mech fuel pump problem. advice?

[vortec]

let me start by saying that i am much more familiar with efi, so this may be a very simple issue. i recently installed my 350 (80-85 in an 82). now that i have it all hooked up, i'm trying to start it, and it'll crank fine, but it's not getting fuel. i have a clear fuel filter before and one after then fuel pump, so i can see that there is fuel between the tank and pump, but not between the pump and carb. i tried disconnecting the line from the carb and dumping fuel into the line. it does not fill the filter and does not appear to be flowing into the other one, through the pump. my guess is that it is going back to the tank via the small return line on the pump. is this feasible? could i just block off that return line? is my pump dead? it worked fine on the old engine, but it's been sitting quite a while. any ideas?

 

[diesel4me]

3 lines?...

If the pump has 3 lines,and you don't need the return line,just block it off with a peice of hose and a bolt clamped in it..my 79 C10 has a pump with 3 lines, and I blocked it off that way with no issues..

I'd guess your pump just plain croaked though...I doubt its pumping all the fuel back into the tank VIA the return line--more likely is its diaphram dried out,during its downtime, and is now ruptured,or gummy stale fuel is preventing the pump from priming,by not letting the check valves work.....if its the diaphram,gas will leak out of the weep hole in the casting,and/or into the crankcase,which can dilute the oil enough to toast the rod and main bearings!... ..

A new pump isnt that costly (at least on my old wrecks!)..I'd start fresh with a new one,its better than having to call a wrecker--I've been cheep too,and tried using an old pump after it sat awhile--once they dry out,they dont live long when you try re-using them in most cases...

 

[vortec]

yes, right after i made my original post, i tried blocking off the return. it did help somewhat, but flow was still crappy and weak. so, dead fuel pump sounds about right. too bad, since it's a major PITA to get that thing in and out, thanks to the general's brilliant smog pump placement. but, it's less than 20 bucks, so it could be a lot (a whole lot) worse.

thanks for the input.

 

[sweetk30]

also if those clear filters are the glass tube and nylon screen throw them out. and get paper filters. thay work 20x better. sounds like a pump to me. it was most likely on its way out when you did the motor swap.

 

[vortec]

ok, this is bugging me.

i put a new pump on, tonight. it behaves in pretty much the same way as the old one! with a sick feeling in my gut, i wonder if the reman shop ground the cam lobe for the pump and forgot about it. my dad thinks gm may have used multiple pump rod lengths and i need a longer one. possible?

i cannot find any leaks in the line where it could pull air. could the tank have formed its own vacuum, stronger than the pump's? i'm starting to grasp at straws here . like i said, i know more about fuel injection. i'd love to just be overlooking something obvious, here.

 

[diesel4me]

one rod...

As far as I know,both SBC and BBC use the same fuel pump pushrod,and there are no "other" lengths ...they can wear down though,but that usually wipes the cam lobe out too..

Your lacking fuel only from the pump to carb??--tried blowing out that fuel line?--maybe its plugged up with gunk??...

I've run gas filters in line before the fuel pump without any issues,but perhaps the one your using isn't letting the fuel pump suck enough gas through it,and its getting airbound or something..is the "sock" filter in the tank clean??...gas cap letting air get in the tank,so it wont restrict the gas flow??..

If the emission canister hoses got hooked up wrong,engine vacuum could build up in the gas tank..highly unlikely though,I'd think the gas cap wouldn't let enough vacuum build up to affect things much..

I'd put an electric fuel pump on (mounted in-line close to the tank) and see if that cures the problem...if it does,I'd guess the cam lobe or pump pushrod is worn enough so the pump gets insufficient "stroke" to pump right..might have to use the electric pump permanently if thats the case...

 

[vortec]

some good ideas, deisel. there is a near-total lack of fuel between the pump and carb, and barely any to the pump from the tank. last night, i tried blowing the line from the tank out with my smaller compressor. when i pulled it away, i got a geiser of gasoline shooting out. way more fuel than i think the line alone could have held, so i guess i pressre built up significantly in the tank, even with the cap off. i called it a night after that. it was about midnight and i didn't feel like firing up an engine that was covered in fuel. hopefully i just had a clog in the line. if not, i hope i didn't accidentally install the pump in such a way that the lever rode up on top of the shaft and isn't being pushed. i don't even know if that can happen. i've certainly never seen it.

 

[onetonbb74]

Make sure the lines on the pump are hooked up correctly. Ive seen them installed backwards and it will pump fuel out of the carb and back to the tank (or air to the tank). Also, there is another filter in carb on the inlet port id check that also or change it. Is there a solid (hard metal) line from the tank to the pump? a rubber hose that long is no good.

 

[vortec]

the line from the tank is metal, except for a small piece near the rear, and one for the last foot or so, where i have it attatched to the larger barb fitting on the pump. it's essentially stock. the pump outlet to the carb is threaded, and that fitting is snug and sealing. i'm actually trying to run without the filter in the carb and use an inline filter spliced into the fuel line, instead. i've seen this done with no problems on musclecars. as far as the pre-pump filter, might it work better closer to the tank instead of close to the pump? oh yeah, the small return line is obviously hooked up to the small barb fitting on the pump. not much other option, there.