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1996 Mercury Offshore- Losing my mind and need help!!!

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Fletcha221

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Started this under another thread where I was certain I had a bad stator, unfortunately, that's not the issue. My mechanic seems to think the flywheel has gone bad (apparently magnets are glued into the flywheel? He seems to think one magnet came loose? If you read below, I THINK its the last logical thing that could be causing the issue.

Has anyone experienced this?

When we broke down, running at 4k rpm, engine just stopped. There was no poor running, just stopped like someone turned the key to "off".

When starting from "cold" the motor comes to life for a split second (sometimes) and hunts around and stalls. It wont stay running. All cylinders have spark (but I'm guessing the timing is off or the spark is weak), all cylinders have equal PSI. There is fuel, and all floats in the carbs are working correctly.

The house systems on the boat are 100 percent mutually exclusive from the engine (Besides the 12v key wire powering the Gauges , I have completely removed the neutral safety switch, and replaced the key switch.

The batteries are good, all grounds and hot leads are clean and secure. (cleaned and retightened). The ground straps for the ECU are clean and tight as well. I pulled a gallon of fuel, there is no water in the fuel. All coils are tested. Carbs have been rebuilt, and did a link and sync on the carbs and I have replaced the following:

1. Crank position sensor (correctly gapped to factory spec)
2. NOS matching CDM (ECU)
3. Tested used stator
4. Mercury Key switch (Ignition)
5. Starter Solenoid
6. Starter
7. Plugs
8. Fuel Pump

It has fuel, spark, and compression......it just wont run. Just sputters, hunts around in RPM then dies, within 5-10 seconds.

I seriously can't think of anything else that could be wrong with the motor, besides it being a Mercury:)

HELP!!!!!
 
I actually have not checked the TPS. I bought, what I thought was the correct diagnostic harness. The hope was that I can plug it in and make sure the resistance on the TPS is within spec, for whatever reason it doesn't fit the connectors. I unplugged it completely and plugged it in, and there is no noticeable difference in regards to getting this thing to run. However, it may have have failed open, so you may be on to something.

in regards tp the flywheel, the thing looks like there is a metal ring on the inside (the part that passes over the stator bobbins). Does this dictate the timing? Just thinking if it came lose and clocked itself + or - and the EDU can't make sense of the signal.

Lastly, the batteries. Ignition on, we are around 12.6V. When running the motor always made 13-15V and kept the batteries strong. I know the EFI version wont run on weak batteries, is it possible this is the case here? The most simple explanation would be that the batteries are strong enough to turn the motor over, but not enough "juice" to properly power the ECU? As Faztbullet explained to me, these early 1996 models would run, even if the CDM failed. It was designed to run strictly off the stator. Will a rope start on a dead battery get this motor to start? If not, I'm wondering if (as in most cases) the simplest explanation is the culprit.....
 
The timing is controlled by cast in teeth on outer edge of flywheel and CPS....I am sure you have you checked flywheel key?
 
I have checked the key, all is good in that regard. Busted off enough keys on smaller outboards using a drill to start them:)


The CPS is used and off a friends boat (replaced hos trying to hunt down a performance issue). I'm not ruling out that it's broken as well. I just want to get everyone's insight before I start throwing parts at a problem.....again:)
 
UPDATE: ISSUE SOLVED

replaced the CPS and TPS, no change. Decided to start getting into the wiring, pulled the loom apart and inspecting the wires. I decided to try and start in (thinking maybe there was a bad wire grounding) and sure enough, she came to life and runs perfectly. There is a break between the main engine plug, and the ignition. Also did some resistance tests from the stator to the ECU, and from the ECU to the coils. The numbers were all over the place.

Basically, the ENGINE HARNESS IS SHOT.

I'm just going to bite the bullet and replace the harness. Everything else is basically new at this point:)
 
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