Fuel Pressure Issue (Wiring? ECU?)

[Viper]

Have you checked the fuel pressure regulator? Is there a vacuum hose hooked up to it? If so, make sure there are no vacuum leaks.

What kind of distributor do you have?

[390Express]

It's a GM electronic distributor. Same type as a Merc MPI system, if that helps. I don't know exactly which make or model, or how to tell. Distributor doesn't seem to be an issue. I have spark, timing, and it fires with starting fluid, just no fuel pressure.

There is a vacuum line that comes off of the throttle body, I'm guessing it goes to the regulator, but the regulator is buried somewhere. I wouldn't think the regulator would keep me from having no fuel pressure whatsoever, and even bypassing 100% of the electronics on the motor, and hooking a hot right to the pump, it still won't build pressure. It will read 2-3 psi on a guage, then go down to 0, even with the pump running continuously. I pressed the schrader valve in with a phillips screwdriver, and a bunch of air came out. I am hoping I just need to get the rest of the air out of the system, and I'll be good to go.

The fuel pump kicks on before and after I push the ignition button, I'm fairly confident the wiring and relays are correct and in working order. The fuel pressure regulator could be bad, the vacuum line could be off, or I could just have air in the system. I'm going to try to bleed it again today. I got quite a bit of air out yesterday. I installed a new "can" style filter (the metal filter located in front of the TBI) yesterday. My last one was toast. I did my best to bleed all of the air out of the filter, and supply line when installed the filter, but given its shape, I'm guessing there's still quite a bit of air in there. Kind of a crappy design, IMO.

[Viper]

If your primary fuel filter is full of fuel, the fuel pump should pick it up and build pressure. You could try attaching a primer bulb temporarily in the line coming from the fuel tank to pressurize that side so it assists the pump. If that doesn't work, the pump is toast. When the pump runs, is it a loud high pitched noise? Difficult to tell if you don't have a refference unless you listen to one that is working properly but a failed pump that still spins can be pretty loud. If it is, it's done. Besides age, running them dry like spinning on a new fuel filter with no fuel in it will kill those fast, the fuel lubricates them so it doesn't take long to ruin one running it dry.

[390Express]

Source of the post If your primary fuel filter is full of fuel, the fuel pump should pick it up and build pressure. You could try attaching a primer bulb temporarily in the line coming from the fuel tank to pressurize that side so it assists the pump. If that doesn't work, the pump is toast. When the pump runs, is it a loud high pitched noise? Difficult to tell if you don't have a refference unless you listen to one that is working properly but a failed pump that still spins can be pretty loud. If it is, it's done. Besides age, running them dry like spinning on a new fuel filter with no fuel in it will kill those fast, the fuel lubricates them so it doesn't take long to ruin one running it dry.

When I put the new fuel line on, I filled it with gas from the lowside, before I plugged it into the Oberg fuel filter. After replacing the Oberg fuel filter, and taking the pump off to inspect it, I filled from the exit of the Oberg to the pump with a small funnel, before I re-connected the opposite side. (the feed side) The pump always had fuel in it, and was never ran dry. The fuel filter that I replaced last is on top of the motor, right before the TBI. (the metal can filter) That filter obviously has some air in it, due to its design. It's shaped like a can, with the inlet and outlet in the middle of the filter, and no way to vent anything to the top of the can.

When I replaced the metal can type filter, I ran the fuel pump with the exit of the filter off, until gas came out of the exit of the top filter. I then disconnected the fuel line from the TBI, and ran the pump until gas came out of that side of the fuel line as well. It only takes a couple of seconds of running the pump to get gas through the fuel lines. When I removed the pump and hooked it up to a batter to test it, fuel shot up out of it about a foot in the air. It seems to be operating properly, I just don't know why the system won't build pressure. The pump is generally quiet, and sounds like a normal operating pump.

If the system won't build pressure after trying to bleed more air out of it, I'll hold my finger over a piece of gas line after the filter, and see if the pump is building pressure there. It has to be a blockage, or air in the line. I just have to figure out where the issue is at.

[Viper]

Did you confirm whether or not you had a return line to the tank?

[bud37]

Just one observation , IMO ,because this pump shoots gas out the line open ended, to me doesn't mean the pump will pump against a head, seems a pump capable of 30+PSI will shoot much higher than a foot thru a small line if all is well..... like you said the pump may be done or the regulator is bad.....have to test between pump and regulator to verify ...actually, do the injectors open on the TB......again good luck with it...thats all I got man.......please be careful with all this gas stuff....

[390Express]

Source of the post Did you confirm whether or not you had a return line to the tank?

Yup, there's a return line to the tank. I didn't replace that line. It was flowing freely, and seemingly working properly. Would it help anything to prime that line as well? I drained this line when I was trying to siphon gas out of the tank, and never added anything back in. (didn't see the point)

[Viper]

One of the advantages of having a twin engine application is that you can use the working engine or its components to troubleshoot the engine not working. If you suspect the fuel pump, do an exchange and see if the problem follows the part or if the working part solves the problem on the non-working engine. Like Bud said, just because the pump moves fluid doesn't mean it can pressurize the system. If that doesn't work, try the regulator.

Your application might be too early for this but just to clarify, you don't have the fuel control cell correct? It's a long canister which has a filter element inside and a couple of wires coming off the top to power a high pressure fuel pump. I assume you've checked to see whether you have both a low/lift fuel pump and a high pressure pump, or just one?

[390Express]

Source of the post One of the advantages of having a twin engine application is that you can use the working engine or its components to troubleshoot the engine not working. If you suspect the fuel pump, do an exchange and see if the problem follows the part or if the working part solves the problem on the non-working engine. Like Bud said, just because the pump moves fluid doesn't mean it can pressurize the system. If that doesn't work, try the regulator.

Your application might be too early for this but just to clarify, you don't have the fuel control cell correct? It's a long canister which has a filter element inside and a couple of wires coming off the top to power a high pressure fuel pump. I assume you've checked to see whether you have both a low/lift fuel pump and a high pressure pump, or just one?

Yea, I believe it's the low psi (15 psi) system, with only one fuel pump. There's no mechanical pump anywhere on the boat, and only one electronic fuel pump, I believe.

It's maddening that I'm getting gas to the TBI, but no pressure. I'll be down there today doing some digging.

[Viper]

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.