Just got my car out of a 10 month storage due to relocation. It was started about once a month during this time.

I pulled all plugs to do a compression test since I have never done this before. I got readings of 220-225 on all cylinders but 7 and only got 205 on it. They all are within the 10% window, but should I be concerned about one cylinder 10% low while all the others are within 2.5%?

Afterwards I was told I should have done this with the engine warm/hot. I did this and it hadn't been started in 2-3 weeks. Cylinder 7 was also the last one checked, could this have caused the problem? Would checking the car cold with no starts for a few weeks cause 7 to be off?

Am I concerned for no reason since I am still within 10% and 7 just may be low because the rings never sealed as good as the others? I also didn't think about dripping some oil in since I was so suprised and trying it again.

For information, this is a 10.6 454 running a 288/296 UD hyd cam degreed in at only 2 degrees cam advance. I have run 93 only on the car for the past 14 month (not counting storage) and never had a problem with pinging. Are these numbers high or about what is expected? Should I be suprised I get away with 93?

Kerry

Having one low cylinder is very, very common. As long as they are all within 80% of the highest I wouldn't worry about it at all.

The fact that # 7 was done last might have had something to do with it. For one thing, the battery might not have had as much oomph as it had when you were testing the first cylinders. The slower cranking speed will net you lower numbers. (If you do your compression check on a hot motor, the engine is bound to have cooled off by the time you get to the last cylinder.) I usually start with cylinder #1, and then recheck cylinder #1 once I've finished. If the numbers for cylinder #1 vary much between the first and second time, you've got other variables involved besides just the condition of the engine.

Mike

Kerry,
The advice you received concerning the engine temperature was valid. The engine should be at operating temp in order to get realistic view of the engine condition. BUT, this wouldn't have anything to do with one cylinder being low.
Mike's points are good ones too. The engine will cool down during the test and can have an affect on the last cylinders tested, to some extent, but probably negligable as long as you completed the project without taking any extended breaks.
Also, did you have the air cleaner removed and the throttle plates wide open during the compression test?? With all of that said, I wouldn't worry too much about the one cylinder being down a little, as it is still within 10% of the others.

Thats really high compression readings for 10.6CR engine. Certainly have healthy cam there! And you can run that on 93 octane?! When checking my readings, had similar low reading on one cylinder. Checked valve springs and found #1 intake spring with very low spring pressure. As this is a race only application I changed out all the springs and compression improved to satisfactory range. The Moroso Valve Spring checker will tell you quickly and easily if you are having spring failure and this is of great importance to save your engine! ;)

Bob , is that becuase the valve wasn't properly seating?

Kerry, I have a large cylinder, #7. CC's a bit more than all the rest.Anyway, if the mill is a slouch because of it, I can't notice! Don't dwell on it, even if it checks out similarly hot.