Fuel Pressure Issue (Wiring? ECU?)

[390Express]

Source of the post

Source of the post....It's maddening that I'm getting gas to the TBI, but no pressure......

The most common reasons are a bad fuel pump, bad regulator, or leaking injectors.

I have PSI after the pump, at the fuel water separator. I'm going to rebuild the throttle body, and install a new regulator. I think the regulator is failing, allowing air back into the system through the TBI. It's the only thing that makes sense to me at this point. I put another 30 gallons of gas in the tank, I know it's getting fuel. It has fuel in the entire system, and primes up to the TBI, then loses pressure up top, and introduces air into the system.

All of the fittings are tight. before the TBI. I can't see any way of that much air getting into the system from anywhere other than the TBI. I think the TBI is back feeding air and introducing air into the due to a faulty regulator in the TBI itself. Hopefully I'll have that repair attempt done tomorrow. It looks like about an hour job, as long as I can source the parts locally. Looks like I may as well add a TBI rebuild kit, and replace the O-rings and injector screens while I'm at it. I don't think new injectors are worthwhile at this point, they seem to be working properly when the system is primed. Thoughts?

[390Express]

Yesterday I put the fuel pressure gauge on the opposite end of the top mount "can" style fuel filter, to eliminate the "return" side of the system, and the TBI. Pressure instantly shot up to 40psi. I did notice that the fuel supply to the pump was a bit erratic, so I may have an issue with either the antisiphon valve (that I just "rebuilt"... it's just an O-ring, plunger and low tension spring), or too much air in my supply line. I'm thinking my supply issue more has to do with the line being 8' long, and leaving too much of it unprimed. I made a solid effort to fill it with a funnel, my hand and a gallon of gas, but very little went into the line. To eliminate the air in the line/fuel supply issue, I by passed the tank and the anti-siphon valve, and duct taped the funnel to the supply line, and kept feeding the funnel with a gallon of gas. Doing this, I still had no fuel pressure at the schrader valuve when the system was hooked back up to the return line.

Next I took apart the TBI and rebuilt it. The entire time I felt like I was wasting my time. The unit looked great from the outside, however that all changed when I removed the fuel pressure regulator bowl. The internal fuel pressure regulator, mounted on the TBI, was completely shot. The spring rusted and busted into three pieces. Replaced that ($31.99), and all is good... Perfect 12-13 PSI, and motor fires right up now.

I primed the supply line as much as possible, and re-connected it to the tank. I'm going to let it run in 20-30 second intervals, 3-4 times, to make sure that I'm not having a problem feeding the supply line. At least for now, I think this motor is 100%.

Why didn't anyone tell me it was probably the fuel pressure regulator!? (I'm kidding... )


Only current issues I'm having are:
1) Tach gauge is jumpy. Boat throttles up fine, and the gauge moves with the motors, but it really bounces around. It's pretty erratic. I think I'm going to check the back side connections at the gauge and clean them.

2) Oil PSI sending unit is bad. Instantly shoots up to 80PSI when I start it.

Other than that, stbd motor is gtg.

[Viper]

Glad you found the issue and that it was as simple as the regulator.

On the back of the tach, you'll likely have a cylinder selection switch/pot. Note the position it's pointing to then turn it back and forth several times. Return it to the position it was before you started and test. Some units have switches that have to be pushed in first before they will turn so don't force it to turn if you experience some resistance. The contacts on these tend to corrode enough over time to affect readings by either making the needle erratic or inaccurate.