2006 GMC Savana van, the other technician had misfire problems and replaced the maf only to find no improvement. I connected the escan to find very negative trim on road test. However vehicle intermittently running rough. Performed volumetric efficiency test and also found numbers off. connected vp and first used transducer on fuel rail, back probed, cyl. 7 injector and the cam sensor. found fuel pressure to drop and rise while running rough, cam signal good. But injector appeared to be firing a second time during compression stroke. Back probed cam and crank to check to see corallation. Seemed good. Probed cyl. 1 injector, crank signal (24x), and trigger of cyl. plug wire, cyl. 1 injector fires twice - posted below. If my theory is right, I believe the pcm to be bad if both cam and crank signals are good. Still new to the lab scope and thought I would post my findings.
Brian
Brian
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