so, 1997 xj6 has a cylinder 1 misfire at all times. new plugs, coils, and injectors. was running fine, its now progressively getting worse... cylinder has air, fuel, spark and compression. cam followers are moving correctly, valves and springs are in order.

my thought is the timing may be off a hair, but i thought that it would affect all cylinders.

im not sure if im missing anything else... would the distributor sending a weak signal affect a specific cylinder? or all cylinders?

any input is appreciated.

 

also, there are no issues with injector pulse....

 

Hi Spanials,

Welcome to the Jaguar Forums!

Your X300 has a completely electronic ignition so there is no distributor. The Engine Control Module (ECM) has the ability to adjust the timing for each cylinder individually based on inputs from the knock sensors and crankshaft position sensor (CKPS). I assume you've identified Cylinder 1 as the culprit via a Diagnostic Trouble Code (DTC)?

Problems with X300 coils are well known, but you've confirmed spark at Cylinder 1.... Any signs of coil arcing to the cylinder head?


I assume you've viewed the pulses with a scope or at least a noid light? Given all the things you seem to have eliminated, the one that comes to mind is the possibility that the Cylinder 1 injector is leaking, siezed or plugged. Pulling the fuel rail isn't difficult, and you could try swapping injector 1 with one from another cylinder to see if the misfire moves.

I'll be anxious to hear what some of our resident X300 experts have to say. In the meantime, you might use the forum SEARCH function near the top of this page to see if others have resolved a similar problem.

Cheers,

Don

 

You seem to have covered all bases with your work so far. Fundamentally if an cylinderhas fuel, air, compression and spark it should run. Can you explain what you mean by a misfire all of the time - is the cylinder dead?

Don has explained the timing well. The device where the distributor would be is just an engine position sensor and the AJ16 engine will run quite happily without any signal from that.

I would go back and double/triple check the things you have looked at. Don't make any assumptions about new parts being good. Prove that they are, empirically.

I would swap injector, plug, coil with a working cylinder as a first step. That would establish that Cyl 1 has either a mechanical issue (unlikely if you have good compression) or a control system issue (injector or spark).

Diagnosing the control system is difficult. If you have checked injector pulse with a noid light that confirms a signal is being received but does not confirm the quality/strength of the signal. Ideally you would need to measure current ramp on the circuits for good and bad and compare them - that requires a scope. You could do some basic resistance tests for the wiring for the coils and injectors and that might throw something up.

 

well, disconnecting the battery and resetting the computer seemed to shake that misfire. it is still running rough though. almost like a vacuum leak. we rechecked all vac lines, also pulled vacuum with the gauge reading normal readings.

just for giggles we unplugged the MAF and the car smoothed out and idled 100% fine. put a MAF in it, still runs rough with it plugged in. we havent had a chance to start checking the PCM yet to see if its faulty in any way.

 

Well that certainly helps. We now know that some sensor is yelling the car to do something it doesn't want to follow, since your idle clears up when disconnecting the MAF.

Usual suspects are:

1. TPS - this guy causes all sorts of problems when failing.
2. Oxygen Sensors - downstream first
3. coolant Temp Sensor - cheapest part
4. Crankshaft Position Sensor
5. MAF Sensor - seems least likely believe it or not because of how rarely they fail