99 Response surging at certain RPM

[Justin_C]

I have a new to me (obviously) 99 Response lx with the monsoon 325 efi engine and at roughly 2600 rpm it starts surging. As I bring the throttle up slowly it continues to surge and not increase rpm until all of a sudden it takes off and settles at around 3100rpm. If I am throttling down, I can throttle down to about 2900 rpm and then it drops to roughly 2600.

Everything above and below those numbers seems and sounds smooth UNTIL I'm skiing/there's more weight in the boat. At this point I can't be sure what all of the numbers are as crew weight and skier weight vary but the other night I was skiing and my ski partners we sling at 32 and 34 mph and the boat worked fine but then when I skied at 36mph it surged the whole time. 

So far I have changed both fuel filters, added some methyl hydrate to the fuel tank in case of water and changed out the spark plugs. My next option would be cap and rotor and plug wires but I wanted to hear other people's thoughts. I also wondered about throttle cable issue or a tps? 

Something else worth noting is that I added perfect pass this spring. It was the third or fourth time I've installed it and I've never had issues before and this happens with pp on and off so I doubt it's related but worth noting.

 

Any ideas? Here's a link to a video I took tonight. Listen closely when it reaches around 2550 rpm so you can hear what I mean by surging.

Thanks!

[UWSkier]

Looks like fuel hammer to me.  In later versions of the Monsoon, the fuel lines that connected the two rails together had rubber sections.  If your crossover lines are stainless, you can replace them with Indmar part number 786129.  99 would likely had stainless lines from the factory.

A way to test if you have fuel hammer is to put a fuel pressure gauge on the rail and see if the problem goes away.  The gauge acts as a bit of a buffer to the hammering issue.

If you already have the rubberized lines, you can have a hydraulic shop make you up some lines that criss-cross instead of making a rectangular flow pattern.  That's been the fix for boats that can't shake the hammer even with the rubberized lines from Indmar.

Cap and rotor are a good idea to swap too though.

Edited July 10, 2023 by UWSkier

[Justin_C]

11 hours ago, UWSkier said:

Looks like fuel hammer to me.  In later versions of the Monsoon, the fuel lines that connected the two rails together had rubber sections.  If your crossover lines are stainless, you can replace them with Indmar part number 786129.  99 would likely had stainless lines from the factory.

A way to test if you have fuel hammer is to put a fuel pressure gauge on the rail and see if the problem goes away.  The gauge acts as a bit of a buffer to the hammering issue.

If you already have the rubberized lines, you can have a hydraulic shop make you up some lines that criss-cross instead of making a rectangular flow pattern.  That's been the fix for boats that can't shake the hammer even with the rubberized lines from Indmar.

Cap and rotor are a good idea to swap too though.

Can you elaborate a bit on the criss cross?

Thanks!

[Kelvin]

@Justin_C I had this exact same issue on a 98 Malibu Response.  The solution @UWSkier describes fixed mine when they changed out the stainless fuel rail cross sections with the rubberized ones.  Hope you find a solution.

[Justin_C]

12 minutes ago, Kelvin said:

@Justin_C I had this exact same issue on a 98 Malibu Response.  The solution @UWSkier describes fixed mine when they changed out the stainless fuel rail cross sections with the rubberized ones.  Hope you find a solution.

So you had to criss cross yours instead of just using that indmar part?

[Kelvin]

For me, the replacement indmar parts did the trick.  

[Justin_C]

1 hour ago, Kelvin said:

For me, the replacement indmar parts did the trick.  

Did you try the fuel pressure tester trick before you replaced it? I just tried that and it is still happening. Just wondering if that's a definitive test or not.

@UWSkier Also interested on your take. Still happening with the fuel pressure tester on the Schroeder valve. I did notice though, that it doesn't happen when in neutral (with or something the tester in place) although I sort of suspected it wouldn't as it seems to increase in severity with more load (I.e. More people in the boat and/or skiing).

[UWSkier]

IDK if the fuel pressure gauge is a definitive trick.  Larry from Indmar once suggested that but I don't know if it's 100% the case.  I would start with the cap and rotor if they're due anyways.

[Justin_C]

@UWSkier That indmar part you reference, do you just need to do the one at the front of the engine? That's what I was assuming but then I looked at another boat with the same engine and it appears to have it on both ends

[Kelvin]

16 hours ago, UWSkier said:

IDK if the fuel pressure gauge is a definitive trick.  Larry from Indmar once suggested that but I don't know if it's 100% the case.

I believe my boat was the first one to have this issue.  When my mechanic was trying to diagnose the issue, they used a pressure gauge on the fuel rail.  With the pressure gauge connected, the boat would not act up.  That is part of how they ultimately identified the fix for the issue.

[DW]

@Justin_C - sounds like fuel hammer, a known issue with that era Indmar.  I would also look in to improving the PP linkage / connection / cable alignment.  Make sure the cable moves freely, the alignment at the throttle connection is properly aligned and the L bracket is free to swivel.  Just a note - a PP system will surge if the throttle is below the set speed, simple to verify, run with PP shut off to see if that is a contributor (your comment of running 36 and having the problem implies that is not it).  PP has video & written troubleshooting guides on their site.

[UWSkier]

1 hour ago, DW said:

@Justin_C - sounds like fuel hammer, a known issue with that era Indmar.  I would also look in to improving the PP linkage / connection / cable alignment.  Make sure the cable moves freely, the alignment at the throttle connection is properly aligned and the L bracket is free to swivel.  Just a note - a PP system will surge if the throttle is below the set speed, simple to verify, run with PP shut off to see if that is a contributor (your comment of running 36 and having the problem implies that is not it).  PP has video & written troubleshooting guides on their site.

No L bracket on a Monsoon, but agreed on the cable/linkage tightness check.  Good point.

[UWSkier]

8 hours ago, Justin_C said:

@UWSkier That indmar part you reference, do you just need to do the one at the front of the engine? That's what I was assuming but then I looked at another boat with the same engine and it appears to have it on both ends

Need two of them.

[Justin_C]

Just though I would update this and say that I had the injectors cleaned and rebuilt and that fixed the issue! I still have a rubber crossover line on its way but the injectors certainly fixed the issue for me!

[Justin_C]

So turns out the issue is NOT fixed and I’m starting to come to a loss. Here’s where I’m at:

 

Injectors cleaned and rebuilt fixed for about 2 outings (a test and 1 ski set) then the issue come back. I did lose the lower bad spot but the upper one around 3600rpm is still there (again, fluctuates with load a bit but stays within a couple hundred rpm of there). Pulled the injectors again to see if more dirt got in, cleaned them out a bit, back in and it worked great again for about the same amount of time. That led me to think either there’s dirt after the fuel filter(this one has the one on the engine) OR it actually has nothing to die with the injectors and actually is because I’m draining the fuel rails and subsequently the pressure in the system. I decided to try just draining and then running again and that seemed to fixit for a quick test outing but then was back pretty quickly. 
 

The fuel pressure is showing around 50 psi at key on and 46 at idle (wasn’t able to check WOT as I was alone and I’m not quite redneck enough to try rigging up a workaround for that). I can’t see the fuel pressure being just slightly high like that causing this big of issue but maybe? Does anyone know of a cross reference for a fuel pressure regulator for the monsoon 325? The indmar one is quite pricey once shipping to Canada and exchange/duty are applied. 
Any other ideas on what to try? I’ve replaced the crossover lines and it hasn’t changed anything (I haven’t made up the X pattern ones yet but nothing really changed or improved with the indmar lines so I’m not sure it would do any better to do the other option? Plus the fact that cleaning the injectors or draining the fuel system is temporarily fixing the issue leads me to think it’s not an issue with those lines. 
 

Any help is greatly appreciated!!

[UWSkier]

Check your fuel pressure with a load on the engine, but those pressures are too high.  You should be 43-45 at key up and 35-38 at idle.

It should be a standard rail-mounted 3-bar regulator for GM.

When you remove it, reinstall it with some red loc-tite or the bolt will leak fuel.

Something like at this link.  Not sure if this is exact one or not.

https://www.amazon.com/Injection-Pressure-Regulator-compatible-CAVALIER/dp/B08L1TYDJB/ref=sr_1_8?crid=2V1URJSSPZMDJ&keywords=45+psi+fuel+pressure+regulator+gm+5.7&qid=1691513268&sprefix=45+psi+fuel+pressure+regulator+gm+5.7%2Caps%2C351&sr=8-8