Yet another Dual Sync failure.

[jft69z]

Count me as another victim of the Dual Sync distributor, intermittent failure.

Car is a '72 Monte Carlo, 454 LS6 big block, 4L85E transmission with Terminator Stealth with Transmission control EFI. Dual Sync distributor & MSD 6 EFI box. Got system running in October 2020 and has around 750 flawless running miles on it, until a couple weeks ago. Started dropping out right after startup, or random cut-outs while driving. Run great for a few days, then a bunch of no-starts. Same thing repeated a few more times. Andrew was kind enough to look at the tune and tweak a few things, then a day later mayhem again. Then this week it got worse. After researching this forum, and knowing from past posts that this was a common problem, I ordered a new distributor. Still, I don't like to throw parts at a problem so I hooked up the Snap-On scanner/lab scope and looked at the spark displays, cam & crank signals, etc.

I was also able to get a good System Log file today (V5.171) and it showed without question that the crank signal was garbage. At that point, I pulled the defective distributor, noticed all sorts of surface rust & corrosion on the innards & also the button on the distributor cap. Sort of annoys me because the car sits in a heated garage in the winters here, with no moisture issues in the building. None the less, others have mentioned the same problems of rust/corrosion, so I wasn't surprised to see it on mine. On a side note, the distributor was programmed for 'No Cam' signal, as it took forever to get the engine started when set up with the default settings. That made a world of difference on how quick it turns over now.

I'll call MSD soon to get this repaired as a spare, since I have the same setup in my '69 Z/28 with a 454, Tremec TKX, etc. In fact, the Monte was the guinea pig before doing the Camaro. Now the clock is ticking as to when the Z/28 Dual Sync distributor is gonna die, LOL.

Moving forward, I also ordered a small cap HEI type distributor as Andrew has suggested in the past, as well as the adapter harness 558-304, and a genuine GM module 19179578 as others here have suggested. That'll be going in the Monte as soon as the parts get here.

Anyways, the post by Danny was the biggest help today on how to properly setup a System Log to troubleshoot crank/cam sensor problems. So Thank you Danny! The post is here:
https://forums.holley.com/forum/holl...-amp-Datalogs=
A couple of pics of before & after if anyone cares. (I tried uploading System Log file, but got an error message). Thanks to all that post here, it really helps when problems arise. Joe T

[Danny Cabral]

Contact Holley Tech Service (LINK).

[jft69z]

Thank you Danny!

[weendoggy]

Yep, seen that twice on one of mine. Call MSD, Holley won't transfer the call. Expect about $150 for repair, that's what mine just cost.

[jft69z]

I was looking at your threads too during my research, that was a big help too.

I was literally just going to pickup the phone and make some calls, LOL. I already printed out MSD's number yesterday as I think you mentioned it in the other thread. Thank you!

EDIT: Just called them, gave me an RMA number and said maybe a 2-3 week lead time for repairs. No circuit boards available as a field service item at this time, for us to repair them ourselves.

[jft69z]

So the new, small cap HEI distributor is installed, along with the adapter harness and associated rewire. Runs good as expected, but have a question about setting it up.

So with the Dual Sync, they have you set the harmonic balancer timing mark at 50°, and the EFI software uses 50° as a Reference Angle value. Checks with a timing light show actual reflects commanded timing, all good.

With the HEI - 'computer controlled' (as the EFI software calls it) option checked to reflect the new distributor, it has a 10° Reference Angle already set & 1.0 usec Inductive Delay.

What's the preferred method here? Set balancer timing mark to 10°, line up rotor on distributor cap at # 1 cylinder and go with it? I checked it with a timing light, and with a Static Timing value programmed, and it was off by a fair amount. Setting the EFI software Reference Angle to zero, and checking it again made it closer. I rotated the distributor a bit to get it lined up with commanded value & left it there.

I'm guessing that as long as the commanded vs. actual timing is the same, any method will work? The distributor instructions were absolutely no help, they just say use the factory procedure/emission label as a reference. Holley & MSD documentation is no help either.

Not much help on a 1972 Monte Carlo, with a big block 454. Looking in GM ESC for a '88 GMC truck (something that this type of distributor would've been used in), the factory just says unplug the 'SET TIMING' connector and adjust to spec. Again, no such option on the '72. Any thoughts or suggestions would be appreciated.