2001 4.6 THOR Sudden misfire

Hi all,

My 2001 4.6 Vogue has been running pretty good for a long while so it was inevitable that soon she would throw her toys out of the pram which happened yesterday.

Drove to the shops and all was well. After getting back in the car and starting it up I had an obvious misfire all of a sudden. Drove home slowly and then plugged in my faultmate. 8 codes were stored though not all showing as persistent so I cleared them down and ran another read of the codes. This is the list of error codes:
THE MOTRONIC FAULT CODE MEMORY CONTAINS CODES FOR THE FOLLOWING CURRENT FAULTS -:

P0300 = EMISSION RELEVANT MISFIRE MULTIPLE CYLINDERS DRIVE CYCLE C, WHICH HAS OCCURED ONCE
(SIGNAL TOO HIGH, THE FAULT IS CURRENTLY PRESENT, THIS FAULT CAUSES MIL LAMP ACTIVATION, THE FAULT HAS BEEN DETERMINED AS PERSISTENTLY PRESENT).

P0308 = EMISSION RELEVANT MISFIRE CYLINDER 8 DRIVE CYCLE C, WHICH HAS OCCURED ONCE
(SIGNAL TOO HIGH, THE FAULT IS CURRENTLY PRESENT, THIS FAULT CAUSES MIL LAMP ACTIVATION, THE FAULT HAS BEEN DETERMINED AS PERSISTENTLY PRESENT).

P0307 = EMISSION RELEVANT MISFIRE CYLINDER 7 DRIVE CYCLE C, WHICH HAS OCCURED ONCE
(SIGNAL TOO HIGH, THE FAULT IS CURRENTLY PRESENT, THIS FAULT DOES NOT GIVE MIL LAMP ACTIVATION, THE FAULT HAS BEEN DETERMINED AS PERSISTENTLY PRESENT).

P1319 = MISFIRE WITH LOW/EMPTY FUEL DRIVE CYCLE C, WHICH HAS OCCURED ONCE
(SIGNAL TOO HIGH, THE FAULT IS CURRENTLY PRESENT, THIS FAULT CAUSES MIL LAMP ACTIVATION, THE FAULT HAS BEEN DETERMINED AS PERSISTENTLY PRESENT).

Looking like a problem with cylinder 8 mostly and 7. Took out #8 plug and it was black and smelling of petrol. Put back a known good plug which made no difference. While running I pulled off the #8 plug cap which made no difference to the running of the motor. I could see some sparks to earth from the end of the plug cap though they looked pretty poor sparks to me.

Car has regular services and the plug leads are less than a year old and from a quality manufacturer. I would have to get a new lead for #8 to really rule out the lead of course.

Then ran some live data captures and below is the Rougness and Timing capture imported into an excel spreadsheet. The bad stuff is in red text:




My current thinking is that the coil pack supplying #8 has gone bad. That does not explain #7 as that's on the other coil pack.

Any idea's guy's?

Thanks,

Carl.....

Get a diesel:rolly:

I found mine was very twitchy about plugs and leads despite having magnecors. I would check for arcing at the coil pack first. Don't get a diesel, theryre slow and smell.

Small update. Swapped out #8 plug lead - No change. Borrowed a known good coil pack and put that on - No change.

So same fault codes come up each time with misfire mostly on #8. I noticed a knocking noise while running, but put this down to the misfire. Now I'm not too sure the noise is because #8 is misfiring rather the noise is the cause of the misfire. I'm starting to think it could be a valve train problem with #8.

Anyone seen a problem like this before?

Just can't help thinking this is going to get real expensive real quick.

At least it's not a diesel.

Have you had a compression test on that cylinder. This would tell you if there is any compression in there or faults with valves. The head gaskets go in that corner , but if its not pressurising or overheating then im stumped. You could have swaped with a poor plug or not put the cap on properly. Do you have magnacore leads on your car?

Yes I have blue magnacore leads fitted. Problem I have now is I'm unwell and cannot touch the car. Also I don't have a compression tester.

Just thnought maybe MAF sensor on air intake .

Sorry for going off the radar with this thread, but I have been rather ill. Because I've been ill I got the car to someone I trust to work on it. It turns out that the rocker shaft has snapped just before the valves of #8.

Very sorry to hear you are not well, hope its just a short term thing. I have a rocker shaft that I can post to you for free if it would help. Its used and I don't know how worn. You might though be advised to get a new one. Also check the rockers (both sides) and oil ways as well. Something caused the break, could be oil starvation?? Don't use Bearmarch rocker shafts as, I am told, they give too much oil flow which is a bad thing!

Did you replace the cam when you did the previous valvetrain work? A heavily worn, seized or snapped rocker shaft usually points to swarf contamination from a knackered cam.

Car is fixed now with a new rocker shaft.
I have never touched the top end of the motor in my ownership. When I got her she only had 57K on it so I'm reasonably happy the motor has not had any major work done on it at all.
As I've not been fit enough to do the work the guy that finished the job is an ex-LR mechanic and he confirms that he has seen them fail as mine did a fair number of times in the past. I have a picture of the shaft that I'll post later.

Sorry, had your motor mixed up with another.