Car is a 1994 Talon AWD, 210 000 KM. (20g, 660c, Walbro, etc.)

So to start off a week or two ago I attempted to do a boost leak test. The engine was cold and when I attempted to apply about 10psi alot of it was just hissing out, theres was a very noticable hiss coming from the open oil filler cap. The tester kept popping off and I couldn't easily locate any other leak so I called it a day.

Today I decided I needed to do a comrpession test based on the hissing I heard durign the boost leak test, I suspected maybe bad pistons rings causing blowby. I warmed up the car and took it for a drive aroudn the block boosting a bit. Parked the car, removed the spark plugs, MPI fuse and coil plug.

I ran the test, I didn't hold the accelerator down though.

Cyl 1: 130
Cyl 2: 130
Cyl 3: 135
Cyl 4: 90

I then performed a wet test (capful of oil), still didn't hold the accelerator down.

Cyl 1: 145
Cyl 2: 145
Cyl 3: 140
Cyl 4: 120

Ive read that the wet test is a little deceiving since we have dished pistons and it will just raise the compression numbers regardless. First it's obvious that something is up with cylinder 4, its far behind the 14psi difference. The wet test raised the results on the better cylinders by 5-15psi but on the bad cylinder it went up 30psi. If the theory that the oil would raise compression regardless was true then the compression number should have risen uniformly no? So by my deductions I'm going to guess that bad rings on cylinder 4 are at least part of the problem.

Can anyone offer their input or advice?

I am tryign to get ahold of a leakdown tester this week. I will redo the compression test with the throttle open (both dry and wet), and then perform the leakdown and hopefully pinpoint the leak.

Another questions I have is that would a cracked valve seal make a hissing noise in the valve cover (during a boost leak test, so a valve would be open)? I've always read that blowby (bad rings) can be heard as oil bubbling in the valve cover, or could it just sound like hissing as well?

And finally, If I pull the head, oil pan and pistons can I somehow check the cylinder bores to see if I can just use a honing tool (one of those drill attachments) and then simply replace rings, headgasket and headbolts/studs and be on my way? I don't really want to do a complete full out rebuild since I'd rather spend my money on a 6 bolt build but I definitely don't have money for that right now.

With one cyl all the way down to 90, there should be other signs.
Is the #4 spark plug notably different?
Is there a slight missfire?

Next time, test Cyl 4 first. That way you can be sure it's not just the battery/starter getting lazy.

The leakdown test should leave no doubt.

On the boost leak test - if a valve seal were to leak that bad, I'm sure you'd be burning lots of oil.
You can turn the crank while testing, and by your logic the hiss might go away.
Air can also get into the crankcase via the turbo/oil return line.

If you have the time and the will to re-ring without a re&re, go for it!

This is indeed going to be an interesting thread. I have also have cyl 4 at 90. cyl 4 is driver side? I have to recheck mine after my timing belt is done, and my timing marks are aligned PROPERLY.

Cyl 4 is the passenger side.

Oopsie I had a feeling, it just makes so much more sense my way well then my # 1 is bad. so complete other end.