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River City Water Boy

Flat spot between 3400 and 3800 RPM

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River City Water Boy

I'm new to the MalibuCrew but was hoping I could tap into all the knowledge that is out there. I have a 99 Sunsetter with a 325 Monsoon that runs great except that it has a "flat spot" between 3400 and 3800 RPM. As I accelerate up to top speed, the engine RPM will rise smoothly until it hits 3400 RPM then will stop rising even though I am still moving the throttle forward, then all of a sudden, when I move the throttle forward far enough, it will jump to 3800 RPM. After this happens the engine will continue to rev smoothly all the way up to WOT. It does the same thing as I decelerate. The revs will drop to 3800 and stop until I move the throttle far enough then all of a sudden the revs will drop to 3400 RPM. No matter how I manipulate the throttle the engine will not operate between 3400 and 3800 RPM but will function perfectly on either side of this RPM range. To me, the obvious problem was the throttle position sensor. So I replaced it with a new one. No effect whatsoever. Same flat spot at the same RPM level. Just for the heck of it, since the problem seemed so obvious I went out and bought second brand new TPS on the off hand chance the first one was defective. The second one had one no effect either. Like I said, the engine runs great, starts great, very smooth with good power, it just has this big hiccup between 3400 and 3800 RPM. The engine is well maintained with fresh plugs and all the appropriate maintenance. Just to make sure there was nothing serious cropping up I checked the compression on all eight cylinders. No problem there either, compression was good (177 to 181 psi) and well balanced across all eight cylinders. The only thing I can figure is one of the other sensors may be bad but I can't imagine which one. Mass air flow? Could the ECM have a problem?

Has anyone out there run into a problem similar to this? Any suggestions? Thanks ahead of time for any ideas you can throw out there.

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Lance B. Johnson

I'm new to the MalibuCrew but was hoping I could tap into all the knowledge that is out there. I have a 99 Sunsetter with a 325 Monsoon that runs great except that it has a "flat spot" between 3400 and 3800 RPM. As I accelerate up to top speed, the engine RPM will rise smoothly until it hits 3400 RPM then will stop rising even though I am still moving the throttle forward, then all of a sudden, when I move the throttle forward far enough, it will jump to 3800 RPM. After this happens the engine will continue to rev smoothly all the way up to WOT. It does the same thing as I decelerate. The revs will drop to 3800 and stop until I move the throttle far enough then all of a sudden the revs will drop to 3400 RPM. No matter how I manipulate the throttle the engine will not operate between 3400 and 3800 RPM but will function perfectly on either side of this RPM range. To me, the obvious problem was the throttle position sensor. So I replaced it with a new one. No effect whatsoever. Same flat spot at the same RPM level. Just for the heck of it, since the problem seemed so obvious I went out and bought second brand new TPS on the off hand chance the first one was defective. The second one had one no effect either. Like I said, the engine runs great, starts great, very smooth with good power, it just has this big hiccup between 3400 and 3800 RPM. The engine is well maintained with fresh plugs and all the appropriate maintenance. Just to make sure there was nothing serious cropping up I checked the compression on all eight cylinders. No problem there either, compression was good (177 to 181 psi) and well balanced across all eight cylinders. The only thing I can figure is one of the other sensors may be bad but I can't imagine which one. Mass air flow? Could the ECM have a problem?

Has anyone out there run into a problem similar to this? Any suggestions? Thanks ahead of time for any ideas you can throw out there.

Try reading through this recent thread. I believe this boat was fixed.

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River City Water Boy

Thank you for the tip. I read through the thread. Sounds like a very similar problem to what I am experiencing. My engine also has the solid fuel crossovers. At the end of the thread the original author (ecj) does not actually specify whether the crossovers with the rubber tube actually solve the problem or not. Or did I miss something?

Thanks again. This definitely has me wondering.

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Lance B. Johnson

Thank you for the tip. I read through the thread. Sounds like a very similar problem to what I am experiencing. My engine also has the solid fuel crossovers. At the end of the thread the original author (ecj) does not actually specify whether the crossovers with the rubber tube actually solve the problem or not. Or did I miss something?

Thanks again. This definitely has me wondering.

I re-read the thread and your right it seems he never got back to tell us if it was fixed. Maybe try a PM and ask him?

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electricjohn

Thank you for the tip. I read through the thread. Sounds like a very similar problem to what I am experiencing. My engine also has the solid fuel crossovers. At the end of the thread the original author (ecj) does not actually specify whether the crossovers with the rubber tube actually solve the problem or not. Or did I miss something?

Thanks again. This definitely has me wondering.

Maybe you missed page 2 of that thread?

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River City Water Boy

My apologies for for the confusion on my last post. I did not notice the thread you attached had a second page to it. I'm glad the new fuel lines worked. I have ordered the two rubber fuel crossovers to replace the solid ones I have now. They should arrive late this week. We'll see how it goes.

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electricjohn

Get back to us after you complete your changeout and test ride. Your feed back helps a lot too.

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River City Water Boy

I will definitely let you know what happens. I should know by this weekend. Thanks again for the help.

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River City Water Boy

Well, with my wallet $170 lighter I installed my new rubber fuel crossover lines and took the boat out for a run. After spending that much money for fuel lines I am happy to report they solved my "hiccup" between 3400 and 3800 RPM completely. Not only did they fix the hiccup they also appear to have improved overall throttle control as well. In the past it always seemed I had to struggle just a little to set and hold the engine at a particular RPM. The RPM level always wanted to "wander" just a little before it settled at a particular point. Now that I have replaced the fuel crossovers the engine runs right up to the specified RPM and settles right in and stays put. Nice! Thanks to Ruffdog and electricjohn for all your help. Very much appreciated!

With that said, if it is not one thing it is another when it comes to boats. Although my fuel system seems to be working much better I had three instances where the ignition (or possibly fuel) "hiccuped" for a half a second while I was testing the fuel lines. This is something my boat has never done before. All three occasions happened when I was throttling back to a lower RPM. The revs would drop down to whatever the new level was (usually dropping from around 4000 down to around 3000 RPM) and after settling at the new lower RPM for a few seconds all of a sudden it seemed like the ignition system would shut off for maybe half a second and and then come right back on. My first guess would be that this is an ignition issue because it happens so suddenly. On the other hand it seems awfully suspicious that this started happening after I changed the fuel crossovers. Does anyone out there have any suggestions on this problem?

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electricjohn

Anything like your original hiccup(fuel related)? Or different?

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River City Water Boy

No, nothing at all like my original hiccup. This problem feels like the ignition is cutting out momentarily almost as if you turned off the ignition key for a split second. The engine is running along fine and just cuts out for second and then continues on. On one hand I want to suspect an electrical/ignition problem because when it cuts out, the engine stops running for a moment and the tach drops like a rock almost as if I had turned off the ignition key. On the other hand I think it is awfully coincidental that this has started happening right after changing the fuel crossover lines. It makes me wonder if I have a fuel pump/pressure problem that is causing the fuel pressure to drop. Also, because each time it happened it was a few seconds after decelerating from a high speed to a lower speed.

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electricjohn

Check your kill switch first, then your key switch, then the ecm/efi relay.

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Lance B. Johnson

River, that is great news....sorta. Keep us posted on the other problems, sounds like John has you started on the right path.

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River City Water Boy

Thanks guys. John you're just full of good ideas. Like a rookie I never would have thought to look at the kill switch. Start with the simple stuff first and then go from there. I'll follow your suggestions and see where they lead. Thanks again.

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SmoothWaterMan

I would also take a peek at the distributor cap to ensure it's not corroded, and looking like christmas trees in there.

Peter

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Dunski

I'm new to the MalibuCrew but was hoping I could tap into all the knowledge that is out there. I have a 99 Sunsetter with a 325 Monsoon that runs great except that it has a "flat spot" between 3400 and 3800 RPM. As I accelerate up to top speed, the engine RPM will rise smoothly until it hits 3400 RPM then will stop rising even though I am still moving the throttle forward, then all of a sudden, when I move the throttle forward far enough, it will jump to 3800 RPM. After this happens the engine will continue to rev smoothly all the way up to WOT. It does the same thing as I decelerate. The revs will drop to 3800 and stop until I move the throttle far enough then all of a sudden the revs will drop to 3400 RPM. No matter how I manipulate the throttle the engine will not operate between 3400 and 3800 RPM but will function perfectly on either side of this RPM range. To me, the obvious problem was the throttle position sensor. So I replaced it with a new one. No effect whatsoever. Same flat spot at the same RPM level. Just for the heck of it, since the problem seemed so obvious I went out and bought second brand new TPS on the off hand chance the first one was defective. The second one had one no effect either. Like I said, the engine runs great, starts great, very smooth with good power, it just has this big hiccup between 3400 and 3800 RPM. The engine is well maintained with fresh plugs and all the appropriate maintenance. Just to make sure there was nothing serious cropping up I checked the compression on all eight cylinders. No problem there either, compression was good (177 to 181 psi) and well balanced across all eight cylinders. The only thing I can figure is one of the other sensors may be bad but I can't imagine which one. Mass air flow? Could the ECM have a problem?

Has anyone out there run into a problem similar to this? Any suggestions? Thanks ahead of time for any ideas you can throw out there.

River City Water Boy.

We took our boat out of storage to kick off our season here this week. I think I am having the same problem as you did. It seems like my throttle is dead between 20-25mph. No matter how I move the throttle I can not hold a speed between those two. The engine runs smooth just as you stated. I have replaced all plugs, wires, dis. cap. So maintenance is up to date. I thought it might be my throttle cable but it sounds like the fuel crossover lines helped you out. I have a 97 sunsetter. Where did you order your parts from. Thanks

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Ndawg12

The Indmar part number for the crossover line is S786129.

Give this number to your local dealer or see if skidim may have it.

Edited by Ndawg12

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Lance B. Johnson

River City Water Boy.

We took our boat out of storage to kick off our season here this week. I think I am having the same problem as you did. It seems like my throttle is dead between 20-25mph. No matter how I move the throttle I can not hold a speed between those two. The engine runs smooth just as you stated. I have replaced all plugs, wires, dis. cap. So maintenance is up to date. I thought it might be my throttle cable but it sounds like the fuel crossover lines helped you out. I have a 97 sunsetter. Where did you order your parts from. Thanks

Assuming you had fresh gas and new fuel filter? Rule this stuff out before shelling out the $$$.

Seems like we have an epidemic here?

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Dunski

Assuming you had fresh gas and new fuel filter? Rule this stuff out before shelling out the $$$.

Seems like we have an epidemic here?

Sorry so long to reply. We spent all of last week at the lake. Anyways, yes everything was fresh. I actually noticed the problem at the very end of the season last year. So it wasn't a new problem. I am going to to give the dealership a call to see if they can get the parts for me. I tried skidim about a week and a half ago and they had never heard of the problem before and said they did not carry what I was asking for. Hopefully the dealership can help me out, but I am not holding my breath. They have not impressed me very much in the past....

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BumbleBee

Hi from OZ, Just stumbled across your thread....

Before you go shell out more cash, try this...

A friend of mine is an "indymar" mechanic, I have similar problem occasionally. Now I'm not joking with this answer but give it a try and go thrash around on the lake full throttle for five minutes every now and again.

Yes I thought it sounds crasy too. However, the RPM range you stated when your engine cuts is where we all sit while boarding or skiing. The throttle gets use to being in that position and sometimes when you want to go that fraction over it does'nt like it.

How we tested it was waited till the symptom came back, then disconected the gear selector harness in the engine bay and gave it a fist full of throttle. Then took it for a flogging down the river.

Problem cured :)

Not sure if your like me but, I dont all ways use full throttle on the hole shot as the boat accelerates way over the set speed. Babying the engine does'nt always do it good.

Their built to be used and used hard.

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electricjohn

Sorry so long to reply. We spent all of last week at the lake. Anyways, yes everything was fresh. I actually noticed the problem at the very end of the season last year. So it wasn't a new problem. I am going to to give the dealership a call to see if they can get the parts for me. I tried skidim about a week and a half ago and they had never heard of the problem before and said they did not carry what I was asking for. Hopefully the dealership can help me out, but I am not holding my breath. They have not impressed me very much in the past....

If your problem just started at the end of last season, then it is not your crossover lines. That would have caused the problem from 1997. A good way to eliminate the crossover lines as the cause, is to run your boat with a fuel pressure gauge connected to the fuel rail and see if the problem goes away.

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h2oskidude

Well, with my wallet $170 lighter I installed my new rubber fuel crossover lines and took the boat out for a run. After spending that much money for fuel lines I am happy to report they solved my "hiccup" between 3400 and 3800 RPM completely. Not only did they fix the hiccup they also appear to have improved overall throttle control as well. In the past it always seemed I had to struggle just a little to set and hold the engine at a particular RPM. The RPM level always wanted to "wander" just a little before it settled at a particular point. Now that I have replaced the fuel crossovers the engine runs right up to the specified RPM and settles right in and stays put. Nice! Thanks to Ruffdog and electricjohn for all your help. Very much appreciated!

With that said, if it is not one thing it is another when it comes to boats. Although my fuel system seems to be working much better I had three instances where the ignition (or possibly fuel) "hiccuped" for a half a second while I was testing the fuel lines. This is something my boat has never done before. All three occasions happened when I was throttling back to a lower RPM. The revs would drop down to whatever the new level was (usually dropping from around 4000 down to around 3000 RPM) and after settling at the new lower RPM for a few seconds all of a sudden it seemed like the ignition system would shut off for maybe half a second and and then come right back on. My first guess would be that this is an ignition issue because it happens so suddenly. On the other hand it seems awfully suspicious that this started happening after I changed the fuel crossovers. Does anyone out there have any suggestions on this problem?

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h2oskidude

I had a 99 Response with the same problem with the solid fuel lines. Indmar had a recall on them back then and sent me new ones for free. You might check with Indmar

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