Possible TKS Band-Aid/4.3

[Flash550]

Hello all, I’ll make a proper intro post when I have time and a running boat.

I have a 2008 Tahoe Q5i with the 4.3 TKS motor, SN 1A078281. Last weekend it left me dead in the water with no power to the ignition switch. Through research done here I found the TKS thermal switch and diode were both bad and had blown the 15 and 20 amp fuses in the circuit. TKS module tests fine on the bench. I have parts on the way...but they won’t be here until next week and the family really wants to get on the water this weekend.

I am thinking about leaving the temp switch unplugged and the diode out, and then running a stand-alone 12v circuit with a switch, relay, and fuse to the TKS module. Then just turn the switch on to energize the circuit and hold the plunger closed once the engine has warmed up. This would only be a temporary measure.

I can’t think of a reason why this wouldn’t work, but I thought I would run it by the big brains on here before I do more harm than good. Thanks for any input or suggestions!

- Flash

 

[alldodge]

I don't see an issue with what your planning

The temp switch mush have shorted internally to ground to blow the 20amp fuse.

 

[Flash550]

AllDodge, thanks for the reply and diagram. According to my multimeter, the temp switch is definitely shorted internally. Where does the 15amp fuse land in that diagram. Thanks again!

 

[alldodge]

I'm not seeing a 15 amp in the TKS wiring, also not seeing one in 4.3 manual (not looking thru all of them), but then again I don't know what 4.3 motor you have?

What color are the wires that connect to the fuse?

 

[Scott Danforth]

I was never a fan of the TKS

 

[Flash550]

I'm not seeing a 15 amp in the TKS wiring, also not seeing one in 4.3 manual (not looking thru all of them), but then again I don't know what 4.3 motor you have?

What color are the wires that connect to the fuse?

I am not sure about the wire colors, but it is the fuse that is behind the carb in the bundle by the distributor. I think it supplies power to the key switch, but I could be wrong about that. Could be why it’s not in the TKS wiring though.

The more I work through this ridiculous TKS system the more I think that if my switch works I’m just going to wire the switch up to the dash and eliminate all the extra garbage.

 

[alldodge]

I don't know, but the motors started putting fuses on the motor when they went to EFI/MPI but prior I just don't know. Maybe something added by a PO or other, :noidea:

 

[Flash550]

I don't know, but the motors started putting fuses on the motor when they went to EFI/MPI but prior I just don't know. Maybe something added by a PO or other, :noidea:

Its a mercruiser installed fuse...and I think it is for the fuel pump. From what I can find it seems that if the TKS diode fails open (allowing current in either direction) that fuse will blow to protect the fuel pump from a reverse current. Why the TKS system is in any way connected to the fuel pump is beyond me.

 

[achris]

Its a Mercruiser installed fuse...and I think it is for the fuel pump. From what I can find it seems that if the TKS diode fails open (allowing current in either direction) that fuse will blow to protect the fuel pump from a reverse current. Why the TKS system is in any way connected to the fuel pump is beyond me.

If a diode fails 'open', it's an open circuit, current doesn't flow, in either direction. If the diode fails in such a way as to allow current to flow in both directions, it has failed 'short'....

It's connected to the fuel pump because the supply to the fuel pump is the only one that is 'disconnected' when the engine stalls and the oil pressure drops. If it was connected to any other (key) switched source, it could be constantly supplied without the engine running... Either from leaving the key on, or the engine stalling unattended.

And there has always only been a 20A fuse in the TKS/temp switch circuit. Where is this 15A fuse? (No wiring diagrams show a 15A fuse anywhere on the engine, and historically, Merc have always only used 20A fuses. Keeps the spares carry down. And makes it impossible for electrically-ignorant mechanics to make a mistake. :facepalm

Chris........

 

[Flash550]

If a diode fails 'open', it's an open circuit, current doesn't flow, in either direction. If the diode fails in such a way as to allow current to flow in both directions, it has failed 'short'....

It's connected to the fuel pump because the supply to the fuel pump is the only one that is 'disconnected' when the engine stalls and the oil pressure drops. If it was connected to any other (key) switched source, it could be constantly supplied without the engine running... Either from leaving the key on, or the engine stalling unattended.

And there has always only been a 20A fuse in the TKS/temp switch circuit. Where is this 15A fuse? (No wiring diagrams show a 15A fuse anywhere on the engine, and historically, Merc have always only used 20A fuses. Keeps the spares carry down. And makes it impossible for electrically-ignorant mechanics to make a mistake. :facepalm

Chris........

You’re right, I misspoke about the diode.

So, the fuel pump doesn’t run until there’s sufficient oil pressure? Doesn’t that somewhat negate the whole advertised benefit of TKS? I get that it’s probably a safety feature to keep the fuel pump from emptying the tank if the float sticks open in the carb. Still seems like a standard electric choke would have been a better option.

I refer to to it as a 15 amp fuse because that was what was in there when I found it blown. Could have been improperly replaced at some point, I’ve only had the boat for about a month. However, there are two fuses: one right by the diode that had a 20 amp and one behind the distributor that had a 15 amp. Both blown.

Thanks for for the help!

- Flash

 

[achris]

You’re right, I misspoke about the diode.

So, the fuel pump doesn’t run until there’s sufficient oil pressure?

Or the engine is being cranked..

Doesn’t that somewhat negate the whole advertised benefit of TKS?

What 'advertised benefits?' The whole reason being the TKS is to bring starting procedures more into line with modern fuel injected car engines. In the bad 'ol days of chokes and carbs, people understood that you have to 'set' the choke before attempting to start the car. A choke relied on a getting a sucking force ABOVE the throttle plate. You did that by closing the choke and opening (slightly) the throttle. When injection in cars came of age, people got used to just turning the key and the engine would start. That's because the ECU would enrich the mixture, and open the idle air valve to induce a 'fast idle'.... All the thinking was removed. You just turned the key.... Now, so many people are used to that, and have forgotten (or never had to learn) how to start a 'choked carb' engine. So, in came TKS. It replaces the choke plate with an enricher system, but in order to work properly, the enrichment fuel needs to be drawn from BELOW the throttle plate, which means keeping the throttle plate closed during cranking. And hence you get.... 'turn key starts', with no requirement to move the throttle, and so all the young people are happy. :facepalm:

I get that it’s probably a safety feature to keep the fuel pump from emptying the tank if the float sticks open in the carb. Still seems like a standard electric choke would have been a better option.

For people who know how to operate a 'choke', yes. For people who've never heard of a 'choke', no, it's a terrible system, they have to actually think about what they are doing.

I refer to to it as a 15 amp fuse because that was what was in there when I found it blown. Could have been improperly replaced at some point, I’ve only had the boat for about a month. However, there are two fuses: one right by the diode that had a 20 amp and one behind the distributor that had a 15 amp. Both blown.

I have a recollection of a 'new' fuse back there. I think Fun Times knows more about that....

Thanks for for the help!

- Flash

 

[Flash550]

The whole reason being the TKS is to bring starting procedures more into line with modern fuel injected car engines.

That would be great if it worked, but it seems like the overwhelming consensus, on here and many other forums I’ve seen, is that the system is a POS and doesn’t age well. An “ease of starting” feature shouldn’t leave you dead in the water when it fails. At worst the engine should be slightly harder to start. Maybe I’m getting old, or maybe it’s because I’ve been working on jet engines for the last 22 years, but simplicity and stand-alone systems are what I want in anything that floats or flys. I think I’m going to have to put fuel pump and enrichment switches on the dash and eliminate all the other BS.

 

[achris]

That would be great if it worked, but it seems like the overwhelming consensus, on here and many other forums I’ve seen, is that the system is a POS and doesn’t age well. An “ease of starting” feature shouldn’t leave you dead in the water when it fails. At worst the engine should be slightly harder to start. Maybe I’m getting old, or maybe it’s because I’ve been working on jet engines for the last 22 years, but simplicity and stand-alone systems are what I want in anything that floats or flys. I think I’m going to have to put fuel pump and enrichment switches on the dash and eliminate all the other BS.

Don't shoot the messenger!

I'm just telling you how it's designed to work. I make no comment on whether it's a good system or not.

Ok... Here's how I see it, from an electronics standpoint. The only real problem with the system is the diode, it's under-specced... And a replacement from Mercury is over-priced. From the service manual, the TKS module resistance shouldn't be any lower than 30Ω, which means a current no higher than 0.5A... You can go to any electronics shop and buy a 1N5408 (which is a 3A diode) for less than 50c! (as opposed to Merc's $22)...

As for the 'aging', like any carburetor, it needs maintaining, which means removing and stripping every 5 to 7 years. Which means you should be just about ready for it's second stripping....

I'm sure in your working on jet engines for 22 years, you have seen a lot more electronics on them, and a greater reliance by the pilots on their instruments and the 'automatics' to fly rather than actually learning to fly properly (2 crashes involving faulty software on Boeing 787-MAX aircraft should be a wake-up call about reliance on systems, instead of skills. But it won't be :facepalm...

So, do the maintenance (boats aren't maintenance-free), understand how things work, and mostly remember.... All those components on your boat engine, boat trailer, all the electronics you have on board, and indeed the boat itself, were built by the LOWEST bidder.... It's naive to expect to get top quality equipment on a budget machine.... As I say to my wife each year, on our first cable car ride of the ski season, "Our lives are in the hands of the lowest bidder"... And so it is with your boat.... Also consider why they're built that way... It's to cater for the lowest common denominator. And in the case of boats, that will be a low IQ red-neck of some description (I've seen the videos :facepalm. You start putting more on the dash than an ON/OFF switch, he's going to get confused....

Chris......

 

[Scott Danforth]

if you want simplicity, yank the TKS carb and install an edelbrock 1409 with a 1485 calibration kit or sell the boat and go with MPI

FAA rules dictate that aircraft must be maintained, and if there is a system found to be problematic, it is replaced. if not followed, the plane is grounded

boating...... well.....the majority of owners do not do maintenance and sell the boat prior to the end of the warranty. majority of them also cant operate anything with a choke, and that included small engines, lawn and garden equipment, outboards, or an I/O with a traditional carb. because of this very reason, marketing pressure to come up with the TKS carb is why it exists.

in addition to the carb having been serviced at least once like Chris mentioned the drive should have been off the boat 11 times now and the bellows replaced twice and the raw water impeller replaced about 3 times.

 

[Flash550]

Don't shoot the messenger!

I'm sure in your working on jet engines for 22 years, you have seen a lot more electronics on them, and a greater reliance by the pilots on their instruments and the 'automatics' to fly rather than actually learning to fly properly

Lol no shots fired!

I should clarify - I am a C-130 Flight Engineer and A&P mechanic. Most of the planes I have flown or wrenched on were built in the 60’s. The jet engines I referenced are turboprops that use speeder springs and flyweights to control engine speed. The systems were designed in the 50’s and are as simple and dead-nuts reliable as they can be. And being military I know all about the lowest bidder! But I get what you are saying.

The boat is an 08, but it only has about 300 hours on it. I have gone through everything and done all the maintenance items, to include rebuilding the carb, and I’m dealing with things that go bad when you let a boat sit. Which is why I said that TKS doesn’t age well. The system seems like a good idea that was poorly executed.

Thanks again for for the input, this is a good conversation.

- Flash

 

[Flash550]

So I ended up making a circuit with a 20a fuse, simple switch, and SPST relay. I made a plug that works with the connector on the TKS module. Start the motor, flip the switch to energize the circuit, and the TKS module works as advertised. Just ran it on the hose for a good 30-40 minutes with no issues at all. Best part is that I didn’t have to splice into the factory harness. Still going to change the temp switch and diode when the parts come in, but I’m definitely keeping this bypass in my tool kit so that this stupid system can’t leave me stranded again.

Thanks again for everyone’s input!

 

[Swoopty]

You’re right, I misspoke about the diode.

So, the fuel pump doesn’t run until there’s sufficient oil pressure? Doesn’t that somewhat negate the whole advertised benefit of TKS? I get that it’s probably a safety feature to keep the fuel pump from emptying the tank if the float sticks open in the carb. Still seems like a standard electric choke would have been a better option.

I refer to to it as a 15 amp fuse because that was what was in there when I found it blown. Could have been improperly replaced at some point, I’ve only had the boat for about a month. However, there are two fuses: one right by the diode that had a 20 amp and one behind the distributor that had a 15 amp. Both blown.

Thanks for for the help!

- Flash

I have the same 20 & 15 amp fuses on my 2008 Q6, in the same locations. I am having an issue with both of these fuses blowing when the boat heats up. I had been having intermittent problems with thing like the tach or temperature gauge only working sometimes. I finally ran across the large plug on the back of the engine going to the wire harness. It twist locks into its mating plug on top of the engine but the other end is plugged into another mating plug and a hose clamp on the outside keeping it together. Found that it was only partially engaged. Once I pushed it all the way in, everything lit up on the dash and the tach and temp gauges worked fine.…until I got out on the water. got about a minute out from the marina and it started losing power then it just went dead. Both fuses were blown. The moment I put my spare 20 amp fuse in, there was a tiny spark and it blew the fuse straight away. for some reason it now has a dead short and I cannot figure it out. Could it be a temperature sending unit? Where is the temp sensor located?