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Slow cranking when checking compression

2587 Views 4 Replies 5 Participants Last post by  rn240sx
The other day I thought I'd check the compression on my 98 4 banger. I followed the procedure in the manual, i.e. relieved and disabled the fuel system, pulled the control wire harness plug from the distributor and then continued to take out all four spark plugs. Threaded in the gauge adapter, put the pedal to the metal and turned the key. The problem was that the cranking speed was reduced to about one third of what it normally is. My compression readings were quite low, in the 130 psi range, which I attribute to the slow cranking speed. When putting everything back together, the engine cranked at normal speed and started just fine.
The funny thing is that the same thing happened when I checked compression on my 96 Honda Civic. Essentially the same procedure, disable fuel system and ignition, full throttle, turn key, and it cranked very slowly. Again, cranking speed returned to normal after the test.
Any idea why this happens and how to achieve normal cranking speed when checking compression?
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as brutal said the speed doesn't change the compression and personally i don't think the speed has really changed in the way you think it has. the thing is with all the the spark plugs out the only cylinder that has any sort of resistance is the one you are testing so instead of hearing the starting speed change when every cylinder hits its compression stroke you only have one cylinder that that is making compression which if thats the only sound your focusing on will make it sound like its going at like 1/4 speed. and explains why you thought it slowed down on your other car too. in reality it is running a little faster because it has less resistance to fight against.
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