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Old 12-13-2018, 10:34 PM   #1
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Default ECM/ICM fails after 20 minutes of cruising

Hey Folks. 1998 3000SCR with twin 4.3L Merc's. Bought the boat in fall, and have failed two Ignition Control Modules (ICM, Mercruiser P/N 8610460-1) now on the same engine. First was on maiden cruise back to my port, about halfway there, lost power, no spark, turned out to be the ICM. Replaced it, and took the boat out a few times, but just short journeys. Fast forward to last cruise of the season, I fail the ICM at the same halfway point as before. Both journeys that resulted in ICM failure were to be about 40 min total, and the ICM failed about 20 minutes after being underway. No other unusual engine conditions were noted while in operation.

I've read about the problem a bit, and most research seems to point to a bad connection somewhere in the engine wiring harness. I'm about to work on this a bit here, so my questions are:

1-Is this theory on track and does it make sense to you guys? Are there any particular connections more prone to failure in the engine wire harness?

2-Does it make more sense to just replace the harness, as opposed to digging around trying to troubleshoot it

3-Is there a recommended way to test this system to confirm the presence of an issue with the wire harness, or not?

Input appreciated. If anybody has battled this before, I'd be interested to hear of your experience.
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Old 12-14-2018, 12:23 AM   #2
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Just to be clear this is a MPI engine, correct?

Where is the ICM mounted? I would use a IR temp sensor and take reading to ensure the mount is not cooking the ICM. i.e. if mounted to exhaust elbow it may be running hot.

Not heard of a harness issue but then again I had not heard of many issues with the MPI other than IAC.
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Old 12-14-2018, 01:04 AM   #3
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Default ECM/ICM fails after 20 minutes of cruising

I just realized I totally biffed my initial post, I actually have the 5.0L engine, I'm not sure if that makes a difference on the MPI question. It looks like it is mounted on the exhaust. I have a failed part, I'm wondering it I disassemble if it'll give me clues between an electrical issue or a temperature issue.
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Old 12-14-2018, 02:41 AM   #4
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It sounds like it is getting over heated...
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Old 12-14-2018, 03:16 AM   #5
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Quote:
Originally Posted by rcsummers View Post
I just realized I totally biffed my initial post, I actually have the 5.0L engine, I'm not sure if that makes a difference on the MPI question. It looks like it is mounted on the exhaust. I have a failed part, I'm wondering it I disassemble if it'll give me clues between an electrical issue or a temperature issue.
Not unless you know how to do a DPA (destructive physical analysis) of the higher power components and some SEM (scanning electron microscope) images of the ingerared circuits. The module should be mounted on standoff’s.

How old is the exhaust?
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Old 12-14-2018, 12:20 PM   #6
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Default ECM/ICM fails after 20 minutes of cruising

Exhaust is original to the boat as far as I know, so it would be 1998. I"ll check on the stand-offs when I go out there tomorrow and then will reply back.
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Old 12-15-2018, 08:13 PM   #7
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Default ECM/ICM fails after 20 minutes of cruising

I took a couple of pictures today of the ECM. It is mounted on the exhaust column. It's mounted on an aluminum plate, which stands off the exhaust column by about 1/2". I thought I had put the new ECM on this engine when I replaced it the first time, but it looks like I had installed the port side engine ECM, and put the new one on the port (still operating). So both ECM's that failed are the old, original P/N 861460-1. Maybe it's just a timing thing that these both went bad around the same time? I didn't find any obvious loose or corroded connections in the wire harness.

Regarding the theory of overheating the module due to its location on the exhaust column, I never noticed any real difference in the operating temp of the engines on the dash. If stbd was cooking the ECU hotter than the port, wouldn't I see it there, or no?
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Old 12-15-2018, 08:19 PM   #8
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Helm gauges only give you the temperature of the engine at the thermostat housing which is the coolant leaving the engine. The exhaust components may be cooler or hotter, use a IR temp sensor to get real readings. Can you post a picture of the engine cowl, trying to determine if this is a throttle body EFI.
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Old 12-15-2018, 08:20 PM   #9
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BTY the elbow looks newer than the manifold and riser.
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Old 12-15-2018, 10:46 PM   #10
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Default ECM/ICM fails after 20 minutes of cruising

Mike, attached is a picture of the engine, sorry it's not very high res.

I also have a serial number: 0L063774
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Old 12-16-2018, 04:15 AM   #11
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Based on the serial number they are EFI throttle body engines. Throttle body looks like a carburetor but has two injectors mounted about where the choke would be on a carburetor.
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Old 12-17-2018, 04:06 PM   #12
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Thanks for that insight. So as far as a next step, should I just replace and then run the boat while getting some surface temp readings on the exhaust? Based on my issues I plan to keep a spare on board as well, but I really need to root cause this thing so I can get some confidence in my vessel.
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Old 12-18-2018, 12:09 AM   #13
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Unfortunately the only way to see if the exhaust is getting too hot is to run the engine. If the riser get to 150 F shut it down and replace the exhaust.
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Old 05-13-2019, 03:10 PM   #14
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Default Module Failure Update

Folks, had my first spring sea trail (finally!) and have some updates. I decided only to install the new ICM and then take some temp readings to see the result I got. Of note is that the first two failures were the old Merc P/N 861460-1, and I now have the 861430-T02 installed. I understand from research that the rev change added some resilience to the part both for engine heat and electrical fluctuation. I ran the boat for over an hour twice over the weekend, and did not fail the new ICM (YAY!!!!). However, after about 20 minutes I get a slight ramp, followed by a decrease in RPM (+/- maybe 200 RPM). The exhaust riser and the ICM temps are stable and comparable between port/starboard engines. I'm happy to have two good trials but I'd like to find the culprit of this RPM flux as I worry it is still stressing the system and could lead to failure at some point. Thoughts on a good next step here? Would an alternator produce this problem?
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Old 05-13-2019, 06:31 PM   #15
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Does the volt meter change readings when this occurred?
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Old 05-13-2019, 06:44 PM   #16
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Mike, no noticeable change in the voltmeter reading.
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Old 05-14-2019, 12:06 AM   #17
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Have you tried swapping ECMs between the two engines to see if the issue follows the ECM?
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Old 06-12-2019, 11:14 PM   #18
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Mike, I did not swap the ECMs, but now have been running for a few weeks and it seems (knock on wood) that the new P/N ECM is resilient enough to withstand any issues I had. Potential culprits still could be the ignition coil or maybe the alternator talking to some mechanics, but RPM variation has pretty well gone away and the new ECM has not failed. I think the updates made when they changed the part number made it stronger.
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Old 06-12-2019, 11:57 PM   #19
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Service manual 24 has an excellent guide on "testing the thunderbolt V ignition" which will help determine if problem is ICM, coil, or ignition sensor, or not. It also has the ohm ranges for checking the ignition coil. I had a recent ignition problem, and it helped me eliminate some ignition components and focus on other causes.
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Old 06-13-2019, 01:35 AM   #20
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Quote:
Originally Posted by rcsummers View Post
Mike, I did not swap the ECMs, but now have been running for a few weeks and it seems (knock on wood) that the new P/N ECM is resilient enough to withstand any issues I had. Potential culprits still could be the ignition coil or maybe the alternator talking to some mechanics, but RPM variation has pretty well gone away and the new ECM has not failed. I think the updates made when they changed the part number made it stronger.
Letís hope itís behind you.
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