Diesel Kiki LIFT PUMP

[philip]

Earlier this week, I nearly got stranded. Thinking back, there were signs of aerated fuel, ie barely perceptable surging at freeway cruising speeds, the occasional misfiring at idle that would clear up by revving the engine once, etc. Roadside diagnosis revealed a lot of foamy diesel fuel from the two bleeder screws on the injection pump while the engine idled.

I had to limp home at 30 mph (less at times) and almost lost the whole game while waiting at a busy intersection.

So ... time for a "Lift Pump" rebuild. Notice that Bosch has updated the primer pump. No longer do you unscrew the plunger, let it spring up, and then pump. This new design stays extended all the time and there is no "seat when not in use" requirement.

Be sure to replace both fiber banjo fitting gaskets on each fitting with the copper ones supplied with the pump kit AND ... clean the little strainer found in the end of the banjo bolt (pump inlet port).

A piston lift pump is used on SD engines fitted with Bosch inline pumps. The cam lobe pushes the piston out. This stroke is the reset stroke. A stiff spring pushes the piston back as the cam lobe turns past its highest point. This begins the intake stroke on the spring side of the piston AND simultaneously the pressure stroke on the gallery (discharge) side. Clever.

Lift pump piston spring then moves to limit fuel pressure to the injection pump. The off flow valve (OFV spring & orifice) vents some second filter fuel begining at 20 psi, sending back to the fuel tank. As you can see, any fuel restriction before the Lift Pump's inlet will affect (lower) any line pressure to the injection pump.

[TheDieseliminator]

Galen, welcome aboard! Glad to see you joined up on the forum and your SD22 turbo sure is sweet. Nothing but an awesome, clean job indeed. As soon as I saw "Knucklehead" on the side of the page I was like well Galen has joined now and great to have him. Looking forward to learning more from you in the future.

Salvy

[Knucklehead]

Ok..., so I'm tying up loose ends on this motor and it occurs to me per a diagram that I must have something backwards on my lift pump. Yes, yes, I look at every picture I have and every picture on this and the other board, and yes, I've got it wrong. How did I do that? Well who knows, it's been years since I took it apart; I can't remember anymore, even though I've rebuilt the pump twice.

So I start to swap things, but no, that won't work,


and hey, what the hell? My fuel inlet on the bottom is on the wrong side!


I get to looking at one of Al's pics and I notice that my arrow points in the other direction!


And I wouldn't have thought anything of it if it weren't for looking at all you guys' backwards pumps
and thinking mine was wrong!

[philip]

Ok..., so I'm tying up loose ends on this motor and it occurs to me per a diagram that I must have something backwards on my lift pump. Yes, yes, I look at every picture I have and every picture on this and the other board, and yes, I've got it wrong. How did I do that? Well who knows, it's been years since I took it apart; I can't remember anymore, even though I've rebuilt the pump twice.

Well Galen ... it looks like you have one of those "undocumented" changes. In addition to the output/primer pump reversal, I notice your pump is missing the metal line for lift pump output and the metal line feeding the injection pump. And, where is your altitude compensator?

This is my (and every other USA spec SD I've seen thusfar) injection pump before lift pump rebuild. The inlet is forward, underneath the primer pump. The FSM does notshow your plumbing. Hmmm!

[AStevens]

Is there a good source for the Zexel kit, or is it a dealer thing?

[asavage]

The lift pump kit can be had "anywhere". Any diesel injection shop, probably forklift places too. I don't recall where I got mine last year.

Since you live in the SW, why not use Southwest Diesel?

[AStevens]

Sweeet! Will do since they're just up the road.

[asavage]

Interesting operation description. I wouldn't have guessed about the recirculation mode for the intake stroke. On diaphragm fuel pumps, the pressure spring is on the other side, and the cam action pulls the diaphragm. But one thing's the same: when the system is up to pressure, the piston floats above the cam. The piston's actual stroke in normal operation (ie non-purge mode) is probably very short.

When I was in my teens, I worked for a fellow who didn't know much about engines, certainly not as much as I did even then. And one thing he said stuck with me, though I didn't think much of it at the time. He believed that running an engine out of fuel would tend to "suck the diaphragm", ruin it.

It wasn't until I got more involved in picking up the theory end of things that I realized that, at least in that statement, he was right. In normal operation, a pressure-regulating diaphragm pump hardly strokes at all. But if the discharge pressure falls (as when you run out of fuel and start trying to compress air instead), the diaphragm full-strokes, which can tear an old diaphragm that hasn't flexed to that extent in a long time.

Bringing that around to the lift pump -- I could imagine that the piston could run into an area of its bore that it hasn't travelled in a long time, and if there was any corrosion or crud in there (there certainly shouldn't be, but the lift pump operates on basicaly unfiltered fuel; we know the primary filter isn't much better than screen-door screen), I could imagine the piston sticking there -- except for that 28 PSI figure. That's gotta be one heck of a heavy spring behind that piston (for a fuel pump).

[EvergreenSD]

Could you give me an idea on how much the kit to rebuild the lift pump should cost?

[philip]

Could you give me an idea on how much the kit to rebuild the lift pump should cost?

More to the point is the price for rebuilding the ENTIRE pump. There is a seal to keep pressurized fuel OUT OF THE CRANKCASE OIL and two one-way check valves that are probably not included in an ala cart primer pump assembly.

[EvergreenSD]

That is in fact what I was trying to ask. The full lift pump rebuild is what you did, am I correct? I was just trying to get a grasp of what the cost of that might be. My new primer pump should already be on the way. Is a diesel specialty shop the best place to buy this full rebuild kit?

[asavage]

Could you give me an idea on how much the kit to rebuild the lift pump should cost?

More to the point is the price for rebuilding the ENTIRE pump.

He said "kit to rebuild the lift pump".

What did you do when you rebuilt yours? I replaced the check valves. The kit I bought didn't have a seal for the piston. Do you have a pic of that seal? And how much was the kit you used?

[philip]

What did you do when you rebuilt yours?

I handed the pump assembly to Edgar and said "Heal".

But understand that I had been picking Edgar's brain on many other diesel
matters and felt obligated to pay retail for SOMETHING! $100.

[EvergreenSD]

Al, I didn't realize that you had rebuilt a lift pump as well. What symptoms prompted you to overhaul yours? Did it help?

[asavage]

On my first SD, I had the wrong primary fuel filter installed. Because I had obvious fuel starvation problems, and because the age of the IP was unknown, and because the new owner wanted it, I bought the Zexel kit:



That "Overhaul Gasket Kit" comes with ONLY the check valves and gaskets. I never removed the lift pump from the IP.

Replacement of the check valves didn't change the fuel starvation symptom of course: I had the wrong Primary filter, and my gauge set test confirmed that the (wrong) Primary filter was the restriction. The Primary "filter" must be an unrestrictive screen ... not paper as is used in the gasoline trucks. The route I took to get to that point was circuitous because there were other things going on at the same time: fuel contamination, and total fuel lines replacement to viton, as well as three tank drops for cleaning.