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Old 05-03-2021, 06:04 PM   #6
142 guy
Board Member
Join Date: May 2014
Location: Saskatchewan, Canada

As a further note, my previous comments were based upon using a starter by-pass switch to operate the starter motor during cranking with the ignition switch off. If you disable the fuel pump and the ignition system, you can crank the engine using the ignition switch in which case the ECU is energized during the test. Under those circumstances you should be able to hold the throttle open with your foot during the compression test.

I think most DBW ECUs will allow the throttle to be held completely open during cranking as that is the common flood clear mode. However, you can find comments on the Internet (source of all that is correct) that some ECUs will prevent this (I would be surprised) or may generate a TPS error code because it is expecting to see a low % open during cranking (that is a possibility). I have never tried because I have always done the test with the ECU off, stick up the throttle body and a remote starter switch.
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