2001 Monsoon (GM 5.7L) bogging down at high RPM

[Garry]

2001 VLX (1200+hrs), indmar Monsoon /GM 5.7L, original owner.

Boat ran fine when launched in May.  starting 2 weeks ago (after motor was was at-temp), I noticed loss of throttle above 4000RPM - Changed fuel filter, ran fine. 

A few days later, after idling around, throttle had nothing above 4K (again), pulled filter into glass (all clear), blew tank line (no restrictions) reinstalled, ran fine for 10 minutes then started bogged down above 4k.   The longer the motor ran the lower the throttle range went when it bogged down, finally happening around 3000k.     Swapped in another fuel filter, and had a spare ICM onboard so swapped it to eliminate that (2 have died in 22 years) just to eliminate it, no change in behavior (no surprise).  The symptoms seem related to motor run-time/temp, E.G. the longer I continually run the motor, the lower the bogging symptoms start...

I purchased a fuel pressure gauge the next day, connected to valve on fuel rail (this is the original fuel pump).   key-ON PSI jumps right to 42PSI, pumps does its typical 'wine' for 3seconds then off.  At Key-OFF, Pressure slowly drops 1-2PSI per minute (seems reasonable).   Key-ON, jumps to 42PSI, Motor-ON drops to 35ish PSI at idle (seems low).  At dock/in Neutral, revving the motor to 15OO+RPM PSI drops to lower 30's (32-33).   Since I didn't have anyone around to help, was not able to test the PSI with boat underway. 

At this point it feels like a slowly-failing fuel pump, and the last few years the fuel pump 'wine' has become more annoying, FWIR in the forum the 1997-2003  fuel pumps are common failure, so Ive got my money worth out of the factory fuel pump at this point...  Have ordered a replacement fuel pump (Indmar #495117 conversion kit) which is due into tomorrow.  I'm hoping the switchover goes smooth, I really don't like performing fuel plumbing/replacement while in the water (one big wave can make a mess) on a V-drive configuration ... 

While I'm waiting, I though I would throw it out there on this forum for any other thoughts or Diagnosis test suggestions...   My only other thought - I have not tested the fuel regulator bypass, which is  mounted on the intake manifold/fuel rail, has a vacuum line running to the top of intake manifold/base of air metering setup, and a high-pressure line back to the fuel pump bracket (E.G. bracket pass-thru to the fuel tank return, according to the conversion kit documentation).   Im sure others have experienced similar symptoms, so appreciate any other diagnosis tips & suggestions.  

Cheers 

Edited July 4, 2023 by Garry
wording correction

[justgary]

It is also possible that the inlet screen to the pump is clogged with crud.  You should be able to pick the screen out of the inlet pipe and clean it.

[Garry]

Success, The OEM Fuel pump was bad.   a few notes about the conversion kit switchover:

• I disconnected the fuel lines (at the gas tank & filter, and at the fuel rails) and removed the entire fuel pump with lines in one piece.  It was much easier to work on once it was out.
• I recommend replacing the gas-tank-side fuel lines while the pump is out. mine were 22y.o. and showing their age, besides it was easier to access to the 2 hangers down in the bilge when the Fuel Pump is out.
• the Fuel Pump IN nipple was noticeably larger than the 3/8 fuel line, it took allot of effort & WD40 to get it on. (do they really run 1/2" line to the tank now??)
• the conversion-kit 2-wire pigtail connector DID NOT work with the existing wiring harness connector.  I called Indmar tech. support to verify, the factory tech. (Al) said "Yea, that happens, just cut bot hwires and butt-splice the wires together they are color-coded".  My reply was "Really, cut a perfectly good engine wiring harness?", he laughed and said "yup, ti happens".  Went ahead with it (I have NEVER  hacked up a factory wiring harness...) so checked that off my bucket list LOL...

Once reassembled I did the (Key-on, Key-off) cycle a few times to pressurize the rails.  She fired right up with no issues.  Ran it for 30minutes, no more fuel pump wine, its all good now!

This fall, I'm going to do a P.M. replacement of the Fuel Pressure Relief valve (Indmar #661111), as I noticed when researching online they are getting hard to find, and NAPA could not cross-reference it (to a GM 5.7L equivalent).  if anyone finds a cross-reference for the part, please let me know.

Enjoy the rest of your summer!

[agetech30]

You can use a fuel pressure regulator from a 96 corvette, $40-$50 at any parts store.  There is no difference to marine regulator.

[Garry]

@agetech30:  Thanks, I asked my local NAPA guy to grab a F.P.regulator for a 96 corvette, but it did look like the pressure regulator in the boat (only 1 bolt 'ear', mine has 2).

 

[agetech30]

On 7/9/2023 at 2:38 PM, Garry said:

@agetech30:  Thanks, I asked my local NAPA guy to grab a F.P.regulator for a 96 corvette, but it did look like the pressure regulator in the boat (only 1 bolt 'ear', mine has 2).

 

Does it use 2 bolts?  Could have 2 ears for mounting either direction.

[Garry]

@agetech30Im about to winterize so when Im "under the hood" will pull it apart for a closer look.  Thanks for the suggestion.

 

[Sasquatch]

Garry..I too have a 2001 VLX (1200+hrs), Indmar Monsoon /GM 5.7L, original owner.

You mentioned a fuel pump conversion kit for your boat. Could you please provide the vendor and part number for the conversion kit? I'm considering replacing my fuel pump as well.

[BlindSquirrel]

paging @Garry

[Steve B.]

Might be something like this. Give these folks a call, or skidim, or bakesonline.

fuel pump