1998 V70 T5M Misfiring, No Compression Cylinder 2

nikolajs · Post by **nikolajs** » 22 Nov 2015, 23:11

1998 V70 T5 manual, 169,XXX miles. Everything in good condition except…

CEL was on a couple months ago (random misfires). Replaced plugs (Bosch Iridium), wires (Bosch premium); cap and rotor (Autozone Brand). Drove about 600 miles, CEL back on for secondary air pump (I forget the code #). Need to get the car thru emissions inspection (Utah) so I reset the codes; while driving it hard the CEL came back on (blinked about 10 times, then solid) but engine running fine at 85+ mph. When I got off the interstate, engine running rough at idle (rpms fine, holding steady at 900 or so but whole car shaking). The shaking seems to go away when rpms pushed above ~1500. Read off the codes: P0302 (misfire cyl 2). Did a compression test:
Dry:
Cyl1: 150 psi
Cyl2: ~20 (audibly not building pressure, can’t count individual cranks)
Cyl3: 149
Cyl4: 151
Cyl5: 148
Wet:
Cyl1: 189 psi
Cyl2: ~20 (audibly not building pressure, can’t count individual cranks)
Cyl3: 200
Cyl4: 220
Cyl5: 172

I think some of the variability in the wet pressures is due to uneven amounts of oil actually making it into the top of the cylinder…the cylinders that got more oil read higher pressures.

So, what next? Is it a burnt valve(s)? Any chance it’s a blown cylinder head gasket? I don’t think the problem is with piston seals because no pressure buildup improvement observed in cylinder 2 on the wet compression test.

Thanks!

Recent work:
PCV, tune up (plugs, wires, cap, rotor), front wheel bearing, heater core, O2 sensor, etc.

Post by **abscate** » 23 Nov 2015, 01:01

You might be able to get a bore scope in to look at the valves.

I think head gasket failures outnumber valve failures here about 5:1

Post by **RussB** » 23 Nov 2015, 07:37

Time to rebuild the head. Sorry

Post by **bmdubya1198** » 23 Nov 2015, 11:55

I haven't seen much about burnt valves on these cars unless a timing belt broke. I would think you'd have at least two cylinders with low compression if your head gasket is leaking.

Post by **rspi** » 23 Nov 2015, 12:17

These cars are know for having burnt valves. It is very common. Especially after getting a car that has been sitting a while or driven passively by the PO.

Post by **rspi** » 23 Nov 2015, 12:20

Post by **j-dawg** » 23 Nov 2015, 18:49

nikolajs wrote: So, what next?

Pull the head! You have to do that to fix it no matter what it is.

Post by **bmdubya1198** » 23 Nov 2015, 19:00

j-dawg wrote:
nikolajs wrote: So, what next?
Pull the head! You have to do that to fix it no matter what it is.

Exactly. Pull the head, check the valves. You're gonna need to do the head gasket either way.

Post by **erikv11** » 23 Nov 2015, 23:39

I'm late to this one but agree with some of the others that 99.99% chance it is a burnt valve. Compression looks good otherwise so it is not a waste to repair, but will cost some time and $. The proper repair is to pull the head, get it reworked at the machine shop with one new valve and all new valve stem seals, then reinstall carefully.

nikolajs · Post by **nikolajs** » 04 Dec 2015, 22:30

Hello

Thanks to all for the input-

I’ll be pulling the head as soon as I find some free time (and a garage to do the work in).

Does it make sense to just replace the one bad vale? Or should all the valves be done once the whole thing is apart? Depending on who I’ve asked, I’ve gotten conflicting opinions on this…

What about the hydraulic lifters? Anything else that’s a must while in there?

Thanks again