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wiring diagram for '03 Indmar 335 Monsoon in a Malibu Sunscape 21 LSV


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Does anyone know where I can get a wiring diagram for my Indmar engine? Indmar has been pretty unresponsive. 

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29 minutes ago, Loshie1056 said:

Does anyone know where I can get a wiring diagram for my Indmar engine? Indmar has been pretty unresponsive. 

You can find it in the MEFI service manual for your version of ECM.  You should be able to download a PDF.

PCM is easier to find than Indmar usually, but the manual is essentially the same.

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The problems have been associated with the engine running very rough, throwing alarms, rpm erratic. I have had four different boat shops look at it. The Malibu dealer was first and they reluctantly took a look because it is older and most the big shops won't take it because of age. They said they didn't have a code reader for the MEFI 4 ECM but suggested I send it to LA to a guy who specializes in ECM diagnostics and repair. I did, and he said there was only one code, which he cleared and reset the software and send back. After reinstalled, same problem. Had one guy take a look at the wiring harness and he gave up on it. I have changed plugs, distributor rotor, cap, ignition module, checked fuel pressure, almost every sensor except the knock sensor and the last guy I had look at it said he thought it was the ECM and felt somehow it was being corrupted by the wiring system somehow. I actually have a spare ECM and it didn't solve the problem either. He didn't think it was the gas or the fuel pump. I bought some software to read the ECM and saved some files on my computer but I am not experienced enough to interpret all the data, but still can't get anyone to look at it. I don't want to spend a bunch of $$ on a new reconditioned ECM assuming I can find one, and discover it doesn't solve the problem. I am going to drain all the old gas and replace with new, along with a new knock sensor and retry. I'm really grasping at straws here. The boat is in good shape by useless in it's current state. Any suggestions are appreciated.  

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Since you have the software to read ECM data, download the manual and go through the diagnostics.  You can also upload some data here (as lists or plots) and maybe we can help you.

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^^^Same diagram that's in Clymer's manual.^^^

Have you checked your ICM and give the distributor a good looking in? Did you test your coil?

Edited by electricjohn
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Thanks for the input. I had both ECM's gone through by OBD Diagnostics in LA, who sent them back, supposedly good to go. I tried both ECM's and the same issues were occurring so that is when I purchased the software and started to read the data myself. I don't know enough about the data to properly diagnose and the last mechanic wasn't interested in my old data and wanted to read their own, only they didn't share their data, they just said it was throwing lots of codes and they were different with the different ECM's and thought somehow the wiring was corrupting the ECM? 

I did not test the coil. I replaced the cap and rotor and ignition control module. I also replaced the engine coolant sensor, MAP sensor and throttle position sensor. The following are links to some files with videos and screen shots of the ECM data. 

https://www.dropbox.com/scl/fi/he7a6oaclakmksb45rui6/IMG_9837-1.MOV?rlkey=1yszbf6am2hf87hqbf1cagvxi&dl=0

https://www.dropbox.com/scl/fi/6ry4iwkay2zpk4g1rb0yw/IMG_9833-1.MOV?rlkey=kixguitg734q4gw6ukahift25&dl=0

https://www.dropbox.com/scl/fi/b3hacosew98gbcvexlctp/IMG_9839-1.JPG?rlkey=r6c5977rp677krfcqy5qsd2yd&dl=0

https://www.dropbox.com/scl/fi/yp0tfmb5vjq5gr83j3gg0/IMG_9835-1.MOV?rlkey=281ag2dhz4wweoyhl14hdo3vi&dl=0

https://www.dropbox.com/scl/fi/i8cdj4brp1j03n0t39r67/IMG_9838-1.JPG?rlkey=t0leql2mrf8md76mwf4kvd2m9&dl=0

https://www.dropbox.com/scl/fi/99eqjlwm3lgbqywe5pduk/IMG_9836-1.MOV?rlkey=966uu1501r1s20b36wuxbue0o&dl=0

https://www.dropbox.com/scl/fi/8ri5tv4b7ymq26q7cjtud/IMG_9834-1.MOV?rlkey=nxzgro6zdqv8t4jqm60ypjlbd&dl=0

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The RPM suddenly "jumping" to off-scale values strongly suggests a poor connection somewhere.  I don't recall if MEFI-4 uses a crank position sensor, but if so I would check the connector there first.  I would also remove and very carefully inspect the ECM connectors.  I had a mechanic do me a favor once on a Pontiac V6, where he probed the circuits at the ECM and bent several sockets in the connector.  In a right turn the connector would open for an instant, and the ECM would stop the spark (rev limiting) because it saw 10,000 RPM.  I only found it with a scan tool recording data driving until it happened.

The point is that you may have to use a dental pick to carefully reshape the spring portions of the sockets in your connectors.  Careful examination and comparison to good sockets is the best way to proceed.  It will stink to do it, but I would spend a few hours and check all of the connectors on the engine.

Everyone, please resist the urge to test sensors, etc. by jamming your test probes directly into a connector socket.

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There is no crank position sensor or oil pressure sensor on my '03 Monsoon 5.7. There is a <6 psi oil pressure switch though.

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Thanks. I will give those a try. Regarding Steve B. initial question, I am the original owner and it has always run well up until a couple of years ago when I was pulling up a heavier skier and the boat was lugging and unable to generate enough power. That is when I started on the plug and distributor route. After changing the plugs and such, it initially ran great for about 5 minutes and then started missing. I thought I had the firing order mixed up but that was all checked out and it was fine. The temp gage on the dash would also peg, but I checked and the water wasn't getting that hot, but i changed the impeller, inspected the housing and also changed the thermostat and sensor. Still the issues continued. That's when I started in with the mechanic's who couldn't figure it out. I agree it sound like some kind of short or bad connection but tracing it out is going to be a bear. I'll try the ignition coil test and the plug wires next, then the knock sensor. After that I guess I will tackle the wiring.  

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