Wire gremlin for fuel pump

J

jrmicko19

Member
Apr 1, 2014
45
CT
Boat Info
2001 Sundancer 260
Engines
7.4 MPI Bravo III
2001 Sundancer 260 7.4MPI

Installed new fuel pump, old one seem to be failing, intermittently working. New one installed, boat fired right up, ran it on and off a couple times while sitting on trailer with muffs. Towed to boat to ramp and dropped in, started at dock and sputtered out after a couple min. Cycling key, I could no longer hear the fuel pump coming on, but I could hear the relay clicking on and off. Cycled key about 15 times, could not get fuel pump to come on. Pulled boat back out of water, unplugged fuel pump and reconnected, checked ECM connections, cycled key, pump came on and boat started. I'm leaning towards possible bad ground? Is there also an oil pressure sensor that could be going bad and cutting fuel?

Grabbing a friends scanner to check for codes, no abnormal beeping from alarm. Just 2 beeps when turning key on.
 
A no spark condition will inhibit the fuel pump.
So, check for spark while cranking. If there is no spark trouble shoot the ignition system with the ignition sensor and or the coil likely suspects.
 
Wanderer 290 said:
A no spark condition will inhibit the fuel pump.
So, check for spark while cranking. If there is no spark trouble shoot the ignition system with the ignition sensor and or the coil likely suspects.
Click to expand...

well before even trying to crank the boat, the fuel pump isn’t kicking on.

I’m in the engine bay now poking around and pump is working consistently at the moment.
 
Relays are cheap, click or no click, I'd change it No oil pressure cut out.
 
Both relays are new, both are clicking, even when the fuel pump isn’t kicking on, the relays are still clicking
 
How old is the fuel pump? Is there power at the fuel pump plug when it's not activating?
 
Just put new pump in as I thought the old one was dying because of intermittent behavior.

cycling key now and the pump is kicking on every single time. Hard to troubleshoot when its working correctly at the moment!

problem likely to act up again when I put the boat back in and try to use it haha. Isn’t that how it always works
 
Try a continuity test and a “wiggle test” of the power wire from the relay to the harness connector.

do the same for the ground wire.

You are looking to see if you lose continuity when you wiggle the wire(s)
 
scoflaw said:
Did you give the fuel pump harness plug a good look?
Click to expand...
Espos4 said:
Try a continuity test and a “wiggle test” of the power wire from the relay to the harness connector.

do the same for the ground wire.

You are looking to see if you lose continuity when you wiggle the wire(s)
Click to expand...

I’ll give that a try next. Just had it running on muffs for about 15min and it died out. Turn key off and back on and pump cycled. Started right back up. This is driving me nuts
 
jrmicko19 said:
2001 Sundancer 260 7.4MPI

Installed new fuel pump, old one seem to be failing, intermittently working. New one installed, boat fired right up, ran it on and off a couple times while sitting on trailer with muffs. Towed to boat to ramp and dropped in, started at dock and sputtered out after a couple min. Cycling key, I could no longer hear the fuel pump coming on, but I could hear the relay clicking on and off. Cycled key about 15 times, could not get fuel pump to come on. Pulled boat back out of water, unplugged fuel pump and reconnected, checked ECM connections, cycled key, pump came on and boat started. I'm leaning towards possible bad ground? Is there also an oil pressure sensor that could be going bad and cutting fuel?

Grabbing a friends scanner to check for codes, no abnormal beeping from alarm. Just 2 beeps when turning key on.
Click to expand...

Recently had a similar fuel pump issue that took me a while to figure out. The fuel pump relay tested OK (+- 12V to the solenoid pins 85/86 would close the relay pins 87/30) and the fuel pump relay socket also tested OK (test light would turn on between 85/86 and between 30/NEG) but i was continuing to have issues with the fuel pump not running all the time. After going through many different tests and trials, I finally noticed that the test light was not lighting very bright when testing 85/86. Turns out there was enough voltage/current to light the light but apparently not to close the fuel pump relay all the time. One of the wires to pins 85 or 86 in the fuel pump relay socket was not a good connection. These are fairly small wires (18 Guage) and they are shoved inside the electronics box (ECM, relays, fuses, slave solenoid, etc) on the engine and it think over the years taking them in and out of there resulted in damage to one of the wires at the relay socket. I purchased a new relay socket and spliced it in, and problem solved.
 
jgoedd99 said:
Recently had a similar fuel pump issue that took me a while to figure out. The fuel pump relay tested OK (+- 12V to the solenoid pins 85/86 would close the relay pins 87/30) and the fuel pump relay socket also tested OK (test light would turn on between 85/86 and between 30/NEG) but i was continuing to have issues with the fuel pump not running all the time. After going through many different tests and trials, I finally noticed that the test light was not lighting very bright when testing 85/86. Turns out there was enough voltage/current to light the light but apparently not to close the fuel pump relay all the time. One of the wires to pins 85 or 86 in the fuel pump relay socket was not a good connection. These are fairly small wires (18 Guage) and they are shoved inside the electronics box (ECM, relays, fuses, slave solenoid, etc) on the engine and it think over the years taking them in and out of there resulted in damage to one of the wires at the relay socket. I purchased a new relay socket and spliced it in, and problem solved.
Click to expand...

This was a thought also. I recently saw another post somewhere with a photo of this merc/seirra replacement relay socket. Any idea on the part number for it?
 
Put a fuel pressure gauge on the fuel rail, turn the key on and it builds pressure to 43ish. When it’s sitting at idle it’s at 38psi.

it almost stalled once, pressure dropped down into the low 30’s and then it bounced back up to 38 without stalling.
 
Last edited:
Reached down to jiggle the plug for the fuel pump, and the plug connection was so hot I couldn’t touch it
 
jrmicko19 said:
Reached down to jiggle the plug for the fuel pump, and the plug connection was so hot I couldn’t touch it
Click to expand...

Hot plug = poor connection in that plug.

For my 1998 454 MAG MPI Horizon the relay is a Merc 86-865202T and the relay plug is a HELLA H84708001280 (Can be found on Amazon). (FWIW - the Merc relay appears to be a HELLA 12193611)
 
jgoedd99 said:
Hot plug = poor connection in that plug.

For my 1998 454 MAG MPI Horizon the relay is a Merc 86-865202T and the relay plug is a HELLA H84708001280 (Can be found on Amazon). (FWIW - the Merc relay appears to be a HELLA 12193611)
Click to expand...

Right now im working on finding the plug that goes on the end of the engine harness where the fuel pump plugs in. Fuel pump is brand new, so im guessing the boat harness plug is prob the culprit since its 22 years old
 
If you haven't found one yet, did you ask merc customer support ? 920-929-5040
 
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