Start and run Mercury 5.7 on stand

[Barracuda6769]

Have a mercury 350 mag mpi out of boat for
some work. Would like to fire up motor on stand before stuffing it back in its hole to make sure all is well because it's a pain to work on in boat.
Looking for info on what wires need to be
connected to fire it up. Has 14 pin harness
connector. I know pin A is hot and pin C is
wake. But when I jump the 2 nothing happens, the fuel pump doesn't cycle, no relays clicking. Engine will spin if I jump across to pin N
Anyone have the scoop on what wires to connect to get it to fire.

 

[alldodge]

Do you have pin B grounded?

 

[Barracuda6769]

Do you have pin B grounded?

No. Just ground it to engine block?

 

[alldodge]

ok, Check fuses, there is at least 3 of them
When power is applied to pin C does the MPR (main power relay) click?

When power is applied is there 12V at the fuel pump?

Note, power energizes the MPR which powers up the ECM. The ECM then applies a ground to the FPR which would turn the pump ON for couple seconds

 

[Barracuda6769]

ok, Check fuses, there is at least 3 of them
When power is applied to pin C does the MPR (main power relay) click?

When power is applied is there 12V at the fuel pump?

Note, power energizes the MPR which powers up the ECM. The ECM then applies a ground to the FPR which would turn the pump ON for couple seconds

View attachment 373467

I have 4 fuses they are good. When power is connected 2 of them are hot the other 2 not. I’ve heard MPR click a couple times when powered but not every time. I don’t have power to fuel pump, it’s never cycled when power applied. It it does work because I have connected power straight to it and it ran.

I do have power going to red/ppl wires at mpr
And power going to pink/Lt green wire going to fuel pump relay.

So here’s the other part if this story, the motor was completely submerged in water. Not for a long time but everything was under water. So we pulled motor cleaned everything out top to bottom. No corrosion in any connectors.
Everything looks good. But, could the ecm be toast or are they pretty water tight? No signs of water in any connections on any relays or plugs.

 

[Scott Danforth]

So here’s the other part if this story, the motor was completely submerged in water. Not for a long time but everything was under water. So we pulled motor cleaned everything out top to bottom. No corrosion in any connectors.
Everything looks good. But, could the ecm be toast or are they pretty water tight? No signs of water in any connections on any relays or plugs.

you may have wanted to lead with that

submerged in fresh water, high-mineral fresh water, salt water, etc? each has its own set of issues.

the wiring will wick water into the harness on the non sealed ends. if the water was salt water, your harness is potentially toast. if fresh water it will be toast as corrosion will slowly eat the harness since they do not use the recommended tinned wire (saves a few $)

the rotating electrics are suspect, and if salt water toast or soon to be toast unless they were pulled apart, cleaned, oiled, etc.

if the ECM was under water, it may be toast as it is only IP65 (meaning rain from above) not IP67 (submersion). you may need to plug in with Rinda and see what is going on.

the relays are IP65. Test your relays

the connectors at the ECM are sealed. the deutsch connectors at the ECM will have sealed up to about 1 meter.

 

[alldodge]

Submerged that helps
I would replace the relays, but could swap them to see if things change. Local auto parts will have the relays that will work the same, just may not look the same. Could also remove the cover off the ECM to see if it needs drying out

If it was salt need to do as Scott mentioned or just replace because your going to have issues later

 

[Barracuda6769]

Originally I was just looking for wiring info to get on the right track, but figured I’d better give the rest of story since we were discussing it a little deeper.
It was fresh water and yes most connectors are sealed connections and look to be dry and no corrosion or signs of water intrusion.
I did have a couple new relays and have swapped them around with no change.
Wondering if I need to have ecm checked.

 

[alldodge]

Wondering if I need to have ecm checked.

The ECM applies grounds to relay coils to energize them, and this isn't happening. If it was mine I would open the ECM (drill rivets out if needed) and see if it needs to be dried out. If all good then have it tested

 

[Scott Danforth]

if there is moisture in the ECM from fresh water. rinse with bottled water, followed by 90% isopropyl alcohol.

then let fully dry.

If you have Rinda, you should be able to see what is going on.