Hi all,
My VR6 has started to "misfire" in low revs. This does not happen all the time and there is no pattern to when, it just randomly does it under 2000 revs.
It seems like the car is running on 5 cylinders for no more than 10 secs and then clears.
A month or so ago, when looking under the bonnet, I noticed that one of the plugs was arcing against the cylinder head. (It had new plugs and leads 12 months ago.) However, I have not seen this since and as the car is rarely used, I put it down to condensation.
The backbox seems to be on its way out, there is no obvious leakage but I believe the baffles could be the key.
Could this cause back pressure and cause the misfire?
Any thought / suggestions?
It had an MOT 1 month ago and passed emmisions.
Thanks all.
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You have seen one spark plug arcing; perhaps a faulty plug, or lead end.
You have a misfire; perhaps on one cylinder only.
I suggest that these two happenings are not coincidental.
number_cruncher
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It does sound like HT lead or spark plug problem. The HT leads need a special tool to remove - depending on where you have the plugs done they may or may not have the tool, so may have used pliers or a good tug on the lead - Not good.
Also does your car have a coilpack or a distributor? If you have a coil pack these are well know to crack giving rise to arcing. Check for sparks in the dark around the coilpack. Some people have suggested spraying a fine mist of water over the coil pack to show up any arcing better - but im not too sure this is a good idea due to the high voltage invoved.
Also, try www.vr6oc.com there are a whole load of very helpful people on there. A search on their forum should give you a few more answers.
(I know linking to other sites is frowned upon, so mods please feel free to remove the above link)
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Thanks for replies.
Coil pack was replaced 8 months ago and is working fine.
I was certain that it was the HT leads, as I saw it arcing, but I haven't seen it since.
The car misfires whilst in low revs, could be in any gear. When the car does misfire a blowing noise comes from the exhaust. However, no leaks.
I just want to make sure that the misfire is connected to just one fault (i.e. ht leads or exhaust) as I don't want to get a new set of leads to find out it is the exhaust causing the problem.
Is it possible for condensation to build up around the HT lead and give a false impression that the HT lead is faulty when in fact it is working ok?
Thanks
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I can understand your desire to make sure that it is the HT leads at fault before buying them. I can imagine the VW price for these is not inconsiderable.
Once a part has begun to break down electrically, i.e., allowing an arc to form, it usually will continue to do so, and if anything get worse over time. Condensation will increase the probability of arcing.
When a car misfires, it can make the exhaust sound different. I suspect that the noise you hear is a symptom of the misfire rather than being a problem in itself.
Is it possible to buy HT leads singly for this model. If that particular HT lead was damaged by removal using incorrect tools, then it is possible that you can create a good repair by only replacing the one you saw arcing, rather than all 6.
Although, having said that, I can guarantee someone will be along in a minute saying that you should only ever change HT leads as a full set!!!
If the arcing was over the surface of the plug, I would put a new plug in there too.
number_cruncher
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Thanks NC,
As you say, I think that buying a single HT lead is probably best action. If it improves, then obviously a new set maybe required.
I wasn't sure if the exhaust was at fault or the plug/leads.
I will let you know what happens.
Cheers
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