it turns out to be coils, just replace them all. They are not that expensive. If not, I haven't spent much and I keep investigating.

 

Fitz, although a bit more money many people in the UK are recommending the icarsoft 930 reader as it will read all the car not just engine. Very near dealer level ability to read every module and engine code,and give live data. The other option is an SDD program that is dealer level allowing key coding and module coding as well as full diagnostics.
I bought a SDD copy program for my XJR and it has helped me so much even told me which parking sensors had failed and the placement on the bumpers. The Jags are very good at not telling generic readers everything that is happening so something a bit more focused at JLR gives much better results and saves a lot of time. Hope you get to the bottom of it soon.

 

Hi Andy. Thanks for the advice. will the 930 tell things like parking sensors and why the wiper sensors don't work? Or is the SDD program required for that? I don't know what an SDD program is. Can you explain?

 

This sounds very much like the problems I had with my XJR, turns out the catalysts were choked up.

Long read but https://www.jaguarforums.com/forum/x...solved-137070/

No codes for misfires, no codes for anything really. Was down on power and the rattling in the top end was either misfires or detonation.

 

To throw codes it needs fairly consistent bad behaviour. The 930 probably won't help with the engine fault any more than the $5 elm327.