External FP users - question

[Sy#26]

Got a problem w/ an externally mounted fuel pump, wonder if any of you guys who run these can help. Pump is mounted inside the frame rail near the front of the tank - so the suction hose is 3' long or so to an added rear sump on the tank. Alls well until I punch it in first gear - then the FP drops toward the end of first - when the accelleration is max. Leans out, misfires, then from there out all is ok through second & third gears.

As far as pump capacity, pressure, etc. goes, all tests ok.

I've heard the ability of these pumps to *draw* fuel isn't so great, although the output pressure isn't a problem.

Could the pump be unable to suck enough fuel against the accelleration force on the 3" inlet hose (1/2" AN)?

Thanks for your thoughts....

 

[TURBO TY]

could it be that you installed the pump backwards?

 

[Sy769]

could it be that you installed the pump backwards?

I sort of doubt the engine would run if the pump was backwards :roll:

As far as pump capacity, pressure, etc. goes, all tests ok

I kind of doubt this because if all those tests were ok then you would not be having this trouble. You should set base pressure with truck off and then you should see one psi of fuel pressure increase per one psi of boost increase. If not something is amiss in the fuel system.

What type and brand of fuel pump? If it is mounted close to the bottom of the tank I don't believe that will cause any probs. The sump design could cause problems if it is not set-up correctly starving the pump for fuel.

 

[ed hess]

I run dual externals off my cell, both mounted in the bed.

They actually draw fom the sump wihich is incorrectly mounted aimed towards the front. The foam in tha cell keeps sloshing from starving the pumps on launch.

so what i am thinking here is:
dont the stock tanks have a baffle in them. suppose that baffle is loose.
on launch the baffle move back and resticts fuel exiting the tank. after launch the fuel and baffle return to their normal position so no more starvation.

Sorry thats the best thing i can think of. unless something is moving and pinching a line on launch. or creating a tempoarary open circuit in the wiring to the pump.

hth

ed

 

[Sy#26]

Thanks for the replies, guys. The pump is one of the good ones sold by a fellow lister - supposed to be of more than adequate capacity. Pump & sump has been in for almost six months, no problems at all in the higher gears. Actually, the problem wasn't there until I started really tuning this truck. The more boost & timing I gave it, the faster it'd run until I hit this 'thresshold'. Electrically, its ok - jumpered the pump right to the battery (bed mounted) - same prob. Plumbing is a bit awkward, so I'm going to redo it this week w/ nice short run to the tank, in-tank prefilter made from some fine brass mesh I got on the net. Baffle in the tank was nice & tight last time I looked which was recently.

Thanks again -

 

[ed hess]

barry

you might try dual pumps.
maybe given what youre doing its maxed out or on the edge of same?

ed

yeah i realize this gets expensive.....

 

[Mike from Jersey]

How much fuel do you have in the tank when this happens, because the symptoms you describe point to fuel starvation. I don't know if you are aware of the "1/2 tank rule for launching" LOL Just a thought

Mike