Hi, I bought a '95 XJ6 several weeks ago; it ran quietly and smoothly on the road and at idle until two days ago, towards the middle of a 250-mile trip. Lots of hills, in the rain, at 70mph, if it matters. Now, it shakes at idle and while driving at low speeds. Seems rougher at high speeds too, but not as noticeable. It's feels like a left-to-right shake. The sound and feel of it is something like driving a manual in a higher gear than it should be, as when leaving it in 3rd while coasting to a stopsign; as if it's trying not to stall. Does it in Drive especially, but also a little in Park. I'm using the proper premium fuel (93). No "check engine" light. Any ideas on what this might be? Any suggestions would be appreciated.

Stephen

 

Well, it does sound like a misfire and these cars are well known for poor OBD misfire detection circuits. It probably would not hurt to change the plugs if they have some miles on them, and check the plug boots for signs of cracking or for condensation while you are at it.
Good luck.

 

Thanks sparkenzap. I replaced all six spark plugs. No Moisture in the boots, or cracks (although I did break one while pulling it off the coil--will have to replace). The change made no difference that I could feel. On the last two plugs (the two closest to the driver), there was a little bit of oil in the spark plug wells. Just a little more than a film, really. I absorbed what I could with a twisted shop towel. Would this be a problem?
Any other suggestions as to what the problem could be? I am noticing a shudder now throughout the driving range, as I accelerate ( or even maintain speed).

Tried putting some gas treatment in it, thinking maybe some water got into the fuel system. Did not help.

 

Might have a coil problem as well.

A few weeks ago had to replace two of 'em on my car to cure some odd rough running issues. In fact, in the last couple days I've felt some roughness again that has me wondering if the others are getting weak. The coils are known to give problems on these cars.

Lacking any cylinder specific mis-fire codes I checked all the coils and replaced the two that were clearly out-of-spec.

Cheers
DD

 

Doug:
what do you mean by "out of spec"? I am assuming you don't tell that by looking at them. Or do you ? heh, heh.

 

I Think Doug is talking about the resistance in the coil but not sure what that is on these cars. Most I have checked are usually 0.6 to 0.7 ohms but that was not on a Jag engine.. I'm sure Doug will know what they are suppose to be..

 

Sure there's a spec. Or at least there is a Jaguar issued diagnostic chart for the X308 that calls out a specific set of resistance range as a go/no-go for the coils. It is probably much the same for a X300.

 

The primary resistance spec is .75 ohm. I had a couple that were twice that amount.

What was odd is that the engine only ran poorly at idle speeds.

Cheers
DD

 

A couple of things come to mind:

-- alternator has not reached full output at idle, so the voltage rail is slightly lower

-- fuel map at idle

-- air column is at lowest velocity at idle

-- less momentum at idle to mask misfires

-- less cylinder swirl at idle to help firing

 

That's my best guess.

Cheers
DD

 

Thanks, Doug.
Yea it would suprise me that it ran at all . Also, if bothcame up at twice resistence, that would imply yhat there are probably two windings in parallel, with one opening up still alowing the other to make some spark, That would probably be a good firt pass for diagosing stumbles.

 

I was mis-remembering :-). Knowing I had marked the resistance on them with a Sharpie I just looked at the old coils. They were 1.2 ohm so, no, not as far out as I mentioned earlier.

Old age and working on multiple cars sometimes gets the best of my memory cells.

Cheers
DD

 

It would be interesting to know what failure mode causes a "partial open" on a coil. I have seen that on a Ford coil myself. A lower resistance can be easily explained by an internal short.

 

Thanks

 

I checked the coils with a multimeter; all six of them are at 0.9 Ohm (cold, after sitting loose for an hour after driving and removal). Unless something caused them all to jump to 0.9, suddenly in the middle of a trip last week, it seems like the coils are not the problem. What do you guys think?

Cleaned the EGR valve. Some carbon build0up, not too much. No difference.

 

Put some injector cleaner in the fuel tank and change the fuel filter. Last but not least, check the fuel pressure from the fuel pump.

 

Will do. Took it to Advanced Auto, just to see if they could pull codes; the Check Engine light goes on when I turn the ignition, but then off when I start the car. Turns out, they were able to pull these codes:
P0301
P0302
P1314
P1313

The first two are clear enough; misfires in cylanders 1 and 2. (How are they ordered? #1 at the front of the vehicle, counting backwards, or #1 closest to the back of the vehicle, counting forwards? I suspect the latter, since I found oil in the two wells closest the the driver). Still looking into the other two codes.

 

Stephen:
Ohhhh- Although X300s apparently do not have too many head gasket problems, that is, unfortunately a possibility for you. I would swap the front two and rear two coils, reset the codes and drive a few miles then check codes again. It is probably a good idea to check the front twocylinder's (cyl 1 &2) compression. Cyl 1 and two are NOT adjacent in the firing order, so I am afraid the head gasket is a reasonable possibility.
Good Luck.

 

Thanks sparkenzap. Swapped the front two and rear two. Same problem. Had the code read, same codes (although I'm not sure the codes were reset from the last time. I uplugged the battery negative terminal for twenty minutes, but the "Check Engine light was on when I put the key in, before starting the car). May need to take it to a shop. Will check the wires leading up to the coil first--I guess holding the live sparkplug against a ground area around the engine will tell me if it's sparking at all.

 

P1313 Catalyst Damage Misfire Bank 1
P1314 Catalyst Damage Misfire Bank 2

Hope this helps somehow..