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Lift pump - choices ?

chris4521

chris4521

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Toronto, Ontario
So i think its time for a new lift pump for my truck. Mine looks original, and I can barely hear it (dont think i even CAN hear it) like i used to before. Used to make an audible buzzing pre-start, now it doesnt seem like it does at all. Truck also doesnt start right up like it used to, takes a second more on the starter to fire.

Ive heard that the 93 lift pumps are the best, but I can't remember why. Why is this??

Shouldn't be too hard of a job to do in the driveway, do you think ? Ive turned a wrench before but im no diesel mechanic.

Thanks guys
 
Easy to change with the 93 lp, slightly more pressure and volume.

Although some people have suggested the Walbro due to similar price but you have to change the plumbing a little.
 
It is easy to replace. Just unplug the wiring harness, loosen the fittings at both ends of the LP - have a jar and/or rags handy to catch the fuel that runs out - shouldn't be much. Best to do on an incline with truck facing uphill.
 
If you do go aftermarket LP I've got the fittings you will need so you won't need to cut your original lines.
Leroy

Welcome to DTR
 
I'd go with the '93 spec lift pump in a mostly stock setup - direct swap with no modding/fabrication.

I started my fresh engine build w/ a '93 spec OEM type lift pump. The fuel pressure gauge (plumbed just before the inj pump) showed only the slightest hint of pulsation (from these solenoid/checkvalve type lift pumps). After installing a Kennedy Diesel chip that raised the max fueling, the '93 lp would let fuel pressure drop to 0.5 - 1.5 psi - and I'd get an occasional fishbite that only happened when fuel pressure dropped below 1.5 psi.

Swapping to the Walbro FRB-5 lp holds fp above 4 psi at my current max fueling. The Walbro's additional pressure & volume causes a 3-5 psi pulsation at idle/low fuel demand. When IP fueling goes above say 45-50 mm3, most of the pulsation goes away. So it appears the OEM fuel pressure regulator on the IP, &/or the return line can't quite return the extra fuel the Walbro is pumping under low fuel demand at idle/cruise.

I'm not certain if these pressure pulses have any negative impact on the IP? The max psi of these pulses appears to be 9-10 psi. Would certainly be interested to hear, from folks on the forum knowledgable on the DS-4 pump, if this pulsation is hard on the IP?

I suspect I can dampen/snub the gauge pulsation with some type of restriction/orifice in the pressure gauge fuel line branch. This should help keep the fp gauge alive, but the IP will still be seeing the actual pulsation.
 
Walbro's specs show max current draw at 2.3 amps. When my engine was out & before I'd looked into these lift pumps current demand, I ran a 12 ga wire lift pump power supply via relay from the battery as I've done on past EFI gasser projects where the fuel pumps pulled far more current & OEM wiring had too much voltage drop. It's certainly overkill for these lift pumps, but at least it takes the temporary load off the OPS, until the OEM lp relay kicks in.

I'll copy the entire specs list below. I see the Walbro website lists an adjustable pressure regulator as an "available option". I'll email them about that. Would guess this low pressure/volume app pressure regulator doesn't have a return, but I'll consult the folks at Walbro.

I'd noticed that with the Walrbo, pressure will bleed down to 0-1 psi overnight - the OEM pump didn't bleed down that low in several days. Had just assumed it had an outlet checkvalve, until scanning the specs below. I may add one as I think maintaining this low positive pressure is a good thing. Then if it starts bleeding down pressure at shut off noticably faster than in the past, you've got flag thrown up to find the leak or other problem.


Performance

Voltage: 12 Volt (9.0 min – 16.0 vdc max)

Minimum Flow Rate: 170 liters per hour (45 gph)

Deadhead Pressure: 56 to 76 kPa (8.0 to 11.0 psi)

Maximum Current Draw: 2.3 amps

Life: >18,000 hours

Dry Lift: 48 inches (120 with optional outlet check valve)

Compatible Fuels: No-lead regular gasoline, premium gasoline, gasoline-alcohol blends, diesel and biodiesel fuels (20% and 100%), and E85

Corrosion Resistance: 96 hour salt spray test (ASTM B-117)

Operating Temperature Range: -40ºF to 155ºF (-40ºC to 68.3ºC)





Electrical

Reverse Voltage Protected

Transient Voltage Protection

Ground: Neutral Ground: Circuit Board is Not Internally Grounded to Pump Body

Electrical Connection: Flying Lead (1); No Connector

Fuse: 5 amp recommended





Mechanical

Inlet & Outlet Size: 1/4-18 NPSF

Inlet Filter Screen: 70 micron

Magnetic Trap: Yes

Outlet Check Valve: None





Available Options:

Adjustable Pressure Regulator 135-631

Outlet Check Valve Fitting 128-3220 (5/16 Hose Barb)

420 micron Filter Screen
 
a 1 ohm 10 watt resistor would probably work real well in line with that, bring the 14V down to 12V, or thereabouts.
I plan on getting one soon, I can give it a try. I also have in cab gauge, which I'll finish up tomorrow. I bought the wrong paint for the gague pod and gauge trim, so gauge is on backseat at the moment, with the pickup and wiring installed.
 
pressure on whatever LP i've used always bled down to zero within an hr after shutdown,right from new,but i never lost prime yet.
the fuel gauge is lots of times erratic(hand is often a blur) this occurs at key on eng off,at idle and cruising,but at times it is also perfectly still on all occasions:dunno:
A new LP will show accurate press only for a short while before the gauge starts bibbbbering again.
 
I'm certainly no mechanic, but found the LP an easy job. The 5/8 flare wrench helps some too.

I put the LP for a '93 on my '98.. seems an improvement.
 
1 ohm resistor at 1.83 amps would drop 1.83V across it and 6.13W, brining the pump down to 12-12.5V, which might allow it to run more smooth at idle low pressure demands. Typically the more voltage the higher pump revs, can pump more, but will hit its internal max regulator quicker at low demand. At lower revs it might not hit the max internal pressure with a small demand. I assume the Walbro has an internal pressure switch that cuts out at 11, and could cause the pulsing pressure Smithville spoke of.

When I get one I'll try that. I was planning to do FTB and Walbro this month, and hopefully an ATT.
 
Those small pressure pulsations will not affect the DS4, and are symptoms of a lift pump that runs continuously with the varying pressure reflecting varying flow: hi-pressure at low flow, normal pressure at normal flow - the oem series of LP's by AC are pump-to-pressure type, where they quit pumping at spec'ed pressure, responding to actual volume of flow - if your AC LP runs continuously at idle, the valves have begun leaking and it is not maintaining spec'ed pressure head - normal operation is pump hard to pressure, stop pumping until flow reduces pressure, pump again, etc, ad infinitum until if fails - which it will, eventually
 
So then i take it ,a guy is better of with a vane or gear type pump with a adjustable press relief valve where the relief valve maintains press,and the pump runs a steady flow.?
 
Thanks GMCTD. Good to know the small (~3-5 psi) pressure pulses don't impact the DS-4. Long as there's no negative impact on the pump, I should be able to snub the gauge response w/ some degree of restriction/orifice in the gauge's fuel line branch.

Both the new '93 spec AC lp & the Walbro appear to pump to pressure, then stop until pressure falls enough to kick them on again. There would often be a few psi pressure remaining after the truck sat for a few days with the OEM type lp.

The Walbro also seems to pump up to pressure & stop, but it appears its internal checkvalves let a little backflow bleed off pressure more quickly than the OEM lp. With the truck not running, the Walbro seems to pulse maybe 1 every 4 seconds or so. The Walbro shows a spec of 48" dry lift, 120" with optional outlet checkvalve. Suppose it's logical that installing an additional checkvalve at the outlet would also slow/lessen any pressure bleed back into the pump, when it has cycled off.

The Walbro's min flow spec is 45 gph, while I've read the OEM type pumps are around 20 gph. This seems to correlate w/ the degree of pulse I see on the gauge with each solenoid throw, for both pumps, pumping from 0 psi, to their kickoff pressure.
 
Isn't the downside to those type of pumps that the inj pump can't pull much fuel thru them when they fail?

bison said:
So then i take it ,a guy is better of with a vane or gear type pump with a adjustable press relief valve where the relief valve maintains press,and the pump runs a steady flow.?
Click to expand...
 
there is allways a trade off somewhere,but these pumps may fail less often.
one more reason to have a fuel press gauge and to carry a spare anyway.
 
Hoesli Diesel recommended the Walbro to me as improvement over the Cummins rotary pump, that I was considering for the FTB mod,

they had no love for the rotary vane pump; Cummins VP-44s die when they don't have constant fuel supply,

For me flow on fail is only way to go, also my set up is parallel lift, Heath h/o on one side of the tee, and Walbro on other, with switched power thru relay for both, I normally run the Walbro, but could run both or other solo if need be, as far as reliability, I'm also a firm believer that we need 10 micron filter before the lift, which will keep out the crud that wears the rubber seats for the check valve.
 
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