No "fuel" issue & Mercruiser EFI 502 Info Needed
 

Hi all,

first post, the 502 i've been working on with my dad wont start, we disconnected the line after the fuel filter and its squirting fuel as the key/engine is turned over.

It will start and stay running with starting fluid, but it is not getting fuel somewhere between after the filter and the injectors.

I am having a hard time finding a service manual online for the Mercruise 502 Magnum EFI, does anyone have an electronic version of the service manual? or know where a service manual can be purchased?

The engine looks exactly like this one:
http://www.tanglewoodmarine.com/part...454/454mag.jpg

it is sitting in a 1992 Wellcraft Scarab Twin 502 boat.

We're trying to get the engine to start and run on the fuel in the tank but not having much luck so far, can someone please provide some info on the EFI system and some diagnosis tips?

Much appreciated,
IOIO

Edit: If someone could also tell me whether this system has an electric fuel pump or a mechanical lift pump with electric fuel pressure pump? This engine gave no pump "whirr" noise when the engines electronics were turned on (for either engine, and the port-side engine started just fine, which leads me to believe it has a mechanical fuel pump with an electric fuel pressure pump)

There is a electric pump and a mechanical lift pump. Electric high pressure pump is in the "VST" tank in your picture you posted. It's at the top left with two silver hoses and a clear yellow hose on it. Lots of posts about it and vapor lock if searched.

Dig around and find the engine serial number, and chances are bup on here can fix you up. That being said there is a screen in the vst that can clog, you'll want to look at that.

The electric fuel pump is inside the VST. Outlined in Red. When you power it up if should run for 2-3 seconds before cranking.

The mechanical pump, pumps fuel into it and the electric pump feeds the rail. The electric pump has 1 harness with2 wires coming out of it. There are also 3 fuses under the lid where the computer is. Make sure those are good. IIRC one is for the pump.

http://i212.photobucket.com/albums/c...psytinpul5.jpg

High-pressure pump and or regulator. Also had if you line collapse due to ethanol eating the inside out check your fuel lines and rail for particles of rubber.

Most likely everything in the VST or least half of the parts could be the problem . There is a bottom filter as well.

here is one serial group of it since you did not post engine serial number. engine serial is one of the most important things you can post - it takes a lot of guess work out and of course it takes a lot of wrong answers out the mix to in which can only help you looking for the correct information in return

. http://www.marineengine.com/parts/me...below-see-note

And another engine serial number group Not a cheap parts buying for anyone if they have this very poor design outdated system.

http://www.marineengine.com/parts/me...sn-up-see-note

If you were to update it what would you do? Aeromotive or something like that or a newer Cool Fuel setup?

I'll leave it to BUP for suggested replacements. I pulled one off my 502 during my last rebuild and went from a MEFI-1 and VST (same as yours) to MEFI-3 and cool fuel. Upgraded because I knew if I ever need to replace it, then it would be costly unless I found a used one, and MEFI-3 was more tunable then the 1. It was working fine when removed, had cleaned it a couple times just for cause and found no issues. They are prone to vapor lock being on top the engine, but that to can be dealt with

^^^^ what is said here and the vapor lock problems. Man I have seen stuff growing in those VST tanks - You have a needle and seat persay with a float along with a fuel filter in the bottom and the high dollar fuel pump among other related parts in that system living in today's fuels - with that said not good things happen inside especially being a 20 plus year old system & set up.

Anyways the gen II cool fuel is much better and so is MEFI 3 or even MEFI 4 if you can get a great tuner person for it.

We have done many carb conversions in past as well for the owners because mainly of a couple reasons, related costs and some even had ECM issues. A lot in my area had vapor lock issues to.

I am sure that it has been posted up here about some of these VST's have related back to engine failures and even hydrolock issues. Surprise no one has one posted currently.

the holley MPI conversion looks good for this as well.

IMO if you have parts replacement needed for the VST and or possible ECM driver issues ( MEFI 1), - I would do some sort of conversion especially a more current conversion option or a carb conversion for a cheaper route.

In my area again Vapor Lock was a huge issue as well even when brand new.

there was a reason that Mercruiser had this VST app around for only 3.5 years and quickly moved on to gen II cool fuel. . just saying

Not to push it, but carb conversion is easy. Keep the mechanical pump and keep the same distributor even. Some people pick up speed too.

Or as Bup has also mentioned, run a more conventional fuel system.

FIxing the vapor lock is easy and cheap also ;) I have 0$ into mine (had the parts in the cabinet form other projects I have a write up on here.

Cliff notes:
The diagram fails, when it dose it can hydrolock, wash down cylinder, thin out oil, ect since it dumps the "over filled fuel into #8 piston.
Mine failed 2 times in 2 years
In stead of having replacing it for $90 every year, have that clear(ish) line back to the tank vs #8.
Now when it fails (witch is a good thing) It send the fuel back to the tank. Thus also cooling the fuel.

Mine has been this way for 2 years. No more fuel problems here. (But i also play it safe, open the hatch 6-8" when idling, run my blowers any time the engine is running, once anchored of at the sand bar, I leave the hatch fully open for 5 min.)

http://www.offshoreonly.com/forums/g...work-pics.html

http://www.boatfix.com/merc/bullet/93/93_26.PDF

Back in the day there was always a problem with the system. And then the fuel started changing causing different issues. Just saying.

You are running in MN come down here when its 105 plus degrees for months and no shade with the lake water temps sky high. Run you engine like most boaters, no blower on and not venting the engine hatch ever. Run for a 30 to 45 min WOT and then shut your engine down to take a break for about 2 or 3 hours. What no start ? very common here.

Mine vapor locked only twice but each time is was a real hot day, and didn't let it cool down enough (just maybe) but IMO the thing that helped more then anything was non-ethanol gas. Either way the real fix seams to always be to run the return back to the tank instead the VST or filter. Indmar seams to have done just that on their motors, don't know why Merc doesn't

All Indmars currently run all fuel pumps in the gas tank and this has 99 % cut out VL, Also some in past years depending on boat manu - Mastercraft has done this for years fuel pumps in the gas. just saying.

Easier install of engines for OEM's. Just 1 fuel line and a harness.