compresion numbers help.. - Third Generation F-Body Message Boards

wannafbody · 11-08-2009, 09:28 AM

ok my l98 was getting a hard miss under throttle after a long extended high rpm run. It isnt smoking and has good oil pressure so i thought it was the ignition but I checked for fire on each cylinder and it seems to be working. So I checked compresion on each cylinder and with a cold motor and no plugs in any cylinder I got these readings.
1=75
3=77
5=80
7=70

2=60
4=75
6=78
8=75

like I said this was a cold engine and the starter wasnt turning very fast it didnt fell like.. Motor has 150K on it.

I just need some verification but the 10-15psi drop on #2 could cause the miss correct?

the funny thing is.. when the engine is idling and i unhook #2 plug wire it bogs down even more as if that cylinder is firing.

jv9999 · 11-08-2009, 05:31 PM

Those are all bad numbers. Are you sure your gauge is accurate? You might want to try it in another engine. You can squirt some oil in the cylinder and see if that raises the number. If it does, it points to rings. If not, valves.

skirkland1980 · 11-08-2009, 07:10 PM

you need a fully charged battery and about 200rpm cranking speed

wannafbody · 11-08-2009, 09:48 PM

yea i though t they seemed low. my banshee is 110 and its a 2 stroke

kkingsrulee · 11-09-2009, 10:44 PM

You need at least 12.6 volts in the battery in order to conduct a compression test.

Retest it with a fully charged battery.

And 60 is only 15% off of the next lowest cylinder which doesn't necessarily point to anything.

However if performed with a fully charged starter the deficit between the two could rise and make a single problem with that cylinder look more probable.