keith2500hd

the block on the starter is fuse, should be 2 wires on small terminal, alt lead and main power to top of engine. plastic block tells amperage, black, red or white. this is fuse that blows when battery hooked up backwards. may have intermittent short, open or ground causing problem. how are air vents to engine compartment open and clear, may be component overheating. look for melting or burn marks. try adding extra ground wire(battery jumper wires will work for testing, just ground side)

pluguglyinhere

So still not fixed. I have checked a lot of wires/conections. I thought maybe it was a voltage problem due to volt gauge showing like 10 volts when it was acting up but showing 13 when it wasnt.

I had access to a new alternator so threw it on and still had the problem. It is wierd for sure. It is somewhat intermitent but seems to have some consistancies.

I threw a new battery in after the new alternator. One of my duals was old and I was going to anyway. The boat seemed to run fine at the begining. It started to act up later.

It idles fine, starts fine then with hard acceleration it cuts out back to about 1000 rpm then tries to rev back up then cuts back again.... up and down. It will eventually start to pop and such if you dont pull back to idle.

It will die on acceleration and have a hard time staying running after a long idle. We have a long no wake in the marina and it will die upon the first acceleration coming from that. I have to wait and it will start then ease into the throttle and all is fine. Anytime it does it is on acceleration moderate to hard. If I baby into it I can usually get it through to any rpm, but if I give a goose it will do it.

It also will cut out at random some times. If we get it to 3000 or whatever rpm and cruise it may just cut out and come back just like above. I back off ease back into it.

So I will continue to check wires because voltage seems weird still. Where does the gauge on the dash get its reading?

Also IAC?

PayCheck

Many years ago we took the little Checkmate down to the marina for another case of beer - great day, flew down the lake on a nice chop. Docked, got the supplies and then wouldn't start. Checked the usual, found no spark. Voltmeter showed about 9 volts with ignition on, 12v at the battery with ignition off.
Tach went bad and decided to short. Boat fired right up once I unhooked the tach.

The point - it might be a similar situation and you'll find the short rather than a bad ground?

Since it appears the fuel pump is questionable - maybe you could isolate the power feed to it?

pluguglyinhere

Thanks Paycheck I still keep looking for a short or loose wire/ground. I can not seem to find one or recreate the problem.

I did find a hose, not sure yet what they are called maybe someone can help. There are some yellow 1/4 inch lines running from my vst, mech fuel pump and tee into the throttle body. I replaced them when I did the mech fuel pump as they were really clogged not complete but bad. I just noticed when I took the throttle body off that there is one from the throttle body to the intake, about 4 inches long. It is also about 90% clogged. Are these the vacuum lines everyone is talking about? I will replace it but what about the fittings, can I pull them out and clean also?

pluguglyinhere

Seems to be fine now, it ran great on a water test last night. I am hoping this small hose was the problem.

The Ace

Did you check the diaphragm in the VST? I had issues that sound like yours and the rubber diaphragm was completely eaten away causing fuel to dump into the #8 cylinder. This would in turn trigger the knock sensor cutting the engine out. If you take the vst apart though the gasket is most likely going to be swollen. Dealer will want $100 for the whole o-ring kit BUT you can order just the gasket for like 10 bucks. Part number 25-803831.

pluguglyinhere

It is still not fxed and my big vavation is a two weeks away. It seems to have got a little better but still doing it. I replaced the last 1/4 inch hose I found from the throttle body to the manifold and took the boat out it seemed fine. It seemed fine for the short lake test. We went out this morning it seemed fine still I tubed, skied the kids for a couple hours all good. We anchored relaxed for about 4 hours took off and it was doing it again. It seems to be much more intermitent than it was but still there.

I will check the VST as Ace said

I replaced all the 1/4 inch lines from the fuel pump to the tee, to the throrttle boady, to the VST and the one from the throttle boady to the manifold. Is there another I am missing?

The Ace

This is a better description taken from another thread. It's from my parts guy here in Vegas:

"Locate your vst tank on the back of the engine. On top there is a yellow tygon hose coming from it. Fire the engine up and pull that hose off and see if you have fuel coming out of it. If there is fuel coming out of it the diaphgram in the vst tank is bad. Remove the cover and flip it uside down there are three phillips screws, remove them and replace the diaphgram. The part number is #808509 for the diaphgram and the part number for the cover oring only is #803831. If you find this pull #7 and #8 spark plugs and see which one looks fouled and replace it. When the diaphgram breaks it will route the fuel from the top of the vst tank threw the tygon hose and push it in the intake plenum and the fuel will go into one of those 2 cylinders. Sometimes even hydraulicing the cylinder.when you have to advance the throttle on and efi engine it will go into whats called clear flood mode to start it. Sometime the map sensor can cause that. You would need to have the engine scaned for codes at that point.
Shane
offshore marine "

xlt86

I was having almost the same problem, different motor i have an older 260 carb motor, it was cutting out under hard throttle like it was running out of fuel, it would sometimes die but if i backed off it would stay running, i checked fuel pressure and threw a new fuel pump on it but it still did it, yesterday i took the elbow off the tank that my antisiphon valve was screwed into and found the screen in it was cloged up, I cleaned it out and threw it back on but have yet to water test it

pluguglyinhere

Well it is fixed and I thank all of you for the help. It was the diaphram in the VST. I finally worked my way to it as I was afraid to open it up. I have never been in one and was afraid I could not get it back together right.

It seemed the next logical step from all of you suggestions and it worked. It was full of nasty black stuff. I cleaned it up and the boat is like new. I think this has been a problem since I have owned because its like a new motor.