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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

how do I compression test?

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Old Aug 31, 2009 | 04:52 PM
  #1  
rascholla's Avatar
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how do I compression test?

I know the basics. I need details. Does anyone know the quickest way to get it done? Let me know.
94 4runner 3vze v6
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Old Aug 31, 2009 | 05:00 PM
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From: Temecula Valley, CA
Get a compression tester with the thread pitch, etc. you need.
Pull all spark plugs.
Pull the EFI fuse or otherwise disable the fuel pump.
Pull the primary coil wire (center terminal on the coil).
Prop the throttle plate fully open.
Install the tester in to #1 spark plug hole.
Crank the engine at least 2 seconds, maybe up to 5, until you get the peak reading on the gauge.
Record that number.
Reset the gauge.
Repeat for the remaining cylinders.
For any cylinder not within 5-10% of the others, squirt some engine oil in to the spark plug hole, rotate the crankshaft a few turns, install the gauge in the spark plug hole and re-test. Record that number as a "wet" test for that cylinder.

Last edited by abecedarian; Aug 31, 2009 at 05:04 PM.
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Old Aug 31, 2009 | 05:02 PM
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can I just pull one sparkplug?

can I just pull one sparkplug?
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Old Aug 31, 2009 | 05:07 PM
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nope. can't do a compression test on one cylinder if plugs are installed in the others, or if the throttle is not held fully open.
You want the engine to spin as fast as possible and let as much air in to the engine as possible.
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Old Aug 31, 2009 | 05:08 PM
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From: Temecula Valley, CA
but you can do a leak down test....
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Old Aug 31, 2009 | 05:09 PM
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if u only want one cylinders compression yes. but if you want them all pull the all!
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Old Aug 31, 2009 | 05:12 PM
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ok got it. this is just what I wanted to read thanks
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Old Aug 31, 2009 | 05:12 PM
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If you want to get useful information do what Abe says.
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Old Aug 31, 2009 | 05:17 PM
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From: Temecula Valley, CA
spark plugs left in cylinders will cause the engine to slow down as the crank spins and the cylinders with plugs left in them build their own compression.
not exactly what you want if you're checking how much air can be sucked in and compressed in any particular cylinder, right?

3-5 cylinders fighting against the one cylinder you want to measure. not fair, is it?

Last edited by abecedarian; Aug 31, 2009 at 05:20 PM.
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