I have been looking over my LT1 Edit logfiles and noticed that under WOT the RPM will sometimes drop 100 or 200 rpm then jump back up again. I thought it was related to when the PCM pulls timing, but it happens even when there is no timing retard. Is this normal? Do others see this in their logs? Below is an example from my log. This is right before the 2-3 shift. Any ideas?

22:22:13 4825
22:22:13 4975
22:22:13 5100
22:22:13 4875
22:22:13 5025
22:22:13 5275
22:22:14 5300
22:22:14 5125
22:22:14 5475
22:22:14 5275
22:22:14 5350
22:22:14 5575
22:22:14 5350
22:22:14 5475

Thanks

 

Almost looks like a bad crank sensor, but being that yours is a 95, that can't be. Is your coil fresh?

 

I installed a Crane PS91 coil 2 years ago so I would assume it should be fine. Plugs and wires are new as of last fall. 75,000 miles and the car seems to run fine otherwise. I can't say that I notice it at WOT either.

 

What is your recent mods? I did a engine swap and left a few grounds loose and mine was doing it very badly. Do you also have a chargin problems?

 

My car does the same right before the 2-3 shift. Except it is very noticable. No one has really given me a definitive answer on what they think it may be.

 

My mods are....MAC headers, MAC cat-back, AS&M CAI, Crane ignition coil, LT4 KM. It's an A4 with 3.23s. I have no problems charging even with the AC and lights on. I will double check the ground connections though, thanks 94blackz.

Could knock be causing it and the sensor is just not picking it up? It only seems to happen above 4800rpm, the lower RPMs do not jump around.

 

What, no one has brought the opti-crap into this yet?

Not saying it's that for sure, but I would blame the ignition for it first.

When the ecm isn't receiving a good signal from the opti the tach starts swinging around like crazy, and is very noticeable at higher rpms.

Getting your car scanned would be a very good idea.