My 94 GS-R was idling rough and seemed down on power. I just purchased this car a day ago. Owned by older people (55+ AARP and such) its entire life. Never modified. Today I am trying to track down the idle issue (which we determined was cyl 2) and I decide to do a compression test on it. Numbers come back
Cly 1:210
Cly 2:35
Cly 3:210
Cly 4:210

After putting a half cap of ATF in cly 2 the compression came back at 60.

There is no smoke coming out of the car, at any RPM, valve train seems quiet and in working condition.
The Oil is completely clean and still fresh, along with the coolant.

I know the possibilities are (in my head)
-Blown Headgasket (not likey as clean as the oil and coolant are)
-Burnt Valve?
-Blown Ring?
-Bent Valve?

Has anyone had any problems like this? It has a 155,xxx miles on it and is in really good condition the only thing is while the older man was driving it (putting around town) he used 87-89 octane in it. But I would think if the car was detonating the other cyl would not be perfect 0% difference across the board. (minus 2 of course). I am well knowledged in automotive engines but I am looking for some people who have had personal experience in something similar happening and what was the culprit. I'm angry since this car was mint but if the engine is no good then... Thanks for the help.

 

Crank the motor over several times, I cranked for about 4 seconds per test and watch the guage climb. In a healthy motor, compression should build up rather quickly. Low compression reading on the first stroke, followed by very gradually increasing compression on successive strokes, indicated work pistion rings. A low compression reading on the first stroke, which doesnt build up during successive strokes, indicated leaking valves or a blown head gasket, which also could be a cracked head. Heavy carbon deposits on the valves could also cause lower than average reading as well as a possibly higher than average reading. Record the highest reading that the guage stops at after cranking for a bit.

 

What's the leakdown rate on cyl 2?

Sounds like a bent valve, but the timing belt would've had to have failed for that to happen. :thinking:

Also, a tankful of 87 octane unleaded wouldn't cause this.
The B18C1 is equipped with a knock sensor, which would've retarded timing and kept the motor on the small cam.

 

Ok, figured that. it was a few years of 87-89 octane regardless. The engine would stay on the smaller cam. Again only owned the car for less than 48 hours at this point the timing belt was replaced at 100,000 miles so its about time, but as far as i know it was never broken.

 

So.. no leakdown numbers at this point?
If so, that'd be my next step before pulling the head.

My hunch is still on the valvetrain. There have been cases where a worn timing belt has failed on startup and that's enough for valves and pistons to collide. All B-series motors are interference, so even a glancing blow at 500 rpm is enough to do it.

It's a damn shame that you found out about this now, but I'd still stick with the car. :hs:

 

Ouch, that's a big drop! Yea, sounds like valves, hopefully just a valve sticking. You could pull off the valve cover and take a look at them. Check and make sure the 4 valves for that cylinder are retracting all the way.

 

valves are functioning properly did a leakdown test its coming out of the exhaust so next step is to take off the head.

 

My guess is a burnt valve. Any oil consumption?

 

Nay, 0 oil consumption

 

figure out what it was? i say head gasket