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Discussion Starter #1
I've had this '84 GTV6 for less than two years and not really done much mechanical work to it, so I decided that some maintenance was due before spring. I've noticed that the engine doesn't run quite as smoothly as I would like, so I performed a compression check. Cylinders 2-6 were good with readings between 167-182 PSI, but #1 was at 128. I put a little bit of oil down the spark plug hole and the compression reading shot way up, so now I'm thinking that I've got ring trouble.

I was ready to change the water pump, timing belt, etc. and adjust the noisy valves, but now I'm questioning what I should do to this engine. I've got a spare engine of unknown condition, but I wondered if anyone else had thoughts on this low compression issue before I start tearing into it.

Thanks,
Scott
 

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Discussion Starter #3
I wouldn't say there is excessive oil consumption, but I have noticed a puff of blue smoke when it starts. The #1 spark plug was oily, and definitely different than the others.
 

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Well,

if you've got an oil consumption event in that cylinder, your compression likely will be fine when the engine is running. I wouldn't worry about it at all, unless there is money burning a hole in your pocket. Oil is a lot cheaper than an engine rebuild, but it's your car right?

It's highly unlikely that the engine "non smooth" issue is due to a low compression reading when cold and dry. I'd check fuel injectors/timing if you suspect that there is a true rough running issue. Oil consumption is rather normal on this car and unless you think a piston ring is broken...I'd say drive and enjoy!
 

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A leak down test will help pinpoint the source of low compression. That might help you decide what to do (if anything) about it.

For the compression test was the throttle propped wide open? Did you test cyl #1 first? Perhaps the engine was dry during the first test and got lubed & loosened up a bit for the subsequent tests and the oil added to the cylinder wasn't needed to seal the rings? (we can dream can't we...)

I agree with Rob - check the other things that could be affecting running. Fouled spark plugs, faulty wires/distributor cap, clogged injectors, etc.
 

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Discussion Starter #6
Thanks for the input, guys.

The fuel and ignition systems are on my todo list. I was just surprised by the compression results and looking at my options. It sounds like I should perform a leakdown test before long.

I had the engine running about 15min before the compression test, so it should have been good and lubed. I thought the same thing, too, so I re-checked #1 after checking all the others, but I got the same result. I didn't prop the throttle open, though. Does that make much difference?
 
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