need help on a Compression test

[clint]

hi guys this may sound silly to most of you however i need some help in performing a compression test..i have a 5.7 v8 1998-2001 carb thunderbolt V ignition..this is how i am planning to do it..

remove spark plug wires
remove spark plugs
attach a compression gauge to each cylinder head
crank engine for 5 secs
take highest reading
repeat to all cyclinder heads

is that all? shall i disconnect some ignition wires beforehand (thunderbolt ignition)? throttle on idle (in the middle) or fully open?

any help will be much appreciated

thanks

[seapuppy]

actually....a warm compression test is recommended...It's ok to do a cold one..but a warm one will give a better reading.....

but other than that...you got it...make sure you disable the coil..ie ..take the pwr lead off so it doesn't accidently arc over anyplace......

let us know how it goes..


SP irate:

[clint]

thanks for your reply seapuppy..

a warm compression test means that i have to get the engine to normal operating temperature before performing the test?

throttle should be fully open right?

can you kindly explain in some more detail when u said disable ignition coil? is the the centre wire entering the distr cap? shall i only disconnect or should i ground it to the engine..anywhere?

apologies for these stupid questions butim kinda new to this and have already spent $$ on mechs..i ned to learn how to do the basic stuff myself at least...

[seapuppy]

a warm test requires the engine up to operating temp....once it's warmed up..you should be able to do the comp. test..

throttle...it doesn't matter if the throttle is open or close...turn it over several times...the compression gauge will show it's highest compression in maybe 2 -3 turns..


if you have elex. ignition...then there is a process to disable the coil....some are just disconnect the pos. lead...others are take the neg lead and ground it out someplace...and with some of the new ones..you can't disable it cuz it's tied to the module....I think since you have the older thunderbolt ig...all you do is take the pos. lead out of the coil...but check your manual to be sure....this should prevent the distr. from sending a spark down to the plug wire..which is hanging someplace close to you........

that's about all there is for one..

SP :mrgreen: