Help! Cylinder 4 Misfire. Mechanic already cost me $2,000 what is wrong?

**brianls** · 11-06-2016,05:30 PM

I had a cylinder 3 misfire and took it to the mechanic. Well they found a valve that was burned. So they took the engine apart and replaced the burnt valve, put it back together. Once I had the car back it ran fine for a while but now the cylinder 4 is misfiring! I replaced the coil pack and swapped spark plugs but it won't fix it.

Can somebody help me?

It is showing a P0304 code. (Cylinder 4 misfire)

**zollaf** · 11-06-2016,05:41 PM

what engine is it ?

**Crasher** · 11-06-2016,06:01 PM

Didn't they replace all the exhaust valves and guides?

**brianls** · 11-06-2016,06:03 PM

2.0t

**brianls** · 11-06-2016,06:04 PM

I think they only replaced the one or two that was burned...

**zollaf** · 11-06-2016,06:06 PM

compression test next then ?

**brianls** · 11-06-2016,06:18 PM

I guess that would be the next thing to do. I just wonder what is making them burn out in the first place?

**Crasher** · 11-06-2016,06:52 PM

Originally Posted by brianls

I think they only replaced the one or two that was burned...

That was stupid, really really stupid

Start again! They burn out because of people using too low a grade of fuel AND in the US, higher levels of Ethanol in said fuel. Which petrol grade do you tend to use?

**brianls** · 11-06-2016,09:43 PM

I always use Premium / 91-93 Octane gas ever since I had it.. But I just bought the car a few months ago and who knows what kind of fuel the previous owners used.

**Crasher** · 12-06-2016,10:53 PM

Yes, the previous owner may have used 89 Octane rating fuel. Petrol's octane rating is expressed as MON for Motor Octane Number or RON for Research Octane Number and this is how it is shown on our pumps but when I have been in the USA it is shown on the pumps as PON or AKI (Pump Octane Number or Anti Knock Index) and this is the average of RON and MON so your 91 is the same as our 95RON and this is OK but a 95AKI (98RON) would be better, the Audi manual it states that 95RON can be used but it results in reduced power and we have learnt that over long periods, it causes valve burning. In the UK we have 95RON (91AKI), 97RON (92AKI) and 99RON (94AKI), all approximate anyway... Is your engine type code BPG or BWT?