Yet another problem with my car, this time I'm truly stumped. 1998 Jaguar XJR with 115k miles.

Just got done replacing my head gaskets and putting the motor back together. I put about 1500 miles or so on the car with no problems what so ever. Then one day as I'm leaving to go to school and turn out onto the main road by my house the motor just dies halfway through the turn. Doesn't exactly die but shakes and sputters shooting flames out of the exhaust.

Long story short I limped it home with a check engine light, back fire noises and 3 foot flames shooting out of my driver side exhaust. I could watch my average gas mileage go down significantly, as in watching drop to about 6 miles a gallon as I drove and I only drove about two miles. At this point don't care if i damaged the thing because I'm probably going to end up burning the car to the ground like the cops do in Superbad.

Pulled all of my plugs and all were wet with fuel and black and sooty. I tried hooking a code scanner up to it and it won't communicate with the car. I thought maybe the code scanner was broken but it works with other cars no problem.

So far I've tried replacing my ignition control modules to no avail and checked every fuse and relay in the car and they were all good, car still runs like **** if it even fires up.

It appears I am getting no spark at all now because I replaced the plugs and ignition modules and tried to turn it over with no luck. Checked the plugs again and they were brand new still you'd figure with intermittent spark they would at least ignite some fuel and get black and sooty.

I have a few thoughts from what I've read so far... The ECM could have just gone out randomly because I can't read any codes? The magnetic sensor on the transmission by the flywheel that tells the thing when to spark could have gone out or anything really.

If anyone has any thoughts on where to look for more problems or if anyone has had a similar situation any help would be greatly appreciated.

 

One other thing is that there appears to be a lot of weird noises coming from my throttle body when I turn my key, I don't remember it being so noisy before but I could be wrong. It sounds as though a motor in it is just constantly going even though I don't think one should be?

 

There is a motor in the throttle body, and there is a fuse for the OBD port, but I don't know where it is in the XJ8. Your service manual has fuse locations.
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Not that I am a tech, but from your description it sounds like you lost spark in some cylinders, or possible it became intermittent across all of them.

It could be something like loose ground that goes to all coils or some other common wire. If problem is limited to one side only - that's where I would look for it.

I never did it on XJ, but on other cars I would take spare spark plug (perhaps with spare coil, or using one of the coils ) and connect it to each cyl one-by-one and simply look if there is spark(while having a helper crank the car). Sometimes this will show which cyls have no spark and that can give ideas where to look for problem.


At the same time, if your car is not getting any air into cylinders because of the throttle body failure - that can also be the reason for the problem you describe.

 

Thanks for the replies guys I'll do some diagnosing when I get home. I did hook up a coil and plug and left it out of the cylinder to check for spark and there was nothing.... But I'll get someone to help so I can be sure.

I'll look into the throttle body tonight too, i can see how that not opening would cause some problems lol and its making weird noises so maybe the motor just went out on the throttle plate or something.

 

When checking for spark make sure spark plug's nut/thread is grounded, using jumper cable for example.

 

Disconnect the battery and remove the ECM. Then remove the cover on the ECM. Inspect it for black or brown stains, white or green powder corrosion and moisture.

The most common failure for ECMs of this age are the electrolytic capacitors which leak corrosive fluid. If you find any visible evidence I mentioned, have the ECM rebuilt.

 

Ah I did not ground the coil, that might be the problem there but I didnt think anything on the valve cover would provide a ground? I will take the cover off the ecu and inspect, already have most of the underbonnet torn apart and the battery disconnected

 

Are you sure it's an ignition problem ? The secondary cam chain tensioners are the new metal bodied ones, right ? Flames shooting out the back could indicate a cam timing problem. While apart you might want to pop the valve covers and see if the cam flats line up.

 

I will be checking the timing too. Im hard pressed to believe thats the problem since I've replaced the tensioners and put everything back together carefully but it is possible

 

I think Jim Legge has it right: flames out the exhaust point to a mistimed engine.

 

A little update to the progress with the car.

I've tried replacing the ignition control modules to no avail.

That's about it, I've been to busy with school and tests to work on it. Hopefully over thanksgiving break I'll have some time to tinker.

Definitely pulling the valve covers to check the cam flats.

I've read that the sensor in the bell housing of the transmission (the one that gets removed to put the crank key in) reads some kind of pickup from the flexplate which then tells the ecm when to fire. Is that true? If so I may look into the possibility of that sensor being faulty.

 

"Crankshaft Position Sensor (CKPS) is another very likely culprit. If the tachometer reads 0 rpm while cranking, that would be my first suspect."
This is from an old post.

 

Did you ever sort your problem? This is a late reply, but I have been absent from forums for a while.
It seems you have a massive over fueling problem, not an ignition problem. I would suspect the fuel pressure regulator, as it works via vacuum, and if the diaphragm ruptures, I think it can dump raw fuel in the inlet manifold.

good luck