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fuel pumps wont turn on

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fireman6942b

New member
Ok, so heres my headache, 1995 Omc Cobra 5.0L.
Wont start b/c it wont send power to relay, when I voltage test the leads is where it geta strange. I am getting the correct 12 volts from the circuit breaker and 12 volts from the ignition switch. But.... on my "ground" my meter is reading 8.5 volts (believe its my purple wire). What is going on, how do I fix it amd who makes engine wire harnesses for this motor?
 
on my "ground" my meter is reading 8.5 volts (believe its my purple wire).
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Ayuh,.... The purple wires are the Ignition Power wires,.....

The Grounds oughta be black wires,.....
 
Sorry they might be, it was dark when i discovered that 3 legs of my relay plug carried voltage ranging from 12volts on two legs to the 8.5 volts which I cant explain. There seems to be no ground for the relay, all the wires have a nice black coating of years of grime and grease.

Looking at the relay diagram, across the coil of the relay is where I'm getting the ignition 12 volts(which I confirmed by turning the ignition switch off and on numerious times) and the 8.5 volts from what I believe should be the ground.

I'm guessing i have a short somewhere thats giving me the 'added voltage across the coil'. Any help would be great to find the leakage of voltage and mostly a wiring schematic. I have diagrams but they are only so helpful when trying to chase individual wires. Thanks
 
So it seems as if this thread has died and I'm the only one still posting, none the less I have progressed to finding the problem with no help from this group. The black / purple is the ignition on voltage, the blue/orange comes from the ECM and "grounds" the relay to activate the pumps. So after finding several wiring schematics and bypassing the ecm, I was able to determine the ECM is bad. More bad news is that the ECM is next to impossible to find. Internal schematics for the ECM are even harder to find. Although I may have found the culprit component that too is next to impossible to locate (a simple logic ic). Bottom line, repairs will cost more than the boat in running condition. Thanks for all the non help, and maybe this will help someone some day in thier time of need.
 
Ayuh,.... Sorry I couldn't help more, the Efi motors are beyond my knowledge level,....

OMC techs are gettin' non-existent,...
 
What are you talking about? the engine ECU is none other than your standard issue Ford truck or Mustang ECU. You can find them for a few bucks on ebay. The thing that makes it rare/expensive is the water resistant housing the ECU lives in. If you crack open the box and look at the ECU you'll see the code for the PROM flash. It'll be like"A9L". Find a corresponding ECU and you are back in bidness. Second, I doubt the ECU is bad. I would sooner suspect a bad fuel pump relay than the ECU, or a bad fuel pump. But I'm not there to look at it...
There is SO MUCH info about Ford fuel injection that it is surprising to me that you cannot find anything on this problem.
If you need a new wiring harness you are SOL since OMC has been out of business for many years and the remaining stock of parts are now handled by Bombardier. They aren't makin any hew parts so you are relegated to existing stock.
If you truly wish to walk away from this thing and you are anywhere near Maryland I'll come get it.
Here's another trick. bypass the ecu and rewire the fuel pump to come on when you key it. Elsewise, carb it and then all your troubles are over.

PS just looked on ebay and there are several for under $50
 
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Issues resolved, wife was right, bad ground to the ECM, expensive mistake on my part. After replacing freeze plugs and exhaust manifold which were equally hard to find, it has been very reliable...oh and a starter solenoid too....yay the Joy's of owning a boat
 
Re-Cap:

This thread is 2+ years old.

fireman6942b said:
Ok, so heres my headache, 1995 Omc Cobra 5.0L.
In 1995 OMC was now owned by Volvo Penta..... so, this would be a Volvo Penta, even while OMC tags showed up on some components.

But.... on my "ground" my meter is reading 8.5 volts (believe its my purple wire). What is going on, how do I fix it and who makes engine wire harnesses for this Engine?
FYI and FWIW....... there is NO Ground within a 12 VDC system..... only Positive and Negative.
Ground or Earth Ground is A/C current terminology.
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fireman6942b said:
Issues resolved, wife was right, bad Negative to the ECM, expensive mistake on my part. After replacing freeze plugs and exhaust manifold which were equally hard to find, it has been very reliable...oh and a starter solenoid too....yay the Joy's of owning a boat
First...... that is great that you found the issue. And yes........ "the joys of owning a boat!" :D
Many of us have been there/experienced that.
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