WOT RPM Too Low - major issue? cause?

07 obv with 5.7 indmar assault 325.
prop is a 13.7x17.5 mvc hc oj prop which i understand is stock diameter and pitch so iiuc the low rpm is not a prop pitch issue and ‘correcting’ the low wot rpm issue by lowering prop would mask a potentially real and serious issue.
Top speed is about ~39 and top rpm is ~4510-4560 (alone or loaded).
spec for my engine is 4600-5200.
per engine manual wot should be on higher end, and others with same boat say they get top end rpm and closer to 45mph.
My concern is not with the speed or performance.

My question is if it’s symptomatic of a real issue, then i do want to track it down. it sounds serious per manual and others to be below minimum and so far from upper range of wot. my concern is the underlying cause - if the engine isn’t performing as it should due to other issues and consequently could cause (long term and or catastrophic) damage.

my speed matches gps (pp stargazer) so it’s not off by 5 mph. i also have tach and pp rpm so i think it takes gauge error out of the mix bc they both get the same signal and give me same rpm.

I revvd in neutral and it would cut out past high 2s/3s so it was like up and cut out, rev up and cut out. was weird.

Any inouts/suggestions?
i realize to track down everything - i could eother go diagnostic first or throw parts first. basically i would prolly start with parts replacement, i would clean flame arrestor, change out fuel filter (is ther just one or low and high pressure?), spark plugs, rotor and cap and wires, and for diagnostics i could check fuel pressure and compression test. before i go down the path of chasing that or paying a fortune to do it - is there any chance nothing is wrong or not serious enough to bother? and any other obvious/easy things to check or replace? really just looking to enjoy our boat every season and get it baselined in a good spot, don’t want to overthink it but getting concerned based on everything i’ve read on the topic since i’m off by hundreds of rpm seems like something is off maybe a single cylinder not firing or all not firing at full potential…


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So to sum up what you described....anytime you hit a RPM during a rev and it cuts out it is either computer lockout or lack of fuel.

ECM lockout isn't limited to that low of RPM since most GM based engines are good to 6000-ish.

Fuel pressure loss is my guess but figuring out why is the hard part. Fuel Filter, fuel pressure regulator (top of sending unit on Fuel tank), fuel pump are the first 3 things. Injectors could need cleaned or have a lazy 1 or 2 that is causing misfires. Again, this sounds like a fuel issue since under 3000 rpm the boat is running fine. If there is a port on the fuel rail, you can hook up a gauge and check pressure. You should be around 60psi.

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Originally Posted by Holdmybeer

So to sum up what you described....anytime you hit a RPM during a rev and it cuts out it is either computer lockout or lack of fuel.

ECM lockout isn't limited to that low of RPM since most GM based engines are good to 6000-ish.

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to be clear the cut out above 2-3k rpm was only when in neutral. When under load i have 0 issues other than wot below the minimum. So is there any reason fuel would cut out in neutral but jot under load? And then in general - why am i maxing at under 4600rpm when propped at correct diameter/pitch, where’s that few hundred rpm gone?…. and is below minimum wot rpm serious enough to care. the neutral cutout was a test i saw someone suggest to see if i could get to top rpm in neutral just jot under load and to my surprise, it cut out…. and would rev up cut out, rev up cutout…


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Rev up...cut out....in neutral could be ecm controlled. This would make since to protect the engine.

If everything is running good and no sputters or misses, check your throttle cable. You could have extra slack in the cable.

Quote:

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Originally Posted by Holdmybeer

Rev up...cut out....in neutral could be ecm controlled. This would make since to protect the engine.

If everything is running good and no sputters or misses, check your throttle cable. You could have extra slack in the cable.

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i have efi so there’s a linkage but no cable right? i can see the linkages moving but don’t know how to confirm the linkage is moving as far as it can when throttle is as far forward as i can physically move it. it has adjustment turnbuckles… need to check service manual for specs unless there’s an easy/obvious trick i don’t know to confirm.


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The indmar manuals are online at the Indmar website.
You could always mark them in current position, then adjust to get more rpm.

If it messes anything up you have marks to put it back to where it was.

Hi, I'm having a similar issue. let me know if i should create a separate thread or if i can tag on to this one.

When experiencing sputters or misses, where is the best place to start troubleshooting?

I have an indmar 325 assault with a sputter or miss above 3000rpm under load. It also seems to loose RPM after reaching WOT under load and when in neutral. It does not sputter in neutral, but does loose RPM when the the accelerator in the full position.

So far: changed the fuel filter, tried injector cleaner but the issue continues.

I added PP GPS a few year back, could that be sending mixed signals to the ECM?

Quote:

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Originally Posted by brenpire

Hi, I'm having a similar issue. let me know if i should create a separate thread or if i can tag on to this one.

When experiencing sputters or misses, where is the best place to start troubleshooting?

I have an indmar 325 assault with a sputter or miss above 3000rpm under load. It also seems to loose RPM after reaching WOT under load and when in neutral. It does not sputter in neutral, but does loose RPM when the the accelerator in the full position.

So far: changed the fuel filter, tried injector cleaner but the issue continues.

I added PP GPS a few year back, could that be sending mixed signals to the ECM?

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OP has a different issue based on description. The boat is running great but won't reach max RPM by manual. I lastly suggested throttle cable linkage or TPS (throttle position sensor). Things could just be out of calibration and not allowing the last few hundred RPM's.

You are experiencing miss and firing issues above 3000rpm. I would suspect mis-fire under load from poor spark components. Easiest way to tell is to pull plugs and keep them organized so you know which 1 is from the removed cylinder. All should be a light to medium dark brown and might have a skight wet or oil look to them but not coated. White is bad (lean condition) and black is rich, oil blow-by, or bad gas causing soot. Also check the distributor cap and rotor. Moisture can cause cross-fires and soot will act as an insulator. Finally the coil. A weak coil won't charge or discharge fast enough will miss.

Check plug wires and harness wires for rub marks. Also while running, what is you oil pressure and engine temp reading. A faulty sensor will cause limp mode and shut the engine down to 3000rpm limit.

Quote:

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Originally Posted by Holdmybeer

OP has a different issue based on description. The boat is running great but won't reach max RPM by manual. I lastly suggested throttle cable linkage or TPS (throttle position sensor). Things could just be out of calibration and not allowing the last few hundred RPM's.

You are experiencing miss and firing issues above 3000rpm. I would suspect mis-fire under load from poor spark components. Easiest way to tell is to pull plugs and keep them organized so you know which 1 is from the removed cylinder. All should be a light to medium dark brown and might have a skight wet or oil look to them but not coated. White is bad (lean condition) and black is rich, oil blow-by, or bad gas causing soot. Also check the distributor cap and rotor. Moisture can cause cross-fires and soot will act as an insulator. Finally the coil. A weak coil won't charge or discharge fast enough will miss.

Check plug wires and harness wires for rub marks. Also while running, what is you oil pressure and engine temp reading. A faulty sensor will cause limp mode and shut the engine down to 3000rpm limit.

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That just about covered it all!

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Quote:

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Originally Posted by brenpire

Hi, I'm having a similar issue. let me know if i should create a separate thread or if i can tag on to this one.

When experiencing sputters or misses, where is the best place to start troubleshooting?

I have an indmar 325 assault with a sputter or miss above 3000rpm under load. It also seems to loose RPM after reaching WOT under load and when in neutral. It does not sputter in neutral, but does loose RPM when the the accelerator in the full position.

So far: changed the fuel filter, tried injector cleaner but the issue continues.

I added PP GPS a few year back, could that be sending mixed signals to the ECM?

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I had the same issue with my boat and a fresh set of spark plugs had it running like new.

Quote:

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Originally Posted by Holdmybeer

Rev up...cut out....in neutral could be ecm controlled. This would make since to protect the engine.

If everything is running good and no sputters or misses, check your throttle cable. You could have extra slack in the cable.

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HMB - thanks for your inputs!

I'm currently far away from the boat, but before I left I was able to try WOT a few more times in different conditions, and took a peek at the spark plug wires.

I noticed upon closer inspection that the Perfect Pass RPMs (digital) were 100-200 less than analog tach depending on the day/speed (see pics), and when I was alone in the boat the last time I was able to get it up to 4600 (digital)/4800 (analog) and 40.4 MPH. Also just realized that the Speeds aren't matching - GPS PP is 40.4 when boat says 42. Both tachs run off the same signal, so not sure why they'd be that far off or which to trust as more definitive...? My wakeplate was all the way down (nose down), not sure if that should have been be as high up as possible to minimize load?... After researching I've seen at least one account (at lower speeds in the 30's) where wakeplate all the way down vs. up was a 2-2.5mph difference. Assuming that's mph and a corresponding RPM difference, seems possible I get a healthy RPM and speed at WOT after raising wakeplate... I normally have wakeplate down so I didn't think about it at first...

The spark wires I looked at were corroded (see pic) and flame arrestor had gunk and needs to be cleaned. So I'm planning to start with the easy stuff (hopefully easy) as part of my winterization this year -> replace Spark Plugs, Spark Plug wires, Distributor Cap and Rotor, Fuel Filter (there's just one not two right?), PCV Valve along with Oil Filter, Engine Oil, V Drive Fluid, Transmission Fluid as part of winterization. I'm planning to do those as the last thing before I pull her out of the water so I can hopefully take it for a spin afterwards and see if anything got better :-)

If I have the time and energy I'll try to test fuel pressure and compression test the engine as well.

I'm amassing all the parts/materials and will plan to report back in a few weeks after I've had a chance to work on it.

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Are you on a river or lake?
Speed from a paddlewheel on a river will compensate for current and give a higher speed depending on traveling up stream or downstream. It would explain speed difference between analog and GPS.

If the rpm input is coming from the same source and the gauge is different than the PP I would assume the gauge may need calibrated and the analog runout from being 15yrs old is what you are seeing. Moisture and age plays havoc on analog electronics.

The plug wires are not horrible, I have seen worse. But doing all the routine maintenance stuff to make sure is just good practice if you don't know the condition from previous owner. Only 1 fuel filter I know of. Primary filter is usually part of the sending unit in the tank and doesn't require changing. Just the metal canister on the backside of the engine.

The drag from the wake plate will out a small load on the boat. If you can get smooth water after all your work try wake plate up once you are moving and you should pickup some speed. Good to see it is running well just not seeing what you expect.

Quote:

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Originally Posted by Holdmybeer

Are you on a river or lake?
Speed from a paddlewheel on a river will compensate for current and give a higher speed depending on traveling up stream or downstream. It would explain speed difference between analog and GPS.

If the rpm input is coming from the same source and the gauge is different than the PP I would assume the gauge may need calibrated and the analog runout from being 15yrs old is what you are seeing. Moisture and age plays havoc on analog electronics.

The plug wires are not horrible, I have seen worse. But doing all the routine maintenance stuff to make sure is just good practice if you don't know the condition from previous owner. Only 1 fuel filter I know of. Primary filter is usually part of the sending unit in the tank and doesn't require changing. Just the metal canister on the backside of the engine.

The drag from the wake plate will out a small load on the boat. If you can get smooth water after all your work try wake plate up once you are moving and you should pickup some speed. Good to see it is running well just not seeing what you expect.

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Lake. Forgot to consider the current factor. Speedo has a calibration knob, but not rpm right... I do actually have a spare tach guage maybe I'll pop that in at some point to compare.

Don’t you have to adjust the frequency on Perfect Pass for the tach freq? I thought this came up in a previous discussion about one of the GPS systems.


2022 SA 450

Quote:

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Originally Posted by 2in2out

Don’t you have to adjust the frequency on Perfect Pass for the tach freq? I thought this came up in a previous discussion about one of the GPS systems.


2022 SA 450

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I remember reading that elsewhere also. Something about 10,000 vs 15,000.

Is it adjusting to the transmission ratio? I think Sonic may have talked about it, or someone who did their own surf system had to make that adjustment on the pulse rate for RPM.

I could be completely off base, but if Holdmybeer remembers it too, that makes us both liars.


2022 SA 450

Quote:

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Originally Posted by 2in2out

Is it adjusting to the transmission ratio? I think Sonic may have talked about it, or someone who did their own surf system had to make that adjustment on the pulse rate for RPM.

I could be completely off base, but if Holdmybeer remembers it too, that makes us both liars.


2022 SA 450

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hmmm - tach should be standard with the only question being how many cylinders just like all tach gauges right? it’s straight engine rpm so not sure what transmission ratio would have to do w it? mine is drive by wire as well. I don’t see any such setting/calibration in the manual.

I did reach out to perfect pass about the pp display vs analog display so if calibration/setting is needed i expect they’ll point me to it. they’ve been super helpful in the past.


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Quote:

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Originally Posted by 2in2out

Is it adjusting to the transmission ratio? I think Sonic may have talked about it, or someone who did their own surf system had to make that adjustment on the pulse rate for RPM.

I could be completely off base, but if Holdmybeer remembers it too, that makes us both liars.


2022 SA 450

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Proof we aren't both crazy. Not sure if it applies here but this could explain why speed is off not RPM.

https://forum.moomba.com/showthread....ighlight=Pulse

Quote:

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Originally Posted by Holdmybeer

Proof we aren't both crazy. Not sure if it applies here but this could explain why speed is off not RPM.

https://forum.moomba.com/showthread....ighlight=Pulse

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Not crazy!!! But this was a diy/homebrew version of perfect pass, not needed for the real thing :)
Or to put it another way, believe pp display would already be calibrated from the factory to the gps signal it comes paired with. This appears to apply only to his speedo, not the rpm. Rpm signal is standard - can plug and play tach gauges and only setting change would be for how many cylinders.

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Correct. You have the real thing. I didn't think this applied.

Thinking more, have you ever checked your speed with a phone app. Use the app to compare the other 2. If PP and the GPS on your phone match then the gauge is off for speed. If phone and gauge then PP is off.

RPM being off is still confusing if they are the same signal. But PP focuses on maintaining speed and doesnt really care about RPM. Correct?

At these 40+ mph test do you have throttle left or is WOT maxed out?

Quote:

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Originally Posted by Holdmybeer

Correct. You have the real thing. I didn't think this applied.

Thinking more, have you ever checked your speed with a phone app. Use the app to compare the other 2. If PP and the GPS on your phone match then the gauge is off for speed. If phone and gauge then PP is off.

RPM being off is still confusing if they are the same signal. But PP focuses on maintaining speed and doesnt really care about RPM. Correct?

At these 40+ mph test do you have throttle left or is WOT maxed out?

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Great idea on phone app, will have to compare.
PP can use speed or RPM set points. In fact according to one of their engineers earlier versions needed RPM signal to work even in speed mode. (bought the boat in February and one of the other gremlins was tach not working on either PP or gauge so he was surprised pp would work even in gps/speed mode without the rpm signal…)

No expert - only beginners and since I had no rpm until i fixed it near the end of season I really only used speed setting so far other than to confirm rpm mode worked too.

So - I have noticed that the last stretch of throttle does nothing to add speed. so I hammer down to say ~80 or 85+% of throttle position and it tops out, then I can still move it down another bit but makes no difference. I have no reference point on whether that’s normal or not.

When off i had my son move throttle all the way forward and back while i looked at the linkage by the engine and it appears to move all the way. ie there is movement past the 80+% point i think. i haven’t checked the tps voltage to confirm it gets to ~4.4v or whatever wot should be. also couldn’t find anything about calibrating or adjusting the throttle linkage in the manual but i’ll have to keep looking bc that would be great to confirm throttle and tps are ‘in sync’ and getting to wot.


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Doing all these runs, the engine isn't mis-firing? No obvious mechanical issues?

This all seems to be electrical based on everything you have checked, just wanting to confirm. Could the TPS sensor be degrading over time? The fact the tach didn't work in February could be part of the issues. What did you do to fix that? Loose ground behind your gauge cluster?

Quote:

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Originally Posted by Holdmybeer

Doing all these runs, the engine isn't mis-firing? No obvious mechanical issues?

This all seems to be electrical based on everything you have checked, just wanting to confirm. Could the TPS sensor be degrading over time? The fact the tach didn't work in February could be part of the issues. What did you do to fix that? Loose ground behind your gauge cluster?

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no obvious mechanical issues i’m aware of.

don’t think there’s a misfire but not sure how to confirm easily without mefi scanner (no cheap options i’m aware of). plan to look at the spark plugs and if that may give me clues.

regarding tach at one point early in season i had a loose ground at ground bus behind dash causing some other intermittent issues but that was fixed. the tach still didnt work though. had a mechanic look and couldn’t figure it out said grey wire had continuity front to back, i tested a new tach still didn’t work (had some voltage but apparently not enough so thought the signal was there when it wasn’t or wasn’t strong enough), neither analog or pp rpm gauge worked (both off same signal). after looking at connections and disconnecting reconnecting the main harness behind the dash and then the 16pin plug at engine iirc, it started working so assuming it was a loose connection.

yeah could be tps or maybe throttle linkage as noted. not 100% sure how to confirm throttle linkage is working as expected. but if it moves all the way and past the ~80% point where throttle moves but doesn’t increase then yeah i should test the tps. is it just one at the engine or also a sensor at the throttle lever?

also a little confused - my 07 is drive by wire hut maybe still has mechanical linkage from throttle to engine. does that mean it does not have electronic throttle control full drive by wire where there would not even be a mechanical linkage just sensor at throttle?…

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Quote:

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Originally Posted by artg

no obvious mechanical issues i’m aware of.

don’t think there’s a misfire but not sure how to confirm easily without mefi scanner (no cheap options i’m aware of). plan to look at the spark plugs and if that may give me clues.

regarding tach at one point early in season i had a loose ground at ground bus behind dash causing some other intermittent issues but that was fixed. the tach still didnt work though. had a mechanic look and couldn’t figure it out said grey wire had continuity front to back, i tested a new tach still didn’t work (had some voltage but apparently not enough so thought the signal was there when it wasn’t or wasn’t strong enough), neither analog or pp rpm gauge worked (both off same signal). after looking at connections and disconnecting reconnecting the main harness behind the dash and then the 16pin plug at engine iirc, it started working so assuming it was a loose connection.

yeah could be tps or maybe throttle linkage as noted. not 100% sure how to confirm throttle linkage is working as expected. but if it moves all the way and past the ~80% point where throttle moves but doesn’t increase then yeah i should test the tps. is it just one at the engine or also a sensor at the throttle lever?

also a little confused - my 07 is drive by wire hut maybe still has mechanical linkage from throttle to engine. does that mean it does not have electronic throttle control full drive by wire where there would not even be a mechanical linkage just sensor at throttle?…

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I wish I could answer your drive by wire questions. I'm not sure how the assault motor is configured. My Raptor is drive by wire but the linkage it for the transmission to engage.

The loose connection makes sense. These boats take some vibrations and hits while on the water. As good as you describe it running I thought you weren't having engine issues.

Quote:

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Originally Posted by Holdmybeer

I wish I could answer your drive by wire questions. I'm not sure how the assault motor is configured. My Raptor is drive by wire but the linkage it for the transmission to engage.

The loose connection makes sense. These boats take some vibrations and hits while on the water. As good as you describe it running I thought you weren't having engine issues.

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so you have only one linkage for transmission? I have two - i guess one for transmission and on for throttle. both move together when moving the throttle handle. can’t find any service manual specific enough to this year of the engine to explain or be helpful or even have diagram of what’s what. guessing it’s a little bit of a tweener - bw the non efi and then the full drove by wire…?

and for cars, seems like the boat engine tech was way behind auto engine tech? like a 97 tahoe was using the same motor i have in a 2007? wonder if it’s always like that with marinized engines using older motors no longer being used by newest cars and with emissions requirements for boats lagging?…the only haynes manual os for the indmar 5.7 2003 and earlier. there isn’t one available for later years that i can find…


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For demonstration, here are pics of the linkages I have. I looked back at video and it appears that the linkage moved fully from 80%+ forward. so maybe not linkage issuebut still could be throttle position sensor issue or of course ignition or fuel related. Wish I were still closer to check immediately…
https://uploads.tapatalk-cdn.com/202...5b50751170.jpg

https://uploads.tapatalk-cdn.com/202...cbd0e1171a.jpg
https://uploads.tapatalk-cdn.com/202...3e25439093.jpg


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One additional note - I did have an issue (seems common with older boats) with neutral safety swotch where it would sometimes not register neutral even though the lever was in neutral position. The mechanic who looked at it had me jiggle it in and out of neutral if/when that happens, was told on a forum i need to replace the neutral safety switch (have it on order), and i did notice an oddity in the linkage in neutral that there’s slop in the linkage and it was almost like there was more room to manually put it into ‘neutral’ with the linkage even after the throttle was in the neutral position if that makes sense. don’t know if there’s anything related there to this issue. another thing to look at more closely.


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Well this should explain the half baked dbw implementation in 06-07 models. Basically looks like pre 06 indmars had throttle cables, and 06-07 at least moomba still hadn’t fully converted so throttle at helm was still mechanical with a throttle mate component at the engine to convert mechanical to dbw signal. They say in this post it was 07 but my 07 still has the frankenstein instead of being integrated into the throttle lever. and i guess it’s not a gm or indmar thing and is sorta tweener years so none of the documentation for the engine says anything about it (that i can find) and diagrams don’t show it. wonder how easy it would be to convert to full on dbw….

https://forum.moomba.com/showthread....0527#post70527


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