Engine/Transmission (1998.5 - 2002) upside down lift pump

[Chasweaver]

Another Lift Pump with a twist. Stock pump,stock location. For a year was pumping 14 to16 lbs solid as a rock. Most pumps draw down at wot my picks up.



Now it idles at 6 and when I put my foot in it on fwy it jumps to 15 to 18 and hangs in there as long as I have my foot in it. 70 mph overdrive it sets at 9. While in town it is 5 to 8 lbs.

Any suggestions.

 

[GHolcomb]

That is an interesting situation. In my mind that would be the preferred way the pump should work. I wonder what you would see if you could check the voltage and current draw of the pump at idle and wot?



My last lift pump would start at about 15 psi when you first start the truck, then after about 30 seconds it would drop to around 3 psi and just stay there.



I took that pump apart and the pump looked perfect, which leads me to think something must be happening with the motor in the pump. I haven't read any posts that venture a guess about why the pumps go bad.



You situation seems to indicate that the computer is giving the lift pump a little more juice as the rpms go up.



Maybe others have a good explanation!



Greg

 

[GCULP]

just another guess, but what kind of shape are you're batteries in? if they are weak then I would think the increased alternator speed is sending more voltage and current to the pump. Do any other electical items like the heater fan speed up at higher RPM's?

 

[Fishin Guide]

When mine was doing that same thing it turned out to be a faulty bypass valve in the lift pump. New pump, issue gone.



Dave

 

[Gary - K7GLD]

Can anyone here spell "C-A-V-I-T-A-T-I-O-N"?



Many of the OEM lift pumps have a tendency to cavitate at their highest PSI point - and then, once flow increases and PSI drops as engine fuel demand increases, cavitation stops and near normal PSI returns...



I'd like to have a dollar for each perfectly GOOD LP that has been tossed due to fuel cavitation - only to be replaced by a new one that quickly does EXACTLY the SAME thing! :-laf



I have one of those donated to me by another member here due to the symptoms in the lead post in this thread - found nothing mechanically wrong with it on disassembly - installed it on my truck and ran it for 40,000 miles, until replacing it with a Walbro purely as a test - the pump was still operating perfectly, and is still residing down on my frame rail as emergency backup in case the Walbro takes ill...

 

[rotohead]

Can anyone here spell "C-A-V-I-T-A-T-I-O-N"?

Many of the OEM lift pumps have a tendency to cavitate at their highest PSI point - and then, once flow increases and PSI drops as engine fuel demand increases, cavitation stops and near normal PSI returns...

I'd like to have a dollar for each perfectly GOOD LP that has been tossed due to fuel cavitation - only to be replaced by a new one that quickly does EXACTLY the SAME thing! :-laf

I have one of those donated to me by another member here due to the symptoms in the lead post in this thread - found nothing mechanically wrong with it on disassembly - installed it on my truck and ran it for 40,000 miles, until replacing it with a Walbro purely as a test - the pump was still operating perfectly, and is still residing down on my frame rail as emergency backup in case the Walbro takes ill...

Gary, I'm just a slep here but why would it work on your truck but not on the OP's?
Chuck

 

[rotohead]

Gary, I'm just a slep here but why would it work on your truck but not on the OP's?
Chuck

Never mind... I thought I read the OP had a different filter system and higher BOMBing level. The OEM pump just can't handle anything other than mild BOMBing of any kind.
Chuck

 

[BTowler]

Gary, cavitation=failure! Any time you have cavitiation the air bubbles produced will start to eat away at any surface they contact, look at a boat prop and you will get the idea.

 

[JKinney]

Gary please help me with this cavitation. I left maine with 14 psi, 12 psi under load, on a pump that has had those #s for 20 thousand miles on the rail with 1/2" line right to the vp 44. 400 miles south and pressure drops to 6 psi cruising at 65. It stayed there till I pressed on the throttle to pass and it jumped right to 12. 5. The pump ran great for another 150 miles then it dropped to 3 psi. I stopped the truck shut her down hit the ignition as in pump priming, the pressure jumps to 14. 5 for 1 sec then drops to 3. I drove the truck three miles to my destination, and installed a campain pump, which starts at 11 runs at 9 and drops to 7 under heavy load. How do I get the old pump to run properly again. I did have this cavitaion problem once just prior to departing, so I replaced the fuel filter.



Now I have two cavitation pumps on the shelf.



Fass or walbro which do I buy this week.....

 

[Gary - K7GLD]

Cavitation can be caused by several sources - most of which involve some form of flow restriction. At about 16 PSI these OEM pumps seem at the ragged edge of cavitation due to their rotating vane design - as I have visually seen in bench testing using clear tubing to actually see what's happening to flow as varying restriction moves pump operating PSI up and down. I had cavitation problems of my own once, after mixing too much used motor lube with my fuel - the resulting change in fuel composition aggravated the tendency for the fuel to cavitate, and my gauge did exactly as is mentioned in the lead post here. My problem - which I recognized - went away as soon as I diluted my oily fuel with fresh new diesel.



BUT, restrictions in the tank fabric filter, due to clogging, kinked line inside the tank, clogged screen inside the LP, clogged engine fuel filter - and a similar list of other restrictions can all cause cavitation problems - and the most clear indication that there is a SYSTEM problem, rather than a LP problem, is when installing a new one doesn't fix the problem!



One thing I did with my own pump/fuel system, was to install an external fuel flow bypass valve - it's primary function was to allow fuel to flow AROUND both the OEM LP and the pusher pump I had added:



#ad




The mechanical design of the above bypass provides enough added PSI leakage to drop overall system PSI slightly, and moves that PSI a bit further away from the fuel's natural cavitation point with the OEM pumps - but not so much as to sacrifice overall system functioning PSI.



Another thing that seems to help avoid cavitation with the OEM LP, is to relocate it down somewhere near the fuel tank - this affects it's performance by making it a "pushing" pump instead of a "sucking" pump - which better suits it's basic function anyway.



As to the "best" pump type - as a test, I am now using a Walbro GSL392 - mounted back by the fuel tank where my Carter pusher pump used to be - the OEM LP which had already been relocated to the same area is still there, but disconnected electrically, and the Walbro simply pushes fuel AROUND it via the bypass setup I mentioned earlier. The Walbro has it's own bypass, and if it fails, it only takes a couple of minutes to transfer power from the Walbro over to the OEM LP, and away we go!



#ad






Good luck with your system - I'm sure you'll get it all worked out...

 

[Chasweaver]

Thanks to all that answered, Yes my Battries are good, I replaced the fuel filter I unplugged the electrical connection to the lp and re-connected. I still do not trust it.

I want to relocate the lp to the frame. I cannot find barbed hose fittings that fit the lift pump instead of the Banjo fittings. No one local can help me.



Gary I see you show threaded fittings on you old lift pump. Can you give me info on what and where to obtain them. . I am told they are Metric.

Thank you Charlie

 

[Fishin Guide]

Thanks to all that answered, Yes my Battries are good, I replaced the fuel filter I unplugged the electrical connection to the lp and re-connected. I still do not trust it.

I want to relocate the lp to the frame. I cannot find barbed hose fittings that fit the lift pump instead of the Banjo fittings. No one local can help me.



Gary I see you show threaded fittings on you old lift pump. Can you give me info on what and where to obtain them. . I am told they are Metric.

Thank you Charlie

Call this guy. www.vulcanperformance.com



He'll have everything you need.



Dave

 

[Gary - K7GLD]

Gary I see you show threaded fittings on you old lift pump. Can you give me info on what and where to obtain them. . I am told they are Metric.



Thank you Charlie

Charlie, I cheated, and found brass fittings that were very close to the LP thread size, then carefully cleaned out the LP threads, applied JB Weld thinly to the threads and threaded them together. No leaks or related problems so far - and I use the same setup on several other similar assemblies, including my regulator valve for my Walbro setup:



#ad




I think you will find that relocating the LP down to the frame will make a big difference, unless other unknown system issues continue to cause problems.

 

[Chasweaver]

Again, Thanks for the quick info.



Gary I have no doubt the JB weld would work, however Dave (

AKA Fishing Guide) gave me an address and I ordered 3 of those pesky fittings.



Wow TDR is really great. . Charlie

 

[JKinney]

On going fuel pressure cavitation. As per my sig, my pump has been pushing, its on the rail. Present campaign pump, 10 psi idle 5 full throtle. I just blew air into the suction line into the tank with cap off, reprimed system, no change in numbers. During prime phase pump will push guage to 12. 5 then at ten when running. Had my fuel system been pluged, seems to me 120 psi of air would have changed the numbers at least a little. This is the 4th pump on the rail that has either cavitated or numbers have dropped to an uncomfortable level. I ordered a walbro system last night via internet.

 

[BTowler]

Good choice, you will be very happy with it.

 

[GHolcomb]

I would like to throw my 2 cents in again.



My experience with cavitation in any kind of pump is that it occurs when the pump can not get enough fluid at the input to keep up with the impeller. Thats when you have the cavities created on the back side of the impeller which then collapse and cause the vibration and pitting of the impeller.



It's hard to have a discussion about a pump without talking about flow and pressure, but I have not seen a situation where cavitation starts when the pressure on the output side of the pump is high. My experience is that for a pump to reach it's max pressure, you have to restrict the flow on the output side, which reduces the tendency to cavitate. The pumps I run in my business will not cavitate if I do one of two things: 1. Restrict the output flow which also increases the output pressure and input pressure and the pump is able to get enough fluid at the input. 2. Increase the pressure into the pump, ie, eliminate any restrictions coming into the pump.



I think Gary is right on about any restrictions from the tank to the LP having potential to cause cavitation, but I'm not sure about restrictions on the output side of the pump causing cavitation. Output restrictions will certainly lower the pressure and flow to the injector pump, which is not good.



I think Gary's "by-pass" idea reduces cavitation by the LP due to a restriction on the input side, simply because it allows the pump to self feed itself, but I don't think it will improve the flow or pressure to the injector pump. That would be interesting to test on the bench.



The good thing about the by-pass is that in the event of LP failure, the injector pump does not have to work as hard to pull fuel to itself. Without the by-pass, the injector pump has to pull the fuel through the bad LP which will make the injector pump cavitate and there goes the pump.



I still think that something is going on with the electric motor in the LP, because I haven't seen any indication of a mechanical problem with the pumps I have taken apart. Also, on the ones I have replaced the problem was solved with a new LP. That would seem to indicate that there was not a system problem, but a local problem in the LP.



Gary, I'd love to hear how you bench tested the LP, where you put the restrictions (input, output), what flow were you observing at the pressures you mentioned, where were you picking up the pressures, what was happening with input pressure vs. output pressure, etc. That may me understand what is going on with these pumps a little better!



Thanks!



Greg

 

[Gary - K7GLD]

Gary, I'd love to hear how you bench tested the LP, where you put the restrictions (input, output), what flow were you observing at the pressures you mentioned, where were you picking up the pressures, what was happening with input pressure vs. output pressure, etc. That may me understand what is going on with these pumps a little better!

Greg, I used a 5 gallon container of diesel fuel, clear fuel lines in and out to/from the pump - the PSI gauge and adjustable restriction were on the output side of the pump. I have no doubt that cavitation could be duplicated with a restriction on the input side - perhaps even easier.



As soon as I restricted fuel flow to near the 15 PSI mark, cavitation started, and the resulting foaming of fuel at the pump output side, and total loss of fuel PSI, was clearly visible.



I have a notion to do that demo again, and make a video of it as an educational tool for those unknowing and unfamiliar with the effects of cavitation. I really think the SINGLE and easiest assist for prevention of cavitation is moving the LP down near the tank - that has the greatest potential for affecting the way the pump itself operates - from a "sucker" to a "pusher"!



Let's face it, these Carter pumps are used in a great many installations - but USUALLY in gassers, where the pump is closer to the fuel source - that's where I used mine in my "gasser hotrod" days - and NEVER had any failure issues - but then too, those were the pumps down in the 5-7 PSI range - lot's further away from that "cavitation threshold" that our LP's are operating.



I personally feel the PUMPS are fine, and entirely adequate for their intended purpose - just poorly inserted in the wrong location for our use, and operated too close to their cavitation point - and then the least restriction or fuel viscosity issue puts them over the edge...



Try installing a FASS, Holly or Walbro up on the engine block as are the OEM Carters, and I have little doubt THEY would suffer the same increase in premature failures as do the Carters!

 

[Fishin Guide]

Try installing a FASS, Holly or Walbro up on the engine block as are the OEM Carters, and I have little doubt THEY would suffer the same increase in premature failures as do the Carters!

Hopefully that won't be the case with my cam driven pump!



Dave

 

[EricBu12]

On a cam driven pump, those are pullers, not pushers. Electric pumps are pushers... ever see an ols ford with a cam fuel pum on the engine? Puller...



I hae a FASS located on the rame by the tank and have 15 psi and that is regulated. I don't see less than 12 when full throttle. 15 at idle and cruise... has been on over a year and no problems. only runn the fass and no carter pump.



Gary, am I right that the 10 micron filter on the fass is the same size for the stock canister? I still use the canister but I heard it was not needed. . that true? and how long should I go on the FASS filter miles wise?