# MKIV VR6 - running 87 Octane causing CEL?



## TUGZ S2K (Oct 30, 2002)

On my last tank of fuel I ran 87 Octane. I noticed right after a morning start-up that the engine had a misfilre under light-moderate throttle load. When the engine reached operating temperature (90degC) the misfire was gone. This also threw a check engine light.
The outside temperature was 6degC and it was damp/raining. The car sat for a day. This exact same thing happend a month ago under the exact same conditions.
Yesterday, I filled up with 91 Octane. This morning's conditions were the same, 8degC...damp/raining. Started the car this morning and the misfire was not there. The only difference this time is the fuel....
So my question is....can 87 Octane trigger a misfire and CEL in the VR6? Im looking for technical answers please.
thanks


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## farfrumlusin (Oct 3, 2006)

*Re: MKIV VR6 - running 87 Octane causing CEL? (TUGZ S2K)*

i know on my car if i dont use 93/premium then it will eventually damage my engine...maybe that is the same for your car


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## TUGZ S2K (Oct 30, 2002)

*Re: MKIV VR6 - running 87 Octane causing CEL? (farfrumlusin)*

thanks for the technical explanation


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## farfrumlusin (Oct 3, 2006)

*Re: MKIV VR6 - running 87 Octane causing CEL? (TUGZ S2K)*

if yourr car misfires it is either your coilpack or spark plugs, gas may have an effect on that


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## bluefox280 (Dec 18, 2003)

*Re: MKIV VR6 - running 87 Octane causing CEL? (TUGZ S2K)*


_Quote, originally posted by *TUGZ S2K* »_So my question is....can 87 Octane trigger a misfire and CEL in the VR6? Im looking for technical answers please.

Yes, it can.
With the lower octane and the high compression of the VR6 powertrain, the engine can produce heavy knock or "auto-ignition".
When the air / fuel mixture is compressed during the compression stroke, the pressure + heat combust the mixture before the spark plug fires...
However, when you recieve a misfire (dictated by the ECU), it's usually electrical based.
And since you said the morning it did this, the weather was damp and raining, there's a very good chance there's a crack in your ignition coilpack.
You need to do the following: scan the ECU first with a VAG-COM to see what fault codes are present.
Second, do a complete sweep of the ignition system, and check plugs, wires, the coilpack and all connections.
From there, you'll get a good indication what the issue is.
- Erik


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## J double R (Dec 1, 2006)

*Re: MKIV VR6 - running 87 Octane causing CEL? (bluefox280)*


_Quote, originally posted by *bluefox280* »_
Yes, it can.
With the lower octane and the high compression of the VR6 powertrain, the engine can produce heavy knock or "auto-ignition".
When the air / fuel mixture is compressed during the compression stroke, the pressure + heat combust the mixture before the spark plug fires...
However, when you recieve a misfire (dictated by the ECU), it's usually electrical based.
And since you said the morning it did this, the weather was damp and raining, there's a very good chance there's a crack in your ignition coilpack.
You need to do the following: scan the ECU first with a VAG-COM to see what fault codes are present.
Second, do a complete sweep of the ignition system, and check plugs, wires, the coilpack and all connections.
From there, you'll get a good indication what the issue is.
- Erik

x2 good prognosis.


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## TUGZ S2K (Oct 30, 2002)

*Re: MKIV VR6 - running 87 Octane causing CEL? (J double R)*

Excellent responces...thanks http://****************.com/smile/emthup.gif


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## diive4sho (Feb 7, 2004)

*Re: MKIV VR6 - running 87 Octane causing CEL? (TUGZ S2K)*

so this is in the 2.7t engine forum for what reason??


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## hyperformance06 (Jun 27, 2006)

*Re: MKIV VR6 - running 87 Octane causing CEL? (diive4sho)*

i was thinking the same thing. somebody is confused.


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