94 175 efi bog under load/fuel pump

Skeetin'

Cadet
Joined
Oct 14, 2013
Messages
12
Hey guys. Just rebuilt my powerhead on my 1994 Mariner 175 EFI 2.5l and took it on its maiden voyage tonight. I pulled out of the no wake, came up on plane and noticed the engine didn't seem to be hitting on all cylinders, so I idled down and was listening to the engine. Tried to get back on plane and the motor wouldn't do it. I changed my plugs all out on the water thinking they could have fouled from running in the driveway on my rich mixed gas, didn't fix the problem. The engine would idle fine and rev through the rpm range in neutral. So I decided to idle back to the dock and load it up. Came home and checked the fuel pressure and it is 45 psi engine off. I have also noticed at times my fuel pump will not prime or cycle, and when this happens the engine will not start due to fuel pressure. According to my manual, power and ground is supplied directly from the ecu. Anyway guys, im looking for any insight I can get. Things that I have tried are spark plugs, fuel pressure test/engine off, examined all engine grounds, fuel filter installed between tank and engine, replaced fuel water separator, new primer bulb, and the gas tank is properly venting. Also all of the fuel injectors were sent out, tested, and cleaned during rebuild. Thanks in advance, Brad.
 
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Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: 94 175 efi bog under load/fuel pump

Could be a fuel pressure regulator or ECU fuel pump driver problem. Check pressure when its acting up and you can remove ground from pump and ground direct to motor and pump will run all the time for testing to see if pump bad..
 

Skeetin'

Cadet
Joined
Oct 14, 2013
Messages
12
Re: 94 175 efi bog under load/fuel pump

Thanks for the prompt response and information. I pulled a fuel sample last night and the fuel is definitely not what I expected to see. I have about a 12 oz glass full with some kind of mixture on the bottom as well as my fuel color as premix is a yellow/green. I only use Pennzoil Marine or Quicksilver which has always given me a rich blue fuel color. So I will be draining the tanks once more and refilling with fresh fuel. As far as the driver for the fuel pump, what does the ecu require as inputs to determine fuel pump ground? And if the driver is bad could I supply my own relay to ground the fuel pump bypassing the ecu?
 
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