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.

[jft69z]

Here's what MSD came up with for the bad Dual Sync distributor and quoted a repair price of $198:
565-200 FAILED TESTS
REPLACED:
MODULE
BEARINGS
OIL SEAL
CAP
ROTOR.

Nobody has any thoughts on the setup question asked before this post?

[Danny Cabral]

Originally Posted by Danny Cabral FYI: Holley EFI now sells their own Dual Sync (LINK) & HyperSpark (LINK) Hall-Effect distributors. They're a small cap design, "plug & play" with Holley EFI, and no need for a modified Firing Order. The Dual Sync crank & cam sensor signals also provide sequential injection capability (MPFI applications). The Dual Sync is "plug & play" (into the 10-pin ignition connector on the EFI Main Harness), and both distributors require a CD ignition box (Instructions), unless the Dual Sync is used with a CNP ignition system. The MSD 6201 Digital 6A CDI box & 8253 HVC-2 coil are a great match. The MSD CD ignition box is wired as shown in the Holley EFI Wiring Manual: http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual - Figure 11, Page 20) https://www.youtube.com/watch?v=AM7r-DauCak (Holley EFI Dual Sync Distributor - YouTube Tech Video) https://www.youtube.com/watch?v=2JpHlS1ymBc (Holley EFI HyperSpark Distributor - YouTube Tech Video) A Dual Sync blank cap is available, if the user decides to convert to Coil-Near-Plug/DIS later (no CDI box). Of course, the Dual Sync distributor can also be used as a crank and/or cam sync/oil pump drive unit. The Custom Ignition Parameters (in System Parameters) for the Holley EFI Dual Sync Distributor: Ignition Type ............. ― "Custom" Crank Sensor Type ..... ― "1 Pulse/Fire" (← Holley Dual Sync Distributor) Sensor Type .............. ― "Digital Falling" Inductive Delay .......... ― "100.0 usec" (← Synchronization info, adjusted per application.) Ignition Reference Angle ― "50°" (← Inherent Ignition Reference Angle & rotor-phasing of this unit.) Cam Sensor Type ........ ― "Single Pulse" (← "Not Used" for TBI, unless CNP ignition.) Sensor Type .............. ― "Digital Falling" Output Setup Type ..... ― "Points Output Fixed Duty Cycle (MSD)" (← MSD CD Ignition Box) ----------------------------------------------------------- Holley CNP Smart Coils and/or GM LSx Ignition Coils (no CD ignition box required): Output Setup Type ..... ― "DIS Coil On Plug" (← Holley CNP Smart Coils and/or LSx Ignition Coils) Dwell Time ................ ― "3.5-5.0 msec" (← See page 1 for Holley CNP coils, and page 3 for GM LSx coils.) https://www.holley.com/brands/holley...efi_dual_sync/ (Holley EFI Dual Sync Distributors) The Custom Ignition Parameters (in System Parameters) for the Holley EFI HyperSpark Distributor: Ignition Type ............. ― "Custom" Crank Sensor Type ..... ― "1 Pulse/Fire" (← Holley HyperSpark Distributor) Sensor Type .............. ― "Digital Rising" (← I prefer Digital Falling, LINK.) Inductive Delay .......... ― "100.0 usec" (← Synchronization info, adjusted per application.) Ignition Reference Angle ― "57.5°" (← Inherent Ignition Reference Angle & rotor-phasing of this unit.) Cam Sensor Type ........ ― "Not Used" (← This distributor doesn't have a cam sensor.) Output Setup Type ..... ― "Points Output Fixed Duty Cycle (MSD)" (← MSD CD Ignition Box) https://www.holley.com/brands/holley..._distributors/ (Holley EFI HyperSpark Distributors) https://www.holley.com/products/fuel.../parts/558-323 (Holley EFI HyperSpark Ignition Adapter)

[jft69z]

Thanks Danny. The distributor I ended up with isn't a HyperSpark though. I have the HEI small cap, which also appears to have a setting in the V5 EFI software called "GM HEI (Computer Controlled)". Also got the adapter harness 558-304 to mate it with the Dominator ECU (Terminator Stealth with transmission control system).

Are you suggesting the HyperSpark settings are also good for this distributor as well?
https://www.holley.com/products/ignition/distributors/chevrolet/parts/8366
https://www.holley.com/products/fuel_systems/fuel_injection/hp_efi/hp_harnesses/parts/558-304

[Danny Cabral]

Are you suggesting the HyperSpark settings are also good for this distributor as well?

No, the Ignition Reference Angle for the GM HEI distributor is 10°. The Inductive Delay is always adjusted the same way (← synchronization info, adjusted per application).

[a b c]

To verify the Reference Angle is acceptable, since you are still dealing with a mechanical air gap system (distributor), I'd set the timing as usual (start with a commanded value of 30°), verify commanded matches actual while at 2500 RPM or so, if not make it do so. Shut the engine off, turn the crank to your verified point of 30°. Remove the distributor cap and see how the rotor lines up with the number one pin. If the rotor is near the middle of the pin, your good to go, if not, start making Reference Angle adjustments until it does while repeating the timing set process.

[jft69z]

Thanks Danny & ABC. I initially set the timing mark at 10° on the balancer, and set the rotor at the # 1 pin on the distributor cap when installing the distributor (sort of like the procedure the dual sync had you do, but at 50° with that setup).

First, I did a timing light check with the fuel pump off, to check crank timing at 15° (all good). Next, did verify actual timing with a light (set Static Timing to 20°, Idle Spark control - OFF), and ran it up to around 3000 RPM to check for drift. Timing seemed stable, so I left the Inductive Delay where it was. Also checked it at various spots with the Static Timing Set back to normal, and it seems to track commanded vs. actual timing. As mentioned earlier, I did tweak the numbers a little bit, but will double check them to make sure Reference Angle is set to 10°.

I looked at the entire thread you posted real quick Danny, and I'll dig into it much deeper in a bit. Lot of good info in there. Thanks again!

[jft69z]

So I checked it this morning. I must have adjusted the Reference Angle to 0° at the time.

I reset it this morning to 10°, turned off Idle Spark control, Static Timing Set test to 20° and rotated the distributor to match 20°. Then ran it up to around 3000 RPM and noticed the timing slowly retard to about 15°. Shut it off, changed the Inductive Delay from the default 1.0 usec to 20 usec. Tried it out, seemed good, so changed it back to 10 usec, still seems good. Set it down to 5 usec and it seemed to drift a little, so set it back to 10 usec. Re-enable the Idle Spark control, etc., and left it. Does that seem reasonable to you guys?

[Danny Cabral]

If the timing is synchronized at idle and higher RPM, you're good to go.
https://forums.holley.com/showthread...087#post255087 (Ignition Timing Synchronization - A Two Step Process)

[jft69z]

It all appears to be good. As always, thanks for your help!