Compression Test Question

[joemathews]

Can you pull the 20a fuse labeled "Engine" from the underhood fuse box to cut power to the injectors? Or do you have to install a switch and/or cut power directly at the fuel pump?

2g guys don't have the MPI fuse, from what I've heard, so I don't know what to do to keep from squirting fuel into the cylinders during the test

Thanks guys.

[1stGenRocks]

you should be able to unplug your cam/crank sensor. without it the computer shouldn't spark or spray fuel

[joemathews]

I just finished the test--you can pull the 20a blue engine fuse from the underhood fuse box to cut power to the injectors (or if not, my nose is off ).

Compression read 180, 170, 175, 180. Considering spec is 178, those numbers seem pretty good to me.

However, my plugs were a little white--which apparently means too hot. Anyone have a clue? This is the first time I've checked the plugs since raising the T25 boost to 17 psi, so maybe that's it.

My main concern was that there was a little oil on, and especially around the plugs, with the most occurring in cylinder 1 (which tested 180!?). I'm thinking that my minor blue smoke-puff problem is most likely the PCV valve (hoping anyway!) with these compression numbers. Are these numbers good enough to rule out piston rings and valve seals?

What do you all think?

[Igovert500]

http://www.sa750.com/plugs/plugs.htm

This should help you read your plugs. has good pics and descriptions of problems.

[joemathews]

Thanks a lot for the link, Igovert500. My electrodes look exactly like the ones they say are in good shape--except they are a little oilier. The white substance is fine, I suppose.

I know I'm burning a little oil somewhere, so I wasn't surprised to find oil fouling the plugs. Where it's coming from is another story...