Hey guys,

Some time ago started having intermittent misfiring while driving. Regardless hot or cold.
Interesting is that when i start the car i can drive without misfire till the next startup of a car. On next startup starts misfiring, one the next after can be normal again.
Sometimes i drive to city without misfire, after work start the car - misfiring all the time. A rough idle and loosing traction while accelerating. When traction is lost at acceleration i hear small explosions in the tail pipe. I assume unburned fuel is burning in tail pipe.

I suspect the coils but i recently changed them all to new ones. Of course they where cheap ones from ebay, but they are only 4 months old.

I changed all spark plugs to champions RC12YC, i thought it helped, but the car ran one week without misfire, after that occasionally misfiring came back. So that was obviously not the case.

Returning to the coil thing, problem for me to find the coil if its faulty , because misfire happens not all the time. And if the coil would be dead i assume the misfire should happen all the time, but now its acting very suspicious.
I had previously dead coil - it was dead and finding it was 2 minute job disconnecting the wires one by one. But this time is much more complicated, since dead coil is not always dead.
And i have no error codes at all.

I start to thing - could it be the failing CPS sensor? Is there any way of testing it?

 

I will be watching closely as I have the same issue. Missing at around 50mph and rougher idle this morning but, smooth as can be on the drive home. I too just put in new Champion RC12YC plugs.

I was actually toying with the idea of taking a chance on 6 Ebay coils for $50.00 and if they cure the issue then buying the good ones. I do know all of my coils are original and the car has just under 75,000 miles.

CPS may be good preventive maintenance as well. I'll see what those in the know tell us.

 

Not to hijack your thread but, could it be a fuel delivery problem? Bad injector or fuel pressure regulator?


I just discovered that my hour ride home yesterday was without misfires. This after the car sat all day.


I drive to work this morning and on a particularly steep section of back road I give the car more and more throttle until the transmission kicks down a gear and from then on I have the misfire.


Pull over to the side of the road, turn the car off, let it sit for a minute, start her back up and away I go with no more misfires. In my case would I be wrong to consider a fuel pump/filter/dirty in-tank pickup? The car did sit in storage for extended periods of time prior to my ownership and I am wondering if the tank was not full could it have developed some rust that is now giving me issues.


I wouldn't think a bad coil, coil wires, CPS, etc... would act like this. Or am I wrong?

 

Could be old fuel as it has set for awhile . Suggest burn off or drain fuel ( new fuel filter ) and put the original coils back in . Your new coil(s) seem to be coil heat related and the coil winding's open up . If you can take one of the new coils and swap through each of the cylinders one day at a time and see how that works out as you drive if the originals don't work out . This is complicated by the possibility that you have more then one new coil defective and you picked a bad testing coil. Bring you spark plugs back down to 0.035 from the 0.040 to compensate for a weak coil . O'Riely auto parts stores have a free instore coil tester Innova 4400 ( adapter # 34 ) but not all stores have them yet . This bench test is different from the real on car considerations . Some of my coils took 3 trys to pass for whatever it is worth as a valid coil tester . Look for carbon tracking in the coils / plug contact area for you may have had a previous higher resistance platinum plug along with oil in the well that left the track behind that shorts out a plug .

 

I have had more than several tanks of fuel though it and I have made another observation.

The misfire/rough idle only happens in the morning. After sitting in the sun all day my hour drive home is misfire free. Would I be wrong to think that moisture overnight may be causing an electrical issue and over the course of the day the heat of the engine and sun dry out any moisture?

I have ordered new inexpensive coils to see if this cure the morning sickness. When then get installed any issues putting dialectic grease on the connectors? I know it's recommended on the coils.

 

My XJR too misfires at idling but drives normal. I have new fuel pumps, new fuel filter, new air element, tank emptied and cleaned and filled new fuel, new injectors, new spark plugs and new CPS so there aren't many other suspects left. According to XJREngineer, there is no need to worry too much if the engine misfires at light load or idling - it is important that the right Champion spark plugs are used, but coils are the prime suspect when car is operating with wide-open throttle. I have six made-in-Japan new coils which are yet to be installed so once Rose is ready for a more rehabilitation work, I shall see if the new coils would partially or totally sort the misfiring issue.

 

Put your scuba gear on for we are going to go in deep . I made a colored wiring schematic of the AJ16 engine controls several months ago but can't find it now . That way it doesn't look like a bowl of spaghetti and be saying Mia Mia Delamacia !!!!! but is easier to follow and not too complex a concept to effectively deal with . I rang out all of the wires from the ECU then so I have tossed that salad . In the end you will have your Jaguar purring like a , purring like a , purring like a Jaguar .

Later , Parker

The air gap resistance of the spark plug increases with increased air pressure . So under free load throttle up ( Goosing it in park ) you will not be in this condition but on the road up a hill you will see it . This points to a weak coil or to large a gap in the plug or both . Suggest bring the gap back down to 0.035 from the 0.040 . The older piston engine airliners had a metal tube around the ignition wires that was pressurized hence even with insulation the electrical power would no bleed off into thin air .

 

Remember that another issue we face with the AJ16 is oil leakage into the spark plug wells from beneath the cam cover.

If the spark plug well fills with oil, this may also introduce misses.

This unfortunately can be a tricky fix if the bottom of the well is deteriorated from arcing or corrosion and creating a good seal is problematic.

.

 

Similar thing happening here that seems a fuel pump / fuel filter issue, but let describe it regardless in case someone sees a flaw in the logic:

It is mostly occurring at either a sudden change in speed (Hard braking) or with swerving (dodging pot holes on roads). In general, anything that would disrupt the natural flow of gravity from the tank to the cylinder.

Haven't checked my spark plugs since changing out the valve gasket and coil o-rings, but I'll get to that in the near. Already have a new filter, real to break down for a pump, though