V70 5th Cylinder misfire or is it?

v70MB · Post by **v70MB** » 17 Nov 2010, 00:08

So my check engine light has been going on and off for a little under a year now. The code is most always a cylinder 5 misfire, but after changing out plugs and coils the CEL still comes on. The CEL will stay on for months and then go off for a couple of weeks before coming back on, so I can't identify the source of the code. The car is not running properly but I really don't know what a misfiring cylinder does feel like; the acceleration is less responsive and a little sticky at times, MPG's are down about 20%. I have been to several shops and they are clueless. In addition to this issue I recently had to replace O-rings in the oil pan due to them being cracked and triggering the low/no oil pressure sensor. After that fix the car did not run any better but the CEL stayed off for over a month and I thought somehow the 2 issues may be related ??? but I'm really not sure. Also my coolant level low light comes on about once a week needing to be topped off. Any thoughts or advice would be greatly appreciated.

Post by **jblackburn** » 17 Nov 2010, 00:28

I would suggest running a compression test or a combustion gases test. Using that much antifreeze, you might have a head gasket leak - they tend to let go on the outer cylinders first. if it was the heater core or something else leaking at that rate, I'm pretty sure you would notice a puddle somewhere.

RaymanSean · Post by **RaymanSean** » 17 Nov 2010, 06:59

What does the plug look like on the number 5 cylinder compared to the others? I tend to agree that you probably have a bad head gasket or something along those lines. I would also consider a bad/ intermittent injector as a possible cause of the missfire if the combustion gas test comes back negative.

v70MB · Post by **v70MB** » 17 Nov 2010, 22:31

The 5thcylinder plug looks fine, but I still put a new plug and coil on just to make sure, and then put those on the first cylinder to see if they were bad but they are all fine. As for it being head gasket leak or bad injector I will look into those possibilities, I had not thought about that. Thanks for the advice, I'm trying to become more educated, and your posts really help. I'll post after the compression and combustion tests to follow up.

RaymanSean · Post by **RaymanSean** » 18 Nov 2010, 06:12

Your headed down the right path. Check for exhaust gas in the coolant if it is positive then you need a new head gasket.

v70MB · Post by **v70MB** » 25 Nov 2010, 17:29

OK its the head gasket, they did a chemical test in the coolant an found other fluids. Its getting fixed now. Thanks for the info everybody.