Can QCSC DAS test RELATIVE COMPRESSION? YES

On this old v6, TBI, we disable the injectors. We put our trigger pickup on the #1 cylinder. We attach QCSC DAS channel #1 directly to the battery +. Next we crank it over.

Two full cycles are represented (1440 + crank degrees). Cylinder #1 hits three times. The 1st and last hits are marked and then we add 12 grid marks to ID 10 degrees BTDC (base timing is 10 deg BTDC). Because we have our trigger on #1, we can measure the RPM, which was about 130 RPM.

It is obvious that as each cylinder hits on the compression stroke, battery voltage drops. Notice that the last cylinder to fire appears, to have more compression than the others.

Next we pull a plug out. We also move the bat+ lead on ch#1 to the starter side of the relay (we know this will show noise as we get away from the battery). We crank it over again and cranking RPM increases to about 155. We mark the firing of #1 twice and then make six grid marks (we zoomed a small section of the screen). The cylinder with no compression is obvious. Notice the last cylinder in the firing order, it still shows better compression than the others.

You no longer need a big bucks engine analyzer to do relative compression testing.

Besides relative compression and cranking RPM, QCSC DAS can simultaneously check cranking vacuum!!

For more info, call: Quad Computer Systems Consultants, 973-472-0328, ASK FOR DAN

EMAIL to; qcscdas@aol.com or; lody@delphi.com or; danbuckley@worldnet.att.net
Please entitle email inquiries -- QCSC DAS

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QCSC DAS Copyright 1997 -- Developed by; Daniel A. Buckley (NIASE GAM-CMAT-L1)

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