5.0 MPI wont start

R

rbryn

Member
May 27, 2009
254
Wilmington, NC
Boat Info
2003 260DA
Engines
350Mag MPI Bravo® III (re-powered 2013)
Have a 2003 5.0 MPI that won't start and I'm looking for ideas. The engine turns over, but just won't start. The last time it was running about a month ago it ran like a champ without a hiccup or hesitation.

1. Replaced battery (it has a brand new battery put in two months ago)
2. pulled one of the spark plug wires and confirmed it's throwing a spark
3. Confirmed fuel flow was getting all the way to the fuel filter.
4. pulled the water/fuel separator to check for water in fuel (none found)
5. took off the flame arrestor to ensure no air flow blockage
6. sprayed starter fluid into throttle body to try force start (no change)

The engine just turns with the starter, over and over and never really fires a single cylinder. At this point I'm completely clueless and looking for a few ideas before I call the Mercruiser Mechanic. I feel like I have to overlooking something simple.
 
rbryn said:
Have a 2003 5.0 MPI that won't start and I'm looking for ideas. The engine turns over, but just won't start. The last time it was running about a month ago it ran like a champ without a hiccup or hesitation.

1. Replaced battery (it has a brand new battery put in two months ago)
2. pulled one of the spark plug wires and confirmed it's throwing a spark
3. Confirmed fuel flow was getting all the way to the fuel filter.
4. pulled the water/fuel separator to check for water in fuel (none found)
5. took off the flame arrestor to ensure no air flow blockage
6. sprayed starter fluid into throttle body to try force start (no change)

The engine just turns with the starter, over and over and never really fires a single cylinder. At this point I'm completely clueless and looking for a few ideas before I call the Mercruiser Mechanic. I feel like I have to overlooking something simple.
Click to expand...


Did you check the kill switch by your throttle?
 
i did. When I turn that off, it kills all power and the starter won't even engage, so that was an easy one to rule out :)
 
I would change the ignition sensor (located under the Dist. cap) They are a common culprit for a no start condition (especially if you have the old "unsealed" stlye.

Here is a pic of new vs old:

100_3373.jpg
 
When I had my 300DA with 5.0L engines, I had a similar thing happen at delivery. Cranked but wouldn't fire. Turned out to be a crankshaft sensor that had come loose. Took the mechanic 5 minutes to find & fix it. The salesman was really sweating for those 5 minutes, though.
 
Another member just went thru this. It turned out to be his Thunderbolt Ignition Control Mod. Start with the pickups as Quint4 has said, then move to the ICM (if you even have one)
 
Pet Peeve:
Those who post a question and then disappear after many have taken the time and effort to try and help them.
 
Quint I agree. Not so much just helping but sometimes it is nice to know what fixed it even if it was done by a dealer so that it can help other members.
 
Mine too ;). I haven't abandoned it yet. Just been too busy with the holidays. I've ruled out everything but the sensors. Waiting on a friend this weekend to hook it up to the laptop for diagnosis.

Sent from my SCH-I545 using Tapatalk
 
Well good luck with it!
 
Friend of mine just had the same problem on 5.0MPI. Replaced cap and rotor- problem solved. It was getting spark to the plugs but apparently not enough.
 
I had a similar thing happen but it was a loose wire on the fuel shut off valve.
 
OK, so I'm coming back to update the thread for any other poor soul that needs the info. It took a while to figure it out and we ended up having to tow her in to MarineMax for a final diagnosis.

They put the computer on it, found no errors, spark was fine, fuel pressure was fine, fuel was fine etc.... pulled the plugs and they were all fouled. Did a compression test and found all cylinders low (some as low as 70psi). So it's time to replace the engine.

For some background...
She had 700hrs, a head job 4 yrs ago and had some overheating issues this summer. My son and I replaced the risers and manifolds ourselves this past spring... It could be any number of issues leading to the demise of the engine (botches manifold install, warped head from overheating etc.) all we know is that it's time to replace the engine.

Going to take this opportunity to step up to a 350Mag.
 
700 hours is nothing. I sure hope mine engines last much longer than that.
 
I'm hoping the next one lasts alot longer :)

Sent from my SCH-I545 using Tapatalk
 
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