long shot wiring question - 5.7EFI

A bit of a long shot here. I'll get pictures this week to help show what I'm talking about, but engine manual and wiring diagrams are not helping me figure this out.

We have Twin 1998 5.7EFI (SN:0L058492) motors of which I had removed the port side exhaust to allow easier access to replacing oil hoses. Getting ready to reinstall them earlier today I was poking around, tightening hose clamps, etc when i found a ring terminal disconnected from an engine block grounding lug. The lug is aft of the valve cover and just below, and has a large gauge black grounding wire attached. This is the opposite side of the starter, for reference. The wire in question is a small-ish gauge and quite stiff with the ring terminal on the end. It gets bundled into a group which appears to be running to/from the ECM. The other motor also has this wire, attached, as well as green grounding wires running to a grounding bus.

I reattached it, but I'd really like to know what it is for. The engine has ran fine for us, the only thing a bit off is the tach bounces below 1500RPM even though it was replaced with a brand new one.

Again, I realize without pictures its basically impossible to tell so I'll get them when I'm at the boat again

i think that may be the grounding wire to put the ignition module into 'base timing mode' when you want to check or set the ignition timing....is it connected to a purple wire?....if so you don't want to leave this wire grounded after the timing is set or the ignition module will not advance the timing properly....

I had the same engine in a previous boat...

cliff

CliffA said:

i think that may be the grounding wire to put the ignition module into 'base timing mode' when you want to check or set the ignition timing....is it connected to a purple wire?....if so you don't want to leave this wire grounded after the timing is set or the ignition module will not advance the timing properly....

I had the same engine in a previous boat...

cliff

Click to expand...

very interesting, now I have to really dig through the service manual to find that wire. I have to figure it's detailed somewhere if that's its purpose.

Also a bit alarming if that's the case since the wire on the other engine is and always has been grounded.

Thanks Cliff, I'll get some pics soon

Strecker25 said:

very interesting, now I have to really dig through the service manual to find that wire. I have to figure it's detailed somewhere if that's its purpose.

Also a bit alarming if that's the case since the wire on the other engine is and always has been grounded.

Thanks Cliff, I'll get some pics soon

Click to expand...

it is OK to leave the ring terminal on the black wire secured to a bolt....you just have to unplug the purple wire from the connector on the other end of the black wire....

cliff

CliffA said:

it is OK to leave the ring terminal on the black wire secured to a bolt....you just have to unplug the purple wire from the connector on the other end of the black wire....

cliff

Click to expand...

Got it, yeah I just found this procedure

EFI / MPI Models
1. Connect timing light to number 1 spark plug wire.
2. Start engine and run at 1300 rpm until it reaches normal operating temperature.
3. Stop engine and connect the scan tool or timing tool to the DLC connector on the EFI/ MPI wiring harness.
4. Start engine, allow rpm to stabilize.
NOTE: MEFI-1 models only, manually adjust remote control throttle lever to get 1200 engine rpm.
NOTE: MEFI-2 and MEFI-3 models only, ECM will automatically adjust engine rpm to approximately 1200 rpm when put in the service mode on a scan tool or when using the timing tool.
5. Check ignition timing. If incorrect, rotate the distributor until timing is correct. Torque clamping screw to 18 lb-ft (25 Nm).
6. Recheck ignition timing.
7. Disconnect scan tool or timing tool from DLC connector.
8. If required, return remote control throttle lever to idle position and shut off engine.
9. Restart engine, increase rpm to 1300 then return to idle position slowly. Ensure that engine returns to idle rpm. Readjust throttle cable, if required.
10. Shut engine off.

The purple wire would be up at the DLC connector near the MEFI module, right?

Strecker25 said:

Got it, yeah I just found this procedure

EFI / MPI Models
1. Connect timing light to number 1 spark plug wire.
2. Start engine and run at 1300 rpm until it reaches normal operating temperature.
3. Stop engine and connect the scan tool or timing tool to the DLC connector on the EFI/ MPI wiring harness.
4. Start engine, allow rpm to stabilize.
NOTE: MEFI-1 models only, manually adjust remote control throttle lever to get 1200 engine rpm.
NOTE: MEFI-2 and MEFI-3 models only, ECM will automatically adjust engine rpm to approximately 1200 rpm when put in the service mode on a scan tool or when using the timing tool.
5. Check ignition timing. If incorrect, rotate the distributor until timing is correct. Torque clamping screw to 18 lb-ft (25 Nm).
6. Recheck ignition timing.
7. Disconnect scan tool or timing tool from DLC connector.
8. If required, return remote control throttle lever to idle position and shut off engine.
9. Restart engine, increase rpm to 1300 then return to idle position slowly. Ensure that engine returns to idle rpm. Readjust throttle cable, if required.
10. Shut engine off.

The purple wire would be up at the DLC connector near the MEFI module, right?

Click to expand...

I just remember the purple wire being on top of my engine.....it was the only purple wire that was not connected to anything and had a connector on one end....

cliff

The heavy gauge wire with the ring terminal is most likely the main system ground connected with a short bolt to the head on that side of the engine.
The timing lead is usually 16Ga, quite a bit thinner.

Bt Doctur said:

The heavy gauge wire with the ring terminal is most likely the main system ground connected with a short bolt to the head on that side of the engine.
The timing lead is usually 16Ga, quite a bit thinner.

Click to expand...

Sounds like you’re right. Here’s a few pics. Obviously I’ve alreqdy reconnected it in these.