1997 850 with misfire, low compression - advice?

[thedancingfiddle]

Hi all,

I haven't posted here in forever, but my trusty 850 is having an issue that I'd like some advice on how to proceed. 1997 850 N/A, manual trans, 270k miles

Cylinder #3 misfire, for the last 5 months now. Runs very rough at idle, has no power on hills. Spark is good, fuel is good.

I did a dry compression test today (finally warm enough to work outside), and the numbers are (1,2,3,4,5):
194, 195, 60, 169, 145

This is bad, and I'm suspecting a burnt valve on #3. The car has used oil the whole time I've had it (6 years), about a quart every 1000 mi. I've tried to keep up on this, but there have definitely been times when it was run quite low for a while.

No signs of oil in the coolant, so head gasket probably fine, yes?

So basically, should I look into getting the engine replaced? I can't do any big work myself, so this would mean dumping quite a bit of money into it. However, the rest of the car is in great shape, and I like driving the stick shift wagon

Thanks!

[erikv11]

Almost certainly a burnt valve given the mileage and data, agreed. I would speculate due to the oil consumption itself, not due to the effect of running on low oil level. If the oil is leaking past the valve stem seals (almost 1005 likely at 270k) then it will not only get consumed but also make hotspots on the valves that can lead to them burning.

No oil in the coolant is not surefire test for no head gasket issue, as there could be a head gasket breach between the other chambers. Head gasket separates oil, coolant and combustion and you can get any one of the one-way or two way leaks with a breach. You could test for combustion gases in the coolant and do a leakdown test, that would help you be sure. but this so far yells out burnt valve.

The remedy is either pull the head and replace all the valves and valve stem seals, or put in another engine. Cost is similar either way, on the order of $2k if you pay a shop to do it. Which way to go depends on the shop and their expertise, and what engine(s) are available to you. Known good, used engines are harder and harder to find for these again 850s. You're basically looking for anything from a non-turbo in the 95-98 years, those are the easiest, but 93-94 or even 99-00 can be made to work without too much trouble.

If I was doing the work myself I'd probably pull the head and chip away at it. If not then budget becomes a major factor. If you have the cash maybe fix it, consider how what you can buy for $2k compares to this car when fixed. Don't be tricked into considering "but the car isn't worth $2k right now so why would I dump that in?" as that is well-known to be a fool's way of looking at this decision. It's what you end up with, not what you start with, that is relevant.

[RickHaleParker]

Could be stuck rings. Do a wet compression test.

If the wet compression test indicates stuck rings.

• 1. Pour Seafoam down the cylinders.
  2. Push rags down the spark plug wells
  3. Let soak overnight.
  4. Crank engine to push out liquid.
  5. Reassemble and run engine until it stops blowing carbon.
  6. Do another compression test.

If you still have it apart. You might as well go ahead and do the above. At the most it will cost you a bottle of Seafoam and a little time. If it pays off, the ROI will be high. Risk/Reward is very favorable.

[thedancingfiddle]

Thanks for all! I did actually do a wet test on cylinder #3, and then the compression was 70. Is an increase of 10 enough to indicate anything?

[RickHaleParker]

Thanks for all! I did actually do a wet test on cylinder #3, and then the compression was 70. Is an increase of 10 enough to indicate anything?

70/60 * 100% = 116.666%
Greater then 10% increase indicates piston rings and/or cylinder walls.

How much 30 weight oil did you put in the cylinder? Too much can give a false reading. You should wet test all the cylinders with the same amount of oil. That way you have base line data for comparison.

If cylinders #1 & # 2 are increasing more then 10% you are using to much oil.

[thedancingfiddle]

I put approx. 1tbsp of oil in #3. (the little cap from the oil bottle filled). This seems like if anything less than what I've seen in various youtube videos Is it possible it was too little?
I can get the compression gauge again and do a wet test in all next time I'm free on a nice sunny day—rare thing this time of year in VT! I'll post the results when I do!

[erikv11]

Please post up the results but, it's not stuck rings. It's never stuck rings. Not stuck for 5 months.

If you can get your hands on a borescope you can eyeball the valves in #3. I once had a broken valve spring did this on a white block, I suppose it could be that too but I doubt it.

[rguzz]

Pull the head, inspect all valves, replace the ones that don't look healthy, re-use the others, replace all valve guide seals and hit the road. A good shop, moonlighting mechanic, etc should be able to do this for around 1600 bucks, depending on labor rates in your area. Worked great for me.

[thedancingfiddle]

Hey all,

I just did another compression test, wet test in all cylinders got me 220, 220, 62, 210, 210

I tested number 3 twice just to be sure, and no change.

Another thing I noticed was that while cranking, the noise it makes while the gauge is in #3 is different than all the others, less distinct cranks with a punctuated start to them, if that makes any sense.

So, any more ideas? Sounds to me like #3 almost certainly has a burnt valve.

[erikv11]

By the way, driving it for the time being is no problem at all if you unplug the #3 fuel injector. In fact you can drive it that way for a very long time if you are OK with performance.