Lift pump isn't getting it done UPDATE: Problem solved!

SD diesels were widely available in the US in the 1981-86 Datsun/Nissan 720 pickups, and in Canada through '87 in the D21 pickup.

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cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Lift pump isn't getting it done UPDATE: Problem solved!

#1

Post by cseger1 »

So I am trying to fire a newly rebuilt motor for the first time and fuel delivery isn't happening. First things first, I am routing my fuel supply line to the bottom of the hand pump, from the top of the pump it goes to the filter, then to the IP. This is correct right?

When routed like this I can't get fuel to draw up from the tank. I can suck it all the way to the filter with a vacuum pump, but as soon as I tie it back to the hand pump it drains back to the fuel tank.

When I use an aux tank suspended over the motor I can gravity feed through this setup and get fuel to the purge screws on the IP but there is always bubbles in the fuel line and I never seem to really get the filter filled or a good supply at the IP.

IF the pump is in good shape I should be able to draw up fluid and shoot it out the top no? Maybe this thing needs seals.
Last edited by cseger1 6 years ago, edited 2 times in total.
Christian
1981 720 SD22
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done.

#2

Post by cseger1 »

I just checked the lift pump by itself and it is moving fuel in the right direction. I also made sure that the OFV orifice filter is clear. It is. And I tightened all the hoses looking for air leaks from the pump throng the filter to the IP. If I fill all the lines with gravity feed it still flows back into the tank and unprimes. I am completely unable to get fuel with only the hand pump.
Christian
1981 720 SD22
waynosworld
Posts: 525
Joined: 8 years ago
Location: Vancouver Washington USA

Re: Lift pump isn't getting it done.

#3

Post by waynosworld »

OK, in the photo attached I have numbered the fuel filter lines/fittings, #1 fitting is the line from the lift pump, #2 line/fitting goes to the front of the injection pump, #3/4 lines are interchangeable, one comes from the injectors as over flow, and the other is the return line to the tank.
Is your filter set up like this?
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I know the voices are not real,
but they have some really good ideas.
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done.

#4

Post by cseger1 »

Yep, that's my setup.
Christian
1981 720 SD22
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done.

#5

Post by cseger1 »

I'm pretty sure that the check valves in the pump a fubar.
Christian
1981 720 SD22
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done.

#6

Post by cseger1 »

Breakthrough! I tested the pump with some gravity feed in reverse to check the check valve and the check valves were definitely bad. Much flow. Luckily I have a good lift pump from my parts truck and it tested fine. Install complete. I will purge the air this afternoon and hopefully fire this motor tonight. Big thanks Wayno.
Christian
1981 720 SD22
waynosworld
Posts: 525
Joined: 8 years ago
Location: Vancouver Washington USA

Re: Lift pump isn't getting it done.

#7

Post by waynosworld »

cseger1 wrote:Breakthrough! I tested the pump with some gravity feed in reverse to check the check valve and the check valves were definitely bad. Much flow. Luckily I have a good lift pump from my parts truck and it tested fine. Install complete. I will purge the air this afternoon and hopefully fire this motor tonight. Big thanks Wayno.


Your welcome, although I don't know if I did anything to help you, I just wanted to make sure you had it piped correctly.
I have a VE pump that is wore out, and if I don't start it regular, it loses it's prime also, sounds like your lift pump needs rebuilt, if you find the parts to rebuild it, let me know.
I know the voices are not real,
but they have some really good ideas.
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done UPDATE: Still losing pri

#8

Post by cseger1 »

So I have the spare pump in and it will flow fuel til the air bubbles cease at the purge screws. Then I turned the motor with the injector lines open until fuel flowed from each of them. Then by the time I had everything buttoned up and ready to fire, I had a large bubble in the fuel line from the filter (the second one, I don't have a primary filter) to the lift pump.

Does this indicate an air leak in the fuel filter or failed check valves in the lift pump? I took the pump apart and made sure that the check valves and springs were moving freely and they are, just still losing prime right before the fuel filter.
Christian
1981 720 SD22
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done UPDATE: Still losing pri

#9

Post by cseger1 »

Excuse me while I talk to myself some more. I read the other threads about lift pumps and did some more trouble shooting. I cleaned the filter input banjo bolt and mating surfaces. I did not replace the gaskets (mine are not crush washers, they are fiber of some sort.) I am now running a leakdown test on the fuel line from the IP through the filter to the lift pump. So far it looks like my air leak was at that banjo bolt and maybe re-seating it has fixed the problem. What a pain. And after it's all bled I get to do it all over again because I am using blue transparent lines everywhere and I've been told they will melt from the diesel. Good times.
Christian
1981 720 SD22
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done UPDATE: Still losing pri

#10

Post by cseger1 »

Nope.. My fuel line is still taking on air at the banjo bolt. Arrrrrrgh! I didn't get any air in the line from the IP to the filter though. Are the seals at the banjo bolt the only thing to worry about or is there another place air can enter within the filter itself?
Christian
1981 720 SD22
waynosworld
Posts: 525
Joined: 8 years ago
Location: Vancouver Washington USA

Re: Lift pump isn't getting it done UPDATE: Still losing pri

#11

Post by waynosworld »

cseger1 wrote:Nope.. My fuel line is still taking on air at the banjo bolt. Arrrrrrgh! I didn't get any air in the line from the IP to the filter though. Are the seals at the banjo bolt the only thing to worry about or is there another place air can enter within the filter itself?


The only banjo bolt that is different is the back one near the mount bolts for the filter, do not get that one mixed up with the other two, I am not sure how that banjo bolt works, but I think it is a one way pin hole that allows air out of the filter housing, but doesn't let air back through from the return hoses coming from the injectors or the return line to the tank, so I suspect that if that banjo fitting has gone bad, got some dirt in it, you will likely have air issues.

I really don't know a lot about these engines, I am kinda a hack, when ever I take one of these engines out, I use my other diesel truck as a guide to put it back together.
I personally have never looked for air in my lines, I just get them started and drive them, although one time I wanted to see how much fuel returned to the tank, imagine my surprise when I found out that at an idle, no fuel returned on my engine, none, that baffles me, but not enough to have me pulling my truck apart to find out why.
I know the voices are not real,
but they have some really good ideas.
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done UPDATE: Still losing pri

#12

Post by cseger1 »

Yeah, I had a thought earlier that I'm overthinking this shit. The tube that develops the bubble is before that OFV valve and I think it (the bubble) gets purged as soon as the engine cranks. I don't have bubbles from the tank to the lift pump, and I don't have bubbles from the secondary filter to the IP. Watching it earlier, I realized that even though this tube gets a little un-primed, it's not sending air to the IP and I've been chasing my tail over this for no reason.

I purged the hard lines to the injectors and tried to fire earlier. I think the battery I am using may be a little too abused for starting a diesel. I got at least one or two cyls to fire before I lost too much charge to get the motor roaring, but I think I am close. I'm not going to worry about that bubble any more.

More tomorrow.
Christian
1981 720 SD22
waynosworld
Posts: 525
Joined: 8 years ago
Location: Vancouver Washington USA

Re: Lift pump isn't getting it done UPDATE: Still losing pri

#13

Post by waynosworld »

I did not think of this till now, do not turn your engine over with anything but a good fully charged battery, half dead batteries are the number one killer of the starters on these engines, it burns up the armature, fully charged is all you want to use.
I hope you got it running by now, my rebuild started fine, but then I had all sorts of issues, mostly things coming loose like the rockers, I am still baffled about that.
I know the voices are not real,
but they have some really good ideas.
cseger1
Posts: 116
Joined: 14 years ago
Location: Houston TX

Re: Lift pump isn't getting it done UPDATE: Still losing pri

#14

Post by cseger1 »

It's been hooked up to a smart charger the whole time. I only crank when it is at100%. I've gotten it running very rough. All the bubbles have been purged. I think at least one of the glow plugs is shot and when I pre glow, I have enough heat to getall four cylinders to fire for a few seconds but thbad plug is failing during afterglow and the idle turns really rough.

I ordered a whole set. They should be here on Saturday. Also, I didn't know about reaming the gp threads. I will be doing that because the threads may have some rust or crud even though the head got rebuilt.

I don't trust my gp system. I am going to bypass it with a farmer solenoid.
Christian
1981 720 SD22
TOYoung
Posts: 16
Joined: 8 years ago

Re: Lift pump isn't getting it done UPDATE: Still losing pri

#15

Post by TOYoung »

I worry you still have air in the fuel. I just replaced two fuel lines with banjo fittings. I re-used the banjo fittings. It took me a while to find copper crush washers for the banjo fittings(couldn't find aluminum either, which work as well).

I found them at a tractor supply but they only had 6. I annealed 2 of the old ones which means-heating them cherry red and dropping them in water.

I smoothed those 2 annealed crush washers on a flat surface with 600 grit paper. Cleaned them up real well and re-installed the new fuel lines and banjo fittings.

Crush washers take some 'crushing'. Starting with a firm tightening, I had to add a bit more torque to a few until all leaks stopped. They do seal well, though and are air tight.

I think you need those banjo fittings to be air tight. Even a little air(hard to see the bubbles) will cause problems.
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