Will QCSC DAS help me find bad cam timing? YES
The 1991 1.9L SEFI Escort would hesitate and lacked power. Manifold vacuum was near normal. Several repair shops had given up. The car passed with no codes from the big RED scanner, it passed a self-induced injector balance test, but it would 'FLIP' on an emissions test.
We know that a SEFI should pulse the injector(s) either on the exhaust stroke or the intake stroke of the appropriate cylinder. We know that the sequential rhythm should repeat from cycle to cycle. Uncle Henry has not told us when the injectors should be pulsed, or what the cam to crank relationship should be.
In the screen below, T1 (transition 1) and T2 mark the firing of #1 spark plug. They also just happen to coincide with the cam ID pulse, thusly, one full cycle (720 crank degrees) is represented between the 2 cam pulses. Each grid mark is 180 crank degrees.
Notice that the #1 injector is being pulsed on or about the #1 power stroke, and also note the missing injector pulse, and that #1 injector is beginning to 'float'.
Clearly we have a problem. Next we measure the cam-crank relationship (offset). We know that it does NOT vary with engine speed. In the screen below, the small pulses on ch#1 represent the #1 plug firing. The 1st line on the left is T1 (cam at carrier voltage crossing), the last line is T2 (cam again), and the middle line (T3) marks the crank sensor missing tooth. The offset from T2 to T3 is 79 degrees. The crank pulse is supposed to occur 90 degrees BTDC.
See Finish Fix a Flipper
For more info, call: Quad Computer Systems Consultants, 973-472-0328, ASK FOR DAN
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QCSC DAS Copyright 1997 -- Developed by; Daniel A. Buckley (NIASE GAM-CMAT-L1)
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