# Misfire under load - ideas for shopping list...



## slabber (Feb 9, 2010)

Hi Folks
My 2.8L 30V (in a 1998 A6 2.8 Q tip saloon) misfires when under load – for example going up a hill at slowish speeds and then pressing the accelerator to maintain or increase speed.
I have VCDS/VAG-COM but have never seen a related fault code. Car is regularly serviced at an independent Audi specialist and in recent months I’ve had the throttle body cleaned and the MAF replaced but this has had no effect.
Research plus a posting on another forum has suggested plugs / leads / coil and coolant temp sender are possible culprits. I’ve just found this dedicated forum and wondered if anyone had anything else to add to the list, or could suggest the best item to change first to keep costs to a minimum.
Many thanks for your suggestions!
Cheers - Graham


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## O_o (Nov 12, 2009)

*Re: Misfire under load - ideas for shopping list... (slabber)*

There are a number of other things it could be. But instead of guessing, why not make use of that VCDS of yours? Take your laptop for a drive and do some logs: misfires, HO2 sensor, and maybe some fuel-trimmy stuff (lambda, LTFT...?... etc.). That will at least give you an idea of whether you have an ignition or fuel problem.


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## VT 4-motion (Jun 14, 2009)

I have a 2002 2.8 30 valve passat, I had the same problem. I replaced plugs, ignition coil, coolant temp sensor, Checked the resistance on the MAF sensor, plug wires, intake temp sensor. I completely over-thought the problem. I put new plug wires in and solved the problem, It has now been good for over a year. When I bent the wires up the resistance read good, when plugged in there was a short. If you have not changed the wires yet, just do it. If it doesn't fix the problem, it is a good idea anyway. 150 for NGK wires at napa.


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## slabber (Feb 9, 2010)

Thanks for the replies. Sorry - forgot to mention that I was planning to use VCDS at the weeknd to do some monitoring. A new use of it for me so should be interesting.
If I can confirm that it is an ignition problem I'll go for changing the leads first.


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## Scurvy Bandit (Sep 12, 2003)

*Re: (slabber)*

plug wires. I am 90% sure this will solve your problem.


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## slabber (Feb 9, 2010)

*Re: (Scurvy Bandit)*

Latest is that I tried to use VCDS (latest version) to log misfires, but channels 14, 15 and 16 didn’t have anything to do with misfires as per the manual. I managed to buy a second hand coil pack off Ebay for £18 including postage. I fitted that but that didn’t fix it however at least I’ve eliminated an expensive part as the culprit. Next task is to buy plugs and leads and hopefully get them fitted at the weekend!


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## Slimjimmn (Apr 8, 2006)

*Re: (slabber)*

channel 14 is misfire counter random, and rpm
channel 15 is cyl 1, 2, 3 , 4
channel 16 is cyl 5, 6, 7, 8
http://****************.com/smile/emthup.gif


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## slabber (Feb 9, 2010)

*Re: (Slimjimmn)*

Thanks Jim - very strange as the labels in VCDS bore no resemblance to the manual. But no matter, as a very helpful chap at the parts shop advised only replacing the plugs in the first instance. Did that - problem all sorted! What was disconcerting though was that all the spark plug 'tubes' (ie where the leads fit) were full of oil. No idea when the plugs were last changed so not sure how long they have been getting this extra lubrication. I'll check in the next couple of weeks to see if the oil has returned, but meantime should I be too worried about this? Engine has done 143k and (now) runs very nicely.


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## O_o (Nov 12, 2009)

*Re: (slabber)*


_Quote, originally posted by *slabber* »_What was disconcerting though was that all the spark plug 'tubes' (ie where the leads fit) were full of oil.

If you're leaking oil into the plug wells, they'll just foul again and misfire. The 30V PCV system is prone to becoming congested, so I'd check that first. If that doesn't stop the bleeding, you'll need to get yourself a new valve cover gasket kit.


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## slabber (Feb 9, 2010)

*Re: ()*

Thanks for this. Is PCV Positive Crankcase Ventilation?


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## O_o (Nov 12, 2009)

*Re: (slabber)*


_Quote, originally posted by *slabber* »_Thanks for this. Is PCV Positive Crankcase Ventilation?

Yes.


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