Compression test howto question
10-30-2016, 09:53 PM
#1
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Compression test howto question
Hi!
I'm looking to buy an old 4runner with a 22re. I just took a look at one and used a compression tester borrowed from Autozone. Two newbie questions about the right way to do a compression test.
1) I disconnected the wire that goes to from the center of the distributor to the coil. I disconnected it from the coil end. When the engine cranked, there was sparking from coil to.. presumably some grounded part near the coil. Is this dangerous at all? Or is this the right way to do it?
2) I had the owner crank the engine, but I don't think he necessarily opened the throttle (i.e. pushed on the gas). How much could this affect readings? 2 of the cyclinders were above 120, and 2 around 90. I didn't get it cause 90 seems terrible. Could this have been a throttle issue?
Thanks greatly
-a
I'm looking to buy an old 4runner with a 22re. I just took a look at one and used a compression tester borrowed from Autozone. Two newbie questions about the right way to do a compression test.
1) I disconnected the wire that goes to from the center of the distributor to the coil. I disconnected it from the coil end. When the engine cranked, there was sparking from coil to.. presumably some grounded part near the coil. Is this dangerous at all? Or is this the right way to do it?
2) I had the owner crank the engine, but I don't think he necessarily opened the throttle (i.e. pushed on the gas). How much could this affect readings? 2 of the cyclinders were above 120, and 2 around 90. I didn't get it cause 90 seems terrible. Could this have been a throttle issue?
Thanks greatly
-a
10-31-2016, 07:10 AM
#2
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For me, I try to refer to the manual whenever I can:
http://web.archive.org/web/200611160.../6compress.pdf
While the manual advises to "disconnect the distributor connector," I haven't. I suppose if I had the gauge in the wrong position and a plug connector arced to the gauge, well, I would be giving you different advice! I don't think the arcing you saw is a problem, and it's probably safer to disconnect the distributor somewhere.
Opening the throttle valve does make a difference; it might even make the 20psi difference between what you saw and the minimum. But what I would have worried about is the DIFFERENCE between readings (which won't be affected by throttle opening). Toyota says 14psi (10% of the minimum), and you've got 30.
Remember, the engine you're looking at IS around 30 years old. It probably hit 171psi without problem in its younger days. You might be willing to accept 140 or so (with the throttle fully open) today.
http://web.archive.org/web/200611160.../6compress.pdf
While the manual advises to "disconnect the distributor connector," I haven't. I suppose if I had the gauge in the wrong position and a plug connector arced to the gauge, well, I would be giving you different advice! I don't think the arcing you saw is a problem, and it's probably safer to disconnect the distributor somewhere.
Opening the throttle valve does make a difference; it might even make the 20psi difference between what you saw and the minimum. But what I would have worried about is the DIFFERENCE between readings (which won't be affected by throttle opening). Toyota says 14psi (10% of the minimum), and you've got 30.
Remember, the engine you're looking at IS around 30 years old. It probably hit 171psi without problem in its younger days. You might be willing to accept 140 or so (with the throttle fully open) today.
