pyro
05-01-2008, 09:32 AM
Mercury EFI ECU's have an enrichment function for cold starts.
This function is enabled when the YEL/RED wire from the ECU harness "sees" +12v.
On most EFI motors, the factory connects this wire to the starter solenoid
where the corresponding RED/YEL wire from the keyswitch also connects.
This causes the ECU to feed the injectors an extra-rich mix while the engine is cranking.
Releasing the key returns the ECU to normal mode. Sometimes a cold motor will stall at this point.
Turn the key and it starts again. Repeat till warm. Annoying!
Later on, re-starting a warm motor may emit quite a puff of smoke or foul a plug. Not good.
Here's a typical EFI wiring diagram, for a 1990 Bridgeport 2.4 EFI. Notice how it shows no connection
for the YEL/BLK wire in the main harness. This is the "push key to choke" wire coming from the keyswitch.
It goes to +12v when the key is pushed, in any position. This wire will likely be cut down short,
wrapped under several layers of tape near the main harness, but it's there.
(BEFORE)
http://i32.tinypic.com/2ut6fev.jpg
Here, the YEL/RED enrichment wire has been disconnected from the starter solenoid trigger lug,
and his been connected to the YEL/BLK harness wire instead.
Now the driver is in control of the enrichment function.
(AFTER)
http://i25.tinypic.com/5md8a8.jpg
This simple modification can be done on a variety of Mercury EFI motors.
I did this mod on my old '89 200 EFI with great results. No more repeat cold re-starts.
If it sneezes or sounds lean, just bump the key in for a second. The 200 EFI
seems to ignore the enrichment when the head temp sensor detects a warm motor.
I also did the same wiring mod to my Bridgeport when it had the analog EFI.
I have my PCU connected this way to date. Having the "push key" enrichment
along with the steamwheel makes it easy to start a stone cold motor right off the trailer,
and idle away from the ramp without stalling, stumbling, or sneezing.
Hope this info proves helpful...
-Chad
This function is enabled when the YEL/RED wire from the ECU harness "sees" +12v.
On most EFI motors, the factory connects this wire to the starter solenoid
where the corresponding RED/YEL wire from the keyswitch also connects.
This causes the ECU to feed the injectors an extra-rich mix while the engine is cranking.
Releasing the key returns the ECU to normal mode. Sometimes a cold motor will stall at this point.
Turn the key and it starts again. Repeat till warm. Annoying!
Later on, re-starting a warm motor may emit quite a puff of smoke or foul a plug. Not good.
Here's a typical EFI wiring diagram, for a 1990 Bridgeport 2.4 EFI. Notice how it shows no connection
for the YEL/BLK wire in the main harness. This is the "push key to choke" wire coming from the keyswitch.
It goes to +12v when the key is pushed, in any position. This wire will likely be cut down short,
wrapped under several layers of tape near the main harness, but it's there.
(BEFORE)
http://i32.tinypic.com/2ut6fev.jpg
Here, the YEL/RED enrichment wire has been disconnected from the starter solenoid trigger lug,
and his been connected to the YEL/BLK harness wire instead.
Now the driver is in control of the enrichment function.
(AFTER)
http://i25.tinypic.com/5md8a8.jpg
This simple modification can be done on a variety of Mercury EFI motors.
I did this mod on my old '89 200 EFI with great results. No more repeat cold re-starts.
If it sneezes or sounds lean, just bump the key in for a second. The 200 EFI
seems to ignore the enrichment when the head temp sensor detects a warm motor.
I also did the same wiring mod to my Bridgeport when it had the analog EFI.
I have my PCU connected this way to date. Having the "push key" enrichment
along with the steamwheel makes it easy to start a stone cold motor right off the trailer,
and idle away from the ramp without stalling, stumbling, or sneezing.
Hope this info proves helpful...
-Chad