Mid-RPM misfire

[DieselSJ]

MS II, V3 board. Car isn't here, so I can't confirm version of the code. The car is about 130 miles from here and it will be a couple weeks before I can get up there to do any data logging.

We are having a misfire from about 1500-2300 rpm. We have a nice smooth idle at about 800 rpm, and if we open the throttle slowly it is great until about 1500 rpm where it starts to miss and stays rough until about 2300 rpm then it smooths out. It is also not load dependent - we get it at no load and under heavy load.

My VE table is very close - less than 5% EGO correction in the affected bins. I'm tuning with a wide band and have tried AFRs from as lean as 15:1 to as rich as 13:1 in those bins, so I think I have eliminated mixture as the problem. I have also tried advancing and retarding the timing about 10 degrees with no affect on the misfire.

We are driving a MSD 6 off the coil driver circuit. We tried changing the MSD box and the coil and still have the problem. System is triggered by the pickup in a MSD distributor (VR sensor).

We have searched for vacuum leaks and have not detected any.

Any ideas?

Thanks!

[bleoh]

Maybe try different predictor algarithms.

[whittlebeast]

What are you using for an ignition/RPM input to trigger the squirt. - off the ignition coil (assuming this is not a diesel), 36-1, pins in the crank with a VR...? All of these methods have different things to look for. We also need the code version to help. All the codes have ways to "predict" when to expect the next rpm trigger. They all treat this a little different.

AW

[krisr]

We are driving a MSD 6 off the coil driver circuit. We tried changing the MSD box and the coil and still have the problem. System is triggered by the pickup in a MSD distributor (VR sensor).

I'm having pretty much the exact same problem except my RPM misfire is very intermitten. I'd be very curious to know if you get it sorted out and vice versa as we seem to be running identical setups.

What code version is yours as mine is 2.35 and i'm using Last Interval predictor.

My thread is here http://www.msefi.com/viewtopic.php?t=17727

[krisr]

As I pointed out in my thread, I set the normal running pulse tol to 17% and it seemed to be ok on a relatively short drive (about 10km round trip). Might help your case?