Merc 502 stalling/dying on acceleration after idling for awhile
- thunder550
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
Lol I like having projects, sometimes it feels like I bit off more than I can chew with this one. Have to keep reminding myself that I'm still working through issues that were present when I bought the boat, other than the water leak (and a new oil leak in one of the remote oil filter lines that I found while digging around today...blah) there have been few new issues come up.
It would be so much easier if I could keep the boat at my house and work a little bit here and there, but each time I want to work on it I have to borrow my wife's SUV, drive the 3 miles or so to the storage place, hook up, drag it home, position it somewhere that the neighbors won't get annoyed (HOA says no working on vehicles in visible places....nobody's complained yet *fingers crossed*), then do whatever I was planning to do. Needed to make a parts run earlier today while I had the VST taken apart, didn't want to tow the boat to Home Depot & Oreilly and slosh fuel around and can't disconnect it on the street (city code), so I rode my bike Always have to anticipate afternoon plans to and start wrapping up an hour or hour and a half ahead so I can have time to clean up and take it back to storage.
Anyway...enough whining. Put VST back together and took the mechanical pump apart. No surprise given what came out of the fill hole yesterday, but when I separated the diaphragm from the pump side there was quite a bit of oily gas that came out. There shouldn't be any in this location. Checked the elliptical inside the seawater pump, it looks ok to me, so I'm going to go ahead and replace just the lift pump part for now and see if that helps out. If the problems continue in the future I'll explore further. Tired of smelling like gas
I don't understand why they did what they did with the VST system. It's like they wanted to keep it kinda like a carb system but then add EFI. Basically the line from the tank goes into the water separator, then through the mechanical lift pump, then up to the VST tank. The float you see in the pics above closes and opens a valve that lets fuel into the tank from the mechanical pump. When the level in the VST tank drops, the float opens the valve and lets more fuel in, then when it fills, the valve shuts off. The high pressure electrical pump draws from the VST tank and feeds the fuel rails and injectors. Unused fuel from the rails feeds back to the VST tank through the return line. All of this is happening right on top of the hot engine, so no wonder the fuel gets hot and vapor locks doing laps in the upper engine sauna.
I've read a lot of threads where people get tired of dealing with VST and replumb everything to be more like a car system, where the fuel goes from the tank, through the water separator, through a high pressure electric pump (note the missing mechanical pump and VST tank), through the fuel rails, then gets returned back to the tank. Seems much simpler and more reliable to me, but what do I know.
It would be so much easier if I could keep the boat at my house and work a little bit here and there, but each time I want to work on it I have to borrow my wife's SUV, drive the 3 miles or so to the storage place, hook up, drag it home, position it somewhere that the neighbors won't get annoyed (HOA says no working on vehicles in visible places....nobody's complained yet *fingers crossed*), then do whatever I was planning to do. Needed to make a parts run earlier today while I had the VST taken apart, didn't want to tow the boat to Home Depot & Oreilly and slosh fuel around and can't disconnect it on the street (city code), so I rode my bike Always have to anticipate afternoon plans to and start wrapping up an hour or hour and a half ahead so I can have time to clean up and take it back to storage.
Anyway...enough whining. Put VST back together and took the mechanical pump apart. No surprise given what came out of the fill hole yesterday, but when I separated the diaphragm from the pump side there was quite a bit of oily gas that came out. There shouldn't be any in this location. Checked the elliptical inside the seawater pump, it looks ok to me, so I'm going to go ahead and replace just the lift pump part for now and see if that helps out. If the problems continue in the future I'll explore further. Tired of smelling like gas
I don't understand why they did what they did with the VST system. It's like they wanted to keep it kinda like a carb system but then add EFI. Basically the line from the tank goes into the water separator, then through the mechanical lift pump, then up to the VST tank. The float you see in the pics above closes and opens a valve that lets fuel into the tank from the mechanical pump. When the level in the VST tank drops, the float opens the valve and lets more fuel in, then when it fills, the valve shuts off. The high pressure electrical pump draws from the VST tank and feeds the fuel rails and injectors. Unused fuel from the rails feeds back to the VST tank through the return line. All of this is happening right on top of the hot engine, so no wonder the fuel gets hot and vapor locks doing laps in the upper engine sauna.
I've read a lot of threads where people get tired of dealing with VST and replumb everything to be more like a car system, where the fuel goes from the tank, through the water separator, through a high pressure electric pump (note the missing mechanical pump and VST tank), through the fuel rails, then gets returned back to the tank. Seems much simpler and more reliable to me, but what do I know.
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1995 Cobalt 252 - 502 Mag EFI - Bravo 1 - 21" Revolution 4
- Big Block Power
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
I gave up carbs and mechanical pumps more than 10 years ago. It's good to see you jump right in there though.
03Cobalt220 8.1gxi DP
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
Re: Merc 502 stalling/dying on acceleration after idling for awhile
It's amazing how close that last picture looks to a 1960 Austin Healey fuel pump diaphragm. No brass washers behind it but still the same. Brings back memories.
2002 Cobalt 262
&
2005 Cobalt 263
496 MagHO
(sold )
Erie, PA
Currently boatless (for now)
will fly for food
(CChat moderator)
&
2005 Cobalt 263
496 MagHO
(sold )
Erie, PA
Currently boatless (for now)
will fly for food
(CChat moderator)
- thunder550
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
We've come so far in 30 years eh?
Anti siphon valve is clean. Nothing left to check. Hopefully the new pump solves the problem.
Done for today, doing some driveway boating now listening to music
Anti siphon valve is clean. Nothing left to check. Hopefully the new pump solves the problem.
Done for today, doing some driveway boating now listening to music
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1995 Cobalt 252 - 502 Mag EFI - Bravo 1 - 21" Revolution 4
- Big Block Power
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
Get r coming.at least you know what you have.
03Cobalt220 8.1gxi DP
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
Re: Merc 502 stalling/dying on acceleration after idling for awhile
T,550
I’m currently living through your boating eyes since it is now 20° here (a heat wave !)
Thanks for posting all your project pictures. It helps take away the cold winter blues.
I’m currently living through your boating eyes since it is now 20° here (a heat wave !)
Thanks for posting all your project pictures. It helps take away the cold winter blues.
2002 Cobalt 262
&
2005 Cobalt 263
496 MagHO
(sold )
Erie, PA
Currently boatless (for now)
will fly for food
(CChat moderator)
&
2005 Cobalt 263
496 MagHO
(sold )
Erie, PA
Currently boatless (for now)
will fly for food
(CChat moderator)
- thunder550
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
Fuel pump is ordered, will be here towards the end of the week.
A7, I'm happy to post, thanks for being there to help and/or commiserate
A7, I'm happy to post, thanks for being there to help and/or commiserate
1995 Cobalt 252 - 502 Mag EFI - Bravo 1 - 21" Revolution 4
- Big Block Power
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
As long as it's here before I get there we are all goodthunder550 wrote: ↑Sun Jan 07, 2018 5:33 pm Fuel pump is ordered, will be here towards the end of the week.
A7, I'm happy to post, thanks for being there to help and/or commiserate
03Cobalt220 8.1gxi DP
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
- thunder550
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
You betcha!Big Block Power wrote: ↑Sun Jan 07, 2018 5:45 pm As long as it's here before I get there we are all good
1995 Cobalt 252 - 502 Mag EFI - Bravo 1 - 21" Revolution 4
- thunder550
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
Well it died on me again Sunday after idling for a long time. Was able to get it to fire off relatively quickly by cycling the key to run, then off, and repeat a few times to cycle the electric fuel pump. Not sure where to look next, my guess would be electric fuel pump but I don't want to just throw parts at it and hope for the best.
1995 Cobalt 252 - 502 Mag EFI - Bravo 1 - 21" Revolution 4
- Big Block Power
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
That bites. Can you put a guage on it and watch it when it happens? So while your moving at idle no wake speed does it just shut down.
03Cobalt220 8.1gxi DP
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
Re: Merc 502 stalling/dying on acceleration after idling for awhile
That does suck.. but to add to BB .. you stated before it stalled as you off idle throttled.. is it just a idle stall now? And you wait until you here the pump rebuild pressure with the 2-3 second buzz and it starts?
You may need a inline pressure gauge poking out of your hatch ( carful as the interior is new)
I was still remembering your " change the fuel filter " and it was fine for 3 months.. that's why I thought water in fuel. ( did you ever check for water???)
But if it restarts and no steady surge once up to speed , I'm leaning to fuel pressure and or hot fuel disapation.
Or we throw parts at it...
You may need a inline pressure gauge poking out of your hatch ( carful as the interior is new)
I was still remembering your " change the fuel filter " and it was fine for 3 months.. that's why I thought water in fuel. ( did you ever check for water???)
But if it restarts and no steady surge once up to speed , I'm leaning to fuel pressure and or hot fuel disapation.
Or we throw parts at it...
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2008 272 , 496 HO fo SHO
California Delta
Table Rock Lake
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California Delta
Table Rock Lake
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
If it stalls going to neutral it could be that switch that's in the cable I believe that makes the engine stall and restart. I had one go bad in my last boat and this one I have now might also be bad but I'm not sure how Volvo did it on the boat I have. Yes I am talking merc for this though. It was only about $800 fit the dealer to change. Hat please:-)
03Cobalt220 8.1gxi DP
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
"Kids in Tow2"
"Pot The Jus" Originator :-)
Neenah Wi
#ItsBu'sfault
#FARCON Marine CC Core!
Re: Merc 502 stalling/dying on acceleration after idling for awhile
Are you using E10 or Ethanol free fuel?
2007 Cobalt 272 with Volvo 8.1 Gi
- thunder550
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Re: Merc 502 stalling/dying on acceleration after idling for awhile
I have a gauge I can put on it, just need to make sure and catch it at the right time. It's happening when I try to accelerate after idling with the engine hot for a long time. Boat starts to come up on plane then acts like I cut the throttle back to neutral, even though the throttle is full forward. After it goes back to idle, it runs rough, and if I try to accelerate again it dies completely.
After it dies, I can either wait 2-3 minutes or cycle the electric fuel pump a few times and it will start up. Once it restarts, it runs great and there are no further issues.
It doesn't stall going to neutral, it stalls when accelerating off idle. Mr Hahn, yes I am using E10. The nearest ethanol-free fuel station (1 of only 4 in AZ) is about 90 miles away from me
After it dies, I can either wait 2-3 minutes or cycle the electric fuel pump a few times and it will start up. Once it restarts, it runs great and there are no further issues.
It doesn't stall going to neutral, it stalls when accelerating off idle. Mr Hahn, yes I am using E10. The nearest ethanol-free fuel station (1 of only 4 in AZ) is about 90 miles away from me
1995 Cobalt 252 - 502 Mag EFI - Bravo 1 - 21" Revolution 4
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