Power cutting at 2000+ rpm

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
After trying to get the boat up to cruising speed for the first time yesterday, power cut out and back to an idle speed very abruptly as I applied the power. The boat had run fine for about 40 minutes up to that point at slow speeds. Initially I thought the transmission may have been slipping; however, I now realize the rpms should have risen and not dropped if that was the case (I think).

The engine revs fine to higher rpms in neutral, it only occurs under load.

Not sure where to start with this seemingly more complex problem. The boat has two new fuel pumps, injectors seem to be spraying really well (5.7 indmar TBI motor), and has brand new filters. Ultimately I am very unsure as to what to check.

Do these motors have a limp mode?- it's a 1996. Maybe it's getting a bad reading from something, or one of the modules on the ecm is bad. Not sure how to start with this thing. A list of common issues or things to check would be super helpful.

I've read about TPS or oil pressure sensors going bad, any particular way to tell if it's one of these?

Thank you all!
 
Last edited:

redneck

Well-Known Member
Mar 2, 2009
1,453
59
Palm Bay FL
It sounds kind of like limp mode. The info on how to check the sensors is online most can be done with a multi meter. Is the ignition timing advancing? If its limp mode i think overheating is one of the conditions that will set it into limp mode. The CTS might be giving the computer a false temp reading. There are software packages/cables on line that you can look at the engine parameters in real time.

 

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
I replaced the oil pressure sender, since I had a new one anyway and it stopped working yesterday. Hoping that is the issue. Unfortunately I don't believe this motor has an obd2 output?.. unless I can't find it.

I also don't believe it is overheating thankfully, because the risers are only warm to the touch believe it or not, even after 45 minutes running.
 

deputyrpa

Well-Known Member
Supporting Captain
Aug 28, 2010
1,199
85
Fort Ann, NY
Here's what I did to make sure everything was operating normally after I set up my long block. Then I brought the boat to a marine service garage and had them plug it in to a diagnostic tool in order to make sure the MEFI 2 computer, which I had sent out to be reprogrammed, was done accurately to provide sufficient fuel for my higher HP engine.

Get a paper clip and cut it in half. Then get a 12 volt resistor LED light.

- Ignition key off
- Remove the cap from the Data Link Connector (DLC). That's the capped plug hanging out in the back of the engine.
- Look closely at it. The terminals are clearly marked with letters.
- Slide the LED probe's positive side into terminal F and the negative side into terminal E.
- Turn the ignition key to the “ON” position. The LED should light with a steady light.
- Insert the half paper clip ends into terminals A and B Do not insert into the wrong terminals. You could damage the MEFI Now you are in Diagnostic or Service Mode and codes will begin to flash on the LED. On your (and my) engine the fuel pump might come on.
- Read codes by observing LED flashes. Pauses separate the digits. one flash, pause, three flashes, long pause - is code 13. 7 flashes, ling pause - is 7. Codes will flash in order of lowest to highest. Continue to read codes until the first code sequence is repeated.

You can also be clear codes (by moving the throttle to 100% and back) and set base timing as I had referenced in my other response, while in this Mode.
 

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
Here's what I did to make sure everything was operating normally after I set up my long block. Then I brought the boat to a marine service garage and had them plug it in to a diagnostic tool in order to make sure the MEFI 2 computer, which I had sent out to be reprogrammed, was done accurately to provide sufficient fuel for my higher HP engine.

Get a paper clip and cut it in half. Then get a 12 volt resistor LED light.

- Ignition key off
- Remove the cap from the Data Link Connector (DLC). That's the capped plug hanging out in the back of the engine.
- Look closely at it. The terminals are clearly marked with letters.
- Slide the LED probe's positive side into terminal F and the negative side into terminal E.
- Turn the ignition key to the “ON” position. The LED should light with a steady light.
- Insert the half paper clip ends into terminals A and B Do not insert into the wrong terminals. You could damage the MEFI Now you are in Diagnostic or Service Mode and codes will begin to flash on the LED. On your (and my) engine the fuel pump might come on.
- Read codes by observing LED flashes. Pauses separate the digits. one flash, pause, three flashes, long pause - is code 13. 7 flashes, ling pause - is 7. Codes will flash in order of lowest to highest. Continue to read codes until the first code sequence is repeated.

You can also be clear codes (by moving the throttle to 100% and back) and set base timing as I had referenced in my other response, while in this Mode.
I'll try to find that plug, I haven't seen any that didn't have wires coming out of it, but I'll look again.

Reading the codes would definitely speed this process along.
 

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
My oil pressure sender fix didn't do the trick. Took it out again to further examine the issue. Starts to surge around 1400 rpm, it will give me a second of power if I punch it but then it almost stalls out and goes back to idle
 

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
I was able to read the code according to the instructions above. That being said, all I got was the code for "self diagnostic system running properly".

Not sure what this tells me, if anything at all. Could this mean I can rule out any sensor issues?

Ultimately I'm even more confused now than previously.
 
Last edited:

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
It doesn't seem that it's going into limp mode unfortunately, because both injectors seem to drop down when it happens. I will try to disconnect that oil pressure switch to see if it helps anyway
 

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
I took it for another ride, with both safety sensors on the port side of the engine disconnected- presumably the oil pressure and temperature sensors. The boat ran the same.

I closely watched the injectors and noticed no change in either of their spray patterns under higher throttle when it started to bog down. So I don't believe it is going into limp mode.

My current theory is that the TPS unit is malfunctioning and the mixture is being thrown off under higher throttle. It's just odd because it runs so smooth at lower RPMs. I have no other theories right now- doesn't seem like fuel lines or vents either, and it can't be the injectors- they're spraying fine.

I think I'll order a new TPS sensor, don't know what else to try at this point.
 


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