1996 Mercury 150 EFI dies at WOT

[Astro Boy]

I have a 1996 bass boat with a 150 hp mercury EFI outboard motor. It runs well until we stop or have ran a few minutes and all of a sudden at WOT it will just die like I shut the gas off? I can throw it in neutral and then turn the key off and back on and it restarts like nothing happened. I take off run a few yards and it does it again. I have replaced the fuel filter, but it had no impact. It ran well until I gassed up and added some Sea foam to the tank to clean the injectors, and then this started happening? I thought maybe it clogged the fuel line so I replaced the filter. I ran it at home and it seemed alright. Went to the lake ran it a few minutes and it did it again. Could it be the electric fuel pump strainer got clogged? It seems to cut off so abruptly and all cylinders at once it's like the gas is shut off or has no pressure. The in line siphon bulb is still firm, and the little gas line filter is not clogged, as I could blow thru it. I had it on the ears at home before replacing the fuel filter and it seemed to be surging when I had it at 1,000 to 1500 rpm.
I know it could be a multitude of possibilities, but I'm leaning toward 1) mechanical fuel pump not keeping up with the demand at high rpms. 2) The fuel pressure regulator dropping out. 3) The strainer being clogged at the bottom of the electric fuel pump. 4) ECU, but why not at low speed?

Thanks for listening and I'm eager to hear what you think.
Astro

 

[jerryjerry05]

Get a pressure gauge and get the reading from the high pressure side.
The low pressure pump if it's got a hole in the diaphragm is the only way it won't keep up for the demand.
Check the high pressure readings.
Not sure what your's is supposed to be but if it's too much it will shut down like your is doing.
I had a 98/225 efi It ran like crap. EVERYONE i talked to even the guru's from Mercury said they had no idea.
I tested the pressure and it was 4# over what it should be.
Again EVERYONE said the regulators just don't go bad so look someplace else for the problem.
I spent hundreds of $$ and eventually followed the directions in the manual and replaced the regulator that EVERYONE said wouldn't go bad.
It was bad.

Also the HP pump if it's had water in there or set dry for any time it can go bad.

 

[Faztbullet]

These are bad about fuse hooder melting internally and dropping power to ECU,check it. Whats your voltage at WOT as if overcharging it can cause ECU to shut off/act goofy.

 

[Dukedog]

Had one a while back actin' same. Pump driver was actin' stupid. Droppin' out intermittingly. Found it after installin' a gauge........First one I've seen do that. Usually work or don't work.

Fuel pressure or what Faz says (loss power ta ecu) usually culprit ta "instant" quit.....

 

[Astro Boy]

Well, I rebuilt the mechanical fuel pump, tested it in the yard on high throttle without the transmission engaged and it ran up okay. I thought I would take the vapor separator unit apart and see if the HP pump strainer was clogged, and it was clean. I took it up[ on high rpm (4000) and it ran well in the yard, so I took it to the lake and sure enough the same thing runs good a few minutes then at WOT it just drops out. So while at the lake I pulled the engine cover and confirmed it has spark to all cylinders, and for giggles I replaced the gas line bulb, as it seemed that the bulb had pressure but under the cowl the gas line seemed softer. Started it up ran a few hundred feet and dropped out. I', wondering now if it is an electrical issue as it seems to be surging some when I have it on the high idle without the transmission engaged. Stator? Trigger? I thought these were candidates but wouldn't they act the same with the engine on high idle with the transmission in or out? I hate to troubleshoot it one part at a time, but nothing jumps out. I still have doubts about the fuel pressure regulator too, but I don't have the fancy tools to troubleshoot it here at home.

Thoughts?

 

[Faztbullet]

You cannot test it at home on a hose ,you have to have a load on it such as backed into water on trailer.

 

[Astro Boy]

I took the boat to a local shop last year ams they said it had a loose hose at the tank. It ran okay until this Tuesday and now it's back. I tightened everything, no better. Replaced all hoses, even removed the primer bulb, no better. It idles okay and runs for a little bit at 4000 rpm, then just dies. It doesn't appear to be lacking fuel, it just stops. Fires right back up after that but runs a few seconds and dies again. HELP!

 

[Faztbullet]

1) ECU loosing power from bad connections 2) Fuel pump driver circuit bad in ECU 3) Fuel pump going bad.. Check the connections first as they are the cheapest fix.

 

[Shawnmm]

As a mechanic who water tests boats all the time, here is what I would do. Get a fuel preassure test gauge from the auto parts store. Even the cheap ones are fine. Hook it to the shrader valve on the vst while on the water. Leave the cowling off and make sure its not getting splashed. Run it up and with a helper and life jackets and safety stuff. Have your helper watch the gauge . If its a fuel supply problem it will show up clearly.
There are plenty of tests from there but you have to isolate. I could write a lengthy diagnostic list, but need to know which direction to go. Since you will be checking the fuel though and to make your trip more worth it, if the fuel pressure drops durring the test, use a volt meeter with aligator clip test leads and see if you have a constant 12 volt reading the whole time. If you lose the 12 volts, obviously its electical.

Get an old school timing light and again run it hooked up watching the spark the whole time. If its loosing spark, again it will show clearly. If it is, check your man over board switch first. Go to the control or dash where ever it is and use your volt meeter to check for continuity or ohms between the two switch wires. You should have a zero reading all the time. Good luck.

 

[MarvinRmaxwell]

I have a1996 mercury ego 150 that has run great however it has a problem this year. It will start and run smoothly. I plane it off go about 100 yards and it shuts off as if I turned the key off. I put it out of gear start it right up. Then I repeat the same scenario. I replaced the high fuel pump no help same thing. I just ordered the low pump. After that what can I do..