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Having timing issues. After a few minutes the timing jumps ATDC to 6 degree..? Coil not within spec.

M

mevsmyself2

New member
Hi,
I am trying to narrow down my engine problem. I have a 1997 Mercruiser 3.0LX EST Ignition. I was checking timing and it reads about 1 degree BTDC and then when disconnecting the jumper and reconnecting the interrupter the timing is about 12. So within spec. Then by this time it has been running a few minutes and then it jumps to 6 degrees ATDC and starts to knock..
I tested the main coil and coil inside the distributor.

Pickup Coil inside distributer: Spec= 500-1500 ohms
mine tested = 880

Main Coil mounted on engine:
Spec from B to body = open
mine tested = open

Spec from B to D = approximately 0.4 ohms
mine tested = 1.1 ohms

Spec from B to C = approximately 0.4 ohms
mine tested = 1.1 ohms

Sec from B to E = 7800 - 8800 ohms
mine tested 8170 ohms

Manual states replace if not approximately 0.4. But could the main coil be the problem? Could the main coil cause the module to overheat? Seems like the module is having issues after a few minutes. Could it be overheated and causing an issue?

Sounds like main coil is out of spec. It does not give a range. Is 1.1 ohms approximately 0.4? It is almost 3x that.

Also does anyone know the GM part# for the Ignition Module just in case? Mercruiser uses it but charges $200. Advanced Auto has a gm: D1943A for $89.. Not sure if it is the correct part#

Also I guess if I need the Main Coil, is there an autoparts store part# for like an AC Delco or GM part#. Do I need a marine version? I noticed the marine ones look painted.

Thanks
 
Bt Doctur said:
should be the same part made by GM
Click to expand...
GM/ AC Delco charges $125 Mercruiser charges $225 for the same part. But I found the latest one for module anyway. AC Delco Module: 19418839 . I will probably go with CDI if I do change it.
I am not sure if I need to change my main COIL it seems to be out of spec. I have been told don’t worry about it. I am thinking I have a out of spec coil and bad module, but waiting for some other thoughts.
 
I doubt your coil is the issue...regarding the testing done, most DVM are not very accurate when they get into the single digit range for resistance.

You can always remove the module and ensure it has a good film of heat sink grease under it...those modules don't tolerate heat very well.
 
makomark said:
I doubt your coil is the issue...regarding the testing done, most DVM are not very accurate when they get into the single digit range for resistance.

You can always remove the module and ensure it has a good film of heat sink grease under it...those modules don't tolerate heat very well.
Click to expand...
I have put fresh thermal paste. About to test with a second multimeter.
 
I have found a short in my tachometer signal wire.
Also my MAIN COIL is GOOD. It tested 0.4 ohms on both ends with my other Multimeter and it tested OK. Multimeters should come with a 1ohm resistor to test them.

Could a shorted tach signal wire cause the module to throw off the timing? I just figured the module sent a signal to the coil (one way).
I looked at the wiring diagram and it seems to just go from main COIL to a TEST LEAD to a HARNESS PLUG to the TACH. So nothing else should be on that wires path. Nothing plugged into the lead, but shorted somewhere. I will start tracing it to find the short.

Could this be my problem or is this just a new issue I discovered??
 
"shorted tach signal wire"....highly unlikely. Depending upon what that wire is shorted to could adversely impact the spark generation.

"shorted' could be a by-product of how the measurement was made.
 
makomark said:
"shorted tach signal wire"....highly unlikely. Depending upon what that wire is shorted to could adversely impact the spark generation.

"shorted' could be a by-product of how the measurement was made.
Click to expand...
I measured continuity from unplugged tach signal wire to unplugged at the coil harness and at the tach test terminal. So seems like a legit interruption there. But regardless of suspecting that I did not measure this right, what do think is the problem?
What would cause the timing to jump 6ATDC steady and knocking, after several minutes? Tach wire or not something is causing this.
 
"continuity" is a different concept than a "short"....but that's a different issue.

In the stand-alone EST system (no ECU), with a good pickup coil and a true running distributor shaft, the only item that varies the ignition timing is the module. Change it and see if the timing still retards...
 
makomark said:
"continuity" is a different concept than a "short"....but that's a different issue.

In the stand-alone EST system (no ECU), with a good pickup coil and a true running distributor shaft, the only item that varies the ignition timing is the module. Change it and see if the timing still retards...
Click to expand...
Ok not a short on the signal wire, but not a un interrupted loop from end to end. I didn’t check ground, or for voltage on the line.
I was thinking the same thing, the module (glad to hear some confirmation with that thought). I have one on order.

The pickup coil is pretty crusty, but within spec on the low end 850. I think the range was 500-1500.

I read a shorted tach signal wire could cause an issue with ignition. Maybe not possible on my EST ignition I don’t know. But there seems to be a break somewhere on the tach signal wire. If there is voltage on the line maybe it could make it back to the module..? Probably not great for the ignition coil anyway. I figured it’s just best to just figure it out. It’s possible another wire might be affected with tach signal wire, so worth taking a look. Part of this 1997 resto process I guess.

The module plugs pins were all really flared open wide. I popped them all out and tightened them up just in case maybe I had a loose connection.

Thanks for your input on this. Unless there are other thoughts, I am fixing tach signal wire, and replacing the module. I will check timing again and follow up in a couple days.
 
When the tach causes issues, it typically has an internal failure and will keep the ignition from creating its high voltage pulses (vs altering the timing of those pulses). It's never a bad idea to disconnect the tach lead when troubleshooting an ignition problem.

As far as the tach wire itself, it should have continuity from the coil to the tach and should NOT have any continuity to ground (or any other circuit)...and of course the tach wire needs to be isolated (disconnected on both ends) to make that measurement.
 
makomark said:
When the tach causes issues, it typically has an internal failure and will keep the ignition from creating its high voltage pulses (vs altering the timing of those pulses). It's never a bad idea to disconnect the tach lead when troubleshooting an ignition problem.

As far as the tach wire itself, it should have continuity from the coil to the tach and should NOT have any continuity to ground (or any other circuit)...and of course the tach wire needs to be isolated (disconnected on both ends) to make that measurement.
Click to expand...
Ok, good to know. So it sounds like this is not causing the timing to change. So module still the most likely cause.

The diagram does not show a resistor on the signal wire, so there should not be resistance on the wire when disconnected on both ends. This measurement shows not an insignificant amount of resistance. I have a multi meter on both ends of the wire, disconnected at both ends. So what the correct deffinition of this problem I do not know certainly. I understand the signal wire is not a circuit, but it could be bridging into another circuit causing a short.. I think I said that correctly. I want it fixed either way :).
 
Markomark, thanks for your input! I do not want to sound like I am arguing. More like clarifying or asking questions. Again, I appreciate it. This is what I was looking for ultimately.
I will follow up when I get this worked out a little further.
 
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