4psi electronic lift pump - Diesel Forum

fishinfreak · 08-31-2007, 06:33 PM

i put a 1.5-4 psi NAPA posi-flo electronic fuel pump in line just before the mechanical lift pump, hoping that it would help me out with purging air out of the fuel system after changing my fuel filter. this is partly because my lift pump is located on the vacuum side of my fuel filter due to veggi conversion.

well, i can't seem to get the air out of the system at all now, wearing out my starter and my batteries trying.

since i have read that this fuel system needs 7psi pumpage?? is this lower rated electronic pump actually creating a whole additional problem?

thanks

oregonmike · 08-31-2007, 10:13 PM

fishin',
Logically that makes sense...while running. If the electric pump will only provide a max of 4 psi, the mech pump *wants* to deliver 7 psi, the electric pump has to be a bottleneck. But, if the electric pump is working with key on, not started, it should be pumping fuel through the mech pump, through the filter & then on through the ip and return lines back to the tank.

Everything I've read (and which I'll follow when my mech pump gives up the ghost) is to put a Holley Red or some other pump that does right about 7 psi and remove the the mech pump, replace the mech pump with a big block Chevy block off plate. If the mech pump loses its diaphragm while the electric pump is going to town, you'll fill up your crankcase with diesel/veggie oil.

Have you measured the output of the fuel after the filter? PSI & volume?

kipamore · 08-31-2007, 10:38 PM

The pump (s) aren't the problem. The problem is air is getting into the lines - doesn't matter where it comes from; it's there.

The stock system has a return circuit at the IP, from each injector, and at the fuel filter output. The return system is what's doing the bleeding, blowing fuel and air "around" the IP such that it always gets fuel. Trust me, I found this one out the hard way.

In my WVO system, the electric fuel pump can be keyed without the engine running. It starts pushing, and since I have a bunch of clear fuel line in the system, I can see it drawing up big air bubbles into the pump, thru the filters, and out the master return line back to the fuel tank. As long as it's an electric pump, it will do this while the glow plugs are going thru their warm up cycle, and by the time I start cranking I've got liquid fuel at the IP - air can never get in there. If I change filters, I don't have to fill them with fuel - I just run the pump for a minute or two and they self-bleed.

I'm not 100% certain, but I'm pretty sure the IP would be able to run the engine without a fuel pump at all. If you just dribbled fuel in via gravity, it would still work ok. But as soon as the IP fills with air, you are done for because it can't pump fuel, and it can't pump out the air. So the lift pump self bleeds by flowing far more fuel "past" the IP than it could ever use. Meter your return line sometime and you'll see its flowing 10s of gallons per hour.

I would guess that you have a plugged return somewhere, most likely at the fuel filter header. There should be a little T fitting there that ties into the return from the output side of the filter, right before the IP. If not, simply T in a return line as close to the IP as possible, or right in front of the tank switch in your lard system. Orient it such that the return output is facing up high, so gravity will let air out before it lets fuel out.

There's a bonus as well; I have these return fittings on both my diesel and lard lines, so as I'm cruising down the road on diesel, I can switch on the lard pump and it will filter fuel and return it to the lard tank without affecting the diesel side. I expect this will be a bonus in the dead of winter, if for nothing else than flowing all the lard lines to make sure everything is warmed up and free flowing.

Kip on Truckin-

fishinfreak · 09-01-2007, 02:42 PM

your system sounds pretty convenient.
i think it's just air in my system though because this has all happened just after changing the stock fuel filter. it happened to me before, but somehow i was able to get the air bled easier last time.

the electric fuel pump cant push fuel through the ip right? the engine has to be cranking to get fuel to go through the ip and the injector lines right? i have gotten a couple of the injectors to weep out a decent amount of fuel, hopefully i'm getting closer to getting this thing started.

cdnsarguy · 09-01-2007, 06:23 PM

There will be NO large amounts of fluid from the injectors at cranking speed.....

94_turbo · 09-01-2007, 08:39 PM

turn switch on--with can under the pump--you need pressure--annddddddddddd--FLOW---how much you got--it might build 80 psi--but if the flow is only 2 teaspoons a minute--so what??? might be bad pump right otu of box---seen it---

kipamore · 09-02-2007, 01:12 PM

The IP is designed to "lock up" the fuel flow when there is no power to it. The fuel shutoff solenoid does this, and that's what happens when you shut the engine off - the IP locks and deprives the engine of fuel. But the IP also locks on the input side to avoid losing it's prime. At shutoff, fuel would naturally want to drain back to the tank or otherwise seek it's lowest level, letting in air or othewise losing prime.

But an electric pump will push fuel even with the engine off as it goes directly into the bypass circuit. IP is still closed for business, but the return side is open.

It's probably not your injectors leaking the fuel. They run at 2000 psi, you would see that. It's probably just seepage at the return fittings.

Kip on Truckin-

fishinfreak · 09-02-2007, 02:01 PM

well, i got fuel at the injectors now, and i replaced two bad glow plugs, but i still couldn't get it started. i'm gonna have my girlfriend tow me down the road and try to pop start it....that should blow all the crap out of the engine. i actually did get it to start yesterday, but then it died after 5 seconds and lots of nasty smoke.

94_turbo · 09-02-2007, 06:54 PM

and air in the lines makes them fun to get started---

fishinfreak · 09-02-2007, 08:49 PM

ok, the pop start in tow thing worked real nice, but i've still got some issues. it was stumbling here and there as i was driving down the road on the highway (higher speed = more air getting sucked into system through possible leaks? or would that be the same at idle theoretically?)

then i swtiched to veggi and the thing ended up dying on the side of the road. luckily i got it started and made it home again, (switched back to biodiesel) and it idled fine for 12 min. in the driveway. would this suggest air coming into the veggi fuel circuit only?

check this out: i started using B100 in my normal diesel tank recently , and a couple weeks after starting to use that i had some stumbling taking place after switching to veggi. you see, when the veggi is on, i have the fuel return looped, so as to keep the hottest veggi possible going through the system. so i'm thinking that the solvent properties of the B100 have loosened up some crap probably that is blocking up the return lines probably, and maybe when it's on veggi there is junk floating around in the loop and clogging it, making it want to stall??

what do you think?

kipamore · 09-03-2007, 05:35 PM

Fish,
I went through similar problems with WVO and fuel pumps and air and whatnot. Two tips for ya:

1. Air in lines has the symptom of surging or speeding up. Don't know why this happens, but if there's air in the system it speeds up.

2. Go to the brass fitting plumbing aisle of Home Depot and buy barbed fuel line couplers, a pile of hose clamps, and clear 3/8th fuel line. All three items are right near each other on the shelf. Install at least a short section of the clear at the output of one or both fuel pumps, and some after the main return junction. Trust me on this one: clear fuel line makes everything easy. You can see clogs, air pockets, air bubbles, and fuel pump failure without having to guess at it. Note: the clear line they sell at Home Depot seems like it's good for about 160 degrees. After that it starts getting soft, and I think it might melt. But I have it all over my system and I haven't had trouble yet. I also went on ebay and got some clear hose called "superthane" which doesn't have this problem.

Kip on Truckin-

fishinfreak · 09-03-2007, 09:45 PM

have you used the reinforced vinyl tubing, or just the clear regular vinyl tubing. i know the reinforced is a bit stronger, but it would be easier to see into the regular clear hose. i don't think it would matter as far as the pressure capability because there isn't much pressure in the fuel system until you get to the ip right?