2003 ox66 225 dying problem

[TimE1234]

I have a 2003 225 ox66. Motor runs fine most of the day. Then starts for about 1/2 second and dies. Then will only turn over. Happens intermittently. Not ever at the same time each time we go out, but always after we've been out awhile. Replaced lift pumps June 2017 and fuel filters October 2017. Didn't change. Took my mechanic fishing with me and it finally acted up right before going in. He checked fuel pressure and determined we had none. Checked power to fuel pump from computer. We had no power. Replaced computer. Still have same problem. Need an expert.

[99yam40]

from what I have read the computer grounds the pump to turn it on.
so If it is not getting !2V + o it ,you need to follow the + back to see where it is dropping

[DennisG01]

I'm not an expert (what about your mechanic?), but... in my non-expert mind it doesn't sound like a computer issue. I would think if it was bad, the engine wouldn't work sometimes and sometimes not. It would just be completely dead. I would start by finding every electrical connection you can find on the way to the pump (AND GROUNDS!), including the battery connections at the battery and the motor, and remove/inspect/clean/install/protect. Clean electrical connections are a priority.

[rodbolt17]

at east you have a spare ECU.
based on your description you may wish to find a trained tech.
supply voltage for the ECU and the HP pump and the injectors comes from the main relay not the ECU.
the ECU supplies the ground path.
if you voltage test between the device and the ECU when the device is supposed to work you will most likely see less than.05V
did anyone check for spark?

[walleye1]

A main relay be alot cheeper.

[rodbolt17]

dunno if it is a relay, could be a failing splice in the harness.
could be a lot of things.
if it cranks and wont start and you get NO audile(assuming you know it works) then the stop circuit is not an issue.
as it cranks over it tell me we have voltage at the keyswitch.
uwhat it does NOT tell me is if I have 12V to the ECU via the yellow wire, does it apply the ground for the main relay?
does it apply the ground at key on to the HP pump for about 3 seconds?

[TimE1234]

Thanks for all responses. Need a wiring diagram. Will check all grounds, splices, etc.

[TimE1234]

Final fix was a resistor in the grounding route of the blue wire coming from fuel pump to computer. A $250 part.