2005 - 5.7L Mercruiser 350 MAG MPI WILL NOT START

S

stelios hondrcolos

Active Member
Apr 11, 2021
175
Boat Info
300
Engines
350 Mag
2005 Sea Ray 300DA with 5.7L Mercruiser 350 MAG MPI HORIZON BRAVO3 ENGINES

The boat is new to us. It had been running perfectly.
Suddenly the stb engine will crank but not start
Port engine runs fine. When I turn on the ignition I can hear a click of the fuel solenoid and whine of the fuel pump. Stb engine - no solenoid click and no fuel pump whine.
Batteries are fine the engine cranks well, just do not fire up
  • Changed fuel filter
  • Engine will start and run if fuel is dripped straight into the intake
  • 20 amp mini fuses on engine (which I believe one of them is fuel pump) look ok
  • I switched both relays from port engine to stbd engine. Still same condition port will run but stb still will not start. Therefore I believe the fuses and relays are ok. It appears to be something causing the fuel pump and fuel shut off solenoid not to get electrical power?
  • Will changing the IAC make a difference? I could not start with increased idle either
Looking for help until I can get a mechanic which is God knows when

Thanks!
 
stelios hondrcolos said:
2005 Sea Ray 300DA with 5.7L Mercruiser 350 MAG MPI HORIZON BRAVO3 ENGINES

The boat is new to us. It had been running perfectly.
Suddenly the stb engine will crank but not start
Port engine runs fine. When I turn on the ignition I can hear a click of the fuel solenoid and whine of the fuel pump. Stb engine - no solenoid click and no fuel pump whine.
Batteries are fine the engine cranks well, just do not fire up
  • Changed fuel filter
  • Engine will start and run if fuel is dripped straight into the intake
  • 20 amp mini fuses on engine (which I believe one of them is fuel pump) look ok
  • I switched both relays from port engine to stbd engine. Still same condition port will run but stb still will not start. Therefore I believe the fuses and relays are ok. It appears to be something causing the fuel pump and fuel shut off solenoid not to get electrical power?
  • Will changing the IAC make a difference? I could not start with increased idle either
Looking for help until I can get a mechanic which is God knows when

Thanks!
Click to expand...
"no solenoid click and no fuel pump whine". This is where you need to direct your energy. Test for 12v power going to the solenoid. If no power, find out why.
 
HawkX66 said:
"no solenoid click and no fuel pump whine". This is where you need to direct your energy. Test for 12v power going to the solenoid. If no power, find out why.
Click to expand...
That's what I am thinking. Any idea were the source of the power comes from? I tried following the wire which disappeared onto a harness maze. I guess I have to dig further.
 
stelios hondrcolos said:
That's what I am thinking. Any idea were the source of the power comes from? I tried following the wire which disappeared onto a harness maze. I guess I have to dig further.
Click to expand...
I don't know your wiring schematic. I'd search for one. It should be pretty clear on that. Are there breakers, one for each side?
 
Make sure you pay close attention to the base of the fuel pump relay as well. These connections can go bad.
 
Highliner said:
Make sure you pay close attention to the base of the fuel pump relay as well. These connections can go bad.
Click to expand...
I switched both relays from port engine to stbd engine. Still same condition port will run but stb still will not start. Th
erefore I believe the fuses and relays are ok.
 
This happened to a dock mate on his 4.3. Turned out to be a bad ECM.

Good Luck
 
Im trying to find all the fuses but cannot locate this one on the attached file in the red box . #32. 20 amp AGC, It doesn't say what it does and I cant find it :(
 

Attachments

  • fuse.pdf
    654.4 KB · Views: 173
The fuel pump relay harnesses have a recall, and a new harness part number was included. You can’t swap the harness, but I just cut mine off, used quick connects, and installed a 40amp/14v relay from auto parts store and it lasted three years. Exact same symptoms. I have the replacement harnesses now, but I never installed them since it uses the more expensive Mercruiser relays and it’s working now.
 
stelios hondrcolos said:
I switched both relays from port engine to stbd engine. Still same condition port will run but stb still will not start. Th
erefore I believe the fuses and relays are ok.
Click to expand...
You swapped relays, but not the harness, my harness went bad. Same exact symptoms.
 
Todd320 said:
You swapped relays, but not the harness, my harness went bad. Same exact symptoms.
Click to expand...

Will a harness go bad so suddenly? Just like that? After 15 years and we had the boat for one day!!!!

how do I test for a bad Harness? Will an analyzer scanner show it ?
 
Following this thread, same thing happened to me this weekend. One of the connectors in the harness is melted. Did not need a scanner for that. Having trouble finding the fix. I have a relay kit on its way and my mechanic mentioned the replacement harness from Mercruiser. Following this for more information.
 
Todd320 said:
The fuel pump relay harnesses have a recall, and a new harness part number was included. You can’t swap the harness, but I just cut mine off, used quick connects, and installed a 40amp/14v relay from auto parts store and it lasted three years. Exact same symptoms. I have the replacement harnesses now, but I never installed them since it uses the more expensive Mercruiser relays and it’s working now.
Click to expand...

Good information - I noticed the connector melted on my harness with the same issue the author of this feed is having. I cannot find the replacement you mentioned - do you have a part number on this?

Could you instead back the wires out of the harness, clean them and reinstall a new harness instead with connectors?
 
My harness does not show any obvious issue. So far I have the following suggestions as any one of the following:
Bad harness
Bad relay
Bad ECM
Bad oil pressure sensor
Bad fuses
 
Are you sure the transmissions are in neutral?

Ask me how I know to ask this question.
 
Drew Schmidt said:
Good information - I noticed the connector melted on my harness with the same issue the author of this feed is having. I cannot find the replacement you mentioned - do you have a part number on this?

Could you instead back the wires out of the harness, clean them and reinstall a new harness instead with connectors?
Click to expand...
I don’t think so, the new harness(es) I have are at the boat, so I don’t have the number. If you have a melted harness, you can be back on the water with a quick trip to auto parts store, I bought quick connects, heat shrink tubing, 2 relays, one was 12v/30 amp, died in 15 minutes on the way to Caladesi island. 14v/40 amp lasted 3 years, 10 minutes to replace on trip to Captiva island. The pins on the Merc relays are thin and appear to generate heat and melt stuff, the ones at the auto parts store are thick blades, and standard size for connectors. Add some heat shrink tubing to seal it, good to go.
 
Do you have a 90 amp circuit breaker on top of engine? Small red button turns power off. Reset is a small white lever on the side. Check +12V on the wire going out of breaker. Could be the fuse powering engine on starter is bad or bad connection. Just happened to me.
 
pyro said:
Do you have a 90 amp circuit breaker on top of engine? Small red button turns power off. Reset is a small white lever on the side. Check +12V on the wire going out of breaker. Could be the fuse powering engine on starter is bad or bad connection. Just happened to me.
Click to expand...
I have the breaker but it has not popped. The starter cranks fine.
 
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