Misfire problem - please help!
Discussion
Our 4.6 Range Rover has started misbehaving. It's been misfiring under load (around 2,800 revs is most pronounced).
It's been into the local garage twice. The first time they replaced the leads and plugs. The issue seemed better, but has returned to missing quite badly over the a 4 week period. So, I took it back and they told me that a hose was lose so water had leaked and damaged one of the leads. The replaced it, and it ran better for a week or so.
It's now back to as bad it ever has been, and I'm not convinced it's run properly since it first showed the issue.
There's also a distinct smell of burning occasionally when I stop the car.
From reading around, the next likely cuprit is one of the coil packs starting to fail.
Could that explain the symptoms? Also, is the coil pack on my '95 4.0 TVR the same as a '00 p38 4.6 Range Rover so that I could swap the components to test?
Any advise would be greatly appreciated, as I've lost faith in the garages troubleshooting skills!
D
It's been into the local garage twice. The first time they replaced the leads and plugs. The issue seemed better, but has returned to missing quite badly over the a 4 week period. So, I took it back and they told me that a hose was lose so water had leaked and damaged one of the leads. The replaced it, and it ran better for a week or so.
It's now back to as bad it ever has been, and I'm not convinced it's run properly since it first showed the issue.
There's also a distinct smell of burning occasionally when I stop the car.
From reading around, the next likely cuprit is one of the coil packs starting to fail.
Could that explain the symptoms? Also, is the coil pack on my '95 4.0 TVR the same as a '00 p38 4.6 Range Rover so that I could swap the components to test?
Any advise would be greatly appreciated, as I've lost faith in the garages troubleshooting skills!
D
jay123 said:
coil packs could be at fault but could also be the MAF.
if the car is fine when cold then misfires when its up to temp then it is likely to be the o2 sensor
if the car is fine when cold then misfires when its up to temp then it is likely to be the o2 sensor
Thanks for the reply. It seems to misfire all the time, so does not seem to be temperature related.
The garage have diagnosed a weak spark on 2 cylinders (4 and 7 IIRC).
I'm told they're both fed by the same coil pack so I'd assume that was the cause.
However, the garage tell me they have another car showing exactly the same symptoms (on the same cylinders) and they've replaced both coil packs and it hasn't helped. They're reluctant to do the same on mine as it means removing the manifolds and a lot of the LPG electronics to do so.
There latest theory is that the ECU is at fault (which sounded unlikely) though I think they've now tried a replacement which has made no difference.
thanks,
D
Is this a n/a engine? I had a problem with my car (not a Range Rover) with the part of the ECU tune that monitored mass air into the cyliners. It was pulling timing big-style but only after I changed the ECU operating system & MAP sensor following a s/c install. Probably way-off but if the ECU is a suspect, maybe have a look. The MAF might have some bearing (mine is MAFless).
Hope you get it sorted.
Hope you get it sorted.
Edited by NAH on Tuesday 19th December 23:25
I'm afraid I don't know the code faults, though I'll ask when I call later.
It's a N/A engine (a 4.6 Rover v8) running on gas and petrol (it misses on both).
I'm told they've tried replacing the ECU with a new one, but that has not fixed the problem.
Apparently, this is the 2nd car they've had which has done this. On both cars they replaced the plugs and leads first (because they were breaking down) which temporarily fixed the problem. A couple of hundred miles later, they both started missing on the same 2 cylinder. I'm not sure whether the new leads just placed more strain on the rest of the ignition system and has caused more failures?
Edited to add: Another commonly mentioned component in a Google search is the Crank Position Sensor. However, you'd imagine the test book would give as pretty accurate assessment of the problem with something like that, wouldn't you?
It's a N/A engine (a 4.6 Rover v8) running on gas and petrol (it misses on both).
I'm told they've tried replacing the ECU with a new one, but that has not fixed the problem.
Apparently, this is the 2nd car they've had which has done this. On both cars they replaced the plugs and leads first (because they were breaking down) which temporarily fixed the problem. A couple of hundred miles later, they both started missing on the same 2 cylinder. I'm not sure whether the new leads just placed more strain on the rest of the ignition system and has caused more failures?
Edited to add: Another commonly mentioned component in a Google search is the Crank Position Sensor. However, you'd imagine the test book would give as pretty accurate assessment of the problem with something like that, wouldn't you?
Edited by _deejay_ on Wednesday 20th December 10:21
_deejay_ said:
I'm afraid I don't know the code faults, though I'll ask when I call later.
It's a N/A engine (a 4.6 Rover v8) running on gas and petrol (it misses on both).
I'm told they've tried replacing the ECU with a new one, but that has not fixed the problem.
Apparently, this is the 2nd car they've had which has done this. On both cars they replaced the plugs and leads first (because they were breaking down) which temporarily fixed the problem. A couple of hundred miles later, they both started missing on the same 2 cylinder. I'm not sure whether the new leads just placed more strain on the rest of the ignition system and has caused more failures?
Edited to add: Another commonly mentioned component in a Google search is the Crank Position Sensor. However, you'd imagine the test book would give as pretty accurate assessment of the problem with something like that, wouldn't you?
It's a N/A engine (a 4.6 Rover v8) running on gas and petrol (it misses on both).
I'm told they've tried replacing the ECU with a new one, but that has not fixed the problem.
Apparently, this is the 2nd car they've had which has done this. On both cars they replaced the plugs and leads first (because they were breaking down) which temporarily fixed the problem. A couple of hundred miles later, they both started missing on the same 2 cylinder. I'm not sure whether the new leads just placed more strain on the rest of the ignition system and has caused more failures?
Edited to add: Another commonly mentioned component in a Google search is the Crank Position Sensor. However, you'd imagine the test book would give as pretty accurate assessment of the problem with something like that, wouldn't you?
Edited by _deejay_ on Wednesday 20th December 10:21
cam or crank sensors wont cause a misfire usually... they will be more associated with sluggish running at low revs...
tempted to say MAF...
Latest theory from the garage is a bad batch of leads so they could have potentially replaced my old leads with new ones which didn't work either.
I'd have though that would be easy to test (by changing the leads around to see if the misfire moves between cylinders) but what do I know. Will leave it with them and hope it comes back working reasonably soon!
D
I'd have though that would be easy to test (by changing the leads around to see if the misfire moves between cylinders) but what do I know. Will leave it with them and hope it comes back working reasonably soon!
D
Well, the car is running better (if not perfect - I think I'm becoming paranoid).
Apparently, the leads they replaced the old ones with were faulty and the new batch sorted it.
To say I'm skeptical doesn't even begin to cover it, but I suppose the outcome is the right one.....
Thanks for all your help on this....
Apparently, the leads they replaced the old ones with were faulty and the new batch sorted it.
To say I'm skeptical doesn't even begin to cover it, but I suppose the outcome is the right one.....
Thanks for all your help on this....
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