So I suddenly lose compression on cylinder # 1.

Brief history on car, cylinder #1 always had low compression (80, 140/oil), but he car ran fine until recently.

PCV system is clogged, bypassed for now with a vented oil fill cap.

Driving on the highway fine, get off, come to first stop light, engine running really rough, definitely not running on all cylinders.

Compression test reveals NO compression on cylinder # 1, NONE, not even a blip, even after adding oil.

Compression test with engine running (forgot to remove coil wire the first time) revealed compression around 60 psi. Is that why it seamed to run ok on the highway (but down on power) ?

Two codes, one for secondary air pump ??, other for cyl. #1 misfire. (soft code)
New sparkplug made no difference. Upon removal, no evidence of it running, plug clean/new.

Did I drop a valve ? Why some compression as running/idle speed ??

Car has 174K on it and is long overdue for a timing belt job, besides the PCV fix.
Is there anything else to check or did I just gain a parts car.

Thanks all.

New sparkplug made no difference. Upon removal, no evidence of it running, plug clean/new.

Wait. The new plug was removed and no gasoline on it either? Is the injector for #1 secure and plugged in? O rings not broken?
--
Keeping it running is better than buying new

Did you try adding a tablespoon of oil to #1 and see if the compression increased? Sounds like a stuck ring rather than a bad valve. Some folks have had luck soaking the rings in Marvel Mistery Oil overnight.

With a history of 60psi in this cylinder, you may now have a broken ring.

--
Keeping it running is better than buying new

"Compression test reveals NO compression on cylinder # 1, NONE, not even a blip, *even after adding oil.*"

I'm no expert, but if it were my car I would eliminate the possibility of a stuck ring before condemning the engine. Research stuck rings, see what you come up with...

With very high mileage, valve seats in these engines will start to leak oil but I've never heard of the bottom end going. They normally pretty much last forever.

Have you previously tried an Italian tune-up?

Maybe some info here?
https://www.matthewsvolvosite.com/forums/viewtopic.php?t=37913
--
Farewell 'black manta' ('97 850) Hello 'rocket sled' ('06 V70R)

This shows valves on intake side. Just the decision if worth it to remove fuel rail, manifold etc, and if it would show enough...
http://forums.swedespeed.com/showthread.php?83564-Another-Squealer-What-should-I-do/page2
--
Farewell 'black manta' ('97 850) Hello 'rocket sled' ('06 V70R)

I'm not a mechanic, but have done the PCV job. When the manifold is off (an not that hard) you do get a partial peek and could see crud(?) If PCV neglected badly, and dino oil used, then maybe the problem such as yours(?) have you used Synth oil? Also, have seen (but not on Volvos) running engine hot to loosen stuck rings(?) just ideas, no first hand knowledge. Vented cap is kinda red flag. Mileage not high at all. Rear main seal should go first if super clogged PCV -curious. If committed, then PCV fix might be worth it. I don't remember cost
--
Farewell 'black manta' ('97 850) Hello 'rocket sled' ('06 V70R)

Thanks for the links.
The vented oil fill cap is just a work-around for the clogged PCV system, as it had pushed out the cam position sensor seal, causing a bad oil leak (right onto the exhaust manifold).

I feel the problem is either a stuck or damaged valve at this point.
I'd like to determine which if possible. Can a stuck valve be unstuck ??
Wishful thinking to to repair a stuck valve so I can drive it as is for the rest of the winter.

I might try blowing some air into the cylinder and listen for leaks.

The engine is not worth a Head job plus timing belt/PCV service.

I have another '97 850 GLT that I'm working to put on the road.
So I think this car ('97 850 NA) just became an organ donor. It's not worth the time & money to fix just to sell it.

You could 'drive' it as a 4 cyl, just unplug the fuel injector. It won't have very good pickup, especially up hills and from stop signs.

The only way to verify the valve problem is to remove the head. Shop around for machine shops that can repair valves and see what their bids are, none will be cheap. When a valve fails, it will have an effect on the valve seat also which requires more than just dropping in a new valve or two.

Who knows, it could even be a simple valve spring.
--
Keeping it running is better than buying new

Agree, that the only way to know for sure is to pull the head. From what I've read, it's more economical to just get a rebuilt head, BUT I don't feel the rest of the car is worth it considering the low compression on the remaining cylinders. plus timing belt, PCV, alternator, set of tires, etc .....

#5=120psi, #4=120psi, #3=145psi, #2=160psi, #1=80psi (before the total loss)

I picked-up a '97 GLT about a year ago that needs some work, but at least the engine is in better shape + Turbo, so that where my moneys going to go.

The '97 NA 850 just became a parts car.

Was just wondering how something like this happens and how to avoid it in the future.

Yes, maintaining used is better than buying new, but sometime ya gotta cut your losses. Was planning on selling it, but I'll never get anywhere near the money back that it will take to fix.

I have to agree with your logic. Around here, 850's aren't worth much, most are under $1500 if driveable. I can't wait until the price starts to go back up in about 10 years or so.

Your GLT will not cost that much to fix up and get road worthy, reliable.
--
Keeping it running is better than buying new

(!)
http://www.atthetipwebs.com/technologyinstructions/head_gasket.htm
--
Farewell 'black manta' ('97 850) Hello 'rocket sled' ('06 V70R)

I second the MMO idea. Give that a try before trying anything else...

Did that first while trying to diagnose the problem.
The engine went from low compression to NO compression & running on 4 cylinders only, all of a sudden.

Did running an engine with low compression burn a valve ?? dunno .....

"Compression test with engine running revealed compression around 60 psi. Is that why it seamed to run ok on the highway?"

I'd say yes.

"New sparkplug made no difference. Upon removal, no evidence of it running, plug clean/new."

How long was the spark plug in there?

"Did I drop a valve?"

Perhaps there is a burned valve or a bad head gasket or a hole in the piston.

"Why some compression as running/idle speed?"

I'd guess that the difference is because the engine is turning at 250 rpm when starting vs. 800 rpm when running. The piston is on the compression stroke 2X per second vs. 7X.

"Car has 174K on it and is long overdue for a timing belt job, besides the PCV fix."

Timing belt won't fix a low compression problem.
PCV issue could be related to the lack of compression. It's (the lack of compression) certainly not helping matters any.

"Is there anything else to check or did I just gain a paprts car."

Are you sure your compression tester is working properly?
Throttle wide open when testing?
What was the compression on the other cylinders?
How much oil does it use?
Is there coolant in the oil or vice-versa?
Any chance you tested for combustion gasses in the cooling system?

The new Sparkplug was only run for a few minutes.

No evidence of a head-gasket problem, coolant looks fine, top of piston has no hole in it nor does it look to have been "steamed cleaned" from a blown head-gasket.

compression tester working fine, tested at WOT & engine running.
Has good spark as indicated by an inline spark tester.

Did not test cyl. # 1 fuel injector for flow.

I know the timing belt replacement won't fix this or any other problem, just was telling myself that it's not worth opening up the engine to fix a valve problem.

Are these engines known for burning valves as they have self-adjusting tappets.

Sticky valve stem from crusty oil build up, worth doing an engine flush ??
Fill the engine up with kerosene and see what happens ??

Oil is relativity clean , car used mainly for short trips to work.

I used to work on a lot of Volvo's back in the day, never saw/heard of problem like this.