1995 5.7L TBI Magnum Skier won't run

[PW]

Ser. #OF562552. Freshwater boat on SE Michigan inland lake, EFI throttle-body engine, running well until yesterday. Was pulling a skier when the engine started cutting out. Dropped that skier and pulled up another, with the boat running fine for about 10 minutes when we finished the last run of the morning and docked.

Tried to go out later in the day and the engine wouldn't start. Cranked fine, but it didn't even try to start. I seem to recall that the throttle-body injectors spray when the engine is cranking, correct? Pulled the flame arrestor and cranked the engine. No injector spray. Put a shot of starter fluid in the throttle-body. Engine ran for a couple of seconds and stalled.

There's a low-pressure mechanical pump that pushes fuel through a canister filter. Then a high-pressure electric pump delivers the fuel to the throttle-body. One or the other bad? I listened to the electric pump cycle and pressurize the system when turning on the ignition on. Clogged fuel line or filter?

Will somebody give me a step-by-step troubleshoot routine? Not quite sure what to check first. Looking for the most efficient process of elimination.

Many thanks for your help, PW

 

[alldodge]

Remove the canister fuel filter and see if its full, then pour contents into a baggie and see if there is something other then clean gas

If its not full, remove the antisiphion valve on the fuel tank. The rubber fuel line which goes to the filter is attached. The valve has a spring and ball inside, see if this ball moves easy or is clogged up

If filter is full, replace filter of old, but if new this season refill and reinstall

Need to test low pressure fuel pump by placing a Tee between the pump and VST. Pressure should be between 4 to 7 psi

If filter was full and low pressure pump is good, need to test the high pressure pump. Get a Tee fitting to connect between the VST and the throttle body (TB). The fitting is part number 91-80609 and pressure should be 30 psi

 

[PW]

Hi AllDodge. This is the same engine I described last summer in my post [h=3]Inboard '95 Mercruiser GM 350 EFI Magnum Skier limited top speed[/h] The VST was removed by a previous owner and replaced with a Walbro GS395 fuel pump, which has inadequate flow to run the engine to WOT. It's run all day at 3200rpm, which is how I've been using it for skiing.

One thing is troubling me. Look at the attached diagram from the Mercruiser Service Manual #17. It does not indicate that there is a mechanical pump feeding the VST. Item G just says "Fuel from tank." Could having the mechanical pump in line be part of the WOT issue?

Last summer, I did all the tests you just recommended. Everything checked out fine. Also replaced the anti-siphon valve. Guess I'll be checking everything again. (I was hoping there might be an easier way out.) Thanks for your help.

 

[thumpar]

Mine is a 1996 EFI. It has the mechanical pump and the high pressure electric pump in the VST. Since you system has the VST removed you may not need the mechanical fuel pump. I think the manual fuel pump is just to keep the VST full because the pump in the VST is just using what is around it and not sucking from a hose.

 

[alldodge]

One thing is troubling me. Look at the attached diagram from the Mercruiser Service Manual #17. It does not indicate that there is a mechanical pump feeding the VST. Item G just says "Fuel from tank." Could having the mechanical pump in line be part of the WOT issue?

Do remember something able the other thread, but have been so many of threads since

Its possible and would depend on where the pump is located. If its to high then the pump will have a hard time drawing fuel. As for the drawing, it doesn't show the mechanical pump but it is designed to be there. The manuals even Mercs have issues

 

[PW]

AllDodge and Thumper, thanks for the input. Found another set of fuel system diagrams that included the mechanical fuel pump. I bought a new high-output Walbro GSL393 last summer, but when I put it in, the engine ran even worse, so I switched back. Walbro recommends the fuel pump be mounted as close to the tank as possible. I'll try doing that with the GSL393 at the end of the season to see if it gets the engine to run at WOT.

Went to the boat last night to start diagnostics. Had the battery on a maintenance charger for a couple of days to top it off, as I'd run it down when the boat wouldn't start. Took off the flame arrestor, turned on the key and heard the electric pump cycle. Turned the engine over, watched the throttle-body injectors spraying and the damn thing started right up! Didn't have time for a test run. Will do that tonite after I change the fuel filter. Any way I could have had a vapor lock?

Got a bad feeling there might be gunge in the fuel tank blocking the feed tube. The boat is a 95 Ski Sanger with a 40-gal. stainless tank behind the rear seat. I can just imagine how much it will cost to have it cleaned and relined. Worst case is I run with an outboard tank for the rest of the season.

Thanks again!

 

[alldodge]

Was pulling a skier when the engine started cutting out. Dropped that skier and pulled up another, with the boat running fine for about 10 minutes when we finished the last run of the morning and docked.

Tried to go out later in the day and the engine wouldn't start. Cranked fine, but it didn't even try to start. I seem to recall that the throttle-body injectors spray when the engine is cranking, correct?

turned on the key and heard the electric pump cycle. Turned the engine over, watched the throttle-body injectors spraying and the damn thing started right up

With first and last post info, I don't think its vapor lock, I think it was just running out of gas

 

[PW]

Apparently the black stuff in the attached photo is enough to clog the fuel filter/water separator. Installed a new filter. Problem solved. I replaced all the fuel lines last summer, so this must be coming from the tank. When the end of this season is near, I post again, asking for a DIY solution for cleaning the tank. If I can't do it, the boat will go to the shot. Thanks for your help.

 

[PW]

The boat will go to the shop.

 

[PW]

Mine is a 1996 EFI. It has the mechanical pump and the high pressure electric pump in the VST. Since you system has the VST removed you may not need the mechanical fuel pump. I think the manual fuel pump is just to keep the VST full because the pump in the VST is just using what is around it and not sucking from a hose.

@ thumpar. I found a used VST! Because the old one was removed, I can't figure out how the used one goes in. Wouldlease send me some photos of how it's installed on your engine? Your help is greatly appreciated. Thank u!