bigozuk

I reported a few weeks ago that I was getting multiple misfires. after filling the car up with high octane super unleaded and taking it for a good blast along the road the fault went away quickly. until yesterday when the misfiring returned - this time again I filled up with super unleaded and the problem disappeared within minutes.

could the low grade fuel really be causing the engine to misfire badly?

Philster

Why did you not fill up with super, and was this at a different petrol station? if so, it might be a crappy petrol station and not the lower-octane fuel.

How to answer your question: Go back to the same station and get the same petrol. Report back. Go back to another station and get the same, lower octane. Report back. if the second station's lower octane petrol causes misfires, then we can be confident that the lower octane and not the source of the petrol is the most likely cause of the misfire.

You might have two variables: You got petrol at an unusual station AND it was lower octane. To answer the question you posed, you need to eliminate both variables.

Stick to your regular petrol provider and stick to premium. Eliminates all variables and misfires you might experience trying to answer the question.

Cheers.

bigozuk

I buy my petrol from the same place every week, and always use the low octane cheap stuff. but after about 4 full tanks of running I start to get misfire, so then one tank of the good stuff and problem goes away for about another 4 tank fulls.....might be a coincidence, but just wondering is something is going on with the fuel

808c2s

Why are you running lower octane than is recommended?

bigozuk

a) because its cheaper (remember in the UK we pay $9/gallon)
b) because I didn't appreciate that I was meant to

PhilD

Sounds like you are getting knocking from lower octane. Takes a few tanks to develop as there is still some high octane in the tank which ups the lower octane just a touch, once you are running on just low octane the knocking develops. Not good for the motor, you are driving a Porsche not a Cortina :-)

neanicu

Sell car buy diesel. Flame away!

Now seriously,the knock sensor detects the lower octane gas and sends the info to your DME. The DME then retards timing to cope with the lower octane gas. These engines are designed to run with higher octane gas. All this info is in your owner's manual. You are only suppose to run low octane gas in emergency situations when high octane isn't available and for short periods of time.
Your question really doesn't make sense because you know what the problem is,yet you're still doing it.
Clean your MAF(mass air flow sensor) too!

808c2s

I would have to agree with everyone here. It's most likely your lower octane that is causing the problem. I know Premium gas is expensive in EU, but a blown engine will be more expensive when you take into account the cost of replacement or rebuild, along with loss of usage of your car.

bigozuk

best answer yet - I got the message now!

bigozuk

so after reading my manual tonight, I'm still a little confused - it states that the engine adjusts for fuels of 95 octane, which is what I've been running. I would have thought if 95 was going to be a serious problem that the manual would have warned against it!

neanicu

Being in Europe,as far as I know the highest octane gas is 98,correct? We're in the US where the highest octane gas is 93 and lowest is 87.
Your manual says that the computer can adjust to 95 octane which I assume it's your lowest rated gasoline,correct? Again,it adjusts to that in an emergency situation and should be run for a short period of time.
So,in your mind you're automatically thinking : " If the car is running fine with 93 in the US,it should fly with 95 in the UK,right? WRONG! The computer mapping is different in Europe than in the US. In other words,the computer mapping in the UK is set to run on 98 and in the US is set on 93.

Finally,I've thrown the MAF in the equation in my last post,as it just so happens that there's a possibility your misfires might not necessarily be related to fuel. That does not change the fact that you should be using the highest octane gas,which BTW is printed on the inside of your gas tank filler neck door.

jhbrennan

98 RON (UK) = 93 CLC/AKI (US) - the computer mapping in the UK is the same as the computer mapping in the US...it's just the difference in the way octane numbers are reported that is confusing you.

neanicu

Very plausible! Thanks for that!

I thought it's different,just like guys need to switch to a different map when running race gas(100 octane) at the track.

It still doesn't change the fact he's running Regular(87 US= 95 UK) when he should be running Premium(93 US=98 UK).

Philster

How many kilometers do you put on the car per month?

How much does premium/super unleaded cost above regular grade petrol?

Let's say premium is 8% more per litre. Let's say you spend 100 pounds on petrol monthly. You're telling me that 108 is that much harder to come up with?

I'd rather sell some junk in my closet on ebay to close the 100 pound annual gap between cheap petrol and super.

Think about it.

bigozuk

I use a full tank per week, so about £80/week. Or £360/month. Which is over £4000/year ! I guess the premium grade would add about £250/year onto that cost.