1994 3.0L No Spark

[mugwump4]

1994 Mercury 225HP, 3.0V6, Carb model. The boat sat for most of the summer unused so I went to add some fuel stabilizer and run it (South Florida winterization) and I now have a no-start condition.

It's been upgraded to the newer Merc CDMs. The stator is at 1170 ohms for all 6 cylinders (+/- 10 ohms) measured at the CDM connectors. I have the forward harness disconnected at the large cannon connector to rule out the ignition switch or kill switch. All 6 coils are disconnected, connecting them one at a time does nothing. The ECU is disconnected. The shift kill switch is disconnected. There is no continuity on the ground circuit (BLK/YEL wire) to ground. And absolutely no spark on any cylinder.

My understanding is that even with the ECU disconnected, it should throw a spark at base timing just off the stator.

My tach reads 200 RPM while cranking (with the ECU plugged in), so I'm ruling out the 12V to the ECU, the ECU itself, and crank sensor as contributors.

What am I missing? I'm going to throw the batter charger on it. CDM's troubleshooting guide says I should have 250RPM when cranking. It doesn't seem to be cranking any slower than usual; will this really make that much of a differnce?

Thanks in advance for any suggestions. I do have a spare stator and ECU I can throw at it, but I'm not convinced either is giving me a no spark on any cylinder condition.

[OnPad]

Get yourself a dva for your multimeter or some sort of peak voltage device to test stator. If that checks out good let me know, and I'll get a magnifying glass and try and read my wiring diagram.

[OnPad]

When disconnecting "forward wiring harness", you would have to apply 12v to purple on engine harness to get power at ecu. Might be a good wire to check out, without good power to ecu, your dead in the water. Also check your stator plug.

I think you can dva stator without special wiring adapter by testing each individual green/whatever tracer color wire that goes to your cdm's. It also might be possible for dva test on white/whatever trace color, checking for trigger voltage out of ecu.
You might also ohm check your cdm's.

Disclaimer: Don't take any of this advice as gospel, I'm just a dumb logger, not a merc tech!

[Chaz]

Same as Pad posted ... I would check the trigger eye as well.



CDM test ..



Stator OHM test ...

[sonicss33]

You probably did this already but just in case you didn’t, did you check the in-line fuse holder near the Switchboxes?

[mugwump4]

Waiting on a better DVOM to arrive, and I’ve been out of town all week. Hopefully I can get some answers next week.

Please explain the power to the ECU - my understanding is that it will run in base timing with no ECU. I had the ignition switch short on me a few miles offshore. I had been chasing an intermittent stall at cruise and it finally just died. Unplugged the forward harness, hit the starter with a remote start switch and she came back to life. So I know it will run without the ECU. As I said, and per the Mercury manual, if the tach is working the crank sensor (trigger?).

I’ll get the batteries topped off and some tests run soonest! Thanks for all the support!!

[OnPad]

I noticed the cdm driver (trigger) wires start at ecu, on wire diagram. I just figured it wouldn't work correctly without ignition power. Not a circuit board wiz, so maybe your right.
My bad, I was looking at wire diagram for a 95, looks like 94 is a little different. Are your driver wires, (white/colored strip), attached to your stator plug? 95 they are not.
1994 carb
1995 carb

[Chaz]

I noticed the cdm driver (trigger) wires start at ecu, on wire diagram. I just figured it wouldn't work correctly without ignition power. Not a circuit board wiz, so maybe your right.
My bad, I was looking at wire diagram for a 95, looks like 94 is a little different. Are your driver wires, (white/colored strip), attached to your stator plug? 95 they are not.
1994 carb
1995 carb

I wouldn't think that the motor would run without the "ignition control box" .. but the early motors do have a stator and field coils .. so anything is possible.
If I wanted to take the boat side out of the equation, I would just use a "repo-man" switch. If I needed to test the ign box .. I would try a different one.

[PanRonnie]

the 1994 has a limp home option they removed that in 1995 and on
you could have a pulse for your tach from the alternator but don,t know that forsure
tha big black squere is a technicians guide pdf for all engines
the crank sensor is a 2 wire sensor so that would mean it is a VR sensor no power required it generates an AC voltage wave pattern as tooth pass
so it does not have to be powered by the ecu to run

[mugwump4]

It’s been more than a few weeks, here’s todays update:

I bought a DVA that wound up not working. It will only display millivolts on the meter.
I decided to start over and began with stator winding checks. #2 cylinder reads megaohms, OK. Now we’re getting somewhere. Not convinced that one winding should kill the whole ignition, tho.

I did recheck the ground circuit and found that all 6 coils read 1M ohms on the blk/yel ignition kill circuit to ground. With all 6 coils connected I have about 1-2M ohms, and zero with all 6 coils disconnected. So I’m pretty confident at this point that for some reason the stator has one open winding. Not sure why I didn’t find that last time, but it’s a direction. And I have a spare.

When I bench check the spare, I get 5 within specs and the same #2 reading 8600 ohms. Way too high. So now I’m thinking that I don’t have a defective stator. But it seems odd I have two with the same failure mode. And neither failure should take out the entire ignition system. (To clarify: the failure is #3 on my sketched connector pinout legend, but actually is wired to #2 coil.

I can back out the two leads for the suspect stator winding and retest the stator on the motor, but I’m just about convinced there’s another failure mode here we haven’t identified. I’ve included photos of the bench test measurements.

I welcome your feedback! I also checked the crank trigger to verify both the DVA wasn’t working and that the resistance was correct.

[OnPad]

You do realize that you have to crank engine to get dva readings on stator, and trigger coils?
Play with your dva some more. Not alot to go wrong with one. A capacitor and diode, I believe.

The only (bad) stator I tried ohming out was all over the place. I hooked 3 different meters to it and got different readings out of all of em. On the problem windings anyhow. Dva is mucho better test process.

[mugwump4]

I thought of one more thing to eliminate so I made some jumper leads to connect a CDI directly to a stator bobbin.

Two different CDIs connected directly to three different bobbins (each) and no love. So I have 6 bad CDIs or a bad stator. I want to recharge the batteries and repeat the test but I’m about convinced I have a bad stator.

My only holdout is that the stator is relatively new. I swapped it out from the spare parts motor a few years ago trying to diagnose an intermittent no spark issue that turned out to be the ignition switch (see above) so I do know the one I bench tested worked when it was removed.

[mugwump4]

You do realize that you have to crank engine to get dva readings on stator, and trigger coils?

Yes. It was 0V DC until I started cranking it. It wouldn’t read more than 2mV. across 6 stator bobbins and the crank trigger. The stator was unplugged and I was checking the stator side, not the engine harness side. I’m sending it back.

[OnPad]

Shift interrupt switch will kill spark on 2,4,6.
One bad cdm kill circuit, will affect the bank that it is on 2,4,6, or 1,3,5 .

Manual states that cdm modules are triggered by ecu under normal conditions, in the event of ecu failure, by the stator.
Not sure why your getting resistance from stator thru kill circuit. Unless your shift interrupt was activated, and then it would only be three cylinders. Or your kill wire was grounded by ignition or kill switch, affecting all 6.

Manual also states if tachometer is reading properly, then crank position sensor is functioning normally.

Sounds like you know most of this stuff.
If your getting bad resistance readings on one bobbin, it sounds like a bad stator, not sure why it causes havoc with the other 5, maybe grounding. Which is why its bleeding into your kill circuit.

[mugwump4]

I bought one of these:https://www.esitest.com/640.html

I'm going to reach out to them directly and see if they can assist with troubleshooting why it isn't working correctly.

I'll keep updating this thread until we get it sorted out. Hopefully it will help someone in the future!