Runs out of gas - let it sit & it starts?

[pismorat]

I'll try and get to the point: 489BBC, large Edelbrock 4 barrel carb, high volume mech. fuel pump (2 yrs. old), Purolator "red" elec. fuel pump at the tank selector for backup/off-road (14 yrs. old). Drive the rig on some technical trails with the elec. pump on and it does great, hit the flat road on the way home and it runs itself out of gas (happened in 2 consecutive outings). The elec. pump is on, but is loud so there is no fuel pumping. I let it sit for 20-30 minutes and it fires up and drives like nothing was wrong. I have a steel braided line going form the mech. pump to the carb. My neighbor who is pretty sharp says the elec. pump is probably bad and causing the issue. Anyone ever experience this and have any thoughts?? Please

 

[AV8TER]

Fuel tank vent system maybe? Next time it does it, crack the gas cap and see if it picks up fuel again. Easy to try.

 

[pismorat]

I did try that, plus I was switching tanks and that didn't make a difference either. Is there a possibility of vapor lock? What is that exactly? The fuel lines didn't feel super hot, so I am not sure there either.

 

[o_fatmike_o]

so it goes fuel tank to electric pump to mechanical pump to carb right? if the electrical pump sounds loud i would bet you need to start there. pull the fuel line turn on electric pump and see if its pumping?

 

[cybrfire]

A vapor lock is when you get the fuel lines hot enough to boil the fuel within the line. This makes air bubbles. Air doesn't pump the same way liquid does.

 

[Deuling]

And gasoline faporizes at a much lower temp than water.


Also make sure you have a return line.

 

[Jester1]

Had trouble like this twice. How close is the electric pump to the tank. If you are much more than 2 feet it caused problems for me.

 

[Deuling]

I didnt realize you have both an electric and mechanical.. Pop that electric one out and put a piece of hose in between and try that. If that works, grab another mechanical pump for backup. They really only take a few minutes and 2 bolts (on a sbc at least) to change if you want a backup.



I had soooo much trouble with vapor lock on my rig. I tried heat shields, heat wrap on the lines, ran a new stainless fuel line on the outside of the frame away from exhaust, ... Nothing worked.

Old guy stopped over thats a big mopar guy, says hey, your return line isnt hooked up, so the fuel thats sitting in the line is getting hot and vapor locks. I say my holley fuel pump has no return fittings on it

He ran home, grabbed some mopar fuel filter that has a return line on it, I cut it in, hooked the return line up to it... Worked beatiful.

 

[diesel4me]

I've told the story here before about my brothers '66 Suburban with a 283,how it ran great until you climbed a long upgrade on a stretch of highway near his town,or when pulling a trailer in hilly areas..it would start surging,buck,and eventually stall like it ran out of gas...let it sit awhile and it would start right up like nothing was wrong and some days it'd never do it again..

He replaced the fuel filter,fuel pump,rebuilt the carb too,and blew the fuel lines out with compressed air,thinking perhaps the sock filter in the tank was clogging up with rust,the tank did have signs of rust in it that showed up in the filters,but not to the point it clogged them--.but it didn't help any..same day he blew it out it did the same thing going up that long incline!..

He tired of not being able to trust the truck and it making him late for work,so he decided to replace the entire fuel line with new tubing...when he crawled under the truck to measure the length he'd need,he noticed the factory steel fuel line near the rear tire on the passenger side had been made in two sections and they were joined by a foot long loop of 3/8" rubber hose that looks like an inchworm...

He went to take it off and noticed it felt lumpy inside,so he took it off and sliced it open lengthwise with a razor blade and saw the inner lining of the hose had separated from the fabric and was all bunched up,and gooey like gum!..he put a new peice of rubber hose on it,and the truck never stalled out again on those long uphill pulls..

I have read here quite a few trucks have had the rubber hose fail that joins the electric fuel pump to the sending unit hose connection on later models too,I guess you need special hose rated for submersion there or it will fail in short order...

 

[pismorat]

Thank you for all the input. This has given me some ideas and things to research. I think I might be on to something...the truck used to have a return line in it from the old SBC mechanical pump, but then when I converted it to the big block I couldn't run the tall mechanical pump. I got a short one off eBay and it didn't have the return line, so I just plugged it. I never had this issue till I took it to about 7000' elevation, then it happened both times after coasting it downhill or just low, steady throttle. Then when I'd go to get on it is when it stalled. My thought is the fuel in the lines got hot, then the pump sucked vapor as I hit the throttle. Does this make sense at all? I'm thinking of trying to find a short pump with a return and hooking it up, then replacing all the rubber line and the 15 year old in-line electrical pump to boot. Thoughts?

 

[diesel4me]

You could get a metal fuel filter that has a return line nipple in addition to the usual feed in and out nipples,and hook the return line to the "third" nipple..much less work than replacing the fuel pump,unless it needs a new one anyway...

I'll have to dig up my WIX catalog and post up the number for the filter I'm talking about..

 

[pismorat]

That'd be great diesel4me! Would it go before or after the fuel pump? I am 200 miles from my truck and going up in a two weeks for a week long trip, so I'm trying to gather all the info and parts I can so I can try and get her on some trails!

 

[diesel4me]

`It would go between the fuel pump and carb or EFI rails...pressure side of the pump..

I'll post up the number later here when I can get to my WIX catalog..

 

[Deuling]

I didnt realize you have both an electric and mechanical.. Pop that electric one out and put a piece of hose in between and try that. If that works, grab another mechanical pump for backup. They really only take a few minutes and 2 bolts (on a sbc at least) to change if you want a backup.



I had soooo much trouble with vapor lock on my rig. I tried heat shields, heat wrap on the lines, ran a new stainless fuel line on the outside of the frame away from exhaust, ... Nothing worked.

Old guy stopped over thats a big mopar guy, says hey, your return line isnt hooked up, so the fuel thats sitting in the line is getting hot and vapor locks. I say my holley fuel pump has no return fittings on it

He ran home, grabbed some mopar fuel filter that has a return line on it, I cut it in, hooked the return line up to it... Worked beatiful.

`It would go between the fuel pump and carb or EFI rails...pressure side of the pump..

I'll post up the number later here when I can get to my WIX catalog..

That's exactly what I was talking about lol. And what fixed my vapor lock issues

 

[pismorat]

I did some searching and think I found the right part numbers, but if you could confirm that'd be great!

WIX 33040 has 5/16" inlet/outlet and a 3/8" return.
WIX 33041 has 3/8" inlet/outlet and a 1/4" return.
WIX 33054 has 5/16" inlet/outlet and a 90deg. 1/4" return.

I know my return is 1/4", but without my truck here at home, I cannot recall the inlet/outlet size. I have a 3/8" line from the tank selector to the mechanical pump, but then don't remember what it is from the pump to the carb. Can you guys point me in the right direction?

 

[diesel4me]

I looked on google images and yes,those are the ones I was refering too...sorry I failed to post back sooner,I didn't get a chance to get into my garage and look them up today..

Most Gm's with V8's that had A/C used 3/8" fuel lines from the carb to fuel pump,but some had 5/16" too,the smaller cubic inch ones under 350 with no A/C especially...sixes had 5/16"..best to measure than guess of course,but I've fudged a 5/16" filter onto 3/8" hoses before,the barb on the nipple fits close and clamps will hold it on,the loss of flow is practically nil too..the "correct" one is always best though..

 

[pismorat]

Thanks...and I messed up too. I have a 3/8" line from the tank selector to the fuel pump...which obviously means I have a 3/8" line up to the carb. On my way to the parts store today!