How can I tell if my NEW non-computer controlled, large cap HEI unit is giving a clean signal to my ECU?

I am using my ECU to control fuel only.

I have a hesitation at idle.

While watching the base fuel map on the lap top, the idle sits nicely at 800 RPM. Then, all of a sudden the engine has a slight hesitation. 1/2 second after that, my base fuel map shows a spike in RPM to about 3500. The pulse width at 3500 RPM and 0% throttle is obviously going to be lower than at idle and 800 RPM.

This happens every 15 seconds or so, with a hot or cold engine.

My dyno guy says that the ECU sees the RPM spike and changes the fuel to a much lower number, which causes the hesitation.

I am trying to figure out if the signal from the coil is causing this. It's either a dirty tach signal or the ECU is bad. The ECU failed to properly control spark, so we abandoned that function.

How can I clean up the HEI tach signal if it is dirty?

 

I'd assume you'd get way better answers in the DIY Prom sections. Because the rest of us here have no clue how you run fuel only off the stock ECM - that's for the chip geeks .

 

Thanks for the reply. I guess my question is how can you tell if an HEI unit is not giving a clean RPM signal, and what is a good way to clean it up?

I am trying to figure out if the distributor is the problem.

The ECU is not stock. Its an Accel unit, but I am trying to eliminate the distributor as the source, before I change the ECU.