4.3 Gxi max rpm 4100

Z3cta

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Hello everyone, new to the forum, wish everyone all the best ! I have a 2006 Pontoon with a 4.3 gxi penta with the dual props in it that will not wanna go over 4100 rpm's. If I push it over the 4100- it will start to feel weird, as if I had hit ground / and / or feels like its cuts off, so I have to throttle back a bit. ( its scared me at first, I honestly thought i hit ground) Other then that boat runs fine, well....on starts cold or warm does not matter, it surges a bit and then it levels and idles normally. Any ideas would be appreciate it...
 

alldodge

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it will start to feel weird, as if I had hit ground / and / or feels like its cuts off

If the motor starts to miss then it could be the tachometer is off and your hitting the rev limiter. If its not missing and more like the prop is hitting something, check the props to see if they are not loose.
 

muc

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Is it possible you are running on 5 cylinders?
 

alldodge

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and the engine will only start cutting off after 4100 RPM's?

Think your tach is suspect, get a hand held tach or a engine scanner and verify its at 4100 and not above 4800 rpm

Maybe get a loaner at automotive store
 

QBhoy

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Hi
The official answer is to get it plugged in and diagnosed really. Other wise it’s a guessing game.
but I can tell you a few things about these Gxi/mpi and their traits. This engine will have a rpm limiter of about 4950 rpm. Not usually the case that the dash tachometer is accurate enough to show this.
Also, a favourite trait of these smaller mpi/gxi engines that causes exactly similar issue, is the well known often and randomly failing of the crap cap distributor cap. These can cause an array of problems including this.

At an attempt to cover all bases though. You really need to get it plugged in. It’s also just as likely (if your tachometer is close to accurate) given your rpm figure stated, when the issue occurs, you could be going into what’s known as 90% guardian mode.

A good start would be checking plugs (making sure they are the gxi required iridium or at least platinum type) and leads...and replace that diz cap. It will fail at some point, if it hasn’t already. That’s a fact.
good luck.
 

Z3cta

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ok, took it out today on a "sea trial". I had a marine scanner plugged in and I can confirm the RPM's are correct. At about 4200 rpm's the engine starts to cut off and can't will not go above 29-30 mps ( on the gps)
Also, no codes, new cap, new rottor, new wires and ( new spark plugs but not 100% the correct ones) , new fuel pump
 

Scott Danforth

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while you are plugged in, what is the duty cycle on the injector pulse? what is the fuel pressure?
 

Z3cta

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while you are plugged in, what is the duty cycle on the injector pulse? what is the fuel pressure?

Can I please send you the diag recording with all the data when I ran the boat so you can evaluate? I have no clue what to look for ?
 

muc

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Can I please send you the diag recording with all the data when I ran the boat so you can evaluate? I have no clue what to look for ?

Post it here and also your serial number.
 

Z3cta

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[No message]
 

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muc

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Can you post the .rec file? So we can see more than just one moment.
Your thermostat is stuck open.
 

Z3cta

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Can you post the .rec file? So we can see more than just one moment.
Your thermostat is stuck open.

I tried but will not let me uploaded. Any recommendation how I can post it here or send it to you ?
 

muc

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Yup, you got a stuck thermostat

We use a cold engine rev limit feature
based on ECT, to prevent high RPMs on a
cold engine. Limit will come into play as
follows:

MEFI 4 and 4b Cold Engine
Rev Limiter
Gi GXi
68 deg F (20C) 4000rpm 4000rpm
104 deg F (40C) 4600rpm 4600rpm
140 deg F (60C) 4800rpm 5200rpm


The cold engine rev limiter limits listed above are approximate and can change.
The purpose of this feature is to reduce the chance of engine damage due to an engine
being run at high rpm’s while still cold.
When the rev limiter is engaged, the ECM kills ½ of the injectors until the rpm comes down
below the rev limit. Then the ECM re-engages the disabled injectors until the rpm limit is
reached again. This can be viewed using the scan tool as “RPM Reduction --- ON or OFF”.
With this system, full rated rpm of the engine can NOT be reached until ECT climbs above
140-145 degrees (F). (60-63 degrees C)
48
 

Z3cta

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Can you post the .rec file? So we can see more than just one moment.
Your thermostat is stuck open.

Thank you
-I will change the thermostat and re-test ( even though this is a new thermostat, like 6-8 months old and yes it is a Volvo OEM part)

Another issue that I had with it in the summer was that when I was at no wake zone ( almost idle) temperature would go to the 180-190 mark. To bring the temp down I would just give it a bit more gas and engine would cool to the normal temp
Any thoughts? Is this issue connected with it now running cold?
 
Last edited:

alldodge

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new thermostat, like 6-8 months old

In this case most probable wuld be the ECT sensor is the problem. The ECM thinks the motor is cold when its not. This isn't the same one which shows on the gauge

Another issue that I had with it in the summer was that when I was at no wake zone ( almost idle) temperature would go to the 180-190 mark. To bring the temp down I would just give it a bit more gas and engine would cool to the normal temp

Impeller or what pump housing or sucking air
 

Z3cta

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In this case most probable would be the ECT sensor is the problem. The ECM thinks the motor is cold when its not. This isn't the same one which shows on the gauge



Impeller or what pump housing or sucking air

Is this the ECT that you are referring to? https://www.cecilmarineonline.com/2...rature-sensor-3862500-in-stock-ready-to-ship/



And how I find the air leak? No water leaking or anything, both the impeller and the water pump new ( well...
water pump was rebuilt)

Thank you so much !
 

alldodge

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That part is an exhaust temp sensor, and not the one I thinking about. I might be off base muc will advise, the computer does not get its temp reading from the gauge sender. I'm thinking its p/n 3850397 but it shows up as a switch at VP parts, but list as sensor in other sites

Place a piece of clear hose on the hose coming from the drive at the thermostat housing. Can get the hose and barbed plastic fittings at the local hardware store. Place in line and with boat in water see if you see bubbles
 
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