1990 Jaguar XJ6 tuneup

BILLARD

MEMBER
1990 JAGUAR XJ6
75,000 MILES

We have replaced the fuel pump, the plugs, the wires, distributor cap. Fuel filter, and the engine quickly starts, but runs in surges, runs fast, then slows, then fast, then slows. Compression is about the same in all cylinders. But when we remove the spark plug wires, one at a time, the engine misses substantially on 3 cylinders, and hardly at all on two cylinders and barely on one cylinder. Is it the fuel injectors, or max flow, or what? Or the injectors?

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Yes the engine will miss worse the more plugs you remove. Are you sure it is missing when all plugs are connected? As far as the surge, have you checked to make sure there are no vacuum leaks on the engine?

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Tuesday, July 2nd, 2013 AT 7:57 PM

BILLARD

MEMBER
2 POSTS

We have not checked for vacuum leaks, but haven't noticed any. I meant it misses worse when some individual plugs are removed. When number one wire is removed, it misses badly, we replace the wire, and when number 6 wire is removed, it misses badly, But, when a single wire: 5, or 3, is removed, You can hardly notice the difference. Why this discrepancy?

We will now carefully check for vacuum leaks.

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Tuesday, July 2nd, 2013 AT 10:49 PM

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

When that happens, those cylinders are not working properly. It could be fuel related, spark related. If you pull those plugs out, are they wet or dry?

I just went through this with a jeep. #3 cylinder made no difference when the plug wire was removed. The plug was dry and getting spark so I check for power to the injector which was good. I then replaced the injector itself and it ran perfect.

Check the plugs and let me know what you find.

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Wednesday, July 3rd, 2013 AT 7:30 PM