Compression Test results questions.

[Jim-Bob]

Normally you test a car with all three plugs out, throttle wide open, coil wire pulled, and with a fully charged battery. I also like to put jumper cables on the battery and attach them to a running car so that there is sufficient charge to maintain RPM across all 3 cylinders. I would also check the compression tester on a known running car to be sure that it is not faulty. Honestly, 0 PSI is pretty hard to achieve unless all three pistons have giant holes in them which is again unlikely.

[pounsfos]

Originally Posted by Jim-Bob

Normally you test a car with all three plugs out, throttle wide open, coil wire pulled, and with a fully charged battery. I also like to put jumper cables on the battery and attach them to a running car so that there is sufficient charge to maintain RPM across all 3 cylinders.

all you do for a compression test is take the spark plug out of the cylender you are testing .

chuck the compression tester in

crank it about 4 times then look at the results for that cylinder.

repeat for each cylinder and dont forget to put the plugs back in

dont know what your on about jim-bob. but thats the most interesting way ive heard someone do it (no offence intended just my 2c)

[Ryland]

I've tested a motorcycle that had a pencil sized hole in it and still had a reading of 10psi, so if you doubt your compression tester then check the same cylinder twice.
pulling all the plugs, wires and coil wire is a good idea to prevent damage but most people don't bother, nor do they see negative results that are strong enough to tell them that they are doing it wrong, but it's still a good idea, jumper cables to a 2nd battery seems a bit much, just make sure your battery is fully charged and you should be fine fore 10 minutes or more of cranking.

[Jim-Bob]

Originally Posted by pounsfos

all you do for a compression test is take the spark plug out of the cylender you are testing .

chuck the compression tester in

crank it about 4 times then look at the results for that cylinder.

repeat for each cylinder and dont forget to put the plugs back in

dont know what your on about jim-bob. but thats the most interesting way ive heard someone do it (no offence intended just my 2c)

The method I described comes from both the factory GM service manual for my 1992 Metro and the factory Nissan service manual for my 1998 Frontier. I will trust the wisdom of engineers working for two of the world's largest automakers over that of others who are not as well versed in the proper methods of servicing an automobile and may or may not be capable of proper spelling.

[sc2dave]

Originally Posted by pounsfos

all you do for a compression test is take the spark plug out of the cylender you are testing .



repeat for each cylinder and dont forget to put the plugs back in

dont know what your on about jim-bob. but thats the most interesting way ive heard someone do it (no offence intended just my 2c)

You disconnect the ign. wire,remove ALL the spark plugs,then check compression on each one.Leaving spark plugs in will just add resistance to the engine spinning.

[2speedranchero]

Jim-Bob is correct "Normally you test a car with all three plugs out, throttle wide open, coil wire pulled, and with a fully charged battery."

Did you notice "throttle wide open" That is the step most forget.

"0 lbs" all three cylinders my bet is a bad gauge or possibly a broken timing belt.
tom

[Jim-Bob]

The other reason you do it with the throttle at WOT is that it puts the ECU in "clear flood" mode. In other words, it shuts down the injector and you can skip the step of pulling the fuel pump relay or fuse to disable it. Failure to disable fuel will potentially fuel wash the cylinders and give a false low reading, not to mention potentially pollute the oil with unburnt fuel.

[pounsfos]

Originally Posted by Jim-Bob

The method I described comes from both the factory GM service manual for my 1992 Metro and the factory Nissan service manual for my 1998 Frontier. I will trust the wisdom of engineers working for two of the world's largest automakers over that of others who are not as well versed in the proper methods of servicing an automobile and may or may not be capable of proper spelling.

fair enough mate, you got me their
haha my car manual doesn't say that but that's justa 28 year old car manual
for ya.
sorry for the bad spelling, i chopped the top of my finger off a wee while ago so its a bit stumpy.....