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

This is more of a distributor question than an ECU question. I am trying to eliminate the distributor as the source of the problem before replacing the 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 0% throttle. (I'm using Alpha N)

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 (based on the fuel map), 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?

 

Well if you have your car set up for EFI then there's no reason to use a non EFI distributor. You can drop in a EFI distributor and wire correctly or change your distributor by locking mechanical advance and disabling vacuum advance and replacing the module with one from an EFI distributor.

The conversions I have seen or done as fuel only needed a tach filter to give the ECM the proper signal. The cost of a tach filter is very high and I have only seen them available at aftermarket EFI company's like Howell. By the time you buy that and install it you could have gone EFI controlled distributor.