Compression Testing with EFI
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Laughing Gas
Joined: Nov 2013
Posts: 871
Likes: 6
From: Orcas Island, WA
Compression Testing with EFI
Are there any concerns or issues about running a compression test on a fuel injected engine? With a carb very little fuel will pass through because the throttle is closed. But with EFI it will be injecting fuel as if trying to start it. Is this raw fuel running into the cylinders an issue, or am I worried about nothing?
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
The throttle should be held wide open when performing a compression test. Wide open throttle in start mode triggers the PCM to NOT fire the injectors.
Elder User
Joined: Jul 2011
Posts: 793
Likes: 2
From: Vernon, BC
I never even thought about that when I did a compression test on my 94. I hooked up my battery charger and then simply took all the plugs out. I had no issues. However, taking out the fuel pump relay is not such a bad idea 
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Laughing Gas
Joined: Nov 2013
Posts: 871
Likes: 6
From: Orcas Island, WA
Jerry, that's what rattled around inside my tired head this afternoon. I'll be doing this single handed with my remote starter on the solenoid. No reason to have the key on, hence no fuel. Sometimes it takes me thinking things through a few times before I tumble on everything.
rla2005, wide open throttle should be no problem at all. At the moment the entire throttle body assembly is off for cleaning. I think that counts as wide open throttle.
rla2005, wide open throttle should be no problem at all. At the moment the entire throttle body assembly is off for cleaning. I think that counts as wide open throttle.
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