Stock tack and Shift light ( Shift light is connected to an Accel 300+ ign box ) appear to be matching up shifting at 6200 RPMs, but when I review the scan the data log is showing 4800 RPMs. Is this possible and what could cause this?

Trying to trouble shoot a recent issue, car runs under light throttle, over 1/2 thottle about 3,000 RPMs the car bucks - goes flat and boost hangs around 4psi, but once you get above 5500 RPMs it clears out and snaps past 6,000 RPMs.

The car ran fine on the dyno and we made multiple pulls and the tune was dead on, now this problem popped up? There are no trouble codes, all the other data appears right, fuel pressure is correct.

Could this be opti or ECM related?

 

I read the original post on the RPM issues, and couldn't think of a good reason. One possibility I thought of later is the fact the 93 is the only year that does not drive the tach off the PCM. It has a wire from the coil, through some sort of "filter". Are you sure the tach is right? Not sure what the filter does, where it is, etc. The ECM reads the RPM off the Opti.

Also, what are you using to scan the ECM?

Fred

 

I think the tach is correct, but only because the shift light is matching it and the shift light is getting the signal from a Accel 300+ ing. box. butt meter says i'm up in the rpms as well/. hehehe

I data logged using DataMaster.

I'm thinking I'm going to try making a few passes holding the RPMs set 4,000, 5,000 and see what the data ogs look like them?

Also going to get a wideband ( already hane a bung in the Y-pipe from whn we had it on the dyno ) because my O2s are showing over 1,000mv when I go up thru the RPMs

 

If it matters, I have converted to the vented opti, but I've been running that for 2 years with issue.