Misses when cold, goes away when warm...
 

Just like the title says, it runs on 3 cylinders when stone cold. (#4 is out to lunch)

Cut the ignition to #4 when cold, makes no difference at all.
I used a compression tester, and #4 is much lower than the rest when stone cold. (By stone cold, I mean parked for a whole day, and started in the morning at 5C - 40F temps or below)

It runs on 3 cylinders at idle and under power.

The thing is, once the oil gets up to around 28-30C, 82-86F, things smooth out, and the car runs great. It runs fine great if I start up and the oil is at or above those temps.
I checked the compression warm, and all 4 cylinders are almost identical then.
The car does not consume oil.

Any ideas before I tear into the engine?

It's a built engine with 84mm 9:1 JE pistons, Mtuned rods, Supertech valves and springs, ARP studs, Gates blue timing belt, etc.

Have you checked bery cold engine valve clearance?

Actually, I thought about valve clearance.
Let's say they are out of adjustment, and the clearance is too tight. That means they would not close properly, and create problems.
But the valve opens much more than the adjustment parameters.
In the case they might be too loose - too wide a gap - the same logic would hold true, as well.
I mean, I think it would not run at its optimum level, but the end result of valves that are out of adjustment would not be a completely unresponsive cylinder.

Am I missing something here?

What gets me is the fact that both cylinder compression and the miss itself gets corrected when it warms up.

What you descrive is consistent with a valve is not fully closing when the engine is cold and fully closeing when hot.
That however would be unlikley, just thinking of what would cause the sinthoms you are describing.

Either the valves or the rings. I hate to say it but there aren't a hell of a lot more choices if it has low compression cold and good compression when hot.

How many miles on the engine?

Bent valve. It sticks when cold, because it's binding. Warmed up, clearances are looser, and it can now move.

I once bought a twin cylinder motor that was "blown" because I needed parts. Had the same symptoms. Got it running again by straightening the valve.

Hmm if the valve is bent it is unlikley to seal right hot or cold, but that reminds me of what hapened to some of the lycoming aircraft engines i worked on, they would build carbon deposits on the valve guides and the exhaust valves would stick open when the engine was very cold and be fine when it warmed up, we would drop the exhaust valve and ream the guide as a precautionary measure at 1000 hs after overhaul, you may want to turn the cold engine over and do a leack down test on # 4 and you will have your answer by lisening to see where the air is going to.

Less than 20K. About 17000 miles.

You know, I did overrev the engine a couple of times. Not intentionally.
But my tach says I went up to 8250ish RPM at least once.

I decided I should check and see if it is blow-by.
I do not have a leak down tester, so I thought I could just verify it visually, and used a sandwich bag as a balloon secured on the oil dipstick.
The idea is, it would show up on the really thin bag as puffs if it was ring blow-by.
Ambient temp was at about 4C, so were the oil and water temps.
Well, no puffs.

Here's a short video:



I guess I will have to look further into the valves.

You can probably rig a hose hooked up to the comp tester adaptor and use compressed air, make sure you have it at tdc#4 on 5th gear and the brakes on, you should be able to hear it clearly on the intake, exhaust or valve cover oil fill cap when open.

^ What he said - Leak down test it cold and hot. If you don't have a proper leak down tester and have a compression tester - just remove the Schrader valve from your tester hose and pressurize the cylinder using an air compressor (most of them share the same fitting and you can use your air compressor regulator to gradually apply pressure) at TDC and listen to determine the location of the culprit. Through the crank case, exhaust, intake...

I (finally had some time and) checked the valve clearances, and one intake valve (rearmost) is either at 0.00 or has a negative value.
I can't get a feeler gauge in there - not even a 0.05 mm, to save my life.
The valve does move freely, tho. I nudged it with the wrong end of a screwdriver, and it moves smoothly.

Generally speaking, the majority of the valves are on the tight side.

Arrgh.

I then hooked up a compression tester hose on #4 and blew into into as hard as I could. (I neither have a leak down tester, nor a compressor). There is very little resistance, and I can hear the air escaping big time.

If the valves are that tight, it could do it.

I seccond that coment, you may need shims or your seats are moving (got bigger valves?)

I have decided to pull the head.
Ordered a gasket set already.

I really do not want to take any short cuts here.
If the valve is failing to close fully, there's always the risk of a burnt valve.

Even if everything's just fine and all I need is an adjustment, I'll still have my piece of mind, knowing it won't bite me in the ass sometime down the line.

And, this engine has just under 17K miles on it. Such a failure could potentially indicate a collapsed valve seat, as well.
I called a good machine shop. I'll remove and take the to them, they will adjust the valves and replace seats if that's what's needed.
(The owner quoted $90 to $116 for the job - gotta love machine shop prices over here)

Hopefully you get it all figured out and fixed! :)

Completely off topic but is fuel really $10 per gallon in Turkey?:vash: Locally we just dropped below $2/gallon(lowest according to gasbuddy today is $1.87 in Temple, Texas average is $2.205 and USA average is $2.434) which hasn't happened since 12/2008 but even the highest it has been was around $4/gallon.

If you are using stock valve springs then it might be good to upgrade a little since you are boosted. The Volvo replacement springs are cheap - part numbers vs855 for a 1975 245, 244, or 242 2 liter.

They will give you 15-20 more lbs of closing force to help overcome the boost pressure trying to keep the intake from closing.

Holy crap that's a steal.

Keep us posted as to what you find. I'm curious as to the root cause.

It dropped as low as $7.35/gallon lately, but that's because the Dollar went up.
Minimum wage is about $365/month after taxes. That should give you an idea.