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kosar

RPM Issue

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kosar

We have a 98 Sunsetter V-drive that has always held it's RPM's fine until this season. The boat will hold steady at any RPM level above 3000 or below 2700 RPM. Unfortunately, the exact speed it will not hold is what is needed for wakeboarding! As soon as the throttle is backed down slight below 3000 RPM it falls abruptly down to 2600.

So far, we have attempted to following to correct the issue to no avail:

- Replaced both fuel filters

- Replaced the knock sensor

- Replaced the throttle bushing

- Unhooked throttle cable from throttle arm and operator manually to rule out throtte control problem

- Cleaned Cap & Rotor

- Spark arrestor is clean

- Added bottle of 'dry gas' & several bottles of fule injector cleaner

Prior to storing for the winter, the boat held it's RPM's like a champ. As soon as the boat was run for the first time this season, this issue appeared. It has been a summer long process to try and trouble shoot and we've still made NO progress.

Any ideas or suggestions would be MUCH appreciated!!!!!

THANKS! :)

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VinRLX

Probably not an issue if you've run without using the throttle, but do you have PP?

Also, have you checked connections of spark plug wires as well as plugs themselves?

Edited by VinRLX

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MoonDawg
Fuel Pump?

I am with you on the fuel pump idea.

I just replaced my fuel pump last week and I noticed that my throttle is really touchy now...So much so, that now I am thinking, that I might need a different pitch prop.

I am running an ACME #515, 13x12 and now I am powering the handle out of Ms. MoonDawgs hands. She is none too happy about this. I never got up with her at the helm. Unbeliveable what effect a fuel pump could have. I am looking at going to the ACME #425, 13x13 just to get a bit more lag in the hole shot.

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kosar

We do not have PP (I've read where that can cause similiar symptoms) so I wish that were the case.

Have not check plugs/wires yet so we'll give that a whirl. Thanks for the suggestions.

Probably not an issue if you've run without using the throttle, but do you have PP?

Also, have you checked connections of spark plug wires as well as plugs themselves?

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kosar

Regarding the fuel pump thought, does anyone know if this would cause an RPM issue consistently at only one spot in the power band. It runs fine and strong except at this one spot. It is just so consistent at this one RPM range that it seems odd. But obvioulsy we're open to ideas down this line of thinking since we already went for the replacement of fuel filters. (rts & Moondawg - thanks for the ideas).

Does anyone think it's conisidence that this issue occurs right at the range required for wakeboaring, thus a lot of hours of small/fine adjustments in this range?

We're open to any ideas so please keep them coming!

One last question (for now), throttle position sensor - any info or thoughts on this being the cause? I don't know much about this.

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RTS

A faulty or failing fuel pump will cause all kinds of issues. When I had one failing, it would cause the RPM's to "porpoise" between 2500-3500 RPM. A new fuel pump fixed it. Remember, these fuel injected engines need that high pressure fuel, and they need it at a steady pressure, or funny things start to happen. I'm assuming you have a fuel injected boat...if you don't, ignore everything I say.

It won't be the cheapest part you've thrown at the problem (they are around $300 if you can install it yourself), but if you are on the original fuel pump, you have gotten more life out of it than most will.

BTW...I have changed mine out myself, and its not too hard, and would be happy to walk you through the procedure, as other here have done for me.

Also...it may just be that you have some debris that got past your filters and lodged itself in the very fine screen below on the fuel pump. This also happened to me, it was a chunk of fuel line. That would be an easy thing to check. Just disconnect the fuel line on the bottom of the pump, and use an inspection mirror to look at the screen. Be careful, and keep a small container handy to catch the fuel that will run out.

If you find debris, it can sometimes be dislodged with gentle compressed air, if you still can't get it out, take the fuel pump off and you can get to the screen better that way.

Good luck to you.

Edited by rts

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MoonDawg
...It won't be the cheapest part you've thrown at the problem (they are around $300 if you can install it yourself), but if you are on the original fuel pump, you have gotten more life out of it than most will...

I changed mine out in less than an hour. The hard part is getting the fittings off without munging them up. You need a 3/8 flare nut wrench to get them off. my pump had 750 hours on it and started leaking from the seal around the top. It could have been very dangerous. I am glad I found it.

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MoonDawg
....One last question (for now), throttle position sensor - any info or thoughts on this being the cause? I don't know much about this.

Yes there could be some wear in your Throttle Position Sensor. It is easy to test. Use an ohm meter connected to the electrical fitting and watch the resistance change. If it jumps around in the region where it would be when wakebording then there is a problem. The sensor should have a nice linear output.

The Clymer manual tells you how to R&R the TPS but does not tell you how to test it...pretty worthless manual in some areas :( The GM MEFI manual is an excelent purchase from skidim. It tells all. basically connect a volt meter to TPS B (blk) is ground and C (blue) is the signal. It should range from .7 volts at idle to 4.8 volts at full throttle.

The instructions for removing the fuel pump are pretty good in both manuals. I have the Delco high pressure pump on my 320HP Monsoon.

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CTSunsetter

kosar,

Please keep us updated on your progress to resolution. My '98 (740 hours) is doing the same thing. I'm not sure the RPMs but it happens around the 31 to 32 MPH where it will jump to 33MPH and not all the time either. We have Perfect Pass and it does it with on or off in MPH or RPM modes. Like you I replaced filters but also cap, rotor, cables, plugs just because it was time for all of that stuff. I can recall my boat doing it for a few seasons but because we mostly foil it hasn't been a problem but now that we are pulling more skiers it's a bit annoying.

...and thanks to everyone else's suggestions which I will check this weekend.

Edited by CTSunsetter

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kosar

CTSunsetter - I will definitely keep you updated on what we find. I don't want to say I'm happy to hear someone else is having similiar/same issues, but perhaps we can help each other figure this one out.

A friend is trying to bring an OHM meter home from work this week so we hope to get out for a little test. If not, we leave to got houseboating for a week this upcoming weekend. Yahoo.gif If we're still having the issues once we hit Shasta Lake, we'll probably grab a mechanic from the Marina to come out for a test ride with us. They're usually pretty cool and will do something like that for a couple of beers. Wow - do I send cheap? I can't be, I own a boat..... :lol:

MoonDawg and rts - you guys have been great and given some valuable information so THANKS for all your input. With any luck (and due to your advise) we'll get to the bottom of it soon. We will report back with what we find out in regards to the TPS and Fuel Pump.

kosar,

Please keep us updated on your progress to resolution. My '98 (740 hours) is doing the same thing. I'm not sure the RPMs but it happens around the 31 to 32 MPH where it will jump to 33MPH and not all the time either. We have Perfect Pass and it does it with on or off in MPH or RPM modes. Like you I replaced filters but also cap, rotor, cables, plugs just because it was time for all of that stuff. I can recall my boat doing it for a few seasons but because we mostly foil it hasn't been a problem but now that we are pulling more skiers it's a bit annoying.

...and thanks to everyone else's suggestions which I will check this weekend.

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kosar
kosar,

Please keep us updated on your progress to resolution. My '98 (740 hours) is doing the same thing. I'm not sure the RPMs but it happens around the 31 to 32 MPH where it will jump to 33MPH and not all the time either. We have Perfect Pass and it does it with on or off in MPH or RPM modes. Like you I replaced filters but also cap, rotor, cables, plugs just because it was time for all of that stuff. I can recall my boat doing it for a few seasons but because we mostly foil it hasn't been a problem but now that we are pulling more skiers it's a bit annoying.

...and thanks to everyone else's suggestions which I will check this weekend.

Sorry that we haven't given any updates but frankly we don't have any. We, every mechanic and Indmar have been defeated. Since it's Spring and the frustration has subsided, we thought we'd throw the issue back out there.

Our boat still has the problem. We had it at Cope's (lake tahoe) for a month last season and they could not figure it out. They were in contact with Indmar and still no luck. Did you happen to get to the bottom of your problem? Believe it or not the advice we are getting these days (even from mechanics) is to sell it. We love the boat and would like to get the problem fixed but we're out of ideas.

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electricjohn

Your ECM mainly looks at the manifold pressure (vacuum) in determining load on the engine. It then adjusts the EST (timing) and pulse width of the injectors. Try swapping out a known good MAP sensor. It's a basic GM part.

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kosar
Your ECM mainly looks at the manifold pressure (vacuum) in determining load on the engine. It then adjusts the EST (timing) and pulse width of the injectors. Try swapping out a known good MAP sensor. It's a basic GM part.

Thanks for the reply. Since the boat is still in storage (with the Clymer manual), can you describe the loaction of the MAP sensor?

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99response

Did you change the injector screens? They are in the injectors and have to be removed with a screw and then new ones pressed back in. They are extreemly fine screens that tend to get plugged up with very fine particulate. Takes about 1 hour on an old monsoon.

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kosar
Did you change the injector screens? They are in the injectors and have to be removed with a screw and then new ones pressed back in. They are extreemly fine screens that tend to get plugged up with very fine particulate. Takes about 1 hour on an old monsoon.

I have not but I will look into changing them when the boat comes out of storage. Thanks for the advice.

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99response

Only reason I suggest it becuase it can be like a clogged fuel filter only worse. Plus the parts are less than $1, it's just your time to change them.

-Chris

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electricjohn
Your ECM mainly looks at the manifold pressure (vacuum) in determining load on the engine. It then adjusts the EST (timing) and pulse width of the injectors. Try swapping out a known good MAP sensor. It's a basic GM part.

Thanks for the reply. Since the boat is still in storage (with the Clymer manual), can you describe the loaction of the MAP sensor?

Mine is on the intake manifold/flame arrestor. Don't know what your intake looks like, but the MAP sensor will have a 3 wire plug going to it.

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SmoothWaterMan

Although you've cleaned your cap/rotor, spend a couple of bucks and install new ones. There is a good chance that a new cap and rotor will fix this problem.

If the rpm jump/drop still happens with new cap and rotor then keep looking in the spark/timing/electrical arena. Plugs, Timing, wires, ignition module, etc. This is all based on the fact that the throttle and throttle body are truly remaining fixed or in a constant spot when the engine jumps up or down.

I don't feel that it would be fuel related, but it's an easy one to rule out by running it with a mechanical fuel pressure gauge hooked up. Unless the pressure drops or climbs way up it's not the issue.

Peter

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kosar
Although you've cleaned your cap/rotor, spend a couple of bucks and install new ones. There is a good chance that a new cap and rotor will fix this problem.

If the rpm jump/drop still happens with new cap and rotor then keep looking in the spark/timing/electrical arena. Plugs, Timing, wires, ignition module, etc. This is all based on the fact that the throttle and throttle body are truly remaining fixed or in a constant spot when the engine jumps up or down.

I don't feel that it would be fuel related, but it's an easy one to rule out by running it with a mechanical fuel pressure gauge hooked up. Unless the pressure drops or climbs way up it's not the issue.

Peter

Since the first post in 2006 we have replaced evrything except the MAP sensor (this was a recent suggestion) and the fuel injectors. I've disconnected the throttle cable and manually moved the linkage with my hand and the problem was the same. At this point I'm open for anything. Thanks for the mechanical fuel pressure gauge suggestion.

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mikenaustin

I'm facing the same problem with my 99 Sunsetter VLX with the 325 Monsoon. It seemed to get better with a tuneup and replacement of the Throttle Position Sensor but it's not completely gone.

Did anyone solve the mystery yet?

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huskyvols

Please keep the suggestions coming. I too have the same issue (can't hold an RPM between 2500 - 2900) on a 98 Sunsetter. I am just beginning my trouble shooting and hope someone here has a break through. Keep all the great info flowing.

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