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Indmar Monsoon 320 bogs down


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I have a 1999 Wakesetter 21 VLX with an Indmar Monsoon 320 engine. Beginning with the first run after winterization last summer the engine would start and run fine for about 10 minutes then the power would reduce to idle. The engine would bog down and run rough. Reducing the throttle to idle for 1-2 minutes would cure the problem. I could then accelerate back to cruise RPM and the boat would run great until repeating the same sequence in another 10-20 minutes. It seemed we could avoid the problem if we ran with the blower on all of the time. This year started with the same issue, only now it happens regardless of whether the blower is on or off. Over the course of the last two summers I have had the boat to two Indmar dealerships and have spent over $2000 with nothing to show. The engine is not throwing off any codes. We've replaced both fuel filters, fuel pickup line, ignition module, coil, removed the floor and thoroughly checked entire fuel system for any venting or line issues, cleaned fuel pump inlet screen, new distributor cap and plugs, and probably a few other things. Fuel pressure is a steady 42 until the bogging occurs, then it fluctuates wildly between 40-50 until I reduce to idle for a couple of minutes. Then it settles back to a steady 42. The mechanic told me when the problem happened with his computer hooked up the timing was jumping between 8 and 24. Shop is leaning towards a new ECM. I would spend the money if that would fix it but I am doubtful. Shop has offered me $8500 towards a trade on another boat. I hate to throw the towel in and give up a 20k Malibu but I am at a loss for a better option to salvage the summer and stop the bleeding. Anyone have any ideas or want to up the offer? The boat is in Virginia. I have to make a decision soon.

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9 hours ago, Dadof3 said:

bog down and run rough

what rpm did this result in?

iirc "limp mode" is in the 3000 rpm range.  it's forced by the ecm because of a high temperature indication and/or, perhaps, a few other sick inputs (tps?, ??).

if your "reduce to idle" is not in that 3000 range then this is likely a red herring.

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Typically when the engine cuts back to idle power it is when we are cruising in the 3000 - 3400 RPM range. It has also occurred at higher RPM but I don't recall it ever happening below 3000.

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The fuel pressure fluctuation is probably normal because the fuel pressure regulator is referenced to the intake manifolds pressure, while the gauge used to measure is referenced to atmospherics pressure.  This is done to keep the same pressure across the injectors at any throttle position (or vacuum level).

You could try the old trick of unplugging various sensors (map, tp, temp , etc) one at a time.  This will do 2 things, set a code to verify the wiring/MEFI, and the MEFI will substitute a "middle of the road" senor reading which should cause the engine to smooth out if the sensor was giving bad readings.

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No clue on a bad ECM, except that from what I understand, they can be quite expensive for older models like ours, as they are no longer in production...as such, I'd make sure to eliminate all other possibilities before going that route.

Just a question: I see you replaced a lot of things such as distributor cap and plugs, but no mention of spark plug wires or rotor?  I would assume a rotor came with the cap but either way I would definitely replace those too if you didn't.  Also inspect the low-voltage wiring going to the coil from the ignition module; someone found that out here recently.

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  • 2 weeks later...

The next thing I would do is buy a complete distributor and put it in.  There is more that can go faulty with a distributor than just a cap and rotor.  I don't know how to set the base timing on the Mefi ignition system so make sure you mark the rotor position as well as the distributor position.  You can get a complete distributor from NAPA.  A Complete distributor should be less than a couple hundred. 

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Sorta of the same thing happened to me on my boat, ended up being a bad raw water pump impeller caused it to go into Limp mode after it heated up. I couldn't go over 10 mph until the engine temp dropped. 

Not sure if the shop has alternative motives by not fixing it and low baller you? Maybe try another place?

Do the simple stuff first(Check list).

Plugs, Wires, Fuel Filter, Cap, Rotor. Clean Flame arrestor, Water Pump Impeller, Timing, Check Fuel pump(Pressure and screen),

Then goto next level:

Clean Injectors, Compression Leak Down Test.

If problem still exist then your into deeper items and thats where the ECM, bad distributor and such become a discussion. 

 

Edited by mgb1974
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  • 5 years later...
Jpandson515s

Hello it's been awhile since this post originally posted but I was hoping someone could help me out. I have a 1996 malibu sunsetter vlx with the 320 monsoon efi with 662 original hours. Took it it out yesterday and it started fine idled fine. But couldn't get over 1900 rpms. Noticed a leak at the back of raw water pump at the rear seal... I recently did a tune up new fuel filters new fuel pump new spark plugs and wires. New distributor cap and rotor. New impeller. New water pump new thermostat. Changed the oil and filter. Drained all the fuel completely aka Took tank out of boat. I am at a loss. Really hoping for a simple fix. Any info at all is much appreciated.

 

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4 hours ago, Jpandson515s said:

Hello it's been awhile since this post originally posted but I was hoping someone could help me out. I have a 1996 malibu sunsetter vlx with the 320 monsoon efi with 662 original hours. Took it it out yesterday and it started fine idled fine. But couldn't get over 1900 rpms. Noticed a leak at the back of raw water pump at the rear seal... I recently did a tune up new fuel filters new fuel pump new spark plugs and wires. New distributor cap and rotor. New impeller. New water pump new thermostat. Changed the oil and filter. Drained all the fuel completely aka Took tank out of boat. I am at a loss. Really hoping for a simple fix. Any info at all is much appreciated.

Test the fuel pressure at key on, idle, and wide open throttle.  They should all be around 42 PSI.

Did it work OK before all of the work, or did you do the work because it wasn't running well?

You can change the seal at the rear of the pump fairly easily if the bearings are OK.

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BoatDoc

Have you tried fresh good gas?  Have you tried running the boat with the engine cover off or up to allow free air flow? (just incase the stringer vents are plugged)

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