1997 Force 40 HP One Cylinder Not Firing

[fatlaz]

I have a 1997 Force 40 HP. This motor has 2 cylinders. Cylinder 1 fires and cylinder 2 does not. When I swapped the CDM from cylinder 1 to cylinder 2, cylinder 2 fires and cylinder 1 does not. I swapped both the input and the spark plug. So, I figured the CDM on cylinder 2 is bad and I bought a new replacement CDM. Put the new CDM on Cylinder 2 and cylinder 2 would not fire. When I put the new CDM on cylinder 1 it does not fire. The original good CDM still makes both cylinders fire with the "bad" CDM in the other position. I thought I must have got a bad replacement CDM, so I sent it back to the manufacturer who tested it and said it passed their tests and sent it back to me. It still doesn't work. I'm swapping the input and the spark plug wire each time. Before starting it up this spring (this boat was new to me this Spring) I changed the spark plugs from the original NGK to a j-style spark plug that crosses to the NGK.

What am I missing? Is there something that would make the original good CDM work on both inputs, but no other CDM?

 

[jerryjerry05]

Try this Force with Mercury Designed Ignitions (1992-1999)
Two Cylinder Engines Using a Separate Switch Box and Ignition Coils
No Fire At All: Disconnect the black/yellow kill wire AT THE PACK and retest. If the engine’s ignition fires now, the kill circuit has a fault-possibly the keyswitch, harness or shift switch. Disconnect the yellow wires from the stator to the rectifier and retest. If the engine fires, replace the rectifier. Check the cranking RPM. A cranking speed less than 250-RPM will not allow the system to fire properly. Check the stator resistance and DVA output as given below:
Motors with Black Stator
	Wire	Read To	Resistance	DVA
	Blue Red	Blue/White Red/White	3250-3650 75-90	180V or more 25V or more
Motors with Red Stator
	Wire	Read To	Resistance	DVA
	White/Green	Green/White	500-700	180V or more
Red Stator Adapter
	Wire	Read To	Resistance	DVA
	Blue	Engine Ground	Open	180V or more
No fire or Intermittent on One Cylinder: If the cylinders are only acting up above an idle, connect a inductive Tachometer to each cylinder in turn and try to isolate the problem cylinder. Check the trigger resistance and DVA output as given below:
	Wire	Read To	Resistance	DVA
	Brown wire (#1) Brown wire (#1) White wire (#2)	White wire (#2) Engine GND Engine GND	800-1400 Open Open	4V or more 1V or more (a) 1V or more (a)
This reading can be used to determine if a pack has a problem in the triggering circuit. For instance, if you have no fire on one cylinder and the DVA trigger reading for that cyli?lder is low — disconnect the trigger wire and recheck the DVA output to ground from the trigger wire. If the reading stays low — the trigger is bad. Check the DVA output on the green wires from the switch box while connected to the ignition coils. Check the reading on the switch box terminal AND on the ignition coil terminal. You should have a reading of at least 150V or more at both places. If the reading is low on one cylinder, disconnect the green wire from the ignition coil for that cylinder and reconnect it to a load resistor. Retest. If the reading is now good, the ignition coil is likely bad. A continued low reading indicates a bad power pack.
Engine will not rev beyond 3000-4000 RPM: Connect an inductive Tachometer to each cylinder in turn and try to isolate the problem. A single cylinder dropping fire will likely be the switch box or ignition coil. All cylinders acting up usually indicate a bad stator. Connect a DVA meter between the stator’s Blue wire and Blue/White wires. Perform a running test. The DVA voltage should jump up to well over 200V and stabilize. A drop in voltage right before the problem occurs indicates a bad stator. (Blue to Engine GND if the engine has a Red stator kit installed). Connect a DVA meter between the stator’s Red wire and Red/White wires. The DVA voltage should show a smooth climb in voltage and remain high through the RPM range. A reading lower than what is on the Blue wire indicates a bad stator.
High Speed Miss: Connect an inductive Tachometer each cylinder in turn and try to isolate the problem. A high variance in RPM on one cylinder indicates a problem usually in the switch box or ignition coil. Occasionally a trigger will cause this same problem. Check the trigger as described above under “No fire or Intermittent on One Cylinder”. Perform a high-speed shutdown and read the spark plugs. Check for water. A crack in the block can cause a high speed miss when the water pressure gets high, but a normal shutdown will mask the problem. Remove the flywheel and check the triggering and charge coil flywheel magnets for cracks or broken magnets. No Fire At All: Disconnect the black/yellow kill wires from the harness and retest. If the engine’s ignition fires now, the kill circuit has a fault-possibly the keyswitch, harness or shift switch. Swap the White/Green and Green White stator wire and retest. If the problem moves to the other cylinder, the stator is likely bad. Disconnect one CDM module at a time and using a set of piercing probes and jumper wires- short the stator and trigger wires to engine ground. Retest. If the other module start firing, the one you unplugged is bad. Disconnect the yellow wires from the stator to the rectifier and retest. If the engine fires, replace the rectifier. Check the cranking RPM. A cranking speed less than 250-RPM will not allow the system to fire properly. Check the stator resistance and DVA output as given below: Wire Read To Resistance DVA White/Green Green/White 500-700 180V or more No fire or Intermittent on One Cylinder: If the cylinders are only acting up above an idle, connect an inductive Tachometer to all cylinders and try to isolate the problem cylinders. Using a set of piercing probes, check the trigger DVA output as given below: Wire Read To Resistance DVA Brown White Brown White Engine Ground Engine Ground 800-1400 Open Open 3V or more 1V or more 1V or more If # 1 is not firing, swap the White/Green and Green White stator wire and retest. If the problem moves to the #2 cylinder, the stator is likely bad. If no change, swap locations with #2 and see if the problem moves. If it does, the module is bad. A continued no fire on the same cylinder indicates a bad trigger. High Speed Miss: Connect an inductive Tachometer to each cylinder in turn and try to isolate the problem. A high variance in RPM on one cylinder indicates a problem usually in the trigger or CDM module. Perform a high-speed shutdown and read the spark plugs. Check for water. A crack in the block can cause a high speed miss when the water pressure gets high, but a normal shutdown will mask the problem. Remove the flywheel and check the triggering and charge coil flywheel magnets for cracks or broken magnets.

 

[fatlaz]

As I see it, since my engine will rev above 3000-4000 rpm in neutral, I don't have a high speed miss and I always have a one cylinder not firing I need to swap the White/Green and Green White stator wire and retest. What's the best way to do this? Be gentle, it's my first summer with a boat.

 

[jerryjerry05]

The sickest of motor can run 3000 in N.
Do a compression test.
They sell a spark tester that measures the strength of the spark.
$6-7 at Auto Zone or any auto parts store.

 

[fatlaz]

I really appreciate your help! The motor will actually go 6000rpm + in N. I assumed it would only go 3000 rmp in WOT because I only have one cylinder firing.

 

[pnwboat]

Something you need to be aware of. The bad CDM may be the one that actually works! The ignition kill circuit in each of the CDMs are all tied together with the Black/Yellow wires. There are some components in each CDM that isolates the ignition kill circuit from the other. If it fails, it may interfere with the other CDM and cause it to not produce any spark. If the isolation component in the original #1 CDM has failed, it might prevent the #2 CDM from working. Try replacing the original #1 CDM and see what happens.

 

[fatlaz]

That was it...replaced the other CDM and now both cylinders fire. I bought the cheap spark tester from Autozone so it was easy to tell I had spark in both cylinders. Now my boat goes about 75% faster.

 

[pnwboat]

There you go! Happy boating!