4.3L TKS Not getting voltalge

[tahoejag]

Engine Ser # OW 380643, 2006 4.3l. Discovered that the diode was overheating and not allowing engine to start. Engine would start and run without diode plugged in. Plugged new diode in and engine starts and runs. TKS at this time still not operating correctly....hissing still after engine warmed up. Discovered a 20 amp fuse was blown, replaced that...engine still starts and runs, tks still hissing/not kicking off after warm up. checked the tks enricher....clean. put back together. did voltage test, not getting voltage at the tks wire harness. the key is on but not started....does this make a diff? does it have to be running? what or where else should i check for this non-voltage??? new diode, new 20 amp fuse was replaced. thanks in advance for any advice.

 

[alldodge]

When key is ON power goes to the TKS module, and since your not getting the voltage there is a disconnect somewhere. With your diode overheating, 20 amp fuse blowing, it may be that the module was is the issue

 

[tahoejag]

Could it be possible that the temp switch is shot also? I am NOT getting any continuity thru the temp switch cold engine or warm.

 

[tahoejag]

Also noticed when initially starting, the idle is down, seems normal...700 rpms or so for only the first say 15 seconds, then the idle jumps up to 1100 rpms at a constant and stays there. ???

 

[alldodge]

Could it be possible that the temp switch is shot also? I am NOT getting any continuity thru the temp switch cold engine or warm.

When the key is on 12V goes thru the diode to the module
When the motor reaches operating temp, the temp switch closes to keep 12V on the module.

As long as the motor is running, or at operating temp, power continues to be applied to the module.

Also noticed when initially starting, the idle is down, seems normal...700 rpms or so for only the first say 15 seconds, then the idle jumps up to 1100 rpms at a constant and stays there. ???

This also says the module is not working. The motor is cool and does not atomize gas very well. In just a few it starts doing it betterm and also the float bowl is now full of gas

 

[Fun Times]

Did voltage test, not getting voltage at the tks wire harness. the key is on but not started....does this make a diff? does it have to be running? what or where else should i check for this non-voltage??? new diode, new 20 amp fuse was replaced.

Yes depending on where you're testing and if the engine is cold or hot, the engine may have to be running or cranking to preform a voltage test....On V6 and 8 engines, the 12v power comes from/through the oil PSI switch.

And yes the temp switch is one/another 12v path as well to the turn key start module and diode systems via the white wire.

You'll want to see if the TKS Module has 12v power when either engine running or hot/engine off also see/feel if the TKS module at the side of the carb is getting warm to the finger touch.

Since you don't seem to mention a loud hissing noise or much of an RPM fluctuation from cold to warm starts, it seems you'll have some sort of TKS module problems either it be 12v power or component type problems which component can turn into power problems of course.

TKS (Turn Key Start) carburetors. When the engine is warm ...

 

[alldodge]

the 12v power comes from/through the oil PSI switch.

Got to disagree FT
During cranking, power to the fuel pump comes from the starter. Turning the key to ON sends power to the module and at the oil pressure switch, once oil pressure builds up then 12V passes to the Fuel pump

 

[Fun Times]

Got to disagree FT
During cranking, power to the fuel pump comes from the starter. Turning the key to ON sends power to the module and at the oil pressure switch, once oil pressure builds up then 12V passes to the Fuel pump

10/4 on the power flow for the fuel pump starts at the starter via the purple/yellow wire when cranking then basically flows into the main purple power wire .. I was just shortening up the power flow sequence staring at the oil switch as a reminder of sorts.

From there to me manual 41 seems to be suggesting the purple/yellow wire also powers up the diode in question then over to the temp switch and TKS module via the white wire at certain times of engine temperature affecting 12v testing of where it's being done at.

If interested, Under "Components" see step 4,
http://boatinfo.no/lib/mercruiser/ma...ser41.html#/12

And #'s 14 - 20 here in the wiring diagram was my bases but there are a number of inconsistent within this one manual alone such as for example trying to figure out all the ohm's testing number sequences for the switches,
http://boatinfo.no/lib/mercruiser/ma...ser41.html#/28

https://forums.iboats.com/forum/engi...7#post10579227

 

[alldodge]

I have manual 41, and did many hours of research on this issue. Even posted it on the forum for discussion and comments to make sure I got it right.

Your last link doesn't work right now but maybe that's iboats

Sure hope I'm right because of so much effort trying to make sure its correct. This is when I made up my drawings

 

[tahoejag]

I discovered that I am not getting any voltage or any type of reading of voltage to the TKS module, to the diode assembly or the the temp thermal switch. This is while the engine is running. I disconnected the diode, the TKS module, unplugged the 20 amp fuse and the thermal switch....engine still runs. I do have oil pressure which is indicated on the gauge as long as it is plugged in but also disconnected the oil pressure wiring from switch and engine still runs...with all the above unplugged. I am still getting a constant hissing noise from carb being the TKS is not operable and a constant higher idle (around 1100 rpm). I do notice that the idle is normal ( say 600-700 rpm for the first few seconds of starting then rises to the 1100 rpm range). note....there is no continuity in the thermal switch either cold or hot engine. I do have a new thermal switch and tks module, but feel that they may not be the culprits. bottom line...I am stumped on this one for I have no voltage anywhere, yet engine still runs. Where or what should I be looking for to get the tks working?? ANY and all advice will be appreciated!! Thanks!

 

[alldodge]

still getting a constant hissing noise from carb being the TKS

The module needs 12V applied to warm up and close down the fast idle port, this is why your hearing the hiss. If it does not get 12V it will never close

With the key turned ON (running or not running) there should be 12V on one side of the diode and one side of the oil pressure switch. If no voltage trace back to where the break is, this is the engine Purple wire.

One side of the Red/Purple wire going to the 20 amp fuse should always have 12V no matter if the key is ON or OFF

Need to trace where your loosing the 12V

 

[tahoejag]

Final result after numerous voltage testing. Culprit was the thermal switch that went into the intake manifold next to the thermostat housing. Replaced and all is good. Thank you all for the advise and info!