Long-time lurker, first time poster here! I need some help from the 960 gurus.

I've got a 1998 V90 wagon non-turbo with 85k miles. It sat idle in Arizona for 2 years before I got it, and was very well maintained before that.

The problem is that it runs rough when it first starts. Sometimes the roughness is mild, but recently it's been very hard to start, with lots of cranking (sometimes several minutes) and some backfiring before it starts. After it runs rough for a minute or two, it smooths out and runs great, and it passed California smog testing with no problems.

It was manageable at first, but has gotten much worse now that I've taken it on a few short highway trips to see if regular driving would straighten things up.

As long as it's warm, it starts and runs smoothly right away. After sitting for a few hours, the rough start comes back. When it's really running rough, it gets progressively smoother, like one cylinder at a time is starting to fire again.

Error codes are P0303, P0304, P0305 - misfiring on cylinders 3, 4, 5 - as well as 3 P0000 codes, using a Scangauge II.

I took it to the shop, and they're puzzled, but have some data. They say that when the cylinders are misfiring, the problem cylinders have no compression, and there's no oil pressure, but the oil pressure light never comes on during these problems. They ran some oil additive through it at high RPM, then changed the oil again.

The shop's leaning towards the oil pump overpressure switch getting stuck open until it warms up, with the resulting lack of oil pressure causing the hydraulic lifters to not work, though I'm not sure why the oil pressure light doesn't come on when it's low.

The problem is that they're not real confident in this fix (replacing the oil pump), and I've already sunk a pile of money into the troubleshooting. I don't mind doing it if it fixes the problem, though.

At this point, I'm trying to decide if it's worth putting any more money into, or just cutting my losses, getting what I can for it, and going with something different. I also have a 97 850GLT and a 99 C70, and while expensive to maintain, they've been good, but I understand the 960 series doesn't have as good a reputation as the 850/V70 style cars.

Any experiences or troubleshooting suggestions would be very helpful!

 

The 960's have coils at each spark plug. Sometimes the wires that go into the coils back out a little causing misfires. Not sure if that is all of your problems but it's a start.

That car also has an air pump that runs for a minute or two when the car is cold. It sits between the battery and engine and has a pipe house looking elbow that comes off the top if it. Maybe it has something to do with the car running rough at cold starts, pump may be out.

Don't have a clue about oil pressure/compression. Hope my little bit of imput helps. I really like my 960.

 

Thanks for the input.

Yeah, I've had 3 out of 5 of the coils fail on my C70 in the last 18 months. I'll try re-seating them, just in case.

I found the air pump, and can't really tell if it's working or not. I'm not sure what it does, so if anyone's got some info there, that would be helpful.

My Volvo shop is usually pretty good, but they don't have much experience with the 960 series, so they're fishing a bit on this one.

Their theory is that the hydraulic lifters run on oil pressure, so the low oil pressure keeps the valves from working right, resulting in no compression and no firing. I've googled some posts that reflect this idea, as well as people thinking sticky valves could be responsible, but that wouldn't explain the low oil pressure.

Anyone other thoughts out there?

 

the oil presure thing makes sense. i let my 960 sit once. when i started it it sounded like rods where coming out of the case. i shut it down, then restarted and it started fine. although it has never idled the same since. it has just a very slight roughness that you feel, well i feel. other people dont feel it but i do. i did not know about the overpressure switch, i figured it was just a lifter issue. my moms 93 has been sitting, i started it not long ago. although it did not make the noise mine did, it did run a little rough but idid not run it long enough to let it starighten out. BTW, my car had about 130k on it at the time.

is this pressure switch servicable? IE, can it be reomoved and perhaps are there some seals that could be rplaced?

the idle thing- i noticed it first on this low mileage 93 i was going to buy. the car sat a lot so it only had around 30-40k miles on it. there was some roughness in the idle. again, not something that you heard, but you could feel it in the car. that bothered me so i did not buy it although it wa a very nice car and a good deal. i ended up buying the 95. i made a point to notice the idle thing and the 95 did not do it. BTW, my parents had their 93 at the time and i dont think theirs did it either. i took my car to a very good mech and friend. he could not find anything wrong, although i am not sure if he really felt the same thing i did. i think all he did was swap some coil packs.

i have always said it is not good to let a car sit, especially higher mileage cars.

i am putting my moms 93 motor in my car now. it has been sitting for quite a while. i am a bit worried that it may have the same issue yours does.

 

Yep, when mine's bad, it sounds like things are breaking under the hood.

The overpressure setup is a spring-loaded valve on the oil pump that bleeds off the high pressure. The idea is if it's stuck open, it keeps the oil pressure from getting up to the rest of the engine.

Apparently, Volvo made the oil pump for a while with a plastic overpressure valve piston, and these can break, causing low oil pressure.

Since you're going to have the engine out, it's probably worth checking this to make sure you have a metal piston. Here's a link to the description:
http://www.volvoclub.org.uk/faq/960_...ilReliefPiston

 

Backfiring is the key here. If the lifters don't pump up, you get reduced valve lift (and reduced cam duration), so it won't cause backfiring. If anything, lifters not pumping up with INCREASE compression. Sorry, but your Volvo shop fails basic internal combustion engine 101.....
I think lifters is totally wrong, forget it and oil pressure. If you want to persist with oil pressure/lifters, drop a pint of kerosene into teh engine oil, idle it for 20 minutes and let it sit a few days, then run it again and dump the oil and filter.
Backfiring is very lean mixtures/ ignition timing way out, is it backfiring through exhaust or intake/airbox?
It could also be base ignition timing going wrong, so it could be a crank sensor or ignition module/ coil drivers, if it has either.
A good old fashioned noid light and oscilloscope/ignition tester will find teh problem in minutes.

Regards, Andrew.

 

OK, problem solved! Boy, do I feel stupid, too, for not trying this sooner, knowing it had been sitting for such a long time.

After Andrew's comment that lead away from the oil pressure (no pressure on valve lifters would keep them sealed, not open), I was back to thinking about sticking valves.

So, I got a bottle of Techron fuel additive at the local shop, dumped it in, filled the tank, and drove around for a few hours, teaching my son to drive. Next time, it started right up. As of now, it's been 4-5 days and a dozen or more cold starts with no problems at all. Looks like the low oil pressure during cranking was just a secondary symptom of not starting.

I've never been a believer in fuel additives, but now, I'm a convert, at least for certain problems.

Thanks to all for the input. I'll give this big beast another chance.