GM EST Ignition on Big Block Crusader

Sleipnir

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May 17, 2010
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We have a 1985 Tiara 31 with dual 454 carbureted Crusaders. Most history is unknown. Starboard engine has a United GM EST Distributor kit. (Port ignition is different system.) We have been unable to get spark advance to behave properly. The United instructions prescribe base timing setting at 12 degrees with a graph showing 20 degrees distributor advance at 3000, so 32 degrees total advance.
When we bought the boat, the distributor had in it an ignition module GM # 193529288H3, which cross reference on the Rock Auto Website to AC Delco D1965A. When base timing was set at 12 degrees, change to run mode would immediately jump idle timing to apx 20 degrees, and total advance at 3000 would be about 30 degrees . Resetting timing to 30 degrees at 3000 in run mode would only drop timing to 24 degree at idle.
On advice that was probably wrong, we tried a couple of D1943A modules, which seemed to deliver only 6 degrees of advance. Resetting timing to 30 degrees at 3000 in run mode would only drop timing to 24 degree at idle. A replacement D1965A is acting similarly. We get only 6 degrees above base setting, and changing from base setting to run changes the idle advance.
Although battery isn't the best, voltage drop on initial start isn't below 10.5. After a number of starts, it drops below 10V, and engine won't run.
Several questions, I guess:
1. Is there a third module that actually should be in this system, rather than the D1965A or D1943A?
2. Assuming one or other module we have is correct, does the momentary voltage drop during engine start (usually to 10.5) somehow reset the module so the advance doesn't work or work properly?
3. If the D1943A or D1965A is correct, is there a troubleshooting process that should be followed to determine why we can't seem to set base timing at 12, switch to run mode and see idle timing still at 12 and total advance at 32, or so?
Thanks
Sleipnir (Charlie Iliff)
 

Scott06

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Apr 20, 2014
Messages
2,378
We have a 1985 Tiara 31 with dual 454 carbureted Crusaders. Most history is unknown. Starboard engine has a United GM EST Distributor kit. (Port ignition is different system.) We have been unable to get spark advance to behave properly. The United instructions prescribe base timing setting at 12 degrees with a graph showing 20 degrees distributor advance at 3000, so 32 degrees total advance.
When we bought the boat, the distributor had in it an ignition module GM # 193529288H3, which cross reference on the Rock Auto Website to AC Delco D1965A. When base timing was set at 12 degrees, change to run mode would immediately jump idle timing to apx 20 degrees, and total advance at 3000 would be about 30 degrees . Resetting timing to 30 degrees at 3000 in run mode would only drop timing to 24 degree at idle.
On advice that was probably wrong, we tried a couple of D1943A modules, which seemed to deliver only 6 degrees of advance. Resetting timing to 30 degrees at 3000 in run mode would only drop timing to 24 degree at idle. A replacement D1965A is acting similarly. We get only 6 degrees above base setting, and changing from base setting to run changes the idle advance.
Although battery isn't the best, voltage drop on initial start isn't below 10.5. After a number of starts, it drops below 10V, and engine won't run.
Several questions, I guess:
1. Is there a third module that actually should be in this system, rather than the D1965A or D1943A?
2. Assuming one or other module we have is correct, does the momentary voltage drop during engine start (usually to 10.5) somehow reset the module so the advance doesn't work or work properly?
3. If the D1943A or D1965A is correct, is there a troubleshooting process that should be followed to determine why we can't seem to set base timing at 12, switch to run mode and see idle timing still at 12 and total advance at 32, or so?
Thanks
Sleipnir (Charlie Iliff)
First get a new battery And make sure cables and connections are clean. I think your module is working properly. When you lock it in base mode you are locking out the electronic advance. When you come out of base mode the ignition should advance like you see, it wont stay at 12. if you can set 12 in base mode then get maximum of 30-32 it is working as it should .
 

Sleipnir

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May 17, 2010
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First get a new battery And make sure cables and connections are clean. I think your module is working properly. When you lock it in base mode you are locking out the electronic advance. When you come out of base mode the ignition should advance like you see, it wont stay at 12. if you can set 12 in base mode then get maximum of 30-32 it is working as it should .
Will be getting a battery, but when it is 12 degrees at base mode, and then max of 32 in run mode, the advance at idle is 24-26 degrees. despite base having been set at 12.
 

Scott06

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Apr 20, 2014
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2,378
Will be getting a battery, but when it is 12 degrees at base mode, and then max of 32 in run mode, the advance at idle is 24-26 degrees. despite base having been set at 12.
You seem to be ignoring what i posted and you dont understand how base mode works. It is normal when you take it out of base mode it doesnt stay at the static setting when it is is out of base mode. Youve tried now three modules with same results right …
 

Sleipnir

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You seem to be ignoring what i posted and you dont understand how base mode works. It is normal when you take it out of base mode it doesnt stay at the static setting when it is is out of base mode. Youve tried now three modules with same results right …
I am not ignoring what you posted, but I agree that I don't understand how base mode works. I appreciate your help. My probably incorrect understanding was that base mode inactivated the advance program built in to the module, thus letting the initial zero-advance timing be set. I expected that setting (12 degrees) to continue in run mode to be the advance at startup and idle, with the module advance curve added to it as RPM increased. What I am seeing is a 12 degree setting as base timing jumping to 20+degrees when the 12V is disconnected from the timing post of the module. That is higher than I'd like for starting.
The two D1943A modules have acted identically - about 6 degree advance only. The two D1965A modules have not acted exactly the same, but one has seemed to give the right total advance at 3000 in run mode after being set in base mode, but then doesn't drop below 20 degrees when pulled to idle.
As I noted, I will certainly get a battery to ensure that input voltage is a bit more stable, but do not understand whether it has a current effect. Except for the few seconds when the starter is engaged, voltage is solidly over 13V.
 

Scott06

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I expected that setting (12 degrees) to continue in run mode to be the advance at startup and idle, with the module advance curve added to it as RPM increased. What I am seeing is a 12 degree setting as base timing jumping to 20+degrees when the 12V is disconnected from the timing post of the module.
I understand what you are seeing …

when you remove the timing shunt it will come out if base mode and start advancing the ignition timing, thats how it works to find best running conditions. I assume when you come out of base mode rpm picks up?

For example If you Google Delco EST you will find that on a MerCruiser 3.0 in base mode you set it at 1° BTDC, But when you remove the shunt it should go up to 12°, thats how it works I don’t know what else to tell you.

what is the run ability issue you are trying to solve ? Or is the timing just not what you expected. is your idle speed high, carb in good shape, not running rich?

For what it’s worth on my 65 gto I‘m running about 8 degrees initial with vacuum advance disconnected, with full manifold vacuum advance plugged in it idles nice about 24-26 total at 750rpm. Your EST does this electronically no moving parts.
 
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Bondo

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I am not ignoring what you posted, but I agree that I don't understand how base mode works. I appreciate your help. My probably incorrect understanding was that base mode inactivated the advance program built in to the module, thus letting the initial zero-advance timing be set. I expected that setting (12 degrees) to continue in run mode to be the advance at startup and idle, with the module advance curve added to it as RPM increased. What I am seeing is a 12 degree setting as base timing jumping to 20+degrees when the 12V is disconnected from the timing post of the module. That is higher than I'd like for starting.
The two D1943A modules have acted identically - about 6 degree advance only. The two D1965A modules have not acted exactly the same, but one has seemed to give the right total advance at 3000 in run mode after being set in base mode, but then doesn't drop below 20 degrees when pulled to idle.
As I noted, I will certainly get a battery to ensure that input voltage is a bit more stable, but do not understand whether it has a current effect. Except for the few seconds when the starter is engaged, voltage is solidly over 13V.
Ayuh,..... Welcome Aboard,...... Yer understanding is wrong,......
The timing changes quicker than the blink of yer eyes, which is why it'll start just fine, with a fresh battery, 'n then advance to optimum,..
 

Sleipnir

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May 17, 2010
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Scott & Bondo:
Thanks a lot for your help. With better understanding what we are dealing with, I think it's fixed. My basic misunderstanding was how early the advance mode comes in. It adds 10 degrees in the idle range starting at 500 RPM. In about 60 years of messing with advance, I'd always set initial where the engine liked it at idle, and then pretty much ignored the curve until above 2000 or so and adjusted springs and weights to get the desired curve to redline. The slope was never steep early on. This morning, the engine is running properly with the original module, that cross-references to D1965A. 12 degrees base goes to 31 at 3500, and shows 24 or so at 800 idle. The replacement D1965A and the two D1943A modules do not give more than 6 degrees advance above base setting. Our thought is that the 1943 modules probably need an ECU to act properly. We haven't a guess why the new 1965 doesn't work.
We jumpered to the other battery with its engine running to reduce starting voltage drop and remove that variable. If weather permits we'll take it out for performance evaluation.
Thanks again.
 

Scott06

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Apr 20, 2014
Messages
2,378
Scott & Bondo:
Thanks a lot for your help. With better understanding what we are dealing with, I think it's fixed. My basic misunderstanding was how early the advance mode comes in. It adds 10 degrees in the idle range starting at 500 RPM. In about 60 years of messing with advance, I'd always set initial where the engine liked it at idle, and then pretty much ignored the curve until above 2000 or so and adjusted springs and weights to get the desired curve to redline. The slope was never steep early on. This morning, the engine is running properly with the original module, that cross-references to D1965A. 12 degrees base goes to 31 at 3500, and shows 24 or so at 800 idle. The replacement D1965A and the two D1943A modules do not give more than 6 degrees advance above base setting. Our thought is that the 1943 modules probably need an ECU to act properly. We haven't a guess why the new 1965 doesn't work.
We jumpered to the other battery with its engine running to reduce starting voltage drop and remove that variable. If weather permits we'll take it out for performance evaluation.
Thanks again.
Good deal, let us know how you make out when you get it in the water
 

Sleipnir

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Good deal, let us know how you make out when you get it in the water
By the time we got it running correctly at the dock, time ran out to winterize the boat. So, although we're confident it's fixed, we haven't yet gotten a cruise or top end test. In the Spring, I'll post results.
 
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