Mercuiser 5.0 cranks fast wont start (for 20 mins)

[Bullinachinashop]

Hi all,
My uncle has a 2002 mercruiser 5.0 in a sea ray. He is not mechanically inclined but I have had several boats, no EFI's though.

I have so far changed water sep filter- I thought it may be bad gas-no dice.
I am going out with a new distributor cap next time

Scenario:
Out running for 20 mins, we shut off, swam around for a bit. When we tried to start the motor was cranking plenty fast, but no attempt to start. Back in the day OMC kill switches were more trouble than they were worth. I flipped the safety switch a few times but no help. I am taking a new distributor out to the lake to see if that's corroded. I checked for spark but I didn't SEE any but hard to be sure in the daylight.

After we sat for 20 mins it started right up-almost like a non-mechanical issue? I guess it did this same thing last time.

What would you recommend I check for troubleshooting? Bilge is pretty clean otherwise no serious corrosion etc. Boat is 1.5 hrs away and I dont have a tow vehicle handy to boot ;-)

 

[Seadooman03]

Re: Mercuiser 5.0 cranks fast wont start (for 20 mins)

Sounds more like an electrical issue rather then mechanical. I would start at the relays/ignition switch and start to trace back from there. Sounds like more of a lose wire. Start with the boat turned on...(if it all out of the water with muffs or by a dock obviously) and wiggle wires around, under the dash, in around the engine back, and down the side that they are run. If that all fails, look in the engine bay for a broken wire. Maybe its a leaky cap with moisture building up?

 

[spktho]

Re: Mercuiser 5.0 cranks fast wont start (for 20 mins)

check voltage to fuel pump when cranking. If no voltage, check all connections related to fuel pump including the lead from the alternator. If there is voltage, check fuel pressure. If no or low fuel pressure, may be fuel pump going out. This would be best done when it won't start.

You also need to make sure there is spark, if all this checks out, time for compression testing.

I'm sure I'm missing something as this is basic.

 

[Bullinachinashop]

Re: Mercuiser 5.0 cranks fast wont start (for 20 mins)

check voltage to fuel pump when cranking. If no voltage, check all connections related to fuel pump including the lead from the alternator. If there is voltage, check fuel pressure. If no or low fuel pressure, may be fuel pump going out. This would be best done when it won't start.

You also need to make sure there is spark, if all this checks out, time for compression testing.

I'm sure I'm missing something as this is basic.

Sure sure makes sense. How should I check fuel pressure on this engine? Is there a fetzer valve I can poke to see if fuel sprays out?

 

[Bullinachinashop]

Re: Mercuiser 5.0 cranks fast wont start (for 20 mins)

I swapped out dist caps. It looked pretty clean, just a bit of green on each contact. I am going to take starting fluid to see if it DOES die again, if a shot of starting fluid helps. If so then may be time for a fuel pump during the cold months