Fuel delivery issue after 10 - 15 min

[jamiewilson3]

1997 Ski Nautique GT40. 340 hrs.

A few weeks ago, the boat started to bog down when driving after being out on the water for a while. I drained a full load from the FCC, looking for water and the gas looked fine. I took it out again and after 15 min or so, it started again.

I ordered a new FCC filter and put it on last night from SkiDIM. I took it out again, same thing.

Water was calm, so I could watch RPM very closely. For the first 5 or 8 min, it ran perfectly. Then it started to waiver just a little bit every 30 - 45 seconds. I was doing about 3000rpm and it would lag down to maybe 2950 for a few seconds then come back up. It did this progressively worse, where maybe 4 minutes later it would bog down all the way to 2000rpm for a second or two before picking back up.

I read through many searched problems and haven't found one that is exactly like this so.....

Any ideas as to what the problem is? Replace the LP fuel pump next?

I don't think I would learn too much by checking flow and fuel pressure, because the issue is so transient. Short of cutting the engine right when it bogs down and checking the fuel in the FCC, I don't know how I would check to make sure it is a delivery issue.

[slob02]

If you think it is fuel related........

Start at the tank and work forward. There is a small screen at the pickup in the tank. Next is the low pressure pump. There is also a screen in it. Some say it is not serviceable, but I have cleaned them before. After that is the high pressure. Have you pressure tested the system when the problem starts? Are you running good gas? Just a few things to think about.

[jamiewilson3]

Yeah, I was planning on pulling the tank and probably changing the low pressure fuel pump this weekend. Any ideas why it takes a while for it to first appear.

[DanielC]

Do this.
http://www.planetnautique.com/vb3/sh...=fuel+pressure

You must know the fuel pressure when the engine is acting up. There is no feedback to the computer on the actual air to fuel ratio, and the computer just assumes the fuel pressure is correct.

I have had problems similar to this on an old Datsun pickup. If there is gunk in the fuel tank, when the engine is running, it collects around the fuel pickup, in the tank, and eventually chokes off the supply of gasoline. When the engine stops, there is no longer any suction holding gunk on the fuel pickup, so it falls off the pickup, and the engine will run good, until the gunk collects again.

[Drock]

When it happens tap the lift pump(low pressure pump) next to the fcc with a screw driver. Mine went last year with similar symptoms. It was a GM excal 330, however.

D

[jamiewilson3]

I have had problems similar to this on an old Datsun pickup. If there is gunk in the fuel tank, when the engine is running, it collects around the fuel pickup, in the tank, and eventually chokes off the supply of gasoline. When the engine stops, there is no longer any suction holding gunk on the fuel pickup, so it falls off the pickup, and the engine will run good, until the gunk collects again.

This type of phenomenon would definitely explain the behavior that I am experiencing. I think that I will hold off on buying a new LP fuel pump for the weekend and clean the screen on the existing and clean the tank screen as well. I'll try and get a fuel pressure gauge installed as well.

[CradGen2]

I've taken the fuel tank out of 96 ski before. I won't use the work easy, but it wasn't hard either. I found that each screw was a different lenght for some reason. it didn't make sense looking at the tank, however I made a templete so I used the same screws in the same location going back.

Also if you are going to pull the tank, I would replace the sending unit while it is out. Cheap item.

[jamiewilson3]

Calling it fixed for now. I pulled the tank pickup out and the screen had a plastic cutting chip (aka gas can material) birds nested in it. Then there was crud packed in the birds nest. I took it out for a few minutes with no issue, but I am pretty low on gas, so I didnt take it for a big spin. I'll take it for a long test drive tomorrow and confirm 100%. Based on what I found though, it had to have been a pretty nasty restriction.

I will still take the LP fuel pump apart and clean, but I will try and save that for after I take the boat out for the winter.

[east tx skier]

Sounds like he has it fixed, but I would add the antisiphon valve to this list between the pickup screen and the low pressure fuel pump.

If you think it is fuel related........

Start at the tank and work forward. There is a small screen at the pickup in the tank. Next is the low pressure pump. There is also a screen in it. Some say it is not serviceable, but I have cleaned them before. After that is the high pressure. Have you pressure tested the system when the problem starts? Are you running good gas? Just a few things to think about.

[slob02]

It is amazing what can get in there even if you try hard to keep things clean.