1999 V70 XC Misfiring Problem

[shaker_chi]

I had multiple misfires on a 98 S70 T5 and it ended up being a bad spark plug wire. I would start there and then look at the plugs themselves. The turbos are very particular. O/E is the way to go here.

[erikv11]

1999 v70 volvos do not have distributors. They have coil packs ...

at me!

Not the first time I have made that mistake ...

[DavidsVolvo]

Ok, the verdict is in. I've run a battery of tests and per precopster's suggestion to check cylinder compression, my 99 V70 XC has bad compression in cylinder #2. Cylinders 1,3,4,5 have 155 psi. Not bad for a turbo that has 170K miles on it. Cylinder #2 has 40 psi. I ran a wet test on Cylinder 2 (ounce of oil in the cylinder) and the pressure is still 40 psi.

I checked the oil and there is no water in it. It's very clean. I looked for leakage around the head gasket. Its dry as a bone. The codes have been suggesting misfire in cylinder 1 or 2. When this started, it happened instantaneously. I was driving on the highway and after slowing down, the misfire was there. It does not get worse or better. It is consistent all the time.

OK, what now? Could it be a valve not seating, bent, burnt or is it something else? Can I see the issue if I take the valve cover off or is there other tests I can do? Suggestions please.

[FLXC90]

If you can get a look inside it may tell something; like this guy did
https://www.matthewsvolvosite.com/forums ... =1&t=66840

[DavidsVolvo]

A borescope...That's a good idea. I would if I had one.

Does anyone have any other suggestions or an experienced diagnosis so I do not have to rip the head off?

[erikv11]

I will speculate 99 to 1 there is a burnt exhaust valve.

Regardless, I don't know of any way to suss out the 40 psi other than a borescope.

If it is say a broken valve spring then you can usually see that by pulling the cam cover, you could pull the cover first then decide whether or not to proceed based on what you see. If it is a stuck valve then you can possibly unstick it by driving for 5-10 minutes at 5500 rpms in a low gear. I've heard of both of those in these cars, but they are rare.

Assuming it is a burnt valve, what would you do with the car? Usually people think about their answer to that one and just pull the head. It doesn't take long to tear it down, even being careful; putting it back together is where you need to be most diligent.

[precopster]

Lots of burned exhaust valves on turbo Volvos.

You could turn the motor according to the firing order then get cylinder 2 to the TDC position by placing a straw in the spark plug hole. On that position you can insert compressed air through a spark plug adapter and I bet you'll hear air gushing out through the exhaust port.

[erikv11]

Oh duh of course, do a leak down test. Compare with how #1 (or one of the other good cylinders) behaves. Thanks Mike :s

[DavidsVolvo]

I agree... Oh duh, of course. This is why I chat on this site. I get great suggestions for a proper diagnosis. I agree, there is something wrong with one or more of the valves in cylinder #2. I'll take the cam cover off and start with a visual inspection of all 4 valves. Then onto a pressure test at TDC. If that shows leakage with no visual spring issues or incorrect relaxed valve height , then I will need to take the head off. Thanks and I'm off to the garage again...stay tuned. I'll send pictures of what I find.

[abscate]

It does sound like a burned valve in Number 2. That's not too bad a repair if you have a place to do the work

No spark plug wires on the coil pack cars, to address post above.