Ok guys, got a curly one with my 2001 Daimler (Jag Van Den Plas) 4litre. It has a random misfire across 7 0f the 8 cylinders, so I suspect the one cylinder not reported as a misfire is simply an aberration. The computer also reported a MAF error, a throttle body sensor error, and one other (sorry, left the blasted codes in the workshop, but all related). Replaced the plugs, identified & replaced two COPS, smoked the intake from the air cleaner to the fuel injector ports and eliminated 5 leaks, checked every individual damned electrical wire & plug (I am going to have to rewire to the COPS as the insulation has cracked, but have individually taped every wire to insulate them). Cleared the error codes, but the random misfire still occurs, the idle revs won't come up, it bogs down half the time when I manually open the throttle but the misfire then becomes steady at about 1200 rpm. Allow the throttle to close and the engine almost stalls but slowly recovers to about 400 rpm. No error codes now registering, but the mis-fire continues. Car has only done 67,000kms (41,600 miles).



All suggestions gratefully received

Cheers,

Languid

 

Could you give us some info like when it started, any odd behavior before?

Also, is it a fresh battery?

You have air- how is the fuel delivery? Once those are confirmed we can start eliminating spark issues one at a time.

 

Sorry to expose ignorance, but if COPS are coils then disregard... I had a very similar problem... Started replacing coils. Persisted... did plugs spliced a few wires... went back to coils. Not until I had replaced all 8 coils (even the ones that checked out as good) that the misfire problem went away. And I did also get throttle error codes

 

Fuel delivery is good, new plugs, battery is new, COPS tested & all working. After clearing no new codes have been generated.

 

Ok then- let's go through the basics:

1. Is compression the same across all cylinders? (or within 10 or so lbs)
2. go through all of the plugs in the engine bay- unplug and replug
3. is the bulkhead connector clean and tight?
4. Is the ground strap clean and tight?
5. Fuel injectors- are the plugs in good order? (disconnect and reconnect) I ran across this one this year on an XJ6- one of the pins was not seated in the plug and the engine ran terribly.
6. CPS- is the plug in good order and is the sensor clean?

Hopefully this provides a good start, I am sure others will chime in.

Still would like to know how it ran before the issue and if any work has been done on it beforehand.

 

Was mis-firing on both banks, which led me to replaced the plugs & check & replace some COPS. But the idle was around 650-700, and the error codes were reported. Now, the idle is low to the point of almost stalling, the misfire is random across all pots, and no error codes are reporting.

Arrgh!!!

Cheers,

Languid