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compression test

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Old 02-08-04, 03:01 PM
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compression test

Ok, I have the intercooler piping/elbow out. I removed the top two sprak pulg wires. Then I reached in and felt the plugs and wondered...what tool do I use to take these off? Any help appreciated

I am doing a compression test....
I am figuring i remove the top 2 plugs and then stick in the compression tester to where the plugs went and crank over engine...is this how it goes?

I cant start my engine but it is still getting air/fuel/spark...so is it still possible to test compression on just having it turn over as much as it can?

Do I need to remove any fuses while turning th engine over?

Thanks for the help guys...always appreciated! =)
Hope results come out good
Old 02-08-04, 11:49 PM
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if you want to know your motor condition without going through all that, you can just check your boost guage.

During idle, your vacuum should be hitting above 450mm/cm^2. If below, most very likely you will be needing motor rebuilt due to low compression.
Old 02-09-04, 12:32 AM
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there is a bunch of procedures to do. There should be a few threads about this.

off the top of my head......

unplug ONE spark plug at a time and use the top one.
take fuel/spark fuse out
press pedal all the way down
take check valve out of compression guage

watch for 3 even bounces

when cold the readings are inaccurate
Old 02-09-04, 06:54 AM
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Originally posted by ooEfiniRx7oo
During idle, your vacuum should be hitting above 450mm/cm^2. If below, most very likely you will be needing motor rebuilt due to low compression.
WTF is 450 mm/cm^2 ??? those are some crazy units, man . If your vacuum is less than 450 mmHg that doesn't mean that you'll need a rebuild soon... My compression is 7.2 for both rotors for all faces and my vacuum on a great day 430 mmHg (usually 410 or 420). It's a stock motor with over 60k on it, so it's a little tired, but it runs hard and will not need to be rebuilt soon. My point is, you can't tell that you need a rebuild from a vacuum reading. As far as your compression check... take it to the dealer or someone who has the appropriatre electronic equipment to read it accurately.
Old 02-09-04, 11:11 AM
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With a street port idle vac will go down.

I think there are too many variables to just check vac at idle.

compression checks are not that hard. I don't think it's worth 70 bucks or whatever to have the dealer tell me my car is fine.
Old 02-09-04, 11:30 AM
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As long as its running dont worry about it. You can pull one leading plug out and a time and pull the main efi fuse then just turn the engine over. Listed for all even bounces.

STEPHEN
Old 02-09-04, 06:51 PM
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compression is 5.2 kg/cm^2 on rear rotor and 12.5 kg/cm^2 on front rotor. Also equals 70 PSI on rear rotor and 185 PSI on front rotor. Looks like i am getting a rebuild.
Old 02-09-04, 07:06 PM
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Originally posted by mr g lord focker
compression is 5.2 kg/cm^2 on rear rotor and 12.5 kg/cm^2 on front rotor. Also equals 70 PSI on rear rotor and 185 PSI on front rotor. Looks like i am getting a rebuild.
Your numbers are not possible, at least on the front rotor. Maximum psi is about 125 psi for a new motor. The difference between rotors looks bad though.
Old 02-09-04, 07:12 PM
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Using the right tool?

Rotaries require a special compression gauge. If you're using a piston gauge, it might explain the numbers you are getting.

Beast
Old 02-09-04, 07:16 PM
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probably..but it atleast showed me what I needed to know. All for plugs were pulled and both readings on front rotor and back rotor were the same. But the rear rotor had only about 1/2 the reading of the front rotor BOTH times so I know I need rebuild....but thanks for letting me know about the #'s
Old 02-09-04, 07:40 PM
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a piston guage will work fine.

you just have to take the check valve out.

Lots of ppl use them.
Old 02-09-04, 07:41 PM
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when you have a suspicion that your motor is blown you dont need a guage to tell you anything. Just pull the fuel pump relay take out 1 of either plugs on each housing out and listen. Do one plug at a time then replace it and go on to the next housing. youll hear a pattern of the motor spinning over it needs to sound the same on all 3 beats or there is a problem

now to do a relative compression test to see what the condition of an old motor is a guage is needed

sorry about your motor
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