Need Help Diagnosing Compression Test Results

A little back ground first. I have a 1991 CRX. 125k. Recently took it on a 1600 mi journey and since then, all hell has broken lose. During this trip I was going through 1qt of oil every 350mi and near the end of the trip, at idle the car felt like it had a dead cylinder (shuttering at idle) and noticeable loss in get up.

There’s is ZERO smoke, tail pipe is dry and no noticeable leaks (although I haven’t gotten it on the lift yet). I changed the valve cover gasket (oil was spilling into spark plug tubes), plugs and PVC valve. I also ran a compression check and here is what I got:

Cyl 1: 150PSI
Cyl 2: 151 PSI
Cyl 3: 65 PSI
Cyl 4: 149 PSI

Obviously cylinder 3 is a problem. I poured a capful of oil into it and tried again, this time producing 90 Psi. Telling me the rings are possibly bad. But I find this puzzling. I’ve never heard of just one cylinder having bad rings, and the symptoms didn’t occur gradually like rings, but suddenly. Does this not sound more like a valve issue?

Any Input?

Finding low compression in a single cylinder is not unusual. But run a leak down test to confirm that the rings are the most significant cause for the low compression. Also check the vacuum.

I would want a “dry” and “wet” compression test for all cylinders before condemning the rings on #3. Or before anything put a vacuum gauge on the engine and tell us what the readings are at idle and 2500rpm.

I think you probably have an exhaust valve that has lost all clearance and is burnt. Pull the valve cover and check the valve lash. You can get away with tight valves for quite a while around town but a long trip will do you in.

The compression is dropping on all of them and I would agree with oldtimer that a tight valve is suspect.

Valve lash should be checked and adjusted ever 30k miles. Most cars do not receive this and my assumption is that yours is untouched in 125k miles like all the rest. Some luck out; some don’t.

If an exhaust valve is tight then a valve job is in the future but considering the dropping compression on the other 3 cylinders some deep thought might be given to spending money on a losing cause. Unless of course, valves are starting to tighten on all the rest of the cylinders.

I bought the thing for $1800 for the winter, so it’s starting to look like I got a bum deal.

Either way, the question I think is gonna be, Is this car worth the time/money or am I better off driving it till it dies.

I was about to say EXACTLTY what OldTimer said… I bet your issue resides there. I devised a little test for this condition that i have used with great success… You need to rotate the engine so it is on the compression stroke on the suspect cylinder… Then use the compression test hose without the gauge REMOVED… Screw the one end of the tester into the suspect cylinder and attach a Pressure Regulated Air Line to the other side of the comp tester hose…turn the pressure down to about 25-30 psi. Once you have Air flowing into the cylinder at 20psi or so…maybe even less pressure?..You can then determine where that air is going…

It will either rotate the engine if compression is sufficient and not leaking fast enuf…OR in the case of a burnt or cracked valve the air will leak out of the relevant valve quickly enuf for you to hear it…and then you will know which valve it is… You can feel it coming out of the exhaust pipe…or hold a lit cigarette near the tailpipe…and see if the smoke is blown out of the way.

This is OF COURSE BEFORE THE DAYS WHEN I HAD BORE SCOPE …The bore scope has a 180 degree reversal head that you can attach to it… Just put the scope into the spark plug hole…and look around… But you need the 180 tip to be able to look back up at the top of the cylinder…

SO…THERE ARE A FEW WAYS TO FINDING OUT where your pressure leak is coming from BEFORE pulling the cylinder head… Once you know that it is NOT the piston rings and is cylinder head related… You can simply pull the head n fix her right up… Its a nice little job for a Sat Afternoon.


The first thing I would suggest is to do a valve lash inspection and adjustment. If number 3 comes into range with the other cylinders then I’d drive it until the end.

That quart of oil per 350 miles is a problem. If the engine appears to run at least decent after a valve lash check you might consider going to a higher viscosity oil. I’m assuming, right or wrong, that you’re running 5W or 10W 20 or something like that right now.

Maybe this weekend, I’ll try to narrow it down some more… The suddenness of the problem makes me think you guys are right on the valves.

I’m running 10w30 right now

Also, would this burnt exhaust valve be the cause of this excessive oil consumption?

I’m getting a leak down tester tomorrow from a buddy, so I’ll know for sure soon the issue

Yes @HondaBlackbird, your instructions for checking leak down are basically a leak down tester without the meter being marked specifically for that purpose.

I am thinking bad fuel injector coking the rings, check the fuel injector and Yamaha ring free is the best I have found if that is the problem.

Also, would this burnt exhaust valve be the cause of this excessive oil consumption?

Maybe an overheated valve doing in a marginal valve seal? (Total guess.)

Is the #3 plug black?