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Discussion Starter #1
Did a compression test on the '75 coupe I bought (currently won't start, fuel delivery suspected). Here are my results, and I don't know if I did the compression test correctly.

#1 - clean plug 190psi
#2 - pretty clean (not as good as #1) 180psi
#3 - blackened but not oily 180psi
#4 - slightly blackened but not as much as #3 180psi
#5 - wet and oily 190psi
#6 - very clean 185psi

I went to Autozone, bought a tester, removed wire from coil to distributor, hooked up the tester, and cranked it.

Do these results mean anything? They sounded pretty good to me.
 

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well that sounds really good for wet and oily plugs...usually that means leaky rings that let the oil get in the C chamber....
 

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Great readings!!! You should consider yourself lucky!

Do a top end clean with seafoam, throw some in your oil too. (Follow the procedures and do the oil and filter change immediately)

Throw in some Fuel Injector cleaner.

Change plugs to an NGK with 5 heat rating. I recommed ZFR5F-11. Many recommend BPR5ES-11

Change PCV valve and clean PCV hose.


Run a tank of gas then measure again.
 

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hmmm speaking of compression, mine plugs are oily often, so i think it may be getting past the rings, and i also burn oil. and all my plugs read around 90-100psi, which seems low, but since they are all the same i guess that means the engine is just old and no real problems in any certain cylinders? what you think should be my next step?

-jas
 

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Jas try a different compression tester.

Also when you check compression, be sure to remove all plugs, make sure engine is hot, open TB.
 

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Discussion Starter #6
They weren't at 180-190 after one crank or anything... I just turned the key and held it for a couple seconds. Also, I removed the plugs one at a time and put them back in after testing each cylinder (so I wouldn't mistake which one went where). The engine was cold, since I can't start it.

Would an oily plug but good compression indicate that the oil is from... valve stem seals? When I drove the car home, I could definitely smell a little oil burning.
 

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Discussion Starter #9
According to blue's tech tips for compression tests, mine are...

decreased 5-15psi for cold engine
decreased by up to 5 for closed throttle
decreased by up to 5 for other plugs in

So, this engine's not stock, I assume? What sort of compression ratio am I looking at here?
 
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