96 Fast Strike 175 - intermittent SloMode

ddakota

Seaman Apprentice
Joined
Jul 11, 2009
Messages
34
Got a strange issue going on and can’t replicate it in my tub at home. 96 Johnson 175 FastStrike, - runs great, bump the key it fires right up, high rpms running great then the hi temp alarm goes off, motor goes into SloMode but immediately comes out and goes into a cycle of slow mode, no issue, slow mode, no issue - real fast - like riding a bucking horse. I mean it’s going in and out of slow mode about as fast as you can say in, out, in, out, like your flipping a light switch on, off, on, off.

It’s happened a couple of times on my last 2 trips. Water pressure gauge shows 25 psi, plenty of pressure and water flow. Temp gauge show 160 or so....not hot.

Immediately pull the throttle back to neutral, alarm goes off, then give it gas and it does it again at around 3000 rpm.

Immediately pull the throttle back to idle, turn the key off. Immediately crank it back up and it runs like a dream. No issue .... until it decides to do it again, if it does.

Pulled my thermostats and they are clean , no scale, everything looks good as new.

Water pressure is great. Running in my tub checking the heads with infra red temp gun - 157-163 degrees on all 6 cylinders, overheating is not an issue.

In fact, in neutral at high rpms in the tub, the temps fall due to the increased water pressure flowing through it.

My thought is If it was overheating the motor would have to sit for awhile to cool down so it would come out of slow mode. It doesn’t have to do that. Just turn the key off then fire it back up and it’s fixed.

Question - could it be the power pack or one of the head temp sensors that feed the slow mode system? It has 2 of those, one in each head. Wouldn’t cost a lot to replace both just to see. Can’t find much on the web about those going bad. Would the temp sensors be feeding info to the power pack to initiate slo mode?

Because it cures itself by turning the key off I’m leaning towards power pack issue.

anybody ever see this?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,074
The temp sensors in the heads do cause SLOW mode. Disconnect them and retest. Yo will find the two wire sensor (for Quickstart and temp) is a fair amount of $

I think turning off the ign, resets SLOW mode. temporarily.
 

ddakota

Seaman Apprentice
Joined
Jul 11, 2009
Messages
34
Thanks. Kinda hard to retest when I can’t replicate it in the shop. I’m convinced it’s an electrical gremlin and those are hard to nail down when its intermittent and difficult to replicate in the shop.

The 2 wire port sensor is about $180, the single wire starboard, $70. Since they are both about 25 yrs old now, may just replace both and see what happens.
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,679
Disconnect them both and take it for a ride. If good Reconnect one and ride some more. You get it.
 
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