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PostPosted: Sun Nov 25, 2007 12:50 am 
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Yes - your "At idle, opening the bleeder screw exhibits exactly what I'd expect: there is positive pressure in the filter, and fuel dribbles out the bleeder." tells the tale - at 5psi lift pump pressure, everything east of the fuel manager head should be quickly drenched with Diesel fuel, not just a dribble, depending on your perspective to 'open'.

5psi at lift pump = 5psi at fuel manager head input = 5psi in filter element = 5psi at bleeder valve = 5psi at fuel manager output = 5psi at CP3 input

5psi @ 72gph?

72gph @ 72mph = 1mpg, no matter how you cut it - your 2.8L engine would barely consume 72gph at WOT for an hour - I would venture out on a limb, here, and say it will consume much less at idle.

Seems to me as tho you do need a fuel guage on it, eh?

I do see one reference to the P74029 for 2-3psi @ 16gph - still should keep up at idle

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PostPosted: Sun Nov 25, 2007 1:28 am 
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George,

I think you have touched on an intersting subject . The selection of Lift pump characterisitics for the Libby CRD. My (engineer geek) point of view follows;

All pumps have a performance reationship between flow and pressure. Typically, the more flow, the less pressure you get. This can bee seen in "pump curves", for example.

See http://www.facet-purolator.com/solidstate.asp where the selonoid type pump curves are shown (hard to read, unfortunately).

The point is, that your carter makes 72 GPH at near zero psi outlet pressure ( 16 GPH at 3 psi). The highest pressure it can make is with zero flow (what I call "dead head" pressure) is going to be around 5 psi, maybe??. The question is, can it make more pressure at a given flow rate that the negative pressure from the CP3?

Keep in mind that (hard)vacuum produces a maximum pressure differential to atmosphere of -14.7 psi (sea level). So, if the mechanical CP3 pulls negative pressure on the outlet of the filter, even at low flow rates the Carter might not be able to push fuel through the filter with enough pressure to prevent negative pressure at the filter bleed point.

What is odd about your case is that you have two different pressures at idle. Does it take a while for the Carter to re-pressurize the system after the filter? Is the Carter just barely able to push fuel through the filter at all and changing temperatures, etc can have an effect?

I think it will be interesting to know what the pressure drop across our filters are and the typical flow rates are.
It would be great if someone could draw a schematic of the fuel system, too.

And yes, it would be good to know if the Airtex / Dodge intank pump can produce sufficient pressure to provide positve pressure conditions at the filter outlet.

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PostPosted: Sun Nov 25, 2007 1:54 am 
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gmctd wrote:
72gph @ 72mph = 1mpg, no matter how you cut it - your 2.8L engine would barely consume 72gph at WOT for an hour - I would venture out on a limb, here, and say it will consume much less at idle.

Seems to me as tho you do need a fuel guage on it, eh?

I do see one reference to the P74029 for 2-3psi @ 16gph - still should keep up at idle


I don't follow you here at all, gmctd. If you're trying to say that the CP3 won't pull more fuel through it than the engine consumes, I'd have to disagree: there's a fuel return line to, well, return the fuel to the tank that isn't used by the engine.

Where did you see the reference for that pump only doing 16gph? Is NAPA blowing smoke? The Carter site didn't have the specs, but NAPA had a sheet they were reading from.

Bill wrote:
What is odd about your case is that you have two different pressures at idle. Does it take a while for the Carter to re-pressurize the system after the filter? Is the Carter just barely able to push fuel through the filter at all and changing temperatures, etc can have an effect?

I think it will be interesting to know what the pressure drop across our filters are and the typical flow rates are.
It would be great if someone could draw a schematic of the fuel system, too.

And yes, it would be good to know if the Airtex / Dodge intank pump can produce sufficient pressure to provide positve pressure conditions at the filter outlet.


Bill, yes, it does take a bit of idle time for the Carter pump to return the main filter assembly to positive pressure. I appreciate your explanation about the different pressures and flow rates, and what you say makes sense. Another useful bit of information might be what the rated flow is across the stock filter: several people are using the Racor 245, which flows 45gph. So if that Carter really were able to flow 72 gph (from what I've seen, I think the 16 that gmctd cited is probably more accurate), then the only way there would be vacuum at the bleeder would be if the filter were somewhat clogged and the bleeder was on the opposite side of the filter medium from the lift pump.

But in the end, I come back to my main question: for people who have installed various lift pumps, look at the bleeder after running the engine under load. Does it pull vacuum? If you have a pressure gauge, does it still read positive? It'd be nice to know which lift pumps are able to keep up with the input of the CP3, so we all know which pumps, or roughly which specs, will work with the self-bleeder circuit.

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PostPosted: Sun Nov 25, 2007 10:48 am 
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I believe the key to a lift pump keeping a positive head at the inlet to the FI pump will be the volume of fuel return to the tank. At 82 mph my CRD only consumes 3.33 gph so in theory any pump could keep a positive head. The reality may be far differant depending on the return, line loss, etc. I have no idea what the line size and fittings are on the fuel intake but at higher rates this could be a factor, as well as any restriction at the prefilter. Even the fuel level will make a differance in the head pressure if the pump is higher then the tank.

If you want a positive head at all time we need to know the max output of the FI pump then engineer the lift pump output to supply that much volmue plus 10% or so at whatever pressure you desire at the FI pump suction.

It may well be that it's not important to keep a positive head at high speeds as the CP3 is designed to run with a negative head anyway.

Botton line though, is that for pumping the best solution is an in tank pump with a coarse filter screen to keep the rocks and alligators from damaging the pump.

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PostPosted: Sun Nov 25, 2007 12:36 pm 
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litton wrote:
Botton line though, is that for pumping the best solution is an in tank pump with a coarse filter screen to keep the rocks and alligators from damaging the pump.


I agreed with everything you said up until this point. To me, an in-line pump that flowed 40gph with 4 psi minimum at the entrance to the CP3 would be better than an in-tank pump that flowed 10 gph and allowed inlet pressure at the CP3 to drop below 0 psi. All those things being equal, the in-tank lift pump is better in some other ways, though.

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PostPosted: Sun Nov 25, 2007 1:48 pm 
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How about this line of reasoning, for discussion purposes;

1. No (large) increase in flow rate is desired. Right?
2. All points in system are to be under positive pressure, except fuel tank at atmospheric pressure.
3. Adding a lift pump will increase pressures downstream and increase flow rate where the two (flow/pressure) are inversely proportional. (You can have much higher pressure or much higher flow, not both). We want the lift pump to pressurize the system, not flow fuel around the circuit faster, right?
4. Adding a valve (or orifice) on the return line, near the tank can serve to reduce flow and increase pressures upstream of the valve.
5. Reducing flow with a valve (or orifice plate) on the return is ok because there is plenty of flow capacity with two pumps (CP3 + lift).

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PostPosted: Sun Nov 25, 2007 2:33 pm 
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Bill.Barg wrote:
How about this line of reasoning, for discussion purposes;

1. No (large) increase in flow rate is desired. Right?
2. All points in system are to be under positive pressure, except fuel tank at atmospheric pressure.
3. Adding a lift pump will increase pressures downstream and increase flow rate where the two (flow/pressure) are inversely proportional. (You can have much higher pressure or much higher flow, not both). We want the lift pump to pressurize the system, not flow fuel around the circuit faster, right?
4. Adding a valve (or orifice) on the return line, near the tank can serve to reduce flow and increase pressures upstream of the valve.
5. Reducing flow with a valve (or orifice plate) on the return is ok because there is plenty of flow capacity with two pumps (CP3 + lift).


Good synopsis, Bill. Where it starts to break for me is in #3: I think perhaps we *do* want to increase the flow around the circuit, because that's the only way we'll get slight positive pressure at the entrance to the main pump without overwhelming it. For one thing, increasing the flow to some degree might be the best way to circulate trapped air back to the tank and get rid of it. Too much circulation, I suppose, and you end up stirring up the tank too much and introducing bubbles, which defeats the purpose. Restricting (any more than the current change in line diameter) the ability of the main pump to discharge fuel back to the tank seems like the wrong thing to do, but I've been wrong before. Or at least my wife tells me so. Frequently. In fact, she just told me I was wrong about this. Nope, never mind...I was wrong about what she was talking about.

The ideal lift pump would be regulated such that it provided a relatively even range of pressure (between 2-4 psi) at the CP3 entrance no matter what the overall demand was. I don't know if these little solenoid units regulate pressure at all...it wouldn't surprise me if the only regulation there was that they can't exceed a certain amount of pressure because the design just isn't that good. Why they bottom out at 0 psi has already been well described by others. It probably wouldn't be difficult to find a pressure regulator and regulate a relatively massive pump, but that promises to be expensive.

All I'm trying to do is find out some other data points: my Carter in-line pump doesn't keep up with demand. I'd LOVE to hear whether the in-tank Dodge pump, the Facet pump someone else has used, or any other relatively inexpensive designs are able to keep a bit of pressure at the filter even under load. Anyone?

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PostPosted: Sun Nov 25, 2007 3:05 pm 
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The facts, ma'm - just the facts.............

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PostPosted: Sun Nov 25, 2007 4:25 pm 
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It may not be a problem if a slight vacuum is present at the pump inlet, because it might take more than a certain amount of vacuum to draw air into the system. This is not a fact or a statement, just a mention of a possibility. I know with vacuum leaks, sometimes it takes more than a certain differential away from atmospheric pressure before the leak exhibits itself.

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PostPosted: Sun Nov 25, 2007 5:14 pm 
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chrispitude wrote:
It may not be a problem if a slight vacuum is present at the pump inlet, because it might take more than a certain amount of vacuum to draw air into the system. This is not a fact or a statement, just a mention of a possibility. I know with vacuum leaks, sometimes it takes more than a certain differential away from atmospheric pressure before the leak exhibits itself.

- Chris


Good point. And provided the "inadequate" lift pump doesn't provide too much of a restriction when the CP3 is wanting full flow, any additional pressure should help.

gmctd, those are nice pictures. Other than the pressure gauges, I have no idea what you're trying to show me. I gather you want me to get a pressure gauge. If I put one under the hood, it'd be hard to read when I'm flooring the Jeep at speed. If all you're trying to say is that it would be easier to have a gauge than to open the bleeder, fine. But I'll confess to not understanding your point.

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PostPosted: Sun Nov 25, 2007 6:09 pm 
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Put a hose on the bleeder valve nipple - other end of the hose in an empty clear water or coke bottle - open the bleeder - turn the key to ON-OFF-ON, lift pump will run 22 seconds - 70gph, no head, that lift pump should fill that 16oz bottle in ~10 seconds .

**********************************OR***********************************

Place either of those guages on the bleeder nipple - anything above 0 (Baro) is +pressure - anything below 0 (Baro) is -pressure, or vacuum, since indications on that guage will be guage pressure, or psig, based on local ambient Barometric Pressure

1rst method you're still guessing

2nd method is just the facts

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Cummins LP module, Fleetguard filter, Filterminder
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PostPosted: Sun Nov 25, 2007 10:08 pm 
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Okay, gmctd...I understand what you're getting at now. However, I don't believe that I need that level of fact. It's enough to know that I have a fair amount of vacuum at the filter now, with the lift pump running, to know that the flow rate (16 or 72 gph or whatever it ACTUALLY is) is insufficient. I don't need to know what the exact underpressure is since I know what vacuum looks like. Those are facts, too.

Please, someone with a different lift pump from my Carter...tell me (whether via a gauge or via just looking at the bleeder) whether your lift pump keeps up with the CP3 when you run wide open for a bit. Especially if you're using the in-tank pump mentioned in this thread, that'd be a really nice piece of information to have.

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PostPosted: Mon Nov 26, 2007 1:20 am 
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Ok, George - I responded Thur 22nov with probable cause and test method -

gmctd wrote:
I'd say the pre filter - but, put a fuel gage in line on the pressure side, see if it pumps ~5psi avg


I responded again with concept and result -
"The concept is beautiful, George - pressure-ize a simple system, and the pressure will be equal at each point in the system.
72gph at 72mph is 1mpg
A fuel pressure guage trumps opinion - put a 20buck guage from autozone on it, post your results, and then we can diagnose any problem"

I responded again with data and test -
"Yes - your "At idle, opening the bleeder screw exhibits exactly what I'd expect: there is positive pressure in the filter, and fuel dribbles out the bleeder." tells the tale - at 5psi lift pump pressure, everything east of the fuel manager head should be quickly drenched with Diesel fuel, not just a dribble, depending on your perspective to 'open'.
5psi at lift pump = 5psi at fuel manager head input = 5psi in filter element = 5psi at bleeder valve = 5psi at fuel manager output = 5psi at CP3 input
5psi @ 72gph?
72gph @ 72mph = 1mpg, no matter how you cut it - your 2.8L engine would barely consume 72gph at WOT for an hour - I would venture out on a limb, here, and say it will consume much less at idle.
Seems to me as tho you do need a fuel guage on it, eh?
I do see one reference to the P74029 for 2-3psi @ 16gph - still should keep up at idle"

I responded again with direct example for testing -
"The facts, ma'm - just the facts.............
22bucks, autozone
20bucks, jcwhitney
220bucks, jcwhitney, my personal favorite "

I responded Sun 25Nov with two test methods -
"Put a hose on the bleeder valve nipple - other end of the hose in an empty clear water or coke bottle - open the bleeder - turn the key to ON-OFF-ON, lift pump will run 22 seconds - 70gph, no head, that lift pump should fill that 16oz bottle in ~10 seconds .
**********************************OR***********************************
Place either of those guages on the bleeder nipple - anything above 0 (Baro) is +pressure - anything below 0 (Baro) is -pressure, or vacuum, since indications on that guage will be guage pressure, or psig, based on local ambient Barometric Pressure
1rst method you're still guessing
2nd method is just the facts"

I'm absolutely stumped, George - you've chosen to ignore my response, and refused to test anything - I absolutely do not know how to help you, at this point - I do know that sitting and reading thru responses will not heal your Jeep - you have to get outside, pop the hood, and apply a little elbow grease to get the job done.

So, I will repeat myself for the at least the fourth time in this thread - with a 30 psi guage the in-tank pump gives steady 9psi pressure at the fuel manager head.

Key On, engine off the needle flashes toward 30psi, then steadies out at 9psi

Key On, engine idling, 10mm3 fuel rate, 4500psi rail pressure = steady 9psi

Key On, 3500rpm rev from idle, fuel rate 70mm3, 22000psi rail pressure = steady 9psi

Key On, 3500rpm leveled out, fuel rate 60mm3, 18500psi rail pressure = steady 9psi

Key On, engine idling again, fuel rate 10mm3, rail pressure 4500psi = steady 9psi

Now - shame on me if I again suggest you go out and hose your system or guage your system to find out what's really wrong with it, instead of wild a** guessing and surmising till the end of the year, but, here it is:

Go out and hose your system, or guage your system, and tell us why yours is the only one that has not responded to auxilliary lift pump installation, out of the ten or so that have done so and succeeded.

That's all I have to offer, George - here it is 4days later and yours is still not functional, and you're still refusing to go out and test it - is it you, or is it me?

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Last edited by gmctd on Mon Nov 26, 2007 3:44 am, edited 1 time in total.

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PostPosted: Mon Nov 26, 2007 2:37 am 
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gmctd,

Thanks for your patient reply. It's nice to get a relatively clear and concise statement of your data, rather than a reply telling me how you think I should obtain my own data. I'm keenly aware that my system isn't working, and it's quite clear that the flow rate of the unit is the issue. Duh. I did a test with the prefilter (removing it) and still saw the same effect I was seeing before. The pump is not pushing at higher loads. I asked you where you saw your 16gph figure, which I suspect is truer than the 72gph figure that you quoted, and you didn't reply. You respond with things like "72gph @ 72mph = 1mpg, no matter how you cut it," which is clearly not true because the pump flows more fuel than the engine uses.

I've gone back through your posts in this thread since I first started asking questions, and I didn't see much in your posts that helped me understand how your system is performing. There was this:

gmctd wrote:
I have no input on that, Dan, having ridden in the Jeep less than 10 times, and only three of those was I briefly driving it - I haven't driven it since installing the lift pump.

I did install a 30psi guage on the fuel manager head for long-term testing - the module immediately pumps 9psi at WTS - it maintains 9psi for a period of time after shut-down, indicating the anti-drainback valve is functional, and no system leakage
Which doesn't really say anything about the pressure under load. But perhaps if you go back and edit it, it'll say what you intended.

Then there were pictures from JCWhitney without an explanation, and no clarification on request. Your suggestion of seeing how fast I could flow a bottle with my lift pump is perhaps a good one if I were trying to prove that my lift pump flows x gph, but I'm not: I know it doesn't do what I need it to, hence my requests to get information about pumps that do work. Heck, I even said that I believed your cited flow rate for this pump over what NAPA told me. I haven't ignored anything, at least not on purpose. I haven't needed to test anything because I know what I have doesn't work...I don't need to know how badly it doesn't work if it doesn't work.

No offense, dude, but chill out. You're a little cryptic at times when you're posting, which makes it hard for idiots like me to understand you. Sincere thanks for posting what you do know, and for doing the research on this in-tank solution. Your last post in particular is actually informative.

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PostPosted: Mon Nov 26, 2007 3:29 am 
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Well put, George -

The testing is to prove why it is not working - you don't know why or you wouldn't be posting, right? I don't know why because I'm umpteens of miles from your Jeep - but I do know troubleshooting procedures that work well, local or long-distance - trying to prove the pump will flow 72gph, by filling the 16oz bottle in the alloted time, you're proving it's capacity - if it doesn't fill the bottle, it's over-rated at point of sale, and under-rated at point of use - if it does fill the bottle, time for the next step - posted test results lead to the next steps, forward or back.

I posted 'put a guage on it' three times - then I posted three suitable guages that measure both pressure and vacuum, two very cheap but ideal for troubleshooting this type problem

It's a simple problem - we shoulda had it solved last Thursday - that's frustrating to me, knowwhuttimean, George?

And btw - I won't post a figure and say 'steady pressure' if it drops anywhere past key On, engine off - the actual operational figures were for another thread

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Pricol EGT, Boost
GDE Hot '11; EDGE Trail switched
SEGR; Provent; Magnaflow;
Suncoast T\C, Transgo Tow'n'Go switch;
Cummins LP module, Fleetguard filter, Filterminder
2.5" Daystar f, OME r; Ranchos; K80767's, Al's lifted uppers
Rubicons, 2.55 Goodyears
Four in a row really makes it go


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PostPosted: Mon Nov 26, 2007 7:37 am 
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I've been MIA for about a week doing other things and am trying to catch up :wink: I have that same posi-flow napa pump and here are my two cents worth on your problem. I get more then a dribble out the bleeder at idel so I think you have a problem at speeds :cry: It's not rocket science, I think you have a air leak, restricted line or bad pump 8)

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Joe Romas wrote:
I've been MIA for about a week doing other things and am trying to catch up :wink: I have that same posi-flow napa pump and here are my two cents worth on your problem. I get more then a dribble out the bleeder at idel so I think you have a problem at speeds :cry: It's not rocket science, I think you have a air leak, restricted line or bad pump 8)


Thanks, Joe. That's a useful data point. After a hard run, if you open your bleeder does it suck in, or is it still pressurized?

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PostPosted: Mon Nov 26, 2007 12:14 pm 
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Vacuum - any reduction in Baro pressure - should never be at the bleeder - if so, the system is restricted = fuel filter is plugged, line is blocked - even at that, you should never see it with engine off, no matter how fast you jumped out opened the hood and cracked the valve, unless the system is severely plugged, where the engine doesn't run well off-idle - small system = small volume - should bleed down quickly.

It can be more evident if engine is running, as the CP3 is designed to get you home - it is spec'ed for draw-from-tank service, so the internal lift pump can develop 20" vacuum at higher rpm

Any lift pump with an anti-drainback function will have a valve to seal the line when power is off - this can be a ball in vertical-only mounted pumps, or for multi-positional mounting, a spring-loaded disk in low-volume low-pressure systems or a spring-loaded ball in high output systems.

Adding a lift pump with anti-drain-back will result in system vacuum at fail - takes positive pressure to open the valve - should only be in inches of water "H2O, but that is determined by the design specs for volume and pressure - can be in "HG, not good for this system.

If the pump was orally tested for flow-thru, that is the slight resistance felt B4 flow began - some even make noise like a duck-call - the greater the resistance, the greater the resultant system vacuum at fail - you will see that slight vacuum at the bleeder when lift pump fails - the CP3 can handle that.

Vacuum at the bleeder, dribble at the bleeder - will replacing the add-on pump do the trick - will changing the fuel filter do the trick - will removing the piece of rubber tubing, lost during installation, from the line do the trick - will removing the crimped bend from the rubber tubing do the trick - will dropping the tank to remove that june-bug or beetle from the fuel-pickup tube do the trick - questions, questions.....................

_________________
'05 CRD Limited
Pricol EGT, Boost
GDE Hot '11; EDGE Trail switched
SEGR; Provent; Magnaflow;
Suncoast T\C, Transgo Tow'n'Go switch;
Cummins LP module, Fleetguard filter, Filterminder
2.5" Daystar f, OME r; Ranchos; K80767's, Al's lifted uppers
Rubicons, 2.55 Goodyears
Four in a row really makes it go


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PostPosted: Mon Nov 26, 2007 12:40 pm 
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LOST Junkie

Joined: Thu Nov 24, 2005 6:22 pm
Posts: 698
Location: Oregon, USA
gmctd wrote:
The testing is to prove why it is not working - you don't know why or you wouldn't be posting, right?


This is where I think we're not connecting: I *DO* know why. Either my lift pump is defective and/or the Carter 74029 model has insufficient flow. And a gauge wouldn't tell me which of those two possibilities is correct. I don't need to know to what degree mine isn't working, but it is helpful to know whether others have pumps that are working and what model they are. That's why I've been asking for that information and not heeding your advice to throw a gauge on it. You helped me out on the SEGR build, and I have a lot of respect for knowledge and expertise you have to offer. I'm not completely naive, though, and I just happen to disagree with you on this one that a gauge is the answer.

If you can tell me where you saw the 16 gph spec for the 74029, that would be helpful.

gmctd wrote:
Vacuum - any reduction in Baro pressure - should never be at the bleeder - if so, the system is restricted = fuel filter is plugged, line is blocked (SNIP)


I've always had vacuum at the bleeder after a hard run, at least since I have been testing how much air is in the filter. I thought I remembered others noting the same thing. I would always expect vacuum at the bleeder when the system is running unless I had a good lift pump. Since there is some vacuum there and at the filter head while the engine is running, and since the filter head conveniently collects a small reservoir of air under partial vacuum while running, it takes a bit for the vacuum to bleed down. Also, I would never expect it to bleed down completely because there is a small column of fuel between the filter and the tank that will cause a slight vacuum.

But if you have a lift pump, and it is operating sufficiently, I'd expect two things on opening the bleeder after a hard run:

1. If you open the bleeder soon enough, you should see a slight pressure at the bleeder
2. I wouldn't expect to see a reservoir of air in the filter head unless there was a leak before the lift pump (haven't found one) or there was heavy aeration in the fuel (shouldn't be because the tank is nearly full of biodiesel) or the heater had vaporized some fuel (shouldn't have because it is unplugged and I use biodiesel).

If you're telling me that a normal Jeep CRD system doesn't act like mine does even without a lift pump, that again is a useful piece of information to have.


PS- I want to make a public statement that I am not anti-guage. In fact, some of my best friends are gauges. Gauges should have the same rights and freedoms the rest of us have. The Anti-Guage Coalition (AGC) is, in my opinion, wrong in their stance that "guns don't kill people, gauges do!" However, I am also pro choice on gauges: I think it is every man's right to choose whether to adopt gauges or abort them. The analog/digital debate is another matter entirely. :wink:

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George Reiswig
2005 Jeep Liberty CRD
Suncoast, SEGR, lift, InMotion tune, homebrew B100
At 138k, new head & gasket, timing belt, rockers and swearing vocabulary


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 Post subject:
PostPosted: Mon Nov 26, 2007 12:49 pm 
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Joined: Sat Jun 23, 2007 1:41 am
Posts: 396
Location: Tucson Arizona
I am having a hard time gauging your reactions, G. :roll:

I have been looking at liquid pressure transducers in omega, autoparts places, ebay, etc. Nothing under $35, most are $100+.

GMCTD... I am not sure a boost gauge designed for gas pressure measurement will survive exposure to diesel?

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----------------------------------------------------------------------
06 CRD LTD - Suncoast TC- Shift Kit - Spicer UJ - FRKNLIFT - F37 - Magnaflow - 22.0 City - 24@65MPH - Fumoto F-102 - AUX T Cooler - Tank Lift Pump


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