Now fixed! Engine starts, but immediately stalls
 

Twin 1999 454 MPI/Bravo 1. Everything was working fine Saturday. After docking for two hours at lunch the starboard engine would start, but would immediately stall. My sonic has two fuel tanks, so I tried using both tanks on engine with same results. After idling back to my marina I changed the fuel filter. Still has problem. The next morning I tried to start it, but still the same problem.

Any ideas for trouble shooting will be appreciated. The next thing I will try tomorrow after work is to bleed off any air via valve near injection rails.

Oh yeah, when the key is turned to the "on" position the fuel pump does kick-in.

Re: Engine starts, but immediately stalls
 

vapor lock find the fuel presure test fitting under the front of the plunim sp. and let the air out of the fuel system andit should start

Re: Engine starts, but immediately stalls
 

Rule out the ignition switch before you drive yourself crazy.

Does it quit as soon as you let off the key or does it stumble a bit before quitting?

Re: Engine starts, but immediately stalls
 

good point but i have seen this motor vapor lock more then once but i would check the switch for sure

Re: Engine starts, but immediately stalls
 

Sometimes it will run for a few seconds and slowly die out. The more people I talk to the more I think it's vapor lock. I'll bleed the fuel pressure fitting tonight and let yawl know how it goes.

Thanks bunches!

Re: Engine starts, but immediately stalls
 

Mine was full of water and was doing the same thing. Was there water in the fuel/water separator when you changed it? I had to have about 3~4 gallons of water/fuel sucked out of my tank before it would run again.

Re: Engine starts, but immediately stalls
 

Can't be vapor lock if it does it after sitting over night.
Does the Merc MPI fuel system have a return line to the tank?
If so it shouldn't have vapor lock. Not with a constant flow of fuel.

How about the fuel pump safety cut-off switch? Does it have one?
Some safeties have a start bypass to provide fuel pressure while cranking.

Re: Engine starts, but immediately stalls
 

I went down during lunch break to look for the fuel pressure test fitting. I pushed it in and air did come out and then a couple drops of gas. Just to compare I did the same for the port engine and nothing came out of that one. Then I realized my boat keys were at home ...dadgumit! I'll try to start it tomorrow morning.

MLitefan, I added gas treatment and filled both tanks to the top during winterizing, so hopefully they are not full of water.

Iggy, I'm not sure if the merc MPI has fuel recirculation. However, when I open the tank access hatch I only see two hose connections per tank. Each hose connects to a different left/right/off switch-over valve. Also, I don't know if the fuel pump has a start bypass. How do I check for that?

Thanks all for the input.

Re: Engine starts, but immediately stalls
 

I have been reading about this problem and think I have a similar one. One of my 502's starts hard after operating temp. Starts fine cold. The way I see it the return line from the presssure regulator goes back to the VST. Seems to me that could put allot of hot fuel in there. I have read some about options with cool fuel but not sure about the applications. I have fuel pressure gages ordered for mine so I can compare one to the other. Next question would be if it is a vapor lock condition how do you stop it? Somewhere I read there may be a service bullitin on this. If anyone knows let us know.

Thanks.

Re: Engine starts, but immediately stalls
 

I'm guessing the MPI engines use an electric fuel pump right?
To see if there's a return line, follow the fuel line on the engine. If it has a return you should see a pressure regulator and a seperate line comming from the engine. Two fuel lines per engine.
You say you only saw two hoses attached to the fuel selector switch? The return lines could be connected to the main refueling hose.

If it does have an electric pump you should hear it turn on when you turn the key to the start position. Once the engine is running the safety switch, which may be controlled by an oil pressure switch or a sensor in the ignition system, will take over and provide power to the pump.
Find the fuel pumps, have someone start the engine while you listen or feel to see if the pump is running. If the pump stops when the key is released back to "RUN" position the trouble is in the safety switch.

BTW I have no knowlage of the MPI systems. I'm only giving you what I know of automotive engines.
Marine EFI, MPI, systems (even carburated engines with electric pumps) should have safety switches to prevent fuel flow if the engine is not running.

Re: Engine starts, but immediately stalls
 

Thanks Iggy. If it doesn't start in the morning I'll start looking at the pump, safety switch and regulator.

Re: Engine starts, but immediately stalls
 

Did you clean out the fuel pickup screen and clean the anti syphon valve if so equipt?

BT :cool:

Re: Engine starts, but immediately stalls
 

Jerry B has a good point about the VST tank, but I'm not sure they have that on a 1999.
Love Machine, if you look at the back of the fuel rail by the distributor, the fuel lines exit and go somewhere. If they go to a VST tank it should be located right off the back of the plenum and it has a screen in it also that filters the fuel and can get plugged. If the VST is causing vapor lock there is a plug on the top of the VST tank that you can pull to relieve any pressure. Need to identify if you have a VST tank when you go to check it out.

Re: Engine starts, but immediately stalls
 

Dumb question. What does VST stand for?

Re: Engine starts, but immediately stalls
 

Vapor Separator Tank, and it's not a stupid question. The way this unit works is that a mechanical fuel pump fills up the VST tank and then the high pressure pump takes the fuel out of the VST to the fuel rail then to the injectors. This about the dumbest setup I have run across, but it was their answer to vapor lock.

Re: Engine starts, but immediately stalls
 

Hey LM, Is your boat still at the boatel? And did you move down to calvert or st marys?

Re: Engine starts, but immediately stalls
 

Ok, I had boat keys in hand this morning :D. However, after bleeding the Fuel Pressure Check valve the engine still would not stay running. I bled it a few times to no avail.

I just spent a butt load having the uppers refreshed, so I called the service manager. He's going to come out and hook up the diagnostic computer to my engine. I'll let him figure it out. Oh well, hope to be back up running this weekend.

Re: Engine starts, but immediately stalls
 

Hey LM .Let us know what he finds. Still sounds like a fuel problem.
Good luck, Jerry.

Re: Engine starts, but immediately stalls
 

I'm not at the boatel now. I moved the boat up to Turkey Point Marina in Edgewater. I live in Prince Frederick though.

Re: Engine starts, but immediately stalls
 

Hey Love Machine,

I this weekend had a similar problem. I ran about 30 min. to get gas and after putting about 100 gallons in went to start the boat and it started but then stalled. After pulling fuel lines checking for blockages I pulled the fuel water seperators and dumped them. Then filled them all the way to the top and reinstalled new filters and turned the key and they both started and ran great. There are 2 fuel pumps one that fills the fuel water seperator that is mech and one that pumps the fuel to the injectors that is the elec pump. Try filling the seperators all the way up if you get a chance..... Good Luck

Re: Engine starts, but immediately stalls
 

When I put on the new filter I didn't fill them. I'll try that before the mechanic comes out. Thanks.

Re: Engine starts, but immediately stalls
 

Had a similar problem last year, turned out to be my MSD module shorting out inside.

It's fixed! Re: Engine starts, but immediately stalls
 

Everyone, thanks for your input. I did fix it myself this past weekend. It ended up being something simple.

I pulled the gas filter and there was hardly anything in it. I filled it all the way up, put it back on and let all air out of the pressure check valve. It started up on the second attempt and has run since.

Still unknown what actually caused it to happen. I took spare filter, gas and tools with me when cruising around to test it out. So far, so good.