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Foiler
09-18-2004, 06:13 PM
I have a 93 prostar with 300hrs, I started hearing the fuel pump wine soon after the motor started stalling. I took it to a marina and he tested the fuel pressure it would start out at 40psig run fine for awhile and then start dropping at about 15psig the motor would stall. Seemed simple right...wrong. After replaceing the fuel pump it acted the same way. Today I filled a 5 gal tank and disconnected the line after the fuel\water separater ran it from there and it seemed to run better. I removed the gas tank and checked gas intake tube it was clean. Before it stalls the fuel pump changes pitch, sound like it's under strain. I changed F\G separater and the inline gas filter, I'm running out of things to try.....any one have any suggestions.

Keith

timandjesi
09-18-2004, 06:18 PM
Is there any type of filter or screen in the tank itself that could be clogged with foreign debris?

lakes Rick
09-18-2004, 07:34 PM
two more things,

Take the gas feed line out of the tank and look for debris stuck to the screen at the bottom.. Apparently while building the boats MC did not clean out the tanks after cutting holes in them..

There might me a on/off fuel valve at the top of the fuel tank.. Make sure it is not closing.. Wire or zip tie it open if its loose.....

Foiler
09-18-2004, 09:27 PM
Thanks guys, I did check the screen on the feed line in the tank eveything looked good.
I'll look tomorrow for a shut off valve, I didn't see one but I wasn't looking for one either.

lakes Rick
09-18-2004, 10:48 PM
My 94 has a 1/4 shut off valve screwed directly into the top of the tank..

Be careful, Jimn on here has stated how you can damage the Electric fuel pump easily when it runs dry......

JimN
09-18-2004, 11:02 PM
Check for an anti-siphon valve on the same assembly as the shut-off valve. This may have some crud in it. Did you check the fuel pickup tube? Just looking at it won't tell you if it's clear. You need to remove it and test it by blowing into it, somehow. You can use a compressor set for low pressure to so this. I would blow into it through the fitting where it attaches to the tank so it blows whatever is in it out the same way it gets into the tube. Make sure the anti-siphon valve check ball moves freely and there isn't anything in the valve body. Look for plastic shavings and carpet fibers.

Foiler
09-19-2004, 08:51 AM
I don't see a fuel shut off valve, I also don't seem to have an anti siphon ball. I assume the shut off would be back on top of the tank and not under the motor cover. I have the tank pulled out and the siphon tube assembly disconnected. I'm starting to think it may be electronic because when the motor starts to slow and the fuel pump changes pitch or starts to wine gas starts feeding back to the tank while the motor is still running through the return line from the pump. It's hard to check at home because it's worse when I put it in gear or under a load on the water. At home idling it seems to run better.

John B
09-19-2004, 10:09 AM
Foiler'
I had somewhat the same problem with my LT1.But it wasn't stalling.
What mine was doing is it would not restart after it had been warmed up.
After we had pull a skier,and stop to change to another skier, it would not start.After the motor had cooled down it would start.(about 2 hr. cool down time)
The fuel pressure when it wouldn't start was 8 psig. when running 40 psig.
I was going to change the fuel pump till I found how much it cost.
I call Inamar and asked about intermittent fuel pump problems,and they said no.
It will work,or it won't work.
Well here what it turned out to be corrosion in the relays,and where the wires from the relay go on the pump.
If you have put a new pump on you should have a good connection at the pump.(was there any corrosion there)
Next thing that I would change the relays.(if you haven't yet)
Good luck, and keep us posted on the outcome.
John

Jorski
09-19-2004, 11:04 AM
Not once, but twice this summer I had a somewhat similar problem. The engine would be running fine and then would be starved for gas over about 3500 RPM...it would just bog.

It turned out to be crud in the fuel system. Both times it had gathered on a small screen just inside the inlet of the fuel pump. Once cleaned out it was just fine. I never had a problem with starting however, it would just collect when there was more suction (and fuel demand) at higher speeds. The crud was not the result of bad fuel, it seemed to be some sort of fluff, I have no idea how it got there in the first place.

anyways, I would make sure that this screen was clear.

JimN
09-19-2004, 12:41 PM
Foiler- the anti-siphon valve is the fitting that the fuel line is attached to. You remove the line from the barb and unscrew that from the aluminum block on top of the tank. If you look into the end, it should have a spring loaded ball bearing at the inlet. This is supposed to be there in case the fuel line is cut or ruptures, so the gas won't siphon into the bilge and become a fire or environmental hazard.

It will almost always run better without a load on it. Have you looked at the fuel pressure regulator yet? This is on the fuel rail and has a small rubber hose connected to it. If the hose is broken or cracked, the regulator won't change when the throttle increases/decreases.

One thing not mentioned before- is the fuel tank sitting on the fuel line or are there any kinks in it? If you notice that it seems to bog less when the tank has less gas in it, this may indicate that the decreased weight of the tank is putting less pressure on the fuel line, letting it flow more freely.

Foiler
09-19-2004, 02:39 PM
You guys rock!!! Thanks for all the replies, After further inspection I found a strip of rubber 1\16" wide by a few inches long in a ball against the siphon ball. I never new there was such a thing and you can't see it by looking up the siphon tube(Thanks Jim) The screen on the siphon tube has just of enough of a opening between screen and plastic to have let it through. I'll be replacing the screen and should be good to go. Now only if that east wind would go away so I could get out to ride.
Thanks Again

Keith

Thrall
09-20-2004, 10:35 AM
Sounds like you may have found the problem, but was that piece stuck in there big enough to starve it for fuel, or just keeping the anti siphon valve from closing properly? With that few hrs on a 12 yr old boat, it would be worth your time to check the entire fuel delivery system from in the tank to the injectors for crud in the system, as it may have sat w/ old fuel in it before.
Also, I read on a previos thread that the LT-1s were not supposed to have a fuel water separator in line. (old MC site) ?This might starve fuel.
If the problem persists, I had fuel delivery problems that ended up being a faulty ECM ( big $$$). There are several other things to look at first , though. If you have more problems, I have copies of some fuel system diagnostic/repair procedures that I can email you. They helped me greatly in diagnosing the problem.

Foiler
09-20-2004, 09:33 PM
I was able to get out today for a few hours and the boat ran great and had smooth power through out. I believe the blockage was the problem, interesting about the water separator.. mine looks factory.
The water is really cooling down fast, good thing is we had the lake to ourself.

Thrall
09-21-2004, 11:58 AM
Glad you got it fixed, Foiler.

lakes Rick
09-21-2004, 06:18 PM
I was able to get out today for a few hours and the boat ran great and had smooth power through out. I believe the blockage was the problem, interesting about the water separator.. mine looks factory.
The water is really cooling down fast, good thing is we had the lake to ourself.

Foiler it is factory.. The 93-94 MC's were the first to go with fuel injection using the OLD Carbureted fuel system... MC changed it due to some fuel delivery problems in 95??.. It was hit or miss on which boats had problems or not.. I bypassed my water filter on my 94 TBI motor and it didn't make any difference... I am going to hook mine back into the system next spring......

footer
10-14-2004, 02:43 PM
If you have more problems, I have copies of some fuel system diagnostic/repair procedures that I can email you. They helped me greatly in diagnosing the problem.

Thrall:
I am also troubleshooting a similar problem. I would really appreciate having a look at the diagnostics that you have. Would that be possible?

Thx, Tom

barefut1@comcast.net

Thrall
10-14-2004, 07:21 PM
Tom, I have just seen your post, however I got your email and have emailed you the diagnostic sheets I have.
If anyone knows how to obtain an Indmar repair manual for LT-1s, let me know. I tried getting one when I had problems, to no avail, but would still like one for future reference. Haven't tried the dealer, but I may. I just fear it'll be really expensive.