GT-40 loses fuel pressure after starting when hot and after sitting for an hour

[slmskrs]

Yesterday after pulling a number of rides, the boat sat for about an hour at the dock (no air flow in engine compartment so the engine compartment became quite warm (normal)). Boat started okay, but after pulling up the next skier and just after entering the course, it died (water temp, etc. normal). I didn't have my fuel pressure gauge with me so got towed back to the ramp and took the boat home. Several hours later I put a pressure gauge on it and it was fine (ran in in the driveway for 20 minutes at high idle with no problem but no load and engine cover was open so engine compartment didn't get hot). So I took it back to the course today to recreate. Sure enough, after pulling a few rides and letting it sit for a while (about an hour), I then started it and about 45 seconds later (about 4 ball), it died again. I put the gauge on, and there was no pressure. I checked, and both pumps were running (both making noise). After about 10 minutes with the engine cover open, I finally got pressure and it ran fine back to the dock and the ramp. I've never had any problems with the low pressure pump. About two years ago a pin hole developed in the hose attached to the high pressure pump, so slowly lost pressure. Replaced the hose, and it has been fine ever since.

Has anyone experienced this before? I'm ready to pull the canister, but because it ran fine and then suddenly starved, I'm almost wondering if the low pressure pump is having a problem when the engine compartment is hot, i.e.: it stops pumping, so the high pressure pump just pumps the gas in the canister until it runs out (which would explain it running halfway down the course before dying).

Because with the engine compartment open and it cooling down, I was not able to pull the output line off the low pressure pump to see if it was pumping, so don't know if it might be that.

I'd prefer it be in the canister, as it has been fairly easy to work with.

Anyway, anyone have any experience like this?

Thanks,

Gordon

[DanielC]

Here is my standard thread about fuel pressure on the GT-40 I generally refer people to.
http://www.planetnautique.com/vb3/sh...=Fuel+Pressure

When your boat starts to have this symptom, check the pressure and FLOW of the low pressure pump. You could pull off the return line from the FCC, and see what kind of fuel flow you get then.

You will notice in one of the pictures there is a jumper hooked up to the test port of the engine. This will turn on the fuel pumps with the key on, engine off.

Be very careful with handling gasoline in your boat, doing fuel pump tests.

[slmskrs]

I don't have 40PSI like your pix!

Thanks Daniel. I actually saw your post last night. I didn't know about the jump to keep the pumps on without starting the engine, so that will be very helpful. Two things I noticed while looking at your post and at the manual, are: 1. You show 41psi; I'm getting about 31PSI but solid (increases slighly when higher RPMs) until it starts acting up--then it is down to zero. And 2. The diagnostic section of the GT-40 manual says that the bleeddown should be no more than 3PSI over 5-10 minutes (I don't remember how long and don't have the file handy). But when my pumps stop, it drops to zero within about 10 seconds. That leads me to believe that it might be the hose connecting the high pressure pump deteriorating (since a few years ago I was getting a loss of pressure and it ended up being a pin hole in the hose). I'm hoping it is that since it is simple/cheap to replace. But what is different this time is the problem happens when the engine compartment is hot, and it will run wtih load for 15-20 seconds before running out of pressure. I'm hoping it is not the pressure regulator (haven't even gone looking for where it is yet). So it looks like the next step is to pull the canister and check/replace the hose). One question on the low pressure pump: If the high pressure pump is not pumping but the low pressure pump is, would you see the 5PSI on the gauge connected to the scrader valvle, or would you have to connect the gauge up directly to the output of the low pressure pump?

Thanks,

Gordon

Gordon

Here is my standard thread about fuel pressure on the GT-40 I generally refer people to.
http://www.planetnautique.com/vb3/sh...=Fuel+Pressure

When your boat starts to have this symptom, check the pressure and FLOW of the low pressure pump. You could pull off the return line from the FCC, and see what kind of fuel flow you get then.

You will notice in one of the pictures there is a jumper hooked up to the test port of the engine. This will turn on the fuel pumps with the key on, engine off.

Be very careful with handling gasoline in your boat, doing fuel pump tests.

[DanielC]

The pressure shown in my picture is with the engine not running, just with the jumper in place, and the key on. With the engine not running, there is no vacuum, and the mechanical fuel pressure regulator acts the same as if the engine was at wide open throttle. Starting the engine creates a vacuum in the intake manifold, and this vacuum causes the fuel pressure regulator to drop the fuel pressure. I believe 31, on a normal running engine at idle is OK, check the manual.

The FCC has an open port that goes to a hose, and then back to the fuel tank. There is no restriction in this hose. Fuel just free flows back to the gas tank. It should not build up pressure inside the FCC.

The low pressure pump has one job. Keep the FCC full of fuel. That is it. The pressure the low pressure pump can make is important, but really the most important thing is the flow of the low pressure pump.

[slmskrs]

I'll examine the HPpump and hoses in the FCC, then check LP pump volume

I get around 31PSI whether the engine is running or not (although I haven't put the jumper on yet, so the 31PSI with engine off that I've seen is with repeatedly turning the ignition on and off). But when the pumps are off, it drops to zero in 5-10 seconds, unlike the 3PSI drop over several minutes. So I'll examine the FCC pump, hoses, etc, and then do a volume test of the low pressure pump (hopefully before the weekend so I can test it Saturday morning on the water). Thanks for the info. Greatly appreciated. Gordon

[slmskrs]

low volume pump 1 quart in 30 seconds (cold)

I measured one quart in 30 seconds (cold). Does that seem low? I wasn't able to get a good reading on the low pressure pump pressure as I didn't have any fitting, and had to hold it by hand (saw about 2psi but it was leaking).

I appreciate learning about the pump jumper that keeps the pumps on with the ignition on. I am able to hear the gas returning to the gas tank, so if I lose high pressure again when it is warm, I will be able to easily determine whether the low volume pump is failing or not. I'll just keep the jumper in the boat until I find what the problem is (nothing wrong with the hose that the high pressure hose connects to).

Gordon

[DanielC]

If you take the llow pressure pump off its mount, and then remove the studs that hold the pump to the mount, the top of the pump will come off. There is a screen inside the pump. Remove the screen, and look for any gunk in it, and put it back together.
Be extremely wary of any fuel leaks, after you do this. Check flow again.

You need to check the flow when you are having the poor running symptoms.

[slmskrs]

Thanks. I was wondering how the low pressure pump came apart. Heading out of town on business so will have to work on it in a week or so. It turned cold (highs only low 50s unlike last weekend when it was in the 70s), so it may be hard to duplicate the warm engine compartment for a few weeks at least. But I will pull the pump out in the meantime, clean out the screen, and then have everything I need with me to check out flow if it acts up again at the pond.

Thanks for all the info. I'll report back once I am able to get to the pump, clean it, and then test it again.

Gordon

[slmskrs]

Removed low pressure pump, where's the screen?

I removed the low pressure pump. But I don't see where the screen is. I couldn't see how to get into the pump after taking off the outside plate. Any suggestions? I don't want to damage it, but want to open it up to see if I can find anything wrong with it.



Thanks,

Gordon

If you take the llow pressure pump off its mount, and then remove the studs that hold the pump to the mount, the top of the pump will come off. There is a screen inside the pump. Remove the screen, and look for any gunk in it, and put it back together.
Be extremely wary of any fuel leaks, after you do this. Check flow again.

You need to check the flow when you are having the poor running symptoms.

[DanielC]

The three bolts, or studs that hold the entire fuel pump on the mount will unscrew from the pump. Then you carefully separate the flat top plate off the pump.

I will try to get a picture of it tomorrow. I have extra fuel pumps out in the (cold) garage, and do not really want to go out there tonight. I would bring it in the house, and take it apart, but fuel pumps tend to be stinky, like gasoline.

[slmskrs]

Got plate off, don't see how to dismantle further

I pulled the pump off last night (before my post), took the three studs off, and separated the top plate from the pump. The problem is I couldn't see any screen; it seems to be another plate with a round "gasket", with a center opening in the gasket. I didn't see how to pull anything apart further. I took a picture, but as I am new to the forum, I couldn't find where to post the picture (since it is expecting an http location). If someone lets me know how to post a picture, I'll post it ASAP.

Thanks,
Gordon

The three bolts, or studs that hold the entire fuel pump on the mount will unscrew from the pump. Then you carefully separate the flat top plate off the pump.

I will try to get a picture of it tomorrow. I have extra fuel pumps out in the (cold) garage, and do not really want to go out there tonight. I would bring it in the house, and take it apart, but fuel pumps tend to be stinky, like gasoline.

[slmskrs]

pix of pump with plate off

Found the pix attachment link. Here's the picture of where I've gotten so far.

So, how do I dismantle further?

I pulled the pump off last night (before my post), took the three studs off, and separated the top plate from the pump. The problem is I couldn't see any screen; it seems to be another plate with a round "gasket", with a center opening in the gasket. I didn't see how to pull anything apart further. I took a picture, but as I am new to the forum, I couldn't find where to post the picture (since it is expecting an http location). If someone lets me know how to post a picture, I'll post it ASAP.

Thanks,
Gordon

[DanielC]

Low Pressure Fuel Pump

Keep going. Carefully pull the gasket off the pump body. There is a plate that may stick to the gasket, that is OK. After removing the gasket, you will see the screen going around the rotary pump.
Here are some pictures. The first one is of the inside of the pump. The inlet on on the left side of the picture.


Here is a picture taken as the parts came out of the pump. The screen is the curved thing in the top of the picture. Yours probably will not be this clean. Carefully clean it.


Here is a picture of the screen reinstalled inside the pump body.


Next, you put the plate on top of the pump rotor. Make sure it is in recess for it, and centered on top of the rotor.


Now, put the gasket on. Keep the gasket in the same orientation as it was before you took the fuel pump apart.


Finally, put the cover on the pump. Make sure the gasket, and the rotor plate do not slip out of the recesses in the pump body for them. Put the three bolts for the cover back into the pump. Turn each bolt backwards until you feel it drop on a thread, and then turn the bolts forward. Tighten each of the bolts a little at a time, by hand. Do not use a wrench or nutdriver to force them. You can easily strip them.

Look at the pump cover edges carefully. Make sure the gasket does not stick out on one side, and not the other. Make the bolts snug, but not as tight as you can get them. The metal in the pump, body is pretty soft, and easy to strip the threads out of. Then you will have to buy a new fuel pump.

Now the disclaimer.
If you are NOT absolutely sure you can do this repair, without fuel leaks, do not do it. Any fuel leaking inside a boat is dangerous, because the fumes cannot escape out of the bilge, and if they build up, they can explode, and possibly start your boat on fire.

[slmskrs]

Diving deeper!

Daniel, Thanks for the great pix. I'll dig deeper tomorrow evening (conflict tonight). My only concern is getting the gasket off without damaging it (I don't see anyone selling new gaskets anywhere).

So, it appears that the only "servicable" part in the pump is the screen. Once it is clean, if there is any other problem with the pump, time for a new pump.

One clarification, once the three studs are seated by hand, do you then use a wrench for the final "light" tightening, or do you never use a wrench at any time and it is only hand-tightened at all times (to avoid stripping)?

One other final question. Is there a third pump in the tank, or am I just hearing the sound of this low pressure pump being transmitted through the fuel lines to the tank?

Thanks!

Gordon

Keep going. Carefully pull the gasket off the pump body. There is a plate that may stick to the gasket, that is OK. After removing the gasket, you will see the screen going around the rotary pump.
Here are some pictures. The first one is of the inside of the pump. The inlet on on the left side of the picture.


Here is a picture taken as the parts came out of the pump. The screen is the curved thing in the top of the picture. Yours probably will not be this clean. Carefully clean it.


Here is a picture of the screen reinstalled inside the pump body.


Next, you put the plate on top of the pump rotor. Make sure it is in recess for it, and centered on top of the rotor.


Now, put the gasket on. Keep the gasket in the same orientation as it was before you took the fuel pump apart.


Finally, put the cover on the pump. Make sure the gasket, and the rotor plate do not slip out of the recesses in the pump body for them. Put the three bolts for the cover back into the pump. Turn each bolt backwards until you feel it drop on a thread, and then turn the bolts forward. Tighten each of the bolts a little at a time, by hand. Do not use a wrench or nutdriver to force them. You can easily strip them.

Look at the pump cover edges carefully. Make sure the gasket does not stick out on one side, and not the other. Make the bolts snug, but not as tight as you can get them. The metal in the pump, body is pretty soft, and easy to strip the threads out of. Then you will have to buy a new fuel pump.

Now the disclaimer.
If you are NOT absolutely sure you can do this repair, without fuel leaks, do not do it. Any fuel leaking inside a boat is dangerous, because the fumes cannot escape out of the bilge, and if they build up, they can explode, and possibly start your boat on fire.

[DanielC]

You do use a wrench to snug the bolts holding the top plate on the pump, but go easy.

There is not a third pump. What you are hearing is an anti-siphon valve on the top of the tank, in the hose that feeds fuel to the engine.

In most direct drive Nautiques, the gas tank sits on the floor of the boat, and the low pressure fuel pump is below the floor. If the hose from the tank to the fuel pump ever got a leak, it would just siphon gas into the bilge.

I just got the digital camera, from Costco, about three weeks ago. Gave them two one hundred dollar bills, and they gave me the camera, and three pennies. It came with a USB cord, to connect to my computer, and a cord with a red, white, and yellow RCA connector that hook up to the TV. It is a Panasonic DMC-ZS6. It really takes much better pictures than my cell phone did, and I no longer have to get film pictures developed, and put on a CD. It will also do short videos, and has a 12X optical zoom. I have not tried it yet, but I think is to going to zoom enough to get good pictures at "waterski rope lengths".