2 Lift Pumps

[rjwest]

OK, I here about and have had injector pump problems.
From what I have been reading, pump problems can be
caused by, 1. Dirt, in fuel 2. Low Fuel volume
causing pump to run hot......

So I decided to install an additional filter
on frame rail. Reading the instructions from
purelator, it says to install on suction side
of lift pump for water seperator function to
work properly. OK Installed to print....

ALL's well, Lost about a lb of fuel pressure
( gage mounted in dash) Min of 3 lbs under heavy pull. OK no problem....So I'm driving over
one of those Super highways with the " Whoops "
built in at each cement joint...
With my truck camper on board, I start to get the roller coster ride at each joint....and I see
fuel pressure droping to zero at each Whoops...

So i'm thinking ( bad move on my part ) that the
additional filter is causing the pump to not be able to draw fuel, seems to happen when i'm down to less than 1/2 tank fuel....

Now the 2 Lift pump question? Can you Send to much fuel to the Inj Pump?
I installed another lift pump between the fuel tank and extra fuel filter. Fuel now goes from tank to pump to filter to pump to filter to inj pump....

I'm getting about 12-13 psi at idle, hav't had a chance to check full load....
Any Expert advise welcome....

[ucdavis]

No expert advice, just my opinion- 12 to 13 is still low pressure & within usual operating range of the components that take this pressure (fuel hose, metal fuel line, lift pump, fuel filter housing (that's the one that might find a leak around the upper o-rings for you where one doesn't exist @ 4#), IP housing & return lines.
I seem to recall seeing upper end of LP range @ 9#. If that's true, you're probably OK. If upper limit is lower, you might check on fuel return lines occasionally (return from IP could backfeed into these if any restriction in return to tank).

[tom.mcinerney]

RJ: A couple months ago I phoned Gomer's with a question about fuel system[i was trying to figure out if all electronic 6.5L engine apps had the same lift pump spec(requirement). They gave me phone number of Delphi {who mfgs most DelcoRemmy stuff, i think} tech servive. I inquired what was diff between $20 and $50 lift pumps, which seemed to have some application overlaps. Delphi svc said that the earlier, cheaper lift pump had output press of approx 6-15 psi{this from memory}. The new $50 pump (which is built within same cannister/housing ), has a mechanical regulator device which limits its output pressure to approx 8 psi {again, memory}. The lower max pressure was said to be easier on the fuel injection pump(???).
I've also added a second filter and lift pump on mine; i intend to use one pump, with second in line as spare....will check press.I think we need 4 psi at FIP input running....To my knowledge there is no downside to an extra pump plumbed in line, fuel will flow thru it with a slight drag...
Also , the dip in press readings over bumps may have been more a matter of the gage needle dipping due to its acceleration , rather than the pump hickuping. But the observation of lower press at lower tank level is probably real; lower inlet press yields lower outlet press, generally.

[ 09-16-2003, 09:53 PM: Message edited by: tom mac 95 ]

[rjwest]

Thanks Tom Mac.....
I am getting about 13 psi max with both lift pumps running.Runs about 9psi at normal speed. With only original running it pulls fuel
through " added pump " but pressure drops to
1 psi on hard pull....
I think i'll just run with 1 pump, and use
2nd pump if pressure drops to low.

May need it to get fuel through filter in cold
weather....

I notice that GM original Pump has lower pressure
than aftermarket....

sure would like to know if higher pressure really
does hurt Inj Pump....

[jbplock]

Originally posted by tom mac 95:
...I inquired what was diff between $20 and $50 lift pumps, which seemed to have some application overlaps. Delphi svc said that the earlier, cheaper lift pump had output press of approx 6-15 psi{this from memory}. The new $50 pump (which is built within same cannister/housing ), has a mechanical regulator device which limits its output pressure to approx 8 psi {again, memory}. The lower max pressure was said to be easier on the fuel injection pump(???)...Tom,

Just curious ... where did you find lift pumps for $20 and $50.

Also, your comment about the lower pressure pump (EP309) being easier on the 6.5 IP is also interesting. Some of us with the Duramax are adding lift pumps to prevent heat/vacuum induced out-gassing from the fuel, but there is a question about how high the pressure should be. I have mine (EP158) set with an external regulator to deliver 0.4 psi to the OEM pump since the Dmax normally runs with a 2-3 inhg vacuum at idle. Some are running higher pressure with no problems…
smile.gif

[tom.mcinerney]

Bill--I was just looking over the listed applications at the GM lift pump section of the Gomer's [TDP advertiser] web page. I telephoned and asked Gomers a question, and they gave me a number to Delphi. I think Gomers may be wholesaling to us...check them out.
The guy from Delphi tech service stated something to the effect that 'when the electronic pumps came online, they found that when the lift pump came up to its regulated pressure , it was somehow difficult for the electronic FIP to operate; the lift pump was modified to decrease its max regulated output from about 14 to about 8'.
However, if the Duramax maintains a constant high-pressure supply to all the injectors, it may not be applicable info....

[ 09-24-2003, 07:08 PM: Message edited by: tom mac 95 ]

[StephenA]

say, what are you guys using to monitor the fuel pressure between the lift pump & the IP? Is it a permanent dash gauage? Also, I went to the Ad page but couldn't figure out which one was Gomer's... Are his pumps AC Delco?
Thanks, Stephen

[rjwest]

I have a dash monted fuel pressure gage..
( Had a Hole left over so I used It).

I have a " TEE" fitting in the fuel line where it goes into the injector pump, easy to cut rubber line and add clamps, 3 inch rubber line to 1/8 copper tubing up to dash, direct reading press gage...

I Know, note supposed to have fuel line in cab...
1/8 inch line minimizes fuel flow..and diesel smells if leaks....electrical gages are also available.... at higher cost....

Nice and reassuring to see fuel pressure....

[Turbine Doc]

Hey RJ try this idea on for size, I'm in thought process for fuel gage myself, shroud the pressurized gage line with a non pressurized one.

Run the 1/8" line inside 1/4" hose or whatever fits, seal the 1/4" hose at the gage back with RTV, then route the open end to where you don't mind a leak so much, but can monitor periodically; that way if you develop a leak it is contained in the hose and run to engine bay or drip can/pan

[StephenA]

Thanks, Guys- who makes the electri gauges- Stewart Warner?

[Turbine Doc]

many vendors auto meter, stewart warner, vdo, do a google search on the web search for gages, check this link

http://www.gauges-ez.com/gauges/0000552_0001749_1.html

and another

http://www.egauges.com/vdo_main.asp?Cart=

[StephenA]

Thanks tbogemirep! Great links for gauges!
Stephen

[jbplock]

Originally posted by tom mac 95:
... The guy from Delphi tech service stated something to the effect that 'when the electronic pumps came online, they found that when the lift pump came up to its regulated pressure , it was somehow difficult for the electronic FIP to operate; the lift pump was modified to decrease its max regulated output from about 14 to about 8'.
However, if the Duramax maintains a constant high-pressure supply to all the injectors, it may not be applicable info.... Thanks Tom, smile.gif

The Delphi comments are interesting. I believe the EP158 is the higher-pressure version while the EP309 is the low pressure model (and more expensive). I have an EP158 on my Dmax but the setup (http://community.webshots.com/album/77018086bLHHHC) has an adjustable bypass regulator that allows the pressure into the OE pump to be set to about 0.4 psi. The Dmax actually has two pumps – a low pressure and a high-pressure pump. With the common rail system, pressure varies from (IIRC) about 5000 psi to 23000 psi depending on load. The stock Dmax is also suction system that runs about 2-3 inHg into the OE Pump. Some of us have added extra filters and the lift pump compensates for vacuum/heat induced outgassing in the filters and fuel lines.

(For those who don’t frequent the Duramax forums and are interested in this subject, there are a multitude of LP posts over there)

I have also been looking for a electric vacuum/pressure gauge that can be mounted in the cab with the sensor mounted near the OE pump inlet. So far I haven't been able to find one. Has anyone ever seen anything like this?

[StephenA]

jbplock:
Check out http://www.racerpartswholesale.com/stewarn6.htm

"Electric Fuel Pressure Gauge-

High Torque Gauge Movement
Front Sealed - Protected From Moisture
Advanced Lighting - Easy To Read Graphics
Custom Engineered, Ultra Bright Balanced Pointer
Maximum Viewing Area
Available With Silver, Black or White Dials and In Two Diameters - 2" and 2 5/8", in 0 - 15 psi and 0 - 100 psi Ranges"

It's about 80 bucks compared to $50 for the one's I've seen that bring diesel into the cab...

If you get one, would you let me know how you like it? I'm considering it. Also, check out

http://www.egauges.com/vdo_main.asp?Cart=


Any idea what pressure would be ideal for my 92 6.5l TD mechanical?
Stephen

[jbplock]

Stephen,
Thanks for the links. The Stuart Warner gauge looks nice but I'm looking for one that reads both vacuum and pressure. The Dmax can go into vacuum operation under hard acceleration even when running a lift pump.

Regarding pressure on your 92 I’m not sure but I would think the EP158 should work for you.

[StephenA]

Yep jbplock, that's what's on it. I'm just trying to verify that it's treating my IP right. Engine runs great, but it was almost as good for the week it took for me to find & fix the OPS which had caused the lift pump not to function. Now it runs fine, but I'm just wondering when I should replace it. Let me know if you find your gauge.
Stephen

[jbplock]

Stephen,

If I remember correctly the 92 6.5's didn't have the relay between the OPS and the lift pump. On later models a relay was added between the OPS and the LP to protect the switch. Some folks have added relays on the older trucks to prevent the premature failure of the OPS. Having the fuel pressure gauge is also a good way to monitor LP operation. This is the reason I want the vac/pressure gauge on my setup. The engine will run if the LP fails so it’s nice to easily see if it’s working.
smile.gif

[StephenA]

Makes good sense, Bill. My 92 has the LP relay stock, which I replaced along with a 20A fuse when I replaced the OPS. An electronic vacuum/pressure gauge would be perfect for monitoring not only the LP & OPS setup, but might also alert us to the dreaded clogged fuel cap syndrone, which collapes the tank & fuel lines...
I'll keep my eye out for this gauge & we can keep eachother posted on what we find?
Stephen :cool:

[tom.mcinerney]

Bill- Regarding, "I have also been looking for a electric vacuum/pressure gauge that can be mounted in the cab with the sensor mounted near the OE pump inlet." I've looked in the 'Digikey' electronic component catalog. [www.digikey.com, Digikey Corp, Thief River Falls, MN 56701-0677]. Didn't find what you call for, but close:
1.)A Co. called 'SenSymICT' sells a 'digital pressure gage', reads -30inHg/100PSIG, resolution 0.1psi. It's a gage that threads into 1/4" npt with 2-AA batteries....$270.00 {pg1151/T033}
2.)A Co. called 'All Sensors' markets a pressure sensor which measures +/- 30 in H2O [figure 10inH20=.4psi, 28inH20=1.0psi]; $85-100. Unfortunately this is only a sensor--it would require some interface to get a reading{it needs a gauge and electronics to mediate}; since its operating temp limit is -25*C to plus 85*C, it would need to be mounted outside the engine compartment(frame-rail/bumper?). {pg1153/T033}
3.) A Co. called 'World Magnetics' sells sensitive 'vacuum switches', with ability to adjust set point {trigger vacuum} from 3" H20 to 12 psi , both normally open and normally closed contacts; $16.{pg1164/T033}
4.)Additionally, Motorola (mfgr of press/baro sensor} sells precision, temperature compensated pressure sensors, with ranges of 0-1.45psi, 0-7.25psi, 0-14.5psi, etc. , for $8-20, and their operating Temp range is -40*C to +125*C.
These, or a combination might help. A surplus aircract instrument supplier might help.
Possibly better approaches would be to contact the sensor manufacturers and see if they suggest circuits for their sensors, or if they refer you to their clients which package the sensors with readouts....Also could contact 'Omega', a lab/process instrumentation/control outfit;
http://www.omega.com/, or http://www.omega.com/literature/transactions/volume2/editorial.html {These puppies are guaranteed to provide a solution a some price!}
However, before doing all that , give a good read to the posts by "TBOGEMIREP"(Tim, member # 4442, from Gautier) from 9/30/2003-10/2/2003, on the topic initiated by 'jlog' on 7/26/2003, "fuel filter", in this '6.5L forum'. Tim mentions Racor sells 'differential pressure switches, specifically designed to indicate when a filter is clogged, so you have an idea of the pressure, and don't have to change elements at arbitrary intervals.