1992 Nissan NS90A alarm at low speed, Dies above 3/4 Throttle

E

EastsideMidge

Recruit
Joined
Jul 22, 2025
Messages
5
I have a 1992 Nissan 90 HP outboard. Lately it has been having issues with running with the boat on plane, anything above 1/2 to 3/4 throttle will kill the engine. It acts like it has the fuel cut out. bogs and stalls. It can sometimes recover by returning the throttle to neutral, sometimes it does not. Usually it will restart, but it cranks slow. Last time this happened, the motor would not restart and I pulled the boat until it can be resolved. My initial impression was it may be a fuel issue, starving for fuel at the upper end of throttle, but I am starting to second guess myself after reading threads about the water pressure switch. I was getting an alarm at low speed that would clear up after 1/4 throttle. I am wondering now if the engine is getting hot under load and cutting out via the high temp sensor or the pressure switch. Any help or opinions are appreciated. I am not sure on the theory of operation of the high temp cutout and water pressure switch, if they could cause an issue like this. I do not have factory Tohatsu/Nissan gauges to indicate whether the motor is getting hot.

For reference, I am running a new-ish fuel line and primer bulb, new-ish aluminum 12gal tanks (2yr old for both) which have not given me issues in the past. I installed an impeller last year. The impeller may have had an extended out of water run event, and is going to be replaced ASAP along with the thermostat. Also on the list is a link and sync. I currently have a factory service manual as well. This is a freshwater boat.

Thanks for any help.
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
43,317
Welcome
Never worked on a Nissan but your getting an alarm and then the motor starts to die. Need to do some testing

Did find that the Nissan is actually a Tohatsu just rebaged

Crank slow can come from a weak battery, bad connections or the motor is over heating. Take a IR temp gun and measure head temp under 1/2 throttle and what happens above that

Don't think it's fuel because there is an alarm and it's 2 stroke
 
A

Arky86

Cadet
Joined
Jul 25, 2025
Messages
9
EastsideMidge said:
I have a 1992 Nissan 90 HP outboard. Lately it has been having issues with running with the boat on plane, anything above 1/2 to 3/4 throttle will kill the engine. It acts like it has the fuel cut out. bogs and stalls. It can sometimes recover by returning the throttle to neutral, sometimes it does not. Usually it will restart, but it cranks slow. Last time this happened, the motor would not restart and I pulled the boat until it can be resolved. My initial impression was it may be a fuel issue, starving for fuel at the upper end of throttle, but I am starting to second guess myself after reading threads about the water pressure switch. I was getting an alarm at low speed that would clear up after 1/4 throttle. I am wondering now if the engine is getting hot under load and cutting out via the high temp sensor or the pressure switch. Any help or opinions are appreciated. I am not sure on the theory of operation of the high temp cutout and water pressure switch, if they could cause an issue like this. I do not have factory Tohatsu/Nissan gauges to indicate whether the motor is getting hot.

For reference, I am running a new-ish fuel line and primer bulb, new-ish aluminum 12gal tanks (2yr old for both) which have not given me issues in the past. I installed an impeller last year. The impeller may have had an extended out of water run event, and is going to be replaced ASAP along with the thermostat. Also on the list is a link and sync. I currently have a factory service manual as well. This is a freshwater boat.

Thanks for any help.
Click to expand...
I have the same engine and am having the same problem. Hoping to get some answers off your post. I have replaced the fuel pump, all the fuel lines, the spark plugs, and the primer bulb thinking it was a fuel issue as well. After mine dies it doesn’t want to idle. Hopefully we can get some answers! I can putt around in mine all day with zero issues, but like yours at 3/4 or more throttle after a short time it dies.
 
E

EastsideMidge

Recruit
Joined
Jul 22, 2025
Messages
5
Arky86 said:
I have the same engine and am having the same problem. Hoping to get some answers off your post. I have replaced the fuel pump, all the fuel lines, the spark plugs, and the primer bulb thinking it was a fuel issue as well. After mine dies it doesn’t want to idle. Hopefully we can get some answers! I can putt around in mine all day with zero issues, but like yours at 3/4 or more throttle after a short time it dies.
Click to expand...
Well, if you learn anything about the issue please share. I am waiting on parts right now. Also just learned that the thermostat is discontinued from Tohatsu. I did order the thermostat from the next (newer) model variant of the motor. the part number was only one character off. Hopefully it fits. The image looks identical to what I had in the motor.

I have also had another thought that the stator may be failing after the motor gets heat soaked. Runs fine at low speed but may create an open/short circuit after getting warm. Next step for me is to replicate the failure and begin some testing on the stator.
 
A

Arky86

Cadet
Joined
Jul 25, 2025
Messages
9
EastsideMidge said:
Well, if you learn anything about the issue please share. I am waiting on parts right now. Also just learned that the thermostat is discontinued from Tohatsu. I did order the thermostat from the next (newer) model variant of the motor. the part number was only one character off. Hopefully it fits. The image looks identical to what I had in the motor.

I have also had another thought that the stator may be failing after the motor gets heat soaked. Runs fine at low speed but may create an open/short circuit after getting warm. Next step for me is to replicate the failure and begin some testing on the stator.
Click to expand...
I certainly will and same to you! I replaced all the fuel lines, filter, primer bulb, and the pump not confident but trying to eliminate things. Hopefully be able to test this weekend. Mine also does an alarm at slow speeds so I have to bump throttle up just like your having
 
E

EastsideMidge

Recruit
Joined
Jul 22, 2025
Messages
5
So here is my latest update: I found that the charging voltage is low, about 12.3VDC at idle to 12.6VDC at 1500 rpm. The voltage from the stator to the regulator was 20VAC at idle and 30VAC at 1500-2000 RPM. Maybe not my primary issue, but certainly an issue. Voltage regulator on the way. Could be a possible cause to the high RPM stalling and slow cranking I was experiencing, if battery voltage dropped too low and the ignition coil didn't have enough power to stay energized could cause this issue, especially at high RPM where the power demand for the ignition system is the greatest.

Other things I am working on diagnosing is a potential CDI box issue. Symptoms match from what I have read, but I need to verify the CDI input voltages first. I found a really good troubleshooting guide here that I am going to use to diagnose the CDI https://www.marineengine.com/parts/...outboard-ignition-troubleshooting/124/#zoom=z
 
E

EastsideMidge

Recruit
Joined
Jul 22, 2025
Messages
5
Here are my latest findings:
I bought a good used voltage regulator on Ebay for about $40. It is not the same as the old one, but the wires and connections are identical. The Tohatsu catalog shows this part has been upgraded, and that looks like the one I got.

So far the charging voltage seems to be better. After replacing I was getting about 12.5VDC at idle and 13.0VDC at 3000+ RPM. This is with a fairly weak battery. So I am going to call the charging system fixed. This is better than my old regulator for sure, but still not up to automotive levels of charging. I don't know if it ever would be, though.

Did this fix my "above 3/4 throttle" stalling issue? That is to be determined. The weather here is already turning. I do not know if I will be able to make it out on the lake and put the motor under load before fall fully hits.

I am one that likes to close out a forum thread, at least for my own sake and diagnostic notes. So I will likely post updates when this is done/verified.
 
You must log in or register to reply here.
Top