Hello all,

I was driving my 2004 XJ8 the other day (2/7/23) when on startup in a parking lot the engine had a violent shake. Out of 3 startups, the first two were accompanied by this shaking, the car shutting itself off, and a solid check engine light (Power Train System), while the third start began with a slight shake/rumble and no check engine light and I was able to limp it back to campus. That day I drove the car maybe 60-70 miles of interstate/ back road miles using sport mode for the first time in a long while. Since Tuesday the 7th the car has run smoothly and the check engine light has since disappeared and the car has crossed the 42k miles threshold. I went to AutoZone to use their OBD reader and the codes are as follows.:

P0300: Random Misfire Detected
P0301: Cylinder 1 Misfire
P0302: Cylinder 2 Misfire
P0303: Cylinder 3 Misfire
P0305: Cylinder 5 Misfire
P1316: 1. Misfire Causing Excessive Emissions 2. Misfire Rate Exceeds Emissions

In the past few months I have noticed an occasional shaking of the car when idled at a stop light or even parked after startup but nothing like what happened the other day. This many cylinder misfires at once is a concern especially with there never being any kind of problem before.

My father and I (plus the guys at AutoZone) have a hunch that it's either spark plugs or bad coil packs causing this issue, but any feedback would be greatly appreciated. Thanks all.

SeanieFutbol

 

Swap some of the coil packs around and see if the fault moves with them. It might also be bad petrol or water in the petrol.

 

Unlikely to be plugs.

Coils may be dead / contaminated.

Be sure to check exact battery & charging voltages.

 

Possible grounding problem at G26.

 

Hey mate, can you elaborate on this ? im just tracking this thread, your comment got me curious on my own issues with my 5.0 SC misfiring cyl 5 and 6.

 

I'm happy to elaborate some. The issue has since been fixed, we ended up replacing all of the coil packs and spark plugs. It turned out that they hadn't ever been changed in the 20 years since manufacture. Since changing out the plugs, the car runs a lot smoother and is far more responsive to acceleration. Gas mileage has also increased to well over 20 miles per gallon.

The original issue was very jarring. The misfires happened the one time in a mall parking lot. The shaking was incredibly violent as a result of 4 cylinders misfiring, there was no doubt about what was happening. The car threw the power train check engine light and then very quickly shut itself down while the ignition was still in the on position. The shaking and rumbling persisted for a few days until we could get the coils and plugs changed.

If you have an obd reader or can go somewhere and get a free reading I would very much recommend it to see what codes are stored with your misfires. The only other thing that we thought could have been an issue causing this was the Engine Control Module, but we scrapped that thought quickly after seeing the randomness of my misfires. Also find a map of the firing pattern of your cylinders and see if there is some kind of routine that is happening when you do experience misfires. A bottle of Dry Gas also wouldn't do the car any harm.

 

On a similar note: few months ago I decided to change the spark plugs, got some cheap ones, and #$ began. Engine not firing on one of cylinders, had it twice so far and replaced two ignition coils (and plugs) to fix it. And today got it for the third time.
The problem I have - I'm far away from the previous shop, visited a different one today - their computer does not see any misfire codes, and they had no time to physically disconnect the coils - it was Friday 5 PM my time. I've tried to do the same with my freeware OBD soft, same story. But the symptoms are identical and I already have a new ignition coil on the way.
What could I do to find out which cylinder is dead? Do you know any software on Google Play that could tell me that? If that would be one of the front cylinders, it should be a 5 min fix for me, wouldn't need to wait until Monday.
If one of the rear cylinders - people that changed the plugs said it was a nightmare to do that, they had to dismount a lot, while the internet suggest there are ways to replace ignition coils even from the very back not touching anything else. Which is true? Any help greatly appreciated.

edit: my footer disappeared - it's a '04 4.2 NA X350.

 

Rear spark plugs can be removed without much trouble
Using extensions along with a universal swivel joint.
The oil filler pipe will unscrew & give you more room.