Mercury EFI: "push key to choke" enrichment, diagram

[pyro]

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)


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)


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

[mackeral5]

thanks for posting, I was planning to do this to my buddy's promax.

[pyro]

They should have just done them all this way from the factory.

[hsbob]

you surprise me sometime pyro. great idea that im going to do asap to my son efi.

thanks again.

[2springers26]

MERCURY makes a kit to do this also but it's Nla.. i have installed a few but the have a diode in the kit & it hooked into the red yellow off the soliniod. kurt

[dwvaughn]

Thanks Pyro
I,ll try it on my motor.

Doug

[SatisfAction]

Chad, I got to looking at this diagram and I noticed there is a set of 3 wires coming out of the ECU and going to the outside switchbox. On my Laser system, I have all 6. I'm wondering what to do now, hook them up? Leave them unhooked? lol This mod sounds helpful though and is something I'll do. Thanks

[whipper]

Chad your the man!! I was looking for two days for that little black and yellow line comming off my ignition harness. Like you said i peeled back the tape a little and there it was! I noticed both yellow/Reds hooked up to my selinoid so I was getting a shot of gas every time I turned over the key! I have been haveing a hard time starting the motor right after a high speed chop and was wondering why it seemed to be flooding? This im hopeing was the answer. With the Brucato ACU the idle settings and all the settings are very persice. At my elevation I was sure I was getting to much fuel at start up but didnt know why. At least Ill have control now of how much fuel she gets starting her up. Hears a shot video of whati did. and a pic of the finished setup. Thanks again for your easy instructions!

[whipper]

Tested the new wiring set up just now at the lake. All my starting issues went away. I was also compensating with idle timming and leaning out the acu at idle to get her to start somewhat beter. I took the timming light with me incase it worked and it did. So I Set the idle timming back to Zero and slowed down the idle from 850 ingear to 650 in gear and she pured like a 225 Promax should! I did some wot chops and plug reads because i drilled out the cowl also. Every thing is perfict now!!! I was compensating hear and there so much because the the enrichment was flooding her out on hot starts that I had the setup all out of wack. Once I got everything back to stock settings were they belong the motor responded and smoothed right out! Thanks Lee for the tips and Tony for the explanation and pyro for this great diagram page! If it wernt for you guys I wouldnt have known what the heck the hot start issue was still. I turned on and off the engine a bunch of times and fired right up every time.

[pyro]

I'm glad I could help your situation. Usually I just piss everybody off.

[HStream1]

Thats a great post Pyro. Could you e-mail me those diagrams? When I try to print them I can only get 3/4 of the page width.

jbcincnc@aol.com.

Thanks,

[HighVelocity]

Hey Pyro,

Is that the case with the newer Motorola ECU's?? I have a 2003 225 EFI and I usually just spin it till it starts and it stalls once in a while I restart and it runs,, or sneezes. The computer finally keeps it running but as the motor is getting older I can tell it takes a bit more correction to keep it going.

Then when it's hot it takes a few shots before she stays running. I never payed it any mind, just figured that was normal. But if I could control that extra shot of gas that would be awesome.

BTW Whipper, that video was great. Why swamp it with gas when it's already hot, makes sense to be able to control that.

[pyro]

If you want the images, just right-click the image and do a "save as..." to your computer.

If it cuts off when you print, see if you can use File --> "Print Preview" in your browser to specify that the printer "fit to page", instead of printing 100% size.

[HighVelocity]

OK Great.

[jhwh]

found it through google actually, doing it tomorrow, it solves exactly what I need as engine fires up real quick, but dies, messing with throttle helps marginally, so guessing this will work real good.