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[stranger_5oh]

After 3 days of sleepless nights of reading forum feeds and staring at evtm's I've come to the conclusion that I have all the wiring correct. The truck has started and ran but seemed to get harder for it to start. No spark or fuel issues so I started looking elsewhere for a problem and indeed found a really big issue. Compression seems to be my culprit. Cylinders 1,7&8 100psi, cylinders 2&3 95psi, cylinders 4&6 90psi and last but not least cylinder 5 @ 65psi. Checked the pushrod to see if it was bent or the lifter had collapsed and those both checked out OK so it looks like the motor has to come back out so I can replace the rings.

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[RonD]

Those numbers are very low, could just be your gauge and if so you may be wasting money on a rebuild at this time.

Generally gasoline engine compression in psi will be 18.3 x Compression ratio
so 5.0l with 9.0:1 compression ratio should be 18.3 x 9 = 164.7psi
That's at sea level air pressure, might be 155psi at 8,000ft
And this is with cold engine.

Actual 100psi on a V8 engine might start but it would be iffy, so the slow to start would fit with low compression.
The 100-90psi spread is 10% so not unusual, 65psi could be a glitch so.............

I would retest
Remove ALL spark plugs for the test, you need good crank shaft speed to get accurate PSI numbers.
Push gas pedal to the floor when cranking engine, this turns off fuel injectors and also allows for good air flow.
Compression gauge needs at least 4 "hits" of that cylinders compression stroke.
Write it down.

If gauge seems OK and numbers are still low then I would suspect timing chain since all cylinders are low, or rocker arm adjustment, yes rings do wear out but those numbers are really too low for bad rings.
If you want to test for ring problems then do the "dry" compression test as above.
Then repeat and add a teaspoon of oil via spark plug hole before testing a cylinder, a "wet" test, the oil will help seal bad rings and compression will jump up 30psi, if only a 10psi or less increase then rings are fine.

Take a straw, drip it in a can/bottle of oil and put your finger over the end of the straw, pull out the straw, put it on a teaspoon and let finger off the end.
mark straw at teaspoon full level then use the straw to get the oil and put it in the cylinder.

 

[bobbywalter]

rons layout is pretty good. and i ass-u-me you are testing wot.

what engine and induction are you using? miles known? cold test or hot test? what did the coolant passages and oil pan look like? did you pull the pan and a few caps to check bearing condition....these are usually enough to let ya know if it needs work or not.


but 100-120 or so psi on a cold pos crown vic or 80's t bird engine that is well worn is normal for a wheezer 302. a head gasket or valve could be the culprit on the 65 psi...or like ron said just a glitch in testing procedure...

so a simple re ring could cure it or just a head gasket. you say fuel is fine so i assume your gauging the psi...