Volkswagen Lupo (1999 - 2004) - 99 1.4 Very bad misfire - cured by restarting

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Tue 16 Feb 2010 22:56
99 1.4 Very bad misfire - cured by restarting - E30Matt
Hello all, I'm at my wits end with our problem child of a Lupo, I'm hoping someone can help!

The car is a 1.4 S (75bhp) on 96K

The car has developed a horrendous misfire that is only cured by stopping and switching off the engine, restarting clears it and it can be driven again, sometimes for half a mile, other times for 15+.

Strangely when the misfire comes, its at all revs, including idle but it never stalls out, the car also seems to be drinking fuel and when the misfire occurs there is a hot smell coming out of the exhaust. No warning lights show and the car is not overheating

The car had a basic service (plugs,filters (not fuel) and oil) less than 300miles ago. My Wife has been saying for some time it felt down on power.

The latest problem came after we ran the tank low, first thought were some crud had been sucked through but the switch off/reset/restart thing is really confusing me!

Hope someone can help

Matt
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Tue 16 Feb 2010 23:12
99 1.4 Very bad misfire - cured by restarting - Peter D
The best thing here is a Vag-com code read as if left this fault could destroy your cat convertor. Did you have the fault before the service.
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Tue 16 Feb 2010 23:17
99 1.4 Very bad misfire - cured by restarting - E30Matt
A very slight possible misfire that was barely noticable, and its been fine in the 2-3 weeks since the service, this new fault came on slightly on Sunday night when we brimmed the tank, ran for about 50 miles ok, then became a real problem today.

Thanks
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Mon 15 Mar 2010 21:55
99 1.4 Very bad misfire - cured by restarting - E30Matt
Okay, this is an update for anyone searching having similar problems, as i believe its now fixed, it may just help you!!

On top of the parts i replaced (plugs/leads/coil pack)

I removed the throttle body ( nice and clean on the topside, utterly filthy on the underside ) and gave it a good clean
I removed the MAP sensor, it was caked in old oil and crap so gave it a good clean.
I removed the Lambda, cleaned it but it didn't need it
Checked all the pipework from the EGR valve and its operation, vac pipes were ok, metal exhaust pipe to the inlet wasn't blocked but it was caked up with old soot at the throttle body end.

Bolted it all back together and took it for a test - the car drove great, pulled cleanly with no hesitation.

Next day the misfire returned once it had warmed up - again cleared by restarting.

I then invested in a code reader, cleared them all, tested the car and an error came back as 00515 - Camshaft Position (Hall) Sensor (G40): Short to Ground. (Ross-tech Wiki is a great site for checking codes and causes/solutions)

Since the sensor had been replaced with a genuine VW one, i started to check the wiring, upon pulling apart the three large plugs (one vertical black one, one brown vertical one and a horizontal black one) i discovered both black ones were full of water/coolant - it had been in there for a long time, evident from the corroded terminals

Terminals cleaned up and the error 00515 has never returned, and the misfire has gone, Its still a mystery how the water got into what should be totally sealed plugs, who knows!!

There is no doubt that at 11 years and 97K an intensive overhaul is a good thing

Hope this helps someone, I'm just glad the damn thing is working again!!

Cheers,
Matt
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Tue 16 Mar 2010 17:19
99 1.4 Very bad misfire - cured by restarting - Gregory II

With what did you clean the lambda sensor, map sensor etc with. I am assuming carb cleaner, but so I don't cause any damage can you confirm.

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Tue 16 Mar 2010 20:50
99 1.4 Very bad misfire - cured by restarting - E30Matt

Hi,

Yes i used carb cleaner, i have read you can use parafin the clean the Lambda sensor but i didnt have any!

Gave them a good blast and left them to dry, - the MAP sensor is a right git to get out because VW helpfully put the dipstick right next to it but it is possible!

Cheers,

Matt

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Wed 17 Mar 2010 23:01
99 1.4 Very bad misfire - cured by restarting - JohnM{P}

Thanks for taking the time and trouble to post the update after the 'quiet period' (but hope I won't need it for my daughter's 1.4 Lupo!)

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