Fuel Pressure Test GT40

[Rideaneversummer]

I've been reading a lot about fuel pressure in the GT40 and how it needs to be checked to make sure it is adequate. Most posts refer to this thread: http://www.planetnautique.com/vb3/sh...=fuel+pressure. Other than a couple of pictures, there isn't really any information on how to test the fuel pressure, or even how to make your own fuel pressure tester. Can anyone post a link to a better description of how to test fuel pressure, or give a better description.

Also, I have read about a tube in the FCC that cracks and causes problems. I'm going to change out the fuel filter and would like to go ahead and change out that tube while I'm in there, but can't seam to find the part number. can anyone help?

Thanks,

[jhersey29]

http://www.nautiqueparts.com/interna...oseforfcc.aspx
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[jhersey29]

Use this to test. Same process for a gt40 bit this shows on a car. http://m.youtube.com/watch?v=_oXLUqE4Sf0


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[Rideaneversummer]

Thanks for the links. That helps quite a bit. I was planning to place my order from Nautiqueparts.com anyway so the link to the part was perfect. I'll have to find a fuel pressure gauge and see if I can test my fuel pressure.

[DanielC]

I would not suggest making your own fuel pressure tester. You really do not want a high pressure fuel leak when checking the pressure, in anything, but especially not in a boat.

You need a fuel pressure tester for a Ford engine, or a tester kit with a Ford adapter.

[jonsquatch]

If you want to save a few bucks the low end fuel pressure testers are like 20 bucks at harbor freight and you can usually scare up a 20-25% off coupon. You can often pick up a used Matco or Snap-on fuel injection tester on Ebay for 30-60 bucks or you might be able to borrow one through a "loan-a-tool" program from your local parts store.

[JayG80]

Harbor Freight $20 fuel tester does not have a fuel pressure bleed line. Is it necessary?

[jhersey29]

You don't need the relief tube. The pressure should top out at 44. Your looking for about 39 to 40. You will have about a teaspoon of gas to clean up. Put a rag under and around the schraeder valve. Wear some glasses for eye protection. I've forgotten many times to press the relief button with no issues.
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[Rideaneversummer]

I picked up the HF fuel pressure tester last year and used it without any issues. Like jhersey29 said, just put a rag around the Schroeder valve when you unscrew it. For $20 it's a nice tool to have for trouble shooting, or just piece of mind.

[JayG80]

Thanks it worked well. Minimal fuel dribble. KeyOnEngineOff pressure was 39 psi and held for over 10 minutes. Engine On pressure is 31 psi at idle and 2,000 rpm. I'm getting poor hole shot so that is why I tested. Time to open the FCC, only 35 hrs on fuel filter since last change.

[JayG80]

I had a new high pressure pump on hand. Put in the new pump along with a 5/16" dia hose. 40 psi now.

[DanielC]

You do not need the pressure bleed line. You can unplug the fuel pump connection to the FCC, or the fuel pump relay, and crank the engine, and the fuel pressure will quickly go to zero.
if the engine is running, pull the safety lanyard. That also stops the fuel pumps.

[jhersey29]

I had a new high pressure pump on hand. Put in the new pump along with a 5/16" dia hose. 40 psi now.

40 while running instead of the 31? Sounds good. Did it fix your power issue? I hope that is the case. 31 psi would definitely give a bit less fuel in the cylinder than 39 to 40.

[JayG80]

Here are my fuel pressures on the GT 40 with a new high pressure pump. Does everything look normal now? I've read 39 psi is the specification but was not certain if that is the pressure at idle too?

Key On Engine Off is 39 psi, turned off the key and at 8 minutes the pressure had dropped to 35 psi, and dropped to 18 psi after sitting for 15 minutes.
Started Engine in the water, 2,000 rpm while in neutral and the pressure is 35 psi
Turned off the engine and pressure leaked down to 32 psi, at 2 minutes it was 25 psi, at 3 minutes it was 20 psi, at 4 minutes it was 15 psi.
Started boat again and and at 2,000 rpm in neutral I pulled the vacuum line and the fuel pressure went to 39 psi.
Ran boat in the lake at around 35 mph and fuel pressure was 40 psi.

Boat seems OK for pulling lighter skiers but heavier skiers seem to drag down the boat during the pull up but is OK once they are up skiing. My fiberglass muffler had a hole that I patched at the same time I replaced the fuel pump. I rarely inspect the muffler but notice now that it flexes when I rev the engine in neutral. Is the flexing normal? It will also give an occasional vibration. I'm also wondering if my muffler has a cracked baffle that might create back pressure and rob some hole shot performance? Temps at 140.

[DanielC]

It is normal for the fuel pressure to drop when the engine is running. The fuel pressure regulator is connected to the intake manifold, and intake vacuum causes it to drop the regulated pressure.

The muffler should not flex noticeably. It is fiberglass, and if it is flexing it is breaking the bonds between the fiberglass, and the resin holding the fiberglass, as well as breaking the fiberglass strands itself.
Do this. Remove the back floorboard, so you can see the muffler. Launch, and start the boat while watching the muffler. Turn the engine off, wait about 30 seconds, to a minute, and watch the muffler again, while starting the engine. The muffler fills with water shortly after the engine is shut off, and restarting it puts then most stress on the muffler until the excess water is pushed out.

I do not want to be too dramatic, but if you get a major hole in the muffler, it is below the water line. The flap on the back of the exhaust pipe outside the hull will slow water down entering the boat, but the exhaust pipe aft of the muffler is a 4 inch hole, through the hull, below the waterline