mfpvette80

I ran a Mallory ignition unit on my 1980 (HEI ignition) and loved the improved fuel mileage. Something went wrong that I never fully figured out and i had to replace the ignition box. I recently read that you have to by-pass the resistor in the tach wire before connecting it to the box. I didn't do that last time. Anybody have any experience with this? Could having the resistor in place make the ignition act weird at > 2000 RPM? Thanks.

7t9l82

yes. it needs full power

mfpvette80

I've had discussions with Mallory (Prestolite) engineers over a period of three years trying to figure this out. I've returned the boxes on two occasions and had them tested to be sure they worked. Every time I've reinstalled the box I experienced ignition problems starting around 2,200 RPM. I was nor aware that the tach signal could cause this. This is the first break I've had in solving the mystery. Any idea why the tach signal with a resistor in place causes this?

7t9l82

i know there is an explanation for it but i am at a loss what it is . i believe it has to do with not having the sustained energy to allow the coil to work properly. i had the same problem some years ago and running full battery voltage to it fixed the problem.

mfpvette80

I agree with the full battery voltage observation. I'm running direct from the starter power source (battery + cable) with a solid ground to the battery negative frame lug. Still the same result. The folks at Mallory said the resistor (filter) in the tach wire should make no difference since that wire is only an output and does not affect the performance of the ignition box. Back to square one again.

cboyd

I am running the MSD 6al box on my 383. With the filter in place my tach would drop back to o once my revs reached around 2000rpm. I removed the tach filter and the tach works as it should. The reason for this I do not know, but removing the filter solved the problem.

mfpvette80

Wish my problem was that simple. The tach works fine. It's the actual ignition that gets wacky. It seems to shift the timing about -50 deg. when you hit around 2,200 RPM. Idle is fine, but as soon as you accelerate, it starts missing and bucking. I've posted on this topic several times in the past without finding an answer. Thanks for trying.