Fuel trouble

[redbo]

Hey guys,

I've got a vortec 4300 from a Chevy silverado in my 69 CJ5.

I've got a walbro gsl 392 fuel pump in it.
Walbro GSL392 Inline Fuel Pump 255LPH HIGH PRESSURE (universal external pump)

The fuel pump has never sounded great, it whines a lot and is quite loud, part of that I just thought was because it was an inline pump on the frame right under me.

But now I'm having a lot of trouble with idling and stalling. It's always been a rough idle, but lately I have been stalling a lot at idle.

All of the fuel lines are new and there's a new fuel tank which is only four years old. I just put in fresh gas and a new fuel filter. No better.

The next part of my troubleshooting I was going to replace the fuel pump.

I had put the fuel pump in before putting a new fuel tank in. The previous tank was pretty rusty and I'm afraid that the bad gas damaged the fuel pump.

My question for the group is should I put in the same fuel pump? Or are there any other thoughts that I can troubleshoot first? I do not have a fuel pressure testing gauge.

Putting in the same pump would be easy because all the fittings are already there.

Thanks!

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[Torxhead]

Having an external mounted electric fuel pump is kinda tricky the way I see it, I have a throttle body injection on my 4.2 and it seems to work o.k. I would suggest touching your fuel pump after a short drive to see if it is warm or not. If it is this would indicate that there is not enough fuel passing through it and either the pump is bad or your fuel system is not allowing enough fuel through it. I use the Airtex E8094 which looks like yours anyway, and have had good results. Fuel pressure is critical for a t.b.i. and should be around 10-14 p.s.i. measured from the back inlet of the throttle body. I installed a brass tee in the back of mine and plug it off when not in use for testing. The fuel return line is just as critical as it should be free flowing back to the fuel tank. The fuel tank you have must be vented and allow the fuel to siphon its way to the pump as they do not suck very well. There should be a free flowing filter mounted before the pump so from the fuel tank does not ruin it. A filter similar to a Fram G3802A should be fine.

 

[redbo]

Thanks for the reply!

Some fantastic information!

So, yes, the fuel pump is getting quite warm.

But...

I don't have a fuel return line and I don't have a vent line. I have a venting gas cap but otherwise the tank only has the siphon off the bottom which goes to a filter and then to the fuel pump. I do have a sending unit on the top, which is sealed and doesn't actually work...

So yeah. Apparently I need more tubes in and out of my tank!

This job might be getting over my pay grade.

 

[Torxhead]

Sounds like you must have a throttle body injection system that I am not familiar with. The fuel pump getting warm does mean you have an issue though. To test for getting fuel to the pump, you can disconnect the fuel line going into the filter and with the gas cap disconnected, the fuel should freely flow out. When you go for a short drive and remove the gas cap, there should be no vacuum inside the fuel tank. How is the spark plug burn? like is it stalling from too much or too little fuel?

 

[redbo]

Thank you for the follow-up!

One possibility is the guy who installed the fuel lines for me when we were working on putting the new motor in didn't do it correctly... there had been a vent and return on the previous tank but those were never reconnected after the motor conversion.

When I disconnected the fuel filter today fuel did flow freely out of the tank and into the fuel pump. However, in hind-sight, I do remember hearing the tank suck in and pop back out when I let the fuel free flow out.... perhaps the lack of vent could be the problem.

I have not noticed a vacuum in the tank when taking off the gas cap. I got a new venting gas cap for the tank two years ago.

I'm not sure about stalling from too much or too little fuel... When it runs, it seems to run smoothly, but that is all in 2nd or 3rd gear.

Looking at the vortec 4300 online, it does seem that it is supposed to have a fuel return line. I'll need to look at the throttle body tomorrow to see if I can sort that out.

Thanks again!

 

[PistolDave]

What generation 4.3 are we talking here? 4.3 covers a lot of possibilities from carbureted to direct port injection. There may have been some of the later versions that used a returnless injection system with PWM control of the fuel pump to vary the speed like some of the later LS based units. If it is a TBI injection system, it needs a return line somewhere to regulate pressure. The return line does not have to come from the throttle body, the bypass output on the TB can be plugged and a bypass regulator installed by the fuel tank.

If you truly do not have any return or a variable speed pump, I don't see how it is running at all if it is an early TBI system. That Walbro pump is rated for 50 gph @ 80psi and is capable of supporting 650+ hp, somewhat overkill for a 140 hp v6.

 

[redbo]

Okay, I did some checking... Sorry for the late reply, just got out of work.

The 4300 is out of a 2006 Silverado.

There is a return line that is right near where the fuel line goes in... and it is plugged.

There is no bypass regulator installed. Perhaps the overkill pump is why it has been working at all? I'm also stumped and a little embarrassed that I didn't know this was a problem until now.

So, I'm a little frustrated that the out-of-town mechanic that helped me with the build didn't either take care of this or let me know that it needed to be done.

I talked to my long-time local mechanic and he is going to installed the return line and put a port into the tank.

Just Empty Every Pocket!
Right?

Thank you again so much for the help.

- Redbo

 

[Torxhead]

On my 90s era t.b.i. it does have an adjustable regulator inside it. Perhaps your does also and it would help to know just what the fuel line pressure is. Perhaps it is already at the factory setting and is working just fine you might just have other issues giving you problems.