I have low compression in one cylinder (#4). I have squirted a bit of oil in the low cylinder and it made no difference to the compresion. Is there anything I can do to further diagnose the origin of the low compression without going to a shop. are there any common problems with volvo heads or valves? I was surprised to find I had low compression cause I only have 200k Km on this car. from what I have seen on the board it is almost new. any suggestions appreciated.

Thanks

Steve

Another possibility is a bad head gasket and or warped head. Have you overheated recently, oil in coolant, coolant in oil? What are your actual compression readings?

I don't recall overheating recently. The readings are 170 170 170 130.

You can do a differential compression test, sometimes called a leakdown test. There are tools made for this, but if you have an air compressor and a pressure regulator you can approximate the test yourself. First put the cylinder on top dead center of the cylinder with low compression. You will need to hold the crankshaft in that position, so either put the car in gear (manual transmission) and set the parking brake, or lock the crankshaft with Volvo tool 5284. There are instructions in the 700/900 FAQ for making the equivalent of Volvo tool 5284. Make or buy a fitting to screw into the spark plug hole (of the affected cylinder) and to connect to the regulated shop air. Connect the regulated air to the adapter fitting and gradually turn the air pressure up with your adjustable air regulator. You will hear air leaking from the cylinder. If the air leaking sound is from the oil fill, you have bad piston or rings. If the air leaking sound is from the exhaust, the leak is from the exhaust valve. If the leaking air sound is from the throttle body, the leak is from the intake valve. Chances are best that you have a bad exhaust valve.

Thanks for the info. I hope to get time to do a leakdown test this weekend. If I do I'll let you know what happened.

I made a mistake when I said to use Volvo tool 5284 on your car. The B21 and B23 series engines have a smooth pulley on the front of the crankhaft. Tool 5284 fits the B230 series engines. You will have to position the piston just before or after top dead center and stop the crankshaft from rotating with a socket on the crankshaft bolt. Position the socket wrench handle againsdt something solid in the engine compartment. The nearer to top dead center you are, the less the force will be.