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:


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.

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