TKS Ignition system hissing/sucking - not working properly

[IS-217]

2008 StarCraft 1800 I/O
Mercury 4.3L V6 TKS Carb
Engine Serial #1A073605

First time posting
First time boat owner
First year boating!

Hello everyone.
Lots of great info and help on here.
Shout out to Don and alldodge for some good posts and info about what I’m trying to figure out. I think I’m on the right track. Hopefully one or both of you can help me figure this out. I’m pretty savvy but I’m no mechanic so be patient with me I’m just learning as I go here lol.

I have been reading a lot of posts on this forum mainly to do with the TKS carb system as that is my issue. The enrichment cycle for the carb won’t turn off and it continues to hiss/suck and run rich constantly.
So far I’ve tested the TKS Module it seems to be working fine other than it took closer to 20mins for the pin to fully extend when hooked direct to the battery.

The diode is no good no continuity both ways looks like it shorted out one pin is grey/burnt looking.

The 15Amp fuse - top stern side of the engine - is also blown. Not sure what this fuse controls.

I’m leaning towards temp switch from what I’ve read but haven’t had a chance to run the boat up to temp to test the sensors continuity cold vs hot.

The boats seems to run fine otherwise. So I didn’t think it would be the oil pressure switch.

It does idle high which makes sense because the enrichment cycle is running constant.

I do have some issues warm restarts and one time after pulling a tube for a while it continued to run for a few seconds after I turned the engine off, then it cut out.

So I’m looking for any and all help here to figure this out.
Why did the 15Amp fuse blow?
Why did the diode blow?

I don’t want to replace these parts until I have a good idea of why or how this would’ve happened.

Anyone have an idea?
Teach me!!!

 

[alldodge]

Welcome

Why did the 15Amp fuse blow?
Why did the diode blow?

Most likely the TKS module is drawing to much current



You have a newer TKS so it could be the fuse was changed from 20 to 15 amp, but could also be it was changed by previous owner because they didn't have a 20

In any case sounds like the module is not working correctly, it should only take about 8-10 minutes for the pin to extend.

The diode needs to be checked with a meter using the diode setting. It can be done without a diode setting but need to see there is a large difference between when meter probes are swapped. Place probes on the pins and resistance should be higher in one direction then when probes are swapped.

The diode isn't shorted because if it was you could not shut the motor off

 

[dingbat]

The diode needs to be checked with a meter using the diode setting. It can be done without a diode setting Place probes on the pins and resistance should be higher in one direction then when probes are swapped.

Resistance when forward biased but a diode that shows any resistance at all in reverse bias is bad. Meter should read open (OL) when reversed

The component needs to be remove from the circuit to properly test.

 

[IS-217]

Welcome

Most likely the TKS module is drawing to much current

View attachment 402041

You have a newer TKS so it could be the fuse was changed from 20 to 15 amp, but could also be it was changed by previous owner because they didn't have a 20

In any case sounds like the module is not working correctly, it should only take about 8-10 minutes for the pin to extend.

The diode needs to be checked with a meter using the diode setting. It can be done without a diode setting but need to see there is a large difference between when meter probes are swapped. Place probes on the pins and resistance should be higher in one direction then when probes are swapped.

The diode isn't shorted because if it was you could not shut the motor off

View attachment 402042

Thanks for the quick response!
So I tested the TKS module last night. I removed it form the carb and hardwired it to the battery to see if it worked. It was pretty chilly last night but it did eventually warm up and extend. It was probably closer to 15mins for it to extend fully, I got a bit side tracked so I am estimating a little here on the time it took. I'm not sure how long its been inactive. I just got the boat in June this year and its made the sucking noise since I've had it. It's probably been this way for a while. The guy I bought it from never noticed it. I'm wondering if it just needs to be used a few times to work better and open faster?...
I tested the diode, it had no continuity both ways this means its not working properly right?
Based on a service bulletin (2006-04) I found about troubleshooting the TKS diode it says if no continuity both ways it means its open internally and will be hard restarts (my situation). If it has continuity both ways it is shorted and engine will continue to run after the key is turned off (only ever happened once for just a few seconds).
Either situation they say diode needs replaced.
As for the fuse. There IS a 20Amp fuse in the wire harness close to the diode. I'm referring to a 15Amp fuse in a wire harness running behind the distributer cap, stern side of engine. Do you know what this fuse is for? Is it part of the TKS wire harness too?
I don't care about replacing the fuse - cheap - I just don't want to replace the diode until I figure out why it failed. They are hard to find near to me so I need to order one to be shipped to a dealer near me. So would just be a pain if I did all that, drove picked it up, then it blows again and have to get another.
I'm trying to figure out the location and part # for the temp sensor switch that feeds this circuit. I read another post similar to my issue and I believe it was a temp sensor or switch that fixed everything. Service guy at my lake's marina told me to test the temp switch. He said if its not working it won't open (or close I forget now) and the power can't get to TKS module to stop enrichment process. Does this sound right? Do you know part # and location?

Thanks again for the help and diagram. I don't quite understand the wiring diagram though.
PS.. the TKS module pin DID extend fully as per the description in manual 41, it just took a little longer to do so.
I'm not currently at the boat, maybe I need to post some pics to show the location of this 15Amp fuse I'm referring to.

 

[IS-217]

Just looking at the wire diagram some more.
The note bottom right says:
"If diode shorts engine will continue to run, If diode opens TKS will not shut off extra fuel until temp switch closes."
Ok so this sounds like what I'm talking about.
Where is this temp sensor located?
Part #?

I am going to post a pic later this eve to show 15Amp fuse location. Maybe it is a separate issue? I haven't noticed any other issues with the boat. Maybe something else not working with this fuse blown?

 

[alldodge]

The diode burned out because the temp switch is shorting to ground or the module is drawing to much current.

The diode does not need to be replaced with a OEM type. You can go to local electronics store or get a 5 watt diode on line. A 5 watt diode is larger then the OEM but it can handle more current if it were to short again

The module is not fully extending the amount needed otherwise the hissing would stop

 

[IS-217]

The diode burned out because the temp switch is shorting to ground or the module is drawing to much current.

The diode does not need to be replaced with a OEM type. You can go to local electronics store or get a 5 watt diode on line. A 5 watt diode is larger then the OEM but it can handle more current if it were to short again

The module is not fully extending the amount needed otherwise the hissing would stop

What do you mean temp switch shorting to ground? What if it is not operating properly.
It won't feed power to TKS module if not closing at operating temp as per the note in the diagram you provided. This would explain TKS not extending.
The TKS DID extend fully I checked/tested it to manual 41 testing specs - all good.
Ok electronic store diode copy that I was wondering about this. How do I hook it up to the harness though. Diode current only goes one way right? What way do I hook it up?

 

[alldodge]

When motor first starts cold power goes from the key, thru the diode and to TKS

Temp switch is open because motor is cold.

When motor warms up Temp switches closes providing another path the feed power to TKS

When motor is shut off warm the Temp switch keeps power going to TKS to keep plunger extended. This is a small amount of current. If diode is shorted power will back feed thru diode to ignition and motor will not be able to be turned off.

If Temp switch shorts to ground, this will blow 20 amp fuse and can cause diode and TKS to over heat depending on how much current it sends to ground

Your not blowing the 20 amp fuse so my guess is its ok. The Temp switch is screwed into the intake manifold and has 2 wires coming out

To use any other diode it will need to be connected to same wires the original diode was plugged into. This is done in most cases by cutting the plug and soldering or crimp connecting the new diode in place. The diode will have a single line round one end of it. That line will be connected to wire going to TKS

 

[IS-217]

When motor first starts cold power goes from the key, thru the diode and to TKS

Temp switch is open because motor is cold.

When motor warms up Temp switches closes providing another path the feed power to TKS

When motor is shut off warm the Temp switch keeps power going to TKS to keep plunger extended. This is a small amount of current. If diode is shorted power will back feed thru diode to ignition and motor will not be able to be turned off.

If Temp switch shorts to ground, this will blow 20 amp fuse and can cause diode and TKS to over heat depending on how much current it sends to ground

Your not blowing the 20 amp fuse so my guess is its ok. The Temp switch is screwed into the intake manifold and has 2 wires coming out

To use any other diode it will need to be connected to same wires the original diode was plugged into. This is done in most cases by cutting the plug and soldering or crimp connecting the new diode in place. The diode will have a single line round one end of it. That line will be connected to wire going to TKS

This is really helpful alldodge, really appreciate the help here thanks for all the explanation of how the system operates.

So like you said, if the 20amp fuse isn’t blown then maybe the only issue here is the diode?
Can the diode just fail over time? Or do you think a grounding issue may of caused this? Problem is I don’t know if the 20amp fuse was blown at some point and then replaced without realizing the diode was affected.
Is there another way the diode could fail besides the temp switch grounding.
How could the temp switch short to ground? Or do you mean stick open or closed? Could you give me an explanation of what you mean exactly or how this could happen.
Is it still be possible for this temp switch to not be working proper? I may be getting confused maybe this will be answered with an explanation of short to ground from above question. I definitely need to check this switch before moving forward. Or would this 20amp fuse have already blown if temp switch not working.
Sorry hope I’m not driving you too crazy here lol.
You said the temp switch is in the intake manifold 2 wires. Are the wires yellow and black? Port side manifold? Part #? Is it 805218T?

Found this pic on my phone wanted to show you for reference this 15Amp fuse I’ve mentioned. Wondering what it is and why it’s blown. I’ll post back later with wire colours and a better pic but maybe you already know what it would be.

Thanks again you’re being very helpful. Really appreciate the help.

 

[alldodge]

So like you said, if the 20amp fuse isn’t blown then maybe the only issue here is the diode?

No, the diode is not in the circuit with the 20 amp fuse. There is interactions on what can happen if it shorts or opens, but don't want to get into teaching electronics 101 course here

The diode is not part of the current problem of running rich or taking to long to fully open.

Is it still be possible for this temp switch to not be working proper? I may be getting confused maybe this will be answered with an explanation of short to ground from above question. I definitely need to check this switch before moving forward. Or would this 20amp fuse have already blown if temp switch not working.

The switch is not shorted to ground because the 20 fuse does not blow. You can verify this by disconnecting it then measure ohms from each connection pin to ground. If motor is warmed up then there should be about zero ohms between the 2 pins

The temp switch is item 5

Don't know what the 15 amp fuse is but might be the fuel pump or ignition. With it blown does the motor run

 

[IS-217]

Yes boat runs fine other than the hissing noise and sometimes hard restart. Usually turns back on second or third try though. Sometimes I increase throttle to get it to go.
Ok so the diode having no continuity doesn't prevent power to TKS?
OK I will check the temp switch tonight.
What about the temp sensor attached to thermostat housing? Anything to do with TKS module closing?
Thanks

 

[Fun Times]

The 15 amp fuses in that area seems to had been more or an additional part of the ignition accessories system that Merc added around that era… it tends to seem to blow if you use other accessories, such as a pump to blow up at inner tube,, raft, etc. from say the helm accessory power plug but if you found symptoms of a wire getting hot at an accessory type device that is motorized with a plunger then possibly it’s somehow intertwined though seems doubtful due to the wiring coloring that I can recall anyways.

I’d also suspect that your engine temperature might not be getting up to full temperature range of 160° in a timely manner?… All within the 8 - 10 minute range at idle…You might need a new engine thermostat as well… if it’s really taken 15 to 20 minutes for the module plunger to fully activate, etc., then that needs to be either possible cleaned, lubed if desired to try to see if it helps speed up the process of moving or more so replaced in my opinion as a slow moving electrical motor may cause symptoms your experiencing.

Post 12 had a solution for this case,

Mercruiser 4.3 TKS -- Blown Ignition Fuse and Shorted TKS Diode

I have a 2008 Sea Ray Sport 205 with a Mercruiser 4.3L TKS engine. Recently the ignition fuse blew and I discovered that the TKS diode was shorted. After I removed the diode and replaced the fuse, the engine started and appeared to run fine. I ordered a new diode thinking that this would resolve...

forums.iboats.com

 

[IS-217]

I don't remember seeing the temp gauge ever reading higher than around 130. Cold lake? lol.. Maybe this is part of the issue. Would this mean possibly thermostat stuck open not letting engine get up to temp?
Helm accessory plug? I don't know what this is. Where is this located?
Never used any accessory plug to do anything.
Just boating and pulling tube or wakeboard.

I will take a better pic of 15amp fuse tonight and see what colours the wire is and post back.
Thanks for joining in!

 

[alldodge]

The TKS module is "not" fully extending, and this is why your hearing the hiss and most likely why it's hard to restart

If the diode is shorted as you say then the temp switch on the intake will not keep the TKS from fully extending. ONLY if the diode is open showing very high resistance in both directions, even infinity, then and only then the issue may be the switch or thermostat

The sensor on the thermostat housing has nothing to do with current issue

 

[IS-217]

The TKS module is "not" fully extending, and this is why your hearing the hiss and most likely why it's hard to restart

If the diode is shorted as you say then the temp switch on the intake will not keep the TKS from fully extending. ONLY if the diode is open showing very high resistance in both directions, even infinity, then and only then the issue may be the switch or thermostat

The sensor on the thermostat housing has nothing to do with current issue

The diode is open. will not allow current to pass either direction.
I'm leaning towards temp switch...
I tested the TKS module it DOES fully extend.
I measured it cold and measured it warmed up and measured the passage it goes into and with the amount it extends the passage would be blocked. (works properly)
I need to test the temp switch.
I thought I read from Don on a previous post that the temp sensor black and yellow wires does control the TKS. I may be confused though need to re read another post.

 

[Fun Times]

The accessory 12 volt power type plug normally would look something like a cigarette lighter plug in a car… it’s usually protected by either a 20 amp breaker or fuse at or behind the dash…. I recall looking up the info on the fuse you found and it’s mentioned as an accessory fuse…. Since it was first found and mentioned here on iboats forums in I believe 2012 or 13, you’re about the eighth member to bring it up over the years so roughly every year and a halfish it’s brought up one way or another.

Yes a thermostat stuck open would make the temperature to low to fully activate the full range of efficiency to this system and 130 is to low… A stuck open thermostat is generally held open by debris/small rocks, etc..

The yellow and black wires at Thermostat housing is more so a digital sensor that goes to the overheating warning alarm and runs to the ICM mounted on the port side exhaust manifold system… not tied into the TKS system.

 

[alldodge]

The diode is open. will not allow current to pass either direction.
I'm leaning towards temp switch...

I'm not trying to be mean or condescending but I/We need to get your attention so Knock, Knock hello.... please read what is being said, not what you think is being said

With the diode being open this changes things to what was said at first, now it's what was said in other post including last post 14

ONLY if the diode is open showing very high resistance in both directions, even infinity, then and only then the issue may be the switch or thermostat

Right now with diode being open and your only reading 130* the switch is NOT closing, so it's not the switch

You need to replace the diode and the thermostat as FT mentioned

 

[alldodge]

You can test the theory without replacing the thermostat or diode

Remove the 20 amp fuse
Install a jumper where the diode use to be

Fire the motor up and see if the hissing stops after running for a while

 

[IS-217]

I'm not trying to be mean or condescending but I/We need to get your attention so Knock, Knock hello.... please read what is being said, not what you think is being said

With the diode being open this changes things to what was said at first, now it's what was said in other post including last post 14


Right now with diode being open and your only reading 130* the switch is NOT closing, so it's not the switch

You need to replace the diode and the thermostat as FT mentioned

No worries.
I’m no mechanic and appreciate the help.
When I Said in my original post that the diode looks like it shorted I just didn’t have the lingo proper lol. But I did say it had no continuity multiple times and eventually corrected myself with reference to the bulletin and your wiring diagram and concluding that it must be open.
I also explained multiple times the TKS module was working fine when tested.
I heard you loud and clear. Maybe you didn’t hear me or missed some info I was trying to provide.
Either way you have been very helpful and have clarified how the system works for me very well so thank you.
I’m glad FT brought up the temperature issue and put focus on something else. Now that we know my engine isn’t getting warm enough it sounds like we may have the fix.

 

[IS-217]

You can test the theory without replacing the thermostat or diode

Remove the 20 amp fuse
Install a jumper where the diode use to be

Fire the motor up and see if the hissing stops after running for a while

Oh great thank you I will definitely try this.
So when you say jumper what do you mean exactly. Point A to point B. Sorry dumb it down a little for me lol.
And if the hissing goes away then the fix is new diode and thermostat? Is this what you’re thinking.
Sure hope so!! I’ll be so thrilled. Love being able to fix an issue and learn while doing so.
Now just need to figure out this 15Amp fuse. FT has an idea. I am going to get some pics and wire colours and report back tomorrow.
I’ll be running the boat this Saturday.
Cross your fingers fellas.
Thanks a bunch guys.
Cheers.