Mercruiser TKS (Mercarb) functionality?

[boatman37]

Have a 2006 Mercruiser with a 2bbl Mercarb with TKS (TurnKey Start). There is no choke mechanism but has an enrichment solenoid for cold starting. Mine is not functioning and tried a different tested solenoid with no luck. Anyone know how these work? Constant 12V? Only 12V after engine is up to temp? Where is it triggered from?

Thanks!

 

[Fun Times]

The theory of TKS operation starts here and should help some with your questions, http://boatinfo.no/lib/mercruiser/manuals/mercruiser41.html#/12

Being an 2006, you may have a bad TKS Diode, http://boatinfo.no/lib/bulletins.html#mercruiser-service-2006_04

 

[boatman37]

Thanks! Will read up

 

[alldodge]

Don't know what motor

 

[boatman37]

Thanks. 5.7. Runs fine but at cold start it wants to stall so i manually raise the RPM in neutral. Seems lie TKS should be doing that itself?

 

[alldodge]

Yes, the TKS module extends a rod into the enrichment passage once warmed up. With the motor cold, the rod should be retracted so air can be pulled thru it.

 

[boatman37]

Yeah I found a PDF for it so been reading that. Have to think it through though. Sounds like it should have 12V when cold then once it warms up the voltage is cut? If that is the case then I must not have any voltage under any condition? Read that there is an inline fuse so hopefully it is that simple. If not I can continue with what I have been doing but my OCD means it has to work as it should...lol

 

[alldodge]

Sounds like it should have 12V when cold then once it warms up the voltage is cut?

NO
Voltage is applied when started. Once engine warms up the temp sender switch closes and keeps 12V on module full time until temp switch goes cold, the it opens switch. This means that once started and warmed up, module is constantly pulling 12V and very low current.

 

[boatman37]

hmmm. ok. Going to have to do some testing and investigating. Thanks and I'll probably be asking more questions once I start testing

 

[boatman37]

Haven't made much progress here but had the boat out last weekend. Other than manually setting high idle when cold everything worked great. Boat ran perfect. Read somewhere about touching the back of the TKS solenoid to see if it is getting hot and it was definitely hot. So it seems to be getting the power to the solenoid. Had granddaughter all weekend so didn't have much time to tinker.

 

[boatman37]

So after reading the manuals linked here and my own research it seems as though I may be getting 12V to the TKS module all the time, not allowing the solenoid to retract? If that is the case then the likelihood is that my temp sensor is bad and stays closed at all times, allowing current? I will be testing this but the logic makes sense? The boat runs fine but always acts as though it is warmed up so that tells me the TKS solenoid never retracts to uncover the fuel enrichment port? Since I had had 2 different carbs with 2 different solenoids and the new one was supposedly tested before they shipped it to me I'm going to 'assume' the TKS solenoid id good. If all of that is accurate then the coolant temp sensor must be bad?

I will try to check it this weekend. Should be open when cold (below 110*). Wonder if I unplug the TKS solenoid and try a cold start? Wouldn't that behave the same below 110*?

 

[alldodge]

Agree, sounds like the temp switch.
Disconnect the switch and it should retract

 

[boatman37]

Well unplugged the coolant temp switch and started it up. Same thing as before. tarted at low idle and ran. Checked it for short. Open when cold then it closed when it warmed up. Just like it should. Checked the 20A fuse and it was good. Didn't check the diode cause from what I read if the diode fails one way the boat won't turn off and if it fails the other way the engine will be hard to start when warm, an it actually starts better when it's warm so I doubt it is the diode.
Aside from that I'm not sure what to look at now. If I don't figure it out then no big deal since I just idle it up manually after I start it but just wanted to get it working the way it was designed...yeah, my OCD...lol.

Any other ideas? I can try to think through it some more but not sure right now what else it could be

 

[alldodge]

When cold is the cylinder did retract, so its working

Not blowing fuse

Closes when warm and restarts good when warm

If it will not idle when its cold then fuel mix is not correct, timing is not correct or idle rpm is not correct

 

[boatman37]

Not that it won't idle. It will idle but barely. Once it warms up it idles fine. It idles at a lower RPM when cold at startup. Maybe 500 RPM, like barely idling. I always manually bump it to about 1000 RPM until it starts to warm then slowly drop it down a little at a time until it's back at the neutral position. I set the idle mixture by ear at about just over 3 turns out. Saw in the manual posted about it should be 3 turns out so I bumped it out slightly today. Engine idle is about 650 RPM when at operating temp, which is what the manual calls for.

I'm going to try to do a little more testing next weekend