for example, does weather, engine temperature, carbon buildup on pistons/valves, etc... affect compression test results?

 

Yeah, your car makes more compression on the guage when its hot. for accurate reading wait till your car is cold

 

What??? Commpression tests should all be made with the motor at operating temp with the ecu pin and all spark plugs taken out, crank the moror 4-5 times with the throttle open. With a cold motor the clerances are bigger and no oil makes bad results, example my motor did 130psi cold, hot it was 220psi.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by leadfoot78 &raquo;</TD></TR><TR><TD CLASS="quote">What??? Commpression tests should all be made with the motor at operating temp with the ecu pin and all spark plugs taken out, crank the moror 4-5 times with the throttle open. With a cold motor the clerances are bigger and no oil makes bad results, example my motor did 130psi cold, hot it was 220psi. </TD></TR></TABLE>

thanks, someone who knows, hehe.
Yeah, he is right, the engine has to be warm, and the other two important things, like he said, is that the engine shouldn't be getting gas neither spark, good luck

 

Why do you need to remove the spark plugs of the other cylinders when testing, since each cylinder is completely separate? I remember the first time I did a compression test I did not remove the other spark plugs =&gt; the engine was running and was taken to WOT with 3 cylinders still functioning. I realize the safety hazards in this, but in terms of compression I don't see how the results are affected. A problematic cylinder would still read a lower pressure. Any problems in my thinking?

 

Ok, try to crank the engine by hand with a ratchet on the crank pulley with the plugs in and try it with out the plugs. Here is the result, you probably won't be able to turn it with your hand with the plugs in the motor. Since the plug is inside there is no place for the air to escape when the piston is on the up stroke, imagine how much strain you are putting on your starter and the flywheel teeth with the plugs in it. Taking out the plugs just makes it easyer on your engine thats all.

PS: And to the person that gave the wrong info, shut up!!!! dont speak when you have nothing good to say, damn ricer!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR &raquo;</TD></TR><TR><TD CLASS="quote">Why do you need to remove the spark plugs of the other cylinders when testing, since each cylinder is completely separate? I remember the first time I did a compression test I did not remove the other spark plugs =&gt; the engine was running and was taken to WOT with 3 cylinders still functioning. I realize the safety hazards in this, but in terms of compression I don't see how the results are affected. A problematic cylinder would still read a lower pressure. Any problems in my thinking? </TD></TR></TABLE>
Doing it with the engine running, you have gasoline being injected into the cylinder, unless you unplug the injector.

Besides, it'll run pretty rough on 3; and if cylinders are inconsistant, it won't run the same speed for all 4 that you measure. When you're measuring the bad cylinder it will be running on 3 good cylinders. When you're measuring a good cylinder it'll be running on 2 good & 1 bad.

Using the starter, if you take out all 4 plugs it cranks faster. That's not fundamentally wrong, but now you don't want to compare your numbers with anybody else who takes them all out.

One other thing that matters is the gauge itself. The internal volume of the gauge and the location of the check valve will influence the measurement. So if my numbers are lower than yours it doesn't mean anything unless you & I used the same gauge.

 

Makes sense to me, since I'm not altering the dimensions of the cylinder or piston.

Thanks.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR &raquo;</TD></TR><TR><TD CLASS="quote">Why do you need to remove the spark plugs of the other cylinders when testing, since each cylinder is completely separate? I remember the first time I did a compression test I did not remove the other spark plugs =&gt; the engine was running and was taken to WOT with 3 cylinders still functioning. I realize the safety hazards in this, but in terms of compression I don't see how the results are affected. A problematic cylinder would still read a lower pressure. Any problems in my thinking? </TD></TR></TABLE>

so it spins faster like the engine is running.
also UNHOOK THE DISTRIBUTOR PLUGS! no cyl position sensor signal=no injectors will open
throttle wide open
normal operating temp
plugs out

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by leadfoot78 &raquo;</TD></TR><TR><TD CLASS="quote">What??? Commpression tests should all be made with the motor at operating temp with the ecu pin and all spark plugs taken out, crank the moror 4-5 times with the throttle open. With a cold motor the clerances are bigger and no oil makes bad results, example my motor did 130psi cold, hot it was 220psi. </TD></TR></TABLE>
haha definately when its hot