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Discussion Starter #1
I have some other threads floating around about having issues on the 748 since I put it back together. I replaced broken plastic quick connects with the metal variety and replaced the fuel lines. I also had to switch everything over to a new fuel pump base plate and in the process had to replace the low fuel lever sender.

Two Questions:

1. Trying to check the fuel pressure. I have a pressure gauge with a T. I pulled both lines that feed into the injectors and put those on either side of the T. When I turn the ignition on, I should get the full 3 bar of pressure once the system primes, correct? If my understanding of the layout is correct, fuel is fed through one of the lines to one of the injectors, where it passes through another line to the other injector. From there, a return line goes back to the tank and meets up with the regulator, which feeds excess pressure back into the tank. As such, the pressure should be uniform through out the fuel lines that are external to the tank. Is that correct?

I'm seeing it jump to between 10-15 PSI and then immediately fall off.

2. Can someone verify that the fuel level sender is the same part on a 2 phase and 3 phase bike? I only have seen a parts catalog back to a MY2000 748, but my bike is 2 phase vs the 3 phase in 2000. The dealer said they were the same, but just looking for a double check again as that was the only unexpected parts swap (plastic nut broke on the original, new part is metal).

Bike will only very barely run.

If the pressure check is correct, then it could be a bad regulator (doubtful, I have swapped regulators already), bad pump, bad relay, clogged fuel filter, or broken line in the tank. Anything else you guys can think of? Thanks.
 

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Old Wizard
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I'm seeing it jump to between 10-15 PSI and then immediately fall off.
The initial run of the pump should bring the line pressure up to the 3 bar (44 psi) rating of the fuel pressure regulator. If the computer doesn't get a crank rotation signal then the pump is shut off for safety reasons.

The pressure in the lines should then be maintained for a good amount of time unless there is a leak somewhere in the system that relieves the pressure. A leaking connector or split fuel line is usually the culprit. A faulty pressure regulator or a stuck open injector/solenoid would also provide a leakage path. The pressure should not fall off so quickly.

The fact that the lines are only reaching 15 psi also tells me there's a leak in the system.
 

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If you replaced the lines in the tank, and the pump primes as it should, that eliminates split lines or a relay issue.

As Shazaam suggests, check for a leak first - aside from the lines, move the tank out of the way and look down the intake funnels to see if an injector is stuck open when the system is pressurized. If you didn't do the in-tank lines, open the gas cap and watch for fuel spraying or rushing when the pump primes (a slight disturbance is normal, that's the return line - heavy fuel movement means there is a leak)

If no, then I would replace the fuel pump. If you get an automotive pump for 40$ from Rockauto, worth trying for that price.

Did you replace the lines and filter while you had the tank apart?
 

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Discussion Starter #4
Problem solved. Line had come loose between pump and fuel filter. Once corrected, fuel pressure goes to 33 psi at prime and jumps to 45 psi once the starter is kicked. Bike now runs!
 

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Good to hear, often it's the simplest things that bugger up.
 
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