Electronic compression test?

[MattL]

Anyone ever heard about this?
Girlfriend is buying a used car and looking to have it checked out. The shop we called said no we dont put a tester on the cylinder we put an analyser on and measuer the rate of difference when we disable the spark from that compression. Sounds a bit fishy..

 

[Spork]

Just don't be suprised when they come back and say everything looks good. :greg:

 

[chevtech]

Anyone ever heard about this?
Girlfriend is buying a used car and looking to have it checked out. The shop we called said no we dont put a tester on the cylinder we put an analyser on and measuer the rate of difference when we disable the spark from that compression. Sounds a bit fishy..

It is actually somewhat legit (used to do it all the time). It is called a cylinder balance test and you can tell how much a cylinder is contributing by how much the engine RPM drops when you kill that cylinder. A cylinder with low compression will not contribute as much to the engines overall RPM and you can tell by the balance test. It isn't necessarilly a replacement for a compression test but if they are all dead even (how much RPM they drop) on a newer engine I'd personally (as a tech with a bit of experience experience) be OK with the engines performance. On the other hand if it is an older engine with anything less than stellar emmissions or any other indications of problems, I'd give that test a little less credibility and would compression test it.