quick question on compression tests

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does the engine have to be warmed up? I bought a compression tester gauge/hose yesterday and I want to play with my b3 before I take it out.. I did it cold and it reads 175 all the way across.

[htchbck]

Engine is supposed to be warmed up yes, but a lot of times thats not possible (especially when one isn't running). I find that my warmed up numbers are usually not much different than my cold numbers though.

[zoom zoom]

eh i'm bored so I'll go ahead and put stuff back together enough to get it warmed up, thanks.

[FeistyFesti]

That sounds like a healthy engine, good numbers. Did you keep the throttle wide open?

[zoom zoom]

No, that was just removing all the spark plugs and doing 1 cyl at a time cranking it over, i've got it about warmed up now, should I let it run and pulg the gauge in 1 cyl at a time?

[Rocketman]

You should remove all 4 spark plugs so the engine can rotate freely, and disconnect the fuel injectors so it isn't injecting fuel. Then do the test with the throttle at WOT

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That term, WOT, is something I don't understand, I've seen it many times and still don't know what it means.

Wide open throttle? >.<

[perucho]

yes

[georgeb]

If you pull the EGI fusable link it won't make spark or pump fuel while you're doing the check.

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It's a 94 aspire, I pulled the egi inj 30A fuse out in the engine compartment, the results are in, 176/174/176/175

This is after being completely warmed up and long enough to recharge the battery (i used a diff battery to get it started) from 9v to 12.76, the reading @ the battery while running was 14.47v

The engine has 165-170k miles, so I guess it's in pretty good shape for it's age?

[91mcnasty]

I'd say so!!!

[zoom zoom]

yah, if only it made another 150 hp I wouldn't have to swap it! It's intimidating looking at the engine bay now, I'm labeling and disconnecting wires and I don't think I'll even be able to re use the harness for a bp, but who knows, this is just going to be a learning experience. Hopefully I can get everything disconnected, maybe even pull the motor tonight?

[bhazard]

BP swap into an aspire is a bit more complicated than a festy...I was gonna attempt it at one point.

[FestYboy]

it should only need a few pins swaped at the ECU harness connector and re-route the injector harness... you can even use the aspire MAF if you get the right ECU.

[Bert]

Your compression results are really nice. Another informative trick is to compare a 'wet' and 'dry' compression test. This gives you some idea of how good the piston rings are. Test the cylinders as is and then once again with a squirt of oil down the spark plug holes. If the numbers don't change the rings are in great shape.