Like Tree0Likes

502 heat soak problem hard to start

Reply
Old 06-26-2006, 11:14 PM
  #1
Registered
Thread Starter
 
Join Date: Apr 2006
Posts: 12
Default 502 heat soak problem hard to start

I have a 94 efi 502 an after I run it for 30mins or so if I shut it off sometimes it will not start back up about 90% of the time. i will have to hold the throttle w.o and it will start up after spinning it over for 10-15 sec. I will run it at 2500 rpms but then pull it back and it will not idle. it does not smoke black like it was flooded out or any thing .
never has died on me at any speed. az speed and marine said it was vapor locking and I need about 2000.worth of new fuel supply can any one help
brent72132 is offline  
Reply With Quote
Old 06-26-2006, 11:32 PM
  #2
Charter Member
Charter Member
Trade Score: (1)
 
Ted G's Avatar
 
Join Date: Jan 2001
Location: Edgerock Baby!!
My Boats: Marlago 35 FS, 18 Neptune CC
Posts: 7,661
Default Re: 502 heat soak problem hard to start

As you probably know, Merc changed to a "Cool Fuel" system in 96 on the EFI motors. This was because the mechanical fuel pump that feeds the VST had a tendency to vapor lock. This sounds like what is happening to your engine. You can switch your system over with some new lines to and from the fuel rail, a fuel cooler, and a new electric fuel pump. Another option would be a low pressure electric fuel primer pump before the mechanical pump. When the system seems to lock up, switch on the primer pump and reprime the system. Or you could plumb in the electric pump to feed the VST and eliminate the mechanical pump from the system completely-just make sure you add a relay and some type of engine-off shut off so the pump won't run if the engine shuts down from a mishap.
__________________
Chesapeake Bay Powerboat Association
www.cbpba.com
Ted G is offline  
Reply With Quote
Old 06-29-2006, 08:17 PM
  #3
Registered
Thread Starter
 
Join Date: Apr 2006
Posts: 12
Default Re: 502 heat soak problem hard to start

thats alot is there any thing else I could do. dont like the ideal of a pump tha I have to shut off
brent72132 is offline  
Reply With Quote
Old 06-29-2006, 08:18 PM
  #4
Registered
Thread Starter
 
Join Date: Apr 2006
Posts: 12
Default Re: 502 heat soak problem hard to start

where do you get a fuel cooler and can I tap it in to the old vst system
brent72132 is offline  
Reply With Quote
Old 06-29-2006, 08:29 PM
  #5
Charter Member
Charter Member
Trade Score: (1)
 
Ted G's Avatar
 
Join Date: Jan 2001
Location: Edgerock Baby!!
My Boats: Marlago 35 FS, 18 Neptune CC
Posts: 7,661
Default Re: 502 heat soak problem hard to start

You could use a standard cooler like an oil or trans cooler, but tha is not your problem. The fuel is cool coming into the engine. But when it sits in the mechanical fuel pump chamber it starts to vaporize from the heat. This causes pressure to go up in the pump and collapses the diphragm against the spring. Now the pump can no longer pump until the pressurized vapor is displaced by liquid fuel, but since the pump doesn't work, the vapor just sits in there till the engine sits and cools. That's why an electric pump is needed to re-prime the system. If you eliminate the mechanical pump you could power the electric from the ignition switch and then it would turn on and off like a regular car fuel pump.
__________________
Chesapeake Bay Powerboat Association
www.cbpba.com
Ted G is offline  
Reply With Quote
Old 06-29-2006, 08:36 PM
  #6
Registered
Thread Starter
 
Join Date: Apr 2006
Posts: 12
Default Re: 502 heat soak problem hard to start

why would az speed tell me I need a cooler??????
brent72132 is offline  
Reply With Quote
Old 06-29-2006, 08:46 PM
  #7
Registered
Thread Starter
 
Join Date: Apr 2006
Posts: 12
Default Re: 502 heat soak problem hard to start

so I would need to remove the low psi pump that is hooked in to the belt drive that is bolted on to the water pump and add a low psi elc. pump up to the line there what type of pump should I use a holley blue????
brent72132 is offline  
Reply With Quote
Old 06-29-2006, 09:14 PM
  #8
Charter Member
Charter Member
Trade Score: (1)
 
Ted G's Avatar
 
Join Date: Jan 2001
Location: Edgerock Baby!!
My Boats: Marlago 35 FS, 18 Neptune CC
Posts: 7,661
Default Re: 502 heat soak problem hard to start

I'm sure they were telling you that you needed a whole cool fuel style system, that would eliminate the mech pump. You could use a Holley pump, it just needs to be regulated to 5-6 psi since the VST is not designed for high pressure coming in.
__________________
Chesapeake Bay Powerboat Association
www.cbpba.com
Ted G is offline  
Reply With Quote
Reply

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
rdoactive
General Q & A
5
08-06-2008 09:03 PM
thebigtman
General Q & A
5
05-30-2005 09:52 PM
Jerry B
General Q & A
2
04-25-2005 09:48 AM
Jerry B
General Q & A
3
05-12-2004 11:10 PM
Lickitysplit
General Q & A
8
02-24-2003 09:19 PM



Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 09:51 PM.


Copyright 2011 OffShoreOnly. All rights reserved.