I'll take low compression for $100 Alex.....(question)
 

A conundrum if you will - Let's say you have a car with 'low compression'

I did, about 60k miles ago. Way back when at 200k miles. It measured about 50-80 per cylinder (except for the burnt valve on a dead cylinder- that was a "zero")

Mechanic said... "It's dead Jim...."

So I drove it home (cause thats how I roll :) ). Coming home over the mountain, I noticed a pickup truck ahead of me blowing all sorts of smoke and stuff.

I wasn't.

"Hmmm...." I thought. Got home, pulled the head, found the burnt valve, and the cylinder walls had original honing marks from when they were made.

Hmmmm.... How would a car with no compression have zero wear on the cylinder walls?
My working theory was - "perhaps the rings never even seated"
So I fixed the valve, and enjoyed the car another 60k miles. Now 260K miles

In yo' face mechanic

NOW.....

I can't get good PCV suction in the engine. Just redid the system. There WERE some leaks in the system- but- Engine runs worse. than before I redid the system.
Still no suction.
Perhaps the rings are worn out? Perhaps I did something wrong?

On one hand, the compression test from long ago sucked, but... the car has some variable timing which might affect compression, or maybe compression is compression-

But... there's not one bit of oil or debri or crap on the rear of the car which all my other cars had when the engines really did wear out. No oil plumes or friends laughing at me. My long since gone 944 literally shat oil on a coworker when I started it once and she was walking behind it- that's a bad sign.

No signs of a rear end nature here.

No "Colon Blow"

What gives?

The compression test 60K ago was done cold. Bad reading. Ignore it.

Trouble shoot for today. What does a leakdown show? I will confess I know nothing about PCV failures.

I believe I've also heard that you can do a test, then add a little oil to each cyl and test again. If compression goes up with the oil, then that shows that it's the rings. I've not done it myself, it's just something that I've heard. It makes sense, but I don't know if it has merit or if that would be the case for any engine bad rings or good.

Do you know what the engine SHOULD be showing?

^^^ leakdown test needed.

What is the car?

What motor is this? Some are more persnickety than others. There are small block chevy engines in '60s pickup trucks, and then there are 2.0L turbo engines in modern cars.

Steve suggests diagnostic steps, and I agree. Yes, oil on rings helps seal them for testing. Heck, when you do a leakdown test, you can listen to the tail pipe (suggesting the air is leaking past valves) and listen to the crankcase/breather (suggesting air is getting past rings). You can pop new bearings, rings and valves in a motor.

Or just get another one. What motor is this?

This is for xc70 volvo 2005. Another esteemed pelican recommended I dump it and just buy another- they are a dime a dozen- but I'm too far in.... :)

Thanks (for new leakdown test idea). I might do that. My gut instinct is that after redoing the engine, both cams might be in a retarded position during cranking until they can get oil pressure and be directed to advance by the computer, might be lagging behind. They've got about a significant degree oil activated advance when fully advanced. I'm scared I will just get another low compression reading- especially with my 'high tech' HF gauge.

I might try dumping some oil into the cylinders to get some lubrication for the test, but the CVVT system really leaves leaway for interpretation. Out of 360 degrees, is seems to be about 80 degrees of play in the preload.

When I redid my PCV system, the intake was shredded, to the point I could put my mouth over the holes and breath comfortably through the leaks. Now there are none, but still no love on negative pressure.

The real kicker here is that the engine is struggling at idle and dying/surging... (it was before I messed with it- and that's WHY I messed with it) and after "my" fix, now backfiring, I think in the intake. I have since replaced injectors and fuel pressure regulator, and Ive got a new fuel filter and pump, and new plugs, so the intake side should be good.

I'm going to change O2 sensors this weekend- but- even if that fixes the idle/surges, that doesn't address the lack of vacuum.

I am coming to terms with pulling the head, dropping the pan, and re-ringing it, but want avoid if possible.... Thanks all. :)

Hmmm. I wonder if the ecu has learned to live with the vacuum leaks and needs a reset…

^^^ great minds think alike! :D:D:D

The other problem, is now, I can't get the engine to throw a code to know where to look, which makes me think I've done something redneck to screw it up...

But.. it did throw one code. "check engine light" no signal...... which is weird and has no internet google references, and I could only relate that to an ecu, but the engine still runs too good for an ecu crap out. (for now)

Also is it possible that an electrical connection isn’t connected or got damaged from your recent surgery?

^ This I'm thinking and will research this weekend. My incredible mind cannot contemplate such oversight from myself, but I will be quietly double checking things this weekend.

To replace the upper 02 sensor, I have the privilege of going back through several pertinent connections

Another revelation from my amazing carnac brain- the knock sensors had the insulation knocked off them. Dumb arse me thought they were grounds, but, they must have been knock sensors. Those will be addressed.

I'm going to go reseach this... Maybe some 20-50 from the p-car oil stash could fix all of this :)

ugh, variable valve timing, fantastic for us, but ouch, that could be a huge pain if it interferes with classic troubleshooting.

Sounds like you need a new Retro Turbo Encabulator.
Or short of investing in a new one right off, get a leak down test.

Your post is a little confusing, to me anyways. The 50-80psi seem low but that is a turbo engine correct? How are you testing PCV vac? I'm thinking timing belt possibly jumped a tooth or cam stuck full retarded or full advanced?

I had a TR6 with worn rings and excessive blow-by that was pressurizing the crankcase and getting oil and crap up into the intake. That car was ancient by 2005 standards, but maybe with the low compression you have a blow-by issue. Just a wild a.. guess.

Volvo engine? Valves not rings is the typical problem in my experience. At a similar mileage my 850 engine bores looked like new. The valves, not so much.

Leakdown test will tell you very quickly.

Also, the Volvo PCV system is a total PIA...and I'm thinking that's not your real problem. Those engines usually run and idle regardless of the PCV condition.

Did you try the Volvo glove test?

Well, I'm going to try the compression test this weekend. Thanks for all the feedback.

One thing I didn't mention- was when I fixed the valve at 200k, I did the whole head, so the valves BETTER be good! :D

What codes is it throwing??


Why not do a proper diag on it? Start with the basics, codes, work through the test plans associated with these codes.

This. Your PCV system is likely shot.