GMRULZ

Little background on the car. 96 OBD2 LT1 stock bottom end no power adder. Has a pretty large came over 230 intake dur, and over 240 exh dur. Lobe sep is extremely tight at 110. 4k vig stall.

Cruising at 2500-3500 rpm`s the check engine light flashes almost continually . Over that nothing, below that nothing. WOT nothing. It pulls the p0300 code. The car does not feel like it`s misfiring but autotap shows misfires all over the place. There is a cam surge that you can feel but its not missing that i can tell. I`m at a loss. New wires, plugs, opti less than a year old, cleaned all the grounds. Made sure nothing was routed beside a plug wire that might pick up interference. Car pulls strong but this light is anoying the heck out of me.

Is it possible the combination of the large cam duration and tight lobe sep is throwing off the obd2 computer since it has a crank trigger and could be causing a false p0300 reading?? Or any suggestions on a fix?

Thanks in advance.

IllusionalTA

Probably turn off misfire detection.. That would be my guess..

Injuneer

The code sets when the PCM compares the crank velocity profile with a known profile for a STOCK engine. If the crank shows speed irreguarities that don't match the profile, it sets the code.

Could be a faulty sensor, loose reluctor gear, some other component on the front of the engine loose.... anything that might cause miniscule variations in the CKP sensor signal. Could even be a nearby high voltage wire that is interfering with the CKP sensor signal (you appear to have checked that already).

The light should go off above 3000rpm because the PCM does not run the diagnostic above 3,000rpm. Does not run the diagnostic unless the throttle position is fairly steady.

In some cases even a rough road can cause the light to flash, but that doesn't seem to be the case here. Could be some unique "harmonic" resulting from the cam duration and overlap that produces a crankshaft revolution pattern that is different than what the PCM expects to see.

Is the misfire count that you see on AutoTap fairly even over all 8 cylinders, or do only certain cylinders show high numbers?

GMRULZ

You are correct it only flashes the code at highway speeds that are constant in the 2500-3500 range, stock tach could be off a little. So it`s definetly running diagnostics which are causing the code, and the light to flash.

The misfires show up on all cylinders, 1, 3, 4 and 8 seem to show the highest total number counts. That would be Lt front, Rt rear and almost in the middle on both sides, which seems to show a pattern I suppose. But again they all have many misfires, those 4 just have the most.

The reluctor wheel could be the issue, last cam install the bolt on the end of the crank tried to crossthread. Redid it several times then Loctited and torqued to spec. its possible that the crank gear is allowing the reluctor wheel to slip slightly. Which could give a false signal to the CPS. I really doubt it is since torqued to spec but you never know.

Can you turn off the misfire detection in LT1 edit or would just unpluging the sensor suffice for it not to run the test? but then again w/ it being OBD-2 I`m wondering if that would cause issues w/ the car running or any of the other systems controled by the PCM.

Any additional info is greatly appreceated, as well as info already givin.

Thanks for the help so far!

GMRULZ

Thanks Steve. By the way thanks again fo the help at the track w/ the diff and all!

Injuneer

If you unplugged the CKP sensor, you would have a code and the SES light for the faulty sensor.

GMRULZ

Too bad its not like the ole infamous low coolant light, unplug and it goes away...

Do you know if LT1 edit has a place to turn off misfire detection?

IllusionalTA

i believe the OBDII Edit has the ability to turn it off..