Possible ECU issue on 200 EFI

[ntxwaterfowl]

Hi everyone, I have a 1998 Mercury 200 EFI, serial# 0G607352, that I picked up with little known history other than “it runs”. (long story for context follows, skip to the *** if you want to just get to the problem lol)

When I first got it and tried to take it to the lake to run it the motor wouldn’t start, nothing, not even a click. I had turned it over on a hose before I bought it so I figured it must be a battery issue. Drive it back home, starts up, runs a little rough but then smooths out and idles. Unfortunately the water pump wasn’t working so I go to replace that. End up with a leak around a motor mount and they were shot anyways so I ordered solid mounts, pulled the power head, replaced them, started it up again and it ran fine, never did the no click again. Unfortunately I had accidentally stepped on the hose before starting it and knocked the water muffs off line and burned up the water pump. Got busy, let it sit for a couple months and finally got back to it.

Replaced it, go to start the motor and the battery is dead. Like 1.4 volts dead. I manage to recondition the battery and now it cranks but doesn’t fire.

*** Went to check the fuel pump since I don’t hear it running and it has 12.8 volts. The problem is, it has 12.8 volts with the key on, off, out of the boat, dash switch on or off. I unplugged the ECU and it still had 4 volts…

So I’m guessing that’s why the battery was dead. My question is, 1- is this an ECU problem, 2- will I likely need to order a new fuel pump as well, and 3- what could of caused this?

[Procraft180Pro]

The only way to know if your ECU is bad is to send it to Brucato Power and have it tested.
Mine on my 93 XRi 150 was on its way out causing fuel pump driver issues so I replaced it with a Brucato ACU.
Problem solved and it runs like new.

[EuropeanAM]

Fuel pump will have 12V on both terminals, key off, battery connected. ECU modulates voltage to the ground side of the pump... tests are outlined in the Service Manual for this circuit.

Reading voltage between the two pump terminals as the key is turned on will tell you if the ECU is providing a ground. Voltage is relatively low when not running or at idle.

[ntxwaterfowl]

Thank you both for the reply, that makes sense that the ECU grounds it. I will look up the service manual and see if I can test it, I sure would rather it not be an expensive ECU. I do know the pump is not running right now because I can’t hear it, there is no voltage change when key is on, and there is no pressure built on the check valve. I will start running through the fuel system and double check everything. This has turned into a bigger project than I wanted, I just bought the boat to swap motors with my boat and it’s been an ordeal.

[EuropeanAM]

Don't forget to check for key-switched power on the PURPLE wire (and clean/slightly spread the male pins in the cannon-plug connector).

No "key switched 12V power" results in no fuel pump and no injector drivers (ie: Sleeping ECU).

[ntxwaterfowl]

So I checked the voltage when turning the key on and it would make a small change in voltage. I also checked the purple wire and it is hot when the key is on. I still had no audible pump running and I checked the pressure just to be sure and it was 0. Next I unplugged the pump and jumped it straight to a battery and nothing. Am I right in assuming the high pressure pump is bad?

[EuropeanAM]

If you supplied both 12V+ and 12V- to the pump (separate from the engine) and the pump did not operate, the pump is likely bad.