I'm running EBL flash with the port mod running a port injection Edelbrock intake (TBI based conversion). It feels like I'm experiencing a misfire at light load cruise (65-70 mph). I'm running open loop and a little rich (12.7-13.0). When I data log I find single lines where the indicated RPM jumps to 4850, the SA jumps to 40 and the DC jumps to 37. The other lines are at 1875 RPM, 33(SA), and 14%DC respectively. (I added a IAT and haven't got the VE right yet but this problem doesn't seem related).

I running a stock small cap HEI and coil. Plug wires and plugs have about 5,000 miles on them. Other: aluminum Edelbrock performer heads, ZZ9 cam, stock exhaust manifolds and CAT, about 10.5:1 355 cu in.

Engine pulls good under load up to 5,200-5,300 where I'm out of injector (+90% DC).

What's the deal with the indicated RPM spike? bad coil? bad pickup coil? or is this just what a misfire looks like in the data log?

 

Attached an .xls file with a few lines of the log.
just noticed that it doesn't always increase the SA. And a few lines before there was a G/S spike but it doesn't seem consistent with other incidents.

 

Can you email the .dat log file to me? That will be helpful in determining whether this is a mechanical issue or an EBL ECM issue.

To the SS, ignore the jumps in duty cycle, this value is calculated in the WUD for display purposes. It simply increases as the RPM increased, hence the DC% is higher.

Which brings us to the jumps in airflow (gms/sec) and the SA value. These values along with the RPM are directly from the EBL ECM.

For the SA jump, check the BIN SA table at 4800 RPM and 50 MAP. If it is around 40*, then the ECM is retrieving it from the SA table. IOW, it isn't a made up value.

The jump in airflow is also likely due to the jump in RPM. Higher RPM equals higher airflow.

The reason the values are inconsistent is that the ECM is looping at 80 times a second, while the WUD is getting data at 17 times a second. And the data is captured as it is streamed, so it has been looped through nearly 5 times for every time we capture a data value.

If you have another distributor to try, I would do that and see if the problem goes away.

RBob.

 

This did turn out to be a distributor problem of some type. Although I'm not sure if it was due to a electronic flaw of some type or due to a lack of shielding around the reluctor wheel. The problematic distributor did not have a metal shield around that area, but the new one did. Anyone familiar with the design on the left in the attached picture? Is the shield missing or is there simply not one used in that design?
Thanks RBob for the help.

 

The one on the right is a stock GM unit. Hopefully it has an AC Delco 369 ICM, if not it would be best to get one for it.

The left distributor is an aftermarket re-man. Hence the different reluctor and star wheel.

RBob.

 

Sure enough, I flipped it over and on the bottom of the plate was stamped 'REMAN'