Fuel Delivery Issue?

[The Black Widow]

So this problem actually started about a year ago last time we were out at Lake Powell. When we would try and start the boat it would either run really rough at idle and then die or not start at all. We put a temporary fix of a hand pump in line and would prime the fuel pump to get it going until we were going faster. The boat would then run great when we were around 1500 rpms or higher. Bring it back to idle and it would be rough and die again if we weren't occasionally squeezing the hand pump.

When we got back home from the trip we replaced our low pressure pump and never had the problem again so we though we had solved it. Well 2 weeks ago we went back to Powell and the first day the same thing happened again! Our only conclusion is that is has something to do with elevation because it only happened in Powell but the lake we go to normally is only 400 feet lower than powell. Would the 400 feet elevation change really make that much of a difference and cause this problem? And if so is there anything we can do to keep it from happening in the future?

[TeamAllen]

I have had a vopor lock issue at LP before. It doesn't sound like the same issues you have had though? I think the altitude, heat and fuel quality have something to do with it?
My vapor lock symtoms would occur after a hard run than stop and float for awhile creating a hot soak environment. Then it would crank over but not restart until it cooled down again. Your rough idle part sounds different.

[Wakeman22]

besides the fuel pumps I would look towards bad gas or gas that is just not up to standards. I have had similar issues and finally chased it down to bad gas.

[Ruger761]

Which motor do you have? Almost sounds like an idle air control valve but have to make sure which model motor you have.

[The Black Widow]

I have a 2006 MP 6.0

Would the idle air control valve change based on elevation?

[Ruger761]

400 ft shouldn't be enough to make any difference, read original quickly thought it said 4000. Would it start and idle with the throttle opened up a bit? Did you buy gas from the same station this time? And was it 100% gas or did it have ethanol in it? A high ethanol content, greater than 10%, requires a larger volume than reg gas which would lead to a bad idle and rough starts. So if the station was miss marked or not marked it could be causing your problem. Our old methanol motors we had to significantly jet the carbs to get them to run and sometimes had to spray methanol into the carb to get them to start.

[The Black Widow]

It would not start at all even with the throttle open. The first few times of trying it with the throttle open it would get closer to starting but after a few times it would only turn over, no start.

I am not sure about the ethanol level. We filled up a full tank on the drive in just outside of Wahweap and the other times were at Antelope marina and Dangling Rope Marina. I will have to look into the ethanol levels there and see what I find. Would the higher level of ethanol only affect the starting/idle and not running at higher speeds?

[Ruger761]

Typically higher ethanol levels won't hurt high speeds as much as it does on idle. But you would think the marinas would know better than to have any ethanol in their fuel. So that might not be the issue either if getting gas at 3 different places all did the same thing. But it still has me stumped why its only doing it at Powell and not at your home lake. A sensor issue should do it both places as well as a fuel pump or fuel pressure issue. Dang I'll have to keep thinking on that one or hopefully someone else has had that issue and knows the answer.

[The Black Widow]

Well we have almost a full tank of gas left over from that trip. Heading out this weekend so we will see if it happens here. If it does we will know its a fuel quality issue...

[Ruger761]

Great! That will give us some good testing for possible answers

[boatwakes]

Quick FYI for all: above 25% open throttle at time of starting, the ECU cuts both spark and fuel injection to the engine for safety. If your idle air control valve is stuck or not operating well, you can open the throttle slightly to bypass the IAC but again opening half to full throttle like if you had a carb will help clear a flooding condition but won't fire due to the above ECU safety features.

[The Black Widow]

Replying to this thread again because the same thing happened over the weekend. We have successfully run the boat with the same gas (adding some each time) once a month over the winter and the problem only happened this last time we took it out. So I don't think its a fuel problem.

For the first hour the boat idled and ran just fine. We were idling for a few minutes and it slowly lost power and shut off. We were able to start it each time but it would shut off right away after. Again, the only way to keep it going was to prime the filters with the hand pump we had installed. After running it at higher speeds for a few minutes it would idle ok for a little while but eventually lose power again.

Any suggestions on what we could check?

[CDAWaves]

Have you changed the fuel filter?

[The Black Widow]

I changed the fuel/water separator filter that is in the canister at the end of the season but have not changed the inline filter yet. Was going to try that this weekend to see if it helps.

[CDAWaves]

Maybe the long tow to Powell stirred up sediment in the tank that got sucked up in the fuel system (particularly if you tow with the tank partially empty)???