Re: How does TKS work (technically)?
Turn Key Start: Theory of Operation copied from the service manual.
The TKS system has been added to carbureted engines to:
? Provide additional fuel to air mixture when starting a cold engine. Idle speed is slightly
increased by supplying the additional fuel / air mixture required to start a cold engine.
? Prevent enrichment when starting a warm engine.
COMPONENTS
1. The TKS carburetor casting allows starting fuel to be drawn from the float bowl and
mixed with air in a chamber. This enriched mixture is drawn into the engine through an
opening in the carburetor body below the throttle plate.
2. The TKS module mounted to the carburetor. When 12V DC is applied, the TKS module
will warm internally, causing a plunger to extend from the module and close the
enrichment fuel air passage in the TKS carburetor.
3. On 3.0L engines, an oil pressure switchprovides a ground (-) path for the TKS module.
Positive (+) voltage is continuously supplied through a 20 amp fuse directly from the
engine circuit breaker.
4. On V-6 and V-8 engines an existing oil pressure switch provides 12V positive (+)
voltage to the TKS module. Ground for the TKS module is continuously supplied.
TKS SYSTEM OPERATION
The TKS Carburetor assembly provides precise fuel and air delivery during startup for all
temperature conditions. An electrothermal valve, the TKS module, is installed on the
carburetor assembly.
Before startup and according to ambient temperature, the TKS Module brass sleeve
retracts, and the enrichment fuel and air valve is opened.
The TKS fuel / air passage is normally open, allowing fuel enrichment mixture through the
carburetor continuously, unless the passage is blocked by the plunger of the TKS module.
With the key switch in the start position, the vacuum of the engine pulls the enrichment fuel
and air into the intake manifold.This starts an electrical warming of the module.
With the circuit completed, the electrothermal TKS module brass plunger extends to block
the enrichment passage.
Once the TKS module brass sleeve is fully extended, the enrichment fuel and valve are
fully closed, and enrichment stops.
In order to keep the TKS module warming and the starting channel in the carburetor closed
when engine is warm a second circuit has been added. For additional information, see the
"Typical Starting System Components" in Section 4A for your particular engine type.
TKS Starting Characteristics
On 3.0 L models - If the engine has not run for a long period of time, it might require a
couple of attempts while the fuel bowl refills. Once the engine has started, it will idle at
700-900 RPM.
On 4.3 L, 5.0 L, and 5.7L models - If the engine has not run for a long period of time, it
might require a couple of attempts while the fuel bowl refills. Once the engine is started, it
will idle around 650 to 700 RPM in idle stabilization mode. If the idle exceeds 700 RPM,
the ECM adds spark, thinking that the operator is trying to accelerate, which could cause
the engine to idle at 700-900 RPM. After the TKS module has shut off the enrichment circuit,
the carburetor will function like a standard carburetor. If the engine is out of idle stabilization
mode, (engine below 700 RPM), you will hear and feel a slight drop in RPM. After the TKS
module has shut off the enrichment passage, the carburetor will function like a standard
carburetor.
Troubleshooting
90-866202 DECEMBER 2004 Page 1C-3
NOTE: When the ambient temperature is -17 - 55? C (0?-50?F), normal engine idle should
be 650-700 RPM in idle stabilization mode.
When the ambient temperature is 10-55? C (50? - 130 ?F), normal engine idle should be
700-900 RPM and exceed the idle stabilization mode, moving into the run spark mode.
Once the enrichment circuit shuts off, the engine will idle at 650 RPM (Idle Stabilization
Mode.)
TKS Special Information
1. There will be a hissing sound for 6 to 10 minutes as the module is warming and the
enrichment channel is being closed.
2. The base gasket on the TKS carburetor is different from the old base gaskets
3. V-6 and V-8 engines use a spacer plate between the carburetor and manifold. The
gaskets have the same part number. The plastic spacer has not been changed and still
has the divider between the carburetor throats.
4. A special tool (PN 91-866201) is available to allow for adjusting the idle mixture on TKS
carburetors. The new adjustable idle mixture screw has a 16? taper and the special cap
has been C.A.R.B. approved to allow mixture adjustment only by dealers using the
special tool. The new taper will provide a finer adjustment.
Idle Mixture Adjusting Tool Part Number
9668
PN-91-866201
5. Do not make any adjustments of idle speed and/or idle mixture unless engine is
thoroughly warm and the TKS enrichment is completely shut off.
6. Generation 1 and Generation 2 carburetors function the same, and there is only a slight
difference in the location of the TKS passage within the body.
7. 3.0L engines will only have Generation 2 carburetors, while V-6 and V-8 engines will
have Generation1 and Generation 2 carburetors.
8. Refer to the parts book for proper service components.
Troubleshooting
TKS Troubleshooting
NORMAL STARTING PROCEDURE
1. Check all items listed in Operation Chart.
2. Place the remote control handle in neutral.
! CAUTION
Overheating from insufficient cooling water will cause engine and drive system damage.
Ensure that there is sufficient water always available at water inlet holes during operation.
Troubleshooting
Page 1C-4 90-866202 DECEMBER 2004
! WARNING
Explosive gasoline fumes collect in the engine compartment. Avoid injury or property
damage, operate the bilge blower for at least 5 minutes prior to starting the engine. If the
boat is not equipped with a bilge blower, open the engine hatch and leave it open while
starting the engine.
3. Turn ignition key to START. Release key when engine starts and allow switch to return
to ON position.
4. Allow engine to warm up (6-10 minutes on first start of the day). The engine will initially
idle at 650-900 RPM and then return to normal idle RPM for the engine.
Normal Engine Idle Specifications Idle in Neutral Idle in Gear
3.0 L 800 RPM 750 RPM
4.3 L, 5.0 L, and 5.7 L 650 RPM 650 RPM
5. If the engine does not start after 3 attempts:
a. Push the throttle only button and position the remote control throttle lever to the
1/4 throttle position.
b. Turn ignition key to START. Release key when engine starts and allow switch to
return to ON position.
6. If engine does not start after step 5:
a. Move the remote control throttle lever to full throttle position, then return to the 1/
4 throttle position.
b. Turn ignition key to START. Release key when engine starts and allow switch to
return to ON position.
7. Inspect the power package for fuel, oil, water and exhaust leaks.
8. To shift into gear, move control handle with a firm, quick motion forward to shift to
forward gear, or backward to shift to reverse. After shifting drive unit, advance throttle
to desired setting.
! CAUTION
Never attempt to shift unit unless engine is at idle RPM. Damage to transmission could
occur.
9. Move the remote control handle to neutral and throttle lever to idle. Allow the engine to
slow to idle speed. If engine has been operated at high speed for a long period of time,
allow the engine to cool at idle speed for 3 to 5 minutes.
10. Turn ignition key to the OFF position.
HARD START - COLD
1. If the engine does not start after third attempt, verify the following:
a. There is sufficient fuel and the fuel shut off valve is open.
b. Ignition system is functioning.
Assuming that the carburetor is the cause of the hard starting condition, the probable cause
will be that the additional fuel flow path is not functioning properly. To get the engine started:
1. Push the throttle only button.
2. Move the remote control throttle lever to full throttle position and then to the idle position.
Do this two times.
3. Place throttle at 1/4 position (throttle only)
4. Attempt to start engine again
Troubleshooting
90-866202 DECEMBER 2004 Page 1C-5
5. If engine still does not start, refer to "Engine Does Not Start."
HARD START - HOT
If the engine does not start when the engine is hot, the probable cause of hard hot-restarts
associated with the TKS carburetor will be the inadvertent opening of the additional fuel
flow path. The temperature switch was added to the system to keep power to the TKS
module to prevent the additional fuel flow path from opening during hot re-starts.
1. Check coolant temperature.
2. If the coolanttemperature is above 43? ? 3? C (110? ?8? F):
a. Verify that 12 Volts Positive (+) and ground (-) are getting to the TKS module. See
Section 4G for details.
b. Operation of the TKS module can be confirmed by placing your finger on the end
of the plastic TKS housing in the center and feeling that the electric heater is
getting warm. A warm TKS module after engine has run for 6 to 10 minutes
confirms that TKS is functioning electrically. See Section 4G for details.
3. Verify that the TKS Module is functioning normally. Follow procedure in Section 4G.
ENGINE DOES NOT START
The possible root causes of the fuel path not functioning include:
? The TKS Module failed in the closed position. See Section 4G and Section 5G.
? The fuel has varnished. See Section 5B.
? There is debris in the fuel path. See Section 5B.
? The float level is out of specification. See Section 5B.
If the engine does not start, check the following:
1. Check that float bowl is full of fuel.
2. Check that the mechanical fuel pump is working. Attach a fuel pressure gauge to the
mechanical fuel pump to verify it is working correctly.
3. Check the enrichment jet emulsion tube, TKS enrichment jet, and the main jets for
damage or debris.
ENGINE DOES NOT IDLE CORRECTLY
If the engine does not idle correctly after starting, verify that the enrichment cycle is fully
closed before adjusting checking the following:
1. The engine idle RPM has been set correctly with a warm engine.
2. Verify the timing of the engine in the base timing mode.
3. Verify there is voltage on the Packard connector attached to the TKS heater.
4. Check the enrichment jet, emulsion tube, and the main jets for damage or debris.
HISSING NOISE
There is a small enrichment air passage for the TKS system in the throat of the carburetor.
Air is drawn through this passage when TKS is in starting mode and does create a slight
whistle or hissing noise. After 6 to 10 minutes when engine has warmed and TKS system
has closed the noise will quit and will only occur again after a cold engine start. If this noise
continues after 10 minutes, this could indicate a problem with the TKS module. See Section
5B.
We had a decent discussion about TKS in the link below a few years back if interested.
http://forums.iboats.com/mercruiser...d-starting-when-sitting-over-week-328531.html
