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View Full Version : RPM's suddenly limited at 2000 RPMs


MrTsuth
09-23-2013, 09:49 PM
I have a 1996 Maristar 225v... It ha run flawlessly all summer long. It missed about 2 weeks between use due to weather... Suddenly, the engine will not throttle higher than 2000 RPMs... I can't tell if it is flooding or starving... Or if there is some sort of safety that is limiting it.... Any suggestions on what it may be and where to begin my troubleshoot?

Ski-me
09-24-2013, 09:48 AM
The LT1 probably went into Limp mode (I've experience it too). Check your T-stats for the correct ones (and no blockages), check your intake impeller and be sure there is not any debris in there. It's very sensitive to engine temps and this can happen. Also might want to replace your temp sensor for good measure too.

These are just generic, basic answers to this problem but a place to start. T-stats should be 142 and 160 with a hole drilled in the top.

skitilldark
10-02-2013, 12:05 PM
I have a 1996 Maristar 225v... It ha run flawlessly all summer long. It missed about 2 weeks between use due to weather... Suddenly, the engine will not throttle higher than 2000 RPMs... I can't tell if it is flooding or starving... Or if there is some sort of safety that is limiting it.... Any suggestions on what it may be and where to begin my troubleshoot?

You have a perfect pass?

neil.anderson63
10-02-2013, 12:53 PM
Are you saying it is going into limp mode? Mine behaved similar to this and it was a bad battery in my 2 battery system. Replaced the bad battery, no trouble since.

MrTsuth
10-06-2013, 07:52 PM
I don't have a perfect pass.... I disconnected the battery and reset the limp mode.... Took it out and it ran perfect for about 15 minutes... Then suddenly got hot and went in to limp mode again.... I noticed that at the same time, the oil pressure dropped significantly at the same time.... I'm thinking that I have some blockage in my raw water intake line has some blockage at the oil cooler.... Could this be the cause??? The blockage at the oil cooler does not allow the oil to cool enough... Letting the oil get too hot, and thin, causing it to go in to limp mode????

JimN
10-06-2013, 08:25 PM
I have a 1996 Maristar 225v... It ha run flawlessly all summer long. It missed about 2 weeks between use due to weather... Suddenly, the engine will not throttle higher than 2000 RPMs... I can't tell if it is flooding or starving... Or if there is some sort of safety that is limiting it.... Any suggestions on what it may be and where to begin my troubleshoot?

2000 RPM is the magic number for overheat-induced RPM reduction, especially if it runs lumpy when this happens. Make sure the impeller is good, the raw water pump cover is tight and well-sealed and no rubber parts from an old impeller are clogging the thermostat(s) or passages. If that is good, look at the wires going to the ECT (Engine Coolant Temperature) sensor. If the wires going to it have melted due to a bad engine overheat, it will tell the ECM that it's overheating, even if it's not. If the wires are good and the plug is fully engaged, measure the sensor's resistance- I have posted a chart here so many times without a mod making it a sticky that there's no reason I should have to do it again.

JimN
10-06-2013, 08:26 PM
I don't have a perfect pass.... I disconnected the battery and reset the limp mode.... Took it out and it ran perfect for about 15 minutes... Then suddenly got hot and went in to limp mode again.... I noticed that at the same time, the oil pressure dropped significantly at the same time.... I'm thinking that I have some blockage in my raw water intake line has some blockage at the oil cooler.... Could this be the cause??? The blockage at the oil cooler does not allow the oil to cool enough... Letting the oil get too hot, and thin, causing it to go in to limp mode????

The oil cooler isn't for the engine, it's for the transmission.

MrTsuth
04-13-2014, 03:27 PM
2000 RPM is the magic number for overheat-induced RPM reduction, especially if it runs lumpy when this happens. Make sure the impeller is good, the raw water pump cover is tight and well-sealed and no rubber parts from an old impeller are clogging the thermostat(s) or passages. If that is good, look at the wires going to the ECT (Engine Coolant Temperature) sensor. If the wires going to it have melted due to a bad engine overheat, it will tell the ECM that it's overheating, even if it's not. If the wires are good and the plug is fully engaged, measure the sensor's resistance- I have posted a chart here so many times without a mod making it a sticky that there's no reason I should have to do it again.
Put the boat away for the winter... Just got it back out and am now working on it again.... Before I took the boat out, I changed the coolant temp sensor and the pigtail. For good measure, I changed the thermostat located just under the air filter... (Not sure where the other one is located)... I have also installed a new impeller...

Still overheating... Any more suggestions before I have to break down and take it in to the dealer??

mgs96ps
04-13-2014, 03:44 PM
The 143 is in the mixer right in front of engine water pump and directly above impeller pump.

JimN
04-13-2014, 04:08 PM
Put the boat away for the winter... Just got it back out and am now working on it again.... Before I took the boat out, I changed the coolant temp sensor and the pigtail. For good measure, I changed the thermostat located just under the air filter... (Not sure where the other one is located)... I have also installed a new impeller...

Still overheating... Any more suggestions before I have to break down and take it in to the dealer??

Overheating, after how long? Is this in the water, or on a trailer? That sender you replaced- one wire? That one doesn't matter for what the ECM reacts to. You need to be concerned with the one that has two wires- one wire is yellow and the other is black.

Do you have a multi-meter? When it's cold, connect it to a water source (NOT A FAKE-A-LAKE!!!!!!!!!), let it idle and immediately remove the harness from the two-wire temp sender so you can measure the resistance of the sender. Post the resistance.

Have you replaced the water circulating pump? If so, did you use an LT-1 pump? You absolutely have to.

jsturvey
04-14-2014, 11:51 PM
You definitely have my attention on this. Definitely post what you find out for us fellow LT1 owners.


Sent from my iPad using Tapatalk

MrTsuth
04-17-2014, 02:40 PM
1. Overheating, after how long?
After about 7-10 minutes of running at 2500 - 3000 RPMS
2. Is this in the water, or on a trailer?
In the water
3. That sender you replaced- one wire?
The two wire with yellow and black wires
4. Do you have a multi-meter?
I will try this tomorrow and post the resistance.
5. Have you replaced the water circulating pump?
No, I have not done that yet.

I am going to replace the 143 thermostat before trying the above items. I am finding that some of the water lines are getting water through them, and some of them are not. IE: the exhaust lines seem to have flowing water and keep cool, others seem as if they are starving for water. To me that either sounds like one of the thermostats or the pump..... More likely a thermostat....

Quick question... Is the 143 Thermostat that is located just above the impeller the same style as the 160 thermostat located on the top? Or should I pull it out and try and match it up before I head to the parts store?

Thank you guys for all of your assistance. It is TRULY appreciated!

JimN
04-17-2014, 09:54 PM
1. Overheating, after how long?
After about 7-10 minutes of running at 2500 - 3000 RPMS
2. Is this in the water, or on a trailer?
In the water
3. That sender you replaced- one wire?
The two wire with yellow and black wires
4. Do you have a multi-meter?
I will try this tomorrow and post the resistance.
5. Have you replaced the water circulating pump?
No, I have not done that yet.

I am going to replace the 143 thermostat before trying the above items. I am finding that some of the water lines are getting water through them, and some of them are not. IE: the exhaust lines seem to have flowing water and keep cool, others seem as if they are starving for water. To me that either sounds like one of the thermostats or the pump..... More likely a thermostat....

Quick question... Is the 143 Thermostat that is located just above the impeller the same style as the 160 thermostat located on the top? Or should I pull it out and try and match it up before I head to the parts store?

Thank you guys for all of your assistance. It is TRULY appreciated!

Does one of the thermostats have at least one hole in it?

If not, someone who has an LT-1 will be along to give you the part number, or mod one without, so it "bleeds" properly.

FoggyNogginz
04-17-2014, 09:58 PM
Just for clarity, be sure to pull the hose from the oil cooler and ensure that you don't have impeller parts lodged up against it as well. This is a very common problem on the Indmar systems with Johnson pumps. Once the impeller goes a little bad, the parts are commonly found against the oil cooler screen, clogging the system and preventing cooling.

JimN
04-17-2014, 10:03 PM
Just for clarity, be sure to pull the hose from the oil cooler and ensure that you don't have impeller parts lodged up against it as well. This is a very common problem on the Indmar systems with Johnson pumps. Once the impeller goes a little bad, the parts are commonly found against the oil cooler screen, clogging the system and preventing cooling.

That's only on the boats after the LT-1. They relocated the oil cooler in about '99.

FoggyNogginz
04-17-2014, 10:04 PM
That's only on the boats after the LT-1. They relocated the oil cooler in about '99.

Gotcha. I stand corrected.

MrTsuth
04-19-2014, 10:28 AM
Does one of the thermostats have at least one hole in it?

If not, someone who has an LT-1 will be along to give you the part number, or mod one without, so it "bleeds" properly.

So I got down to removing the 2nd Tstat and decided since I was down that far already I would replace the water pump...

My question is this.... Will a standard LT1 water pump suffice if I cap the extra heater port coming out of it? Indmar wants $550 bucks for theirs, NAPA wants $100.00 for the standard corvette LT1 water pump. Capping the heater port should be simple and we'll worth $400 savings if that is an ok thing to do...

Will that work ok?

Table Rocker
04-19-2014, 10:45 AM
So I got down to removing the 2nd Tstat and decided since I was down that far already I would replace the water pump...

My question is this.... Will a standard LT1 water pump suffice if I cap the extra heater port coming out of it? Indmar wants $550 bucks for theirs, NAPA wants $100.00 for the standard corvette LT1 water pump. Capping the heater port should be simple and we'll worth $400 savings if that is an ok thing to do...

Will that work ok?
The water pump is not a "marine" part and the auto version will do fine. A '92 Corvette LT-1 water pump does not have the extra ports that you would have to block off. Does your boat have a heater? You can use a pump with the extra port to relocate your heater hose for better heat.

JimN
04-19-2014, 11:25 AM
So I got down to removing the 2nd Tstat and decided since I was down that far already I would replace the water pump...

My question is this.... Will a standard LT1 water pump suffice if I cap the extra heater port coming out of it? Indmar wants $550 bucks for theirs, NAPA wants $100.00 for the standard corvette LT1 water pump. Capping the heater port should be simple and we'll worth $400 savings if that is an ok thing to do...

Will that work ok?

You don't need to go to Indmar for the pump, but it absolutely MUST be for an LT-1 because this engine uses 'reverse-cooling', which means the heads are cooled before the block and no other pump will work.

Yes- cap off the heater port and you're good.

If your pump is working, there's no reason to replace it.

Table Rocker
04-19-2014, 01:19 PM
The LT-1 water pump is shaft driven, so the chances of putting the wrong pump on without realizing it are very slim. You would need a pulley and a different belt, etc.

I agree, if the pump is not leaking there is no reason to replace it. If it is leaking, you should replace it, but it isn't as urgent as a closed loop system.

mikeg205
04-19-2014, 01:42 PM
So I got down to removing the 2nd Tstat and decided since I was down that far already I would replace the water pump...

My question is this.... Will a standard LT1 water pump suffice if I cap the extra heater port coming out of it? Indmar wants $550 bucks for theirs, NAPA wants $100.00 for the standard corvette LT1 water pump. Capping the heater port should be simple and we'll worth $400 savings if that is an ok thing to do...

Will that work ok?

yes - use extra 400 for beer and gas.. :)

MrTsuth
04-19-2014, 10:48 PM
You don't need to go to Indmar for the pump, but it absolutely MUST be for an LT-1 because this engine uses 'reverse-cooling', which means the heads are cooled before the block and no other pump will work.

Yes- cap off the heater port and you're good.

If your pump is working, there's no reason to replace it.

I am officially so confused!

I have now replaced both the 160 and 143 thermostats. I used indmar parts. I replaced the water pump.

Still having an overheating problem.

Like I stated in a previous post, the water lines going to the exhaust risers and the risers themselves seem to stay cool... But the line going into and out of the water pump seem to remain very hot.. The water flow seems to be limited.... (Not as much flow as the exhaust lines) and the temp is bearable by touch.... But the motor is in fact overheating.. However, it only went into limp mode once, even though the gauge was pinned at 240...

While I had everything off, I checked thoroughly for debris and blockage... And everything appeared to be clear..

The boat actually ran great!!! It just overheats after about 7-10 minutes at about 3000 rpms..

I am so confused...

I may be to the point that I have to take it to the dealer unless there are anymore recommendations. I just hate that price tag!

Rockman
04-19-2014, 11:27 PM
Be careful with the rising temp on your LT1...you cold do alot of damage that will just cause more headaches and cost alot!

Only thing I can think of with you saying flowage is limted is SOMETHING is clogged somewhere, this assuming no issues with the water pump and T Stats...


Did you have the boat in the water testing or on the hose? I think by your comments, you were in the water.

I would suggest starting to pull hose by hose, check the intake, and rule out everything piece by piece...hope you get this fixed asap!

Table Rocker
04-19-2014, 11:47 PM
As a shade tree mechanic, I would pull the thermostat from the top of the water pump and see what the result is. Leave the mixing thermostat in. As Rockman said, make sure the hoses from the water pump to the mixer are clear. I also think we are all assuming your impeller and your raw water pump are good.

MrTsuth
04-20-2014, 12:27 AM
I have been doing a lot of research tonight due to my confusion and frustration...

I have come across service bulletin mc 96-100.... Moving the breather from the rear of the heads to the front of the heads... This upgrade has not been made on my boat. Further, the problem began to occur late in the fall, when water temps began to cool... And thus far, water temps have not began to warm up.

My assumption is that this could create steam pockets much easier...

If you think this may be my problem, could someone provide a copy of the bulletin? I can't find an exact copy. I get the gist of it, but a parts list would help tremendously..

MrTsuth
04-20-2014, 12:29 AM
I have made sure all hoses are clear... And I've replaced my impeller... My raw water pump/impeller seem to be doing their job..

Table Rocker
04-20-2014, 08:59 AM
http://www.mastercraft.com/teamtalk/showthread.php?t=31626
http://www.mastercraft.com/teamtalk/attachment.php?attachmentid=50078&stc=1&d=1249099294