Mercruiser 5.0 EFI won’t start after stopping to swim?

Jim Coady

Member
Apr 18, 2021
43
Kansas
Boat Info
2001 SeaRay 190SD, 5.0 efi Mercruiser, alpha 1, gen II, Vengeance 14.75” x 21” SS prop.
Engines
Mercruiser 5.0 EFI, Alpha 1 , gen II drive
2001 Mercruiser 5.0 EFI, ran fine all day for approximately 5 hrs or so, just general boating, a little bit of wake boarding during that time. Then, we decided to stop, anchor, and swim a bit, probably a 30-45 min stop. Sons girlfriend was sitting in drivers seat, and we needed to move up a bit, to pull anchor in. My son told her to start it up. She turned the key on quickly, then once again, and it wouldn’t start. So, I traded seats, and I tried, after running blower for several minutes, still wouldn’t start. It wanted to, coughed, sputtered but no go. We waited a few minutes and tried again, no luck either. Kind of thought it might have been flooded, so pushed neutral button gave it full throttle, same results. My son then tried, he pumped the throttle, motor wanted to start, but wouldn’t. Fuel guage indicated little over half a tank. Seemed like a fuel issue, not flooded, but starved for fuel. We waited a bit longer, text a few friends telling them we may need a tow. For some reason I thought I might try and remove gas cap, thinking it was a venting problem. So, when I did, and son tried to start the motor, it fired right up. I put fuel cap back on, and away we went. Motor ran fine, we were ready to leave anyway, so we headed to the ramp and loaded it up.
So, any ideas what the issue is, or was, and what do I need to start checking tomorrow
Thanks
Jim
 
Could be vapor lock from sitting while hot. If it was truly a fuel tank vent issue, I think you would have experienced fuel starvation while running it during the 5 hours.
 
I have experienced the same problem having just bought my 260 at the end of February and now boating in FL 90 degree water. After much research I am convinced it is a vapor lock issue. There are a number of ways to remedy this and I am currently deciding how to tackle the problem. You can refer to the attached and that will help, but no fool proof way offered for a fix.
What you will not see in the SB is the suggestion to re-route the fuel return line to the fuel tank. Many blogs I have read suggest this as a good fix, however there is little information available on the subject. What I have learned thus far:
1) The return line should direct fuel close to the bottom of the tank and away from the pickup.
I am about to re-route the return line but am concerned that putting an anti-siphon valve in place (required by USCG) will restrict the returning fuel causing a problem...hoping for some input from club members on this.
 

Attachments

  • vaporlock - Merc SB.pdf
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check distributor cap and rotor. i've had an engine start and run all day and then just decide the corrosion was too much to keep going lol. changed em out and starts like a champ every time
 
Vapor lock is a common problem. There are many postings on the subject if you do a search.

One recommendation I can make from personal experience is to let your engine idle with the blower running for several minutes before turning the engine off. That way cool water can circulate thru the engine before it gets turned off. I did that as a common practice myself after experiencing vapor lock on hot days and it seemed to make a difference.
 
Vapor lock is a common problem. There are many postings on the subject if you do a search.

One recommendation I can make from personal experience is to let your engine idle with the blower running for several minutes before turning the engine off. That way cool water can circulate thru the engine before it gets turned off. I did that as a common practice myself after experiencing vapor lock on hot days and it seemed to make a difference.

Thank you Dave. I will be installing a new blower for that reason and hope for better results: https://www.amazon.com/Attwood-Turbo-Water-Resistant-Line-Blower/dp/B00J5O9H10
 
check distributor cap and rotor. i've had an engine start and run all day and then just decide the corrosion was too much to keep going lol. changed em out and starts like a champ every time
Dont think thats my problem, as if I wait about 20-30 minutes, it fires right up and never misses a beat rest of day, IF I dont stop to swim for awhile. Done this last two times we went out.
 
I have experienced the same problem having just bought my 260 at the end of February and now boating in FL 90 degree water. After much research I am convinced it is a vapor lock issue. There are a number of ways to remedy this and I am currently deciding how to tackle the problem. You can refer to the attached and that will help, but no fool proof way offered for a fix.
What you will not see in the SB is the suggestion to re-route the fuel return line to the fuel tank. Many blogs I have read suggest this as a good fix, however there is little information available on the subject. What I have learned thus far:
1) The return line should direct fuel close to the bottom of the tank and away from the pickup.
I am about to re-route the return line but am concerned that putting an anti-siphon valve in place (required by USCG) will restrict the returning fuel causing a problem...hoping for some input from club members on this.
Ray260, thanks, I had downloaded the service bulletin in the past, so had it on file on my computer. Since my motor is a EFI, Im thinking I might explore these two paragraphs in the bulletin.

EFI and MPI engines with the ‘Cool Fuel’ system should have the fuel cooler temperature
measured after the engine is shut off. The coolant hose going to the ‘fuel
cooler’ should not get much hotter to the touch after the engine is shut off for 10-20
minutes than what it is with the engine running. If it gets hot after the engine is shut
off, hot water from the cylinder block might be siphoning back. Installing the Check
Valve Kit will stop this backward water flow.

NOTE: Carbureted and EFI/MPI with VST models only: The Water Separating Fuel Filter
can be removed from the engine to a lower, cooler location. Use a Coast Guard approved
fuel line between the filter and the fuel pump.

thanks for the input,
Jim
 

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