89 Johnson 150 going into slow mode

[droutte]

My moter is going into slow mode after running good for 15 to 20 minutes. I am getting a stream of water, and no horns are sounding. How can I pinpoint the problem.<br />Model # J150STLCEM<br /><br />Thanks<br />Dan

 

[droutte]

Re: 89 Johnson 150 going into slow mode

Any suggestions appreiciated

 

[Dhadley]

Re: 89 Johnson 150 going into slow mode

What kind of water pressure? What boat? Jackplate? If so, manual or hydraulic? Has it always done this or just started? Anything mounted in front of the lower unit within 12" of either side? Has the water pump been changed? If so, what brand and part number? Thermostats and pressure relief valve in or out?

 

[fireman57]

Re: 89 Johnson 150 going into slow mode

Are you sure you aren't losing spark to a cylinder? When it goes to slow mode stop it and pull the plugs. If one is wet then I would suspect the coil going to that plug.

 

[angus63]

Re: 89 Johnson 150 going into slow mode

#1- How do you know it is going into slow mode? What are your normal WOT RPM and Current WOT RPM?<br /><br />#2 - Fireman, dropping one cyl does not affect wot rpms nearly as much as slow mode (one cyl appx 500 rpm vs slow mode 3000 rpm difference).<br /><br />#3 - Have you shorted temp and oil alarms to verify horn?<br /><br />#4 Please describe exactly what happens when you encounter this problem.

 

[fireman57]

Re: 89 Johnson 150 going into slow mode

Angus63 you are right if he is actually in slow mode. I have seen a lot of posts where they lose power and call it slow mode. The powerpack gets hot and shorts across. You are right in what you are saying about the rpms and that he needs to give you guys more info.

 

[droutte]

Re: 89 Johnson 150 going into slow mode

1989 Ranger bass boat.No jack plate. It has ran great until now. Same water pump but don't know water presure. <br /> I take it out and it runs great for 20 minutes. I will get up on plane the second or third time after fishing and it will fall on its face and limp back at lower speeds OK. I will get plenty of RPM's with no load. RPM meter is not working.<br />I have replaced all the coils & plugs, and has a fairly new power pack, stator and timer base. <br /> I do not know about the thermostat or presure relief valve (don't know where they are). Do not know how to verify horns

 

[Dhadley]

Re: 89 Johnson 150 going into slow mode

OK. When it goes into SLOW you should be able to stop, shut it off and restart it and it'll be OK. Shutting it off resets the sysytem. If it doesnt run correctly after a restart then its not going into SLOW. It may just be an ignition problem.<br /><br />Lets start there.

 

[angus63]

Re: 89 Johnson 150 going into slow mode

Since you are getting high rpms in neutral with no load ( if by high you mean over 2500), then you are not in slow mode. I recommend a tach and verifying the alarms before you move ahead. Simply ground the tan wires from the temp senders in the head with the key on and listen.<br />One other easy thing to check is the shift interrupt switch. Make sure it is adjusted correctly and you are not dropping 3 cyls occassionally (I believe that year had that feature).