Current draw?

[mercrazy]

How much current does a merc efi ecu draw? I get a little spark when hooking up battery cable. This is a complete rebuild. Just wondering if I have a short somewhere?

[skialot2]

If you had an actual short you would know it. A slight draw can cause a spark. The ECU is always power on. The ground shuts it on or off. If you are not just connecting the motor, there are thing in the boat the always draw slight current. Like a GPS speedo. or a radio with memory presets.

[mercrazy]

If you had an actual short you would know it. A slight draw can cause a spark. The ECU is always power on. The ground shuts it on or off. If you are not just connecting the motor, there are thing in the boat the always draw slight current. Like a GPS speedo. or a radio with memory presets.

Not hooking to boat. Engine is on a stand. What do you mean ground turns it in or off?

[skialot2]

According to the manual, the ECM power lead is always hot if the battery is connected. The ground connection is controlled by the switch.

[rock]

If you check your fuel pump you will find both posts are hot. The ecu completes the circuit by supplying the ground.

Rock

[mercrazy]

Think I found the problem. Unhooked the rectifiers and no current draw. CDI unit tested bad on 1 yellow wire. Don’t see any draw on the ecu.

[tlwjkw]

pretty sure tha ecu gets its power from a switched purple from tha key ign.....

[skialot2]

It's in the manual. The ECM is always hot. I think the red wire supplies constant power and the purple switched power. The fuel pump is also always hot. Check it with a voltmeter with the key off. According to the manual, both the positive and negative will have 12V. Turning the key on brings the negative down to ground.

[tlwjkw]

i know what it says but i'll be damned if i can find it anywhere in tha harness... show me what wire (feedin' tha ecu) thats hot with tha key off???.. its not red either... other than tha + at tha pump.....

harness pin number and color would be helpful................

[skialot2]

Number 6 wire to the ECM is a red wire hooked directly to the battery hot on the starter solenoid. It is the same wire that goes to the positive terminal on the EFI fuel pump and the injector harness. It is always hot. I checked mine. The EFI ECU, fuel pump and injector harness positive wire is always hot even with the key off.

[tlwjkw]

not one of my diagrams (in manuals) shows that wire... they also show a red/purple on - side of pump...only go ta '02.............. what year is that dia.?

[skialot2]

Really. Both diagrams I have show #6 ECM wire is a red constant hot.

Link to the online manual so you can enlarge it. Page 2D-5 cover

The later manual page 2D-21 cover

[tlwjkw]

calf rope!.. OK,, mines tha blackest... had ta blow 'em up way big....

[skialot2]

Huh? But I had to blow them up large too.

[tlwjkw]

gettin' old REALLY sucks.... eye site (depth perception) is main reason i got outta tha hot rods so i should expect bein' half blind................