Fluxuating fuel pressure - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 11 (permalink) Old 02-04-2008, 11:05 PM Thread Starter
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Question Fluxuating fuel pressure

Dodge 2500, 2001, 24v turbo.
I have a FASS system and recently the pressure would be ok at startup and in park, but when I drive the pressure drops down to 5 psi or below and then starts to climb back up to between 10/14 psi. Under hard throttle the pressure drops then climbs back to around 10 psi when the demand is taken off the engine.
What I've tried: Took the tank off and cleaned it and the in-tank filter screen. Changed the FASS filter. Checked the return valve in the FASS pump body to make sure it wasn't stuck open. Bled the isolator under the hood for the pressure guage.
The pressure, when I first installed the FASS system, used to come up to 15 psi when I turned on the key to wait for the "wait to start" light to go out and the pressure would drop slowly , but now it goes to 15 psi and drops immediately.
Could the diaphram in the VP44 be bad and if so, is it an owner replaceable item? I've heard that there is a thicker diaphram available, but my local Dodge dealer won't even discuss it, unless I take the truck to them.
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post #2 of 11 (permalink) Old 02-04-2008, 11:10 PM
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Well I would do the fuel pump diagnostic...
http://mopar.mopar1973man.com/2002%2...ift%20pump.htm

As for servicing the VP44 there is no part that you can replace... You must replace the entire VP44 as unit...

Michael Nelson - 2002 Dodge Cummins & 1996 Dodge Ram 5.9L Gasser
116K Miles On My VP44 - 4 Years of 2 Cycle Oil Diet! - Mixed at 128:1 Ratio - 25.3 MPG maxed out!
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post #3 of 11 (permalink) Old 02-05-2008, 12:19 AM
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If you do your VP44 eventually make sure you do it yourself. Its really not that hard. you just need the pump press and its a $35 part if you know someone who deals with snapon tools. The dealer will rape you if you take it to them. Also if you do replace it a good on completly reman. is gonna run you between $1500 and $2000. you get what you pay for with them so don't cheep out. The damage might already be done to your VP44 depending on how many times you let it go below 5 PSI. Like mopar 1973 said get your fuel system diagnosed before doing anything else.
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post #4 of 11 (permalink) Old 02-05-2008, 12:55 AM
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5 PSI is certain death for a VP44...

I lost my first one at 8 PSI... So I know that 10 PSI limit is a very safe limit... If your hitting below 10 PSI at WOT remember that 90%-100% of the fuel is being pumped to the injectors and very little remaining for cooling and lubing purpose. This is what causes the VP44 to fail... Then put ULSD diesel on top of it with lower lubricity it certain death below 10 PSI for any length of time...

As for VP44 replacement it not to hard to do... Here is the replacement write up.
http://mopar.mopar1973man.com/2002%2...eplacement.htm

You might try adding a shot of 2 cycle oil to the fuel to help extend the life of your current one till you can get the money to replace it...
http://mopar.mopar1973man.com/2002%2..._cycle_oil.htm

But I would keep an eye on the error codes... Here is a write up on how to dump error codes and how the ECM/PCM self-erase old codes...
http://mopar.mopar1973man.com/2002%2...rror_codes.htm

Here is the injection pump puller...
https://www.thedieselgarage.com/forum...ad.php?t=27380

If you got a 98.5-2000 your going to need a scanner here is a really good scanner for diagnostics on your truck...
http://mopar.mopar1973man.com/2002%2...scangauge2.htm

I better stop...

Michael Nelson - 2002 Dodge Cummins & 1996 Dodge Ram 5.9L Gasser
116K Miles On My VP44 - 4 Years of 2 Cycle Oil Diet! - Mixed at 128:1 Ratio - 25.3 MPG maxed out!
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post #5 of 11 (permalink) Old 02-05-2008, 02:39 PM Thread Starter
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Checked the fuel system. Have good suction and flow. No apparent air leaks. It's almost like the return-fuel-to-the-tank valve in the VP44 is stuck open, or partially open.
BTW, I haven't noticed any decrease in performance. I like the Scan Guage that Mopar1973 recommended, and the idea of adding 2 cycle oil. Maybe I can get some more mileage out of my VP
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post #6 of 11 (permalink) Old 02-05-2008, 03:24 PM
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Your overflow valve might be bad too... This is the proceedure of how to test the overflow valve... Also the fuel pressure could be too high but the only way to find out is to test it with a pressure gauge...


Quote:


DESCRIPTION



The overflow valve is located on the side of the


injection pump (Fig. 58). It is also used to connect
the fuel return line (banjo fitting) to the fuel injection
pump.


OPERATION


Fuel volume from the fuel transfer (lift) pump will
always provide more fuel than the fuel injection
pump requires. The overflow valve (a check valve) is
used to route excess fuel through the fuel return line
and back to the fuel tank. Approximately 70% of supplied
fuel is returned to the fuel tank. The valve
opens at approximately 97 kPa (14 psi). If the check
valve within the assembly is sticking open, fuel
drainage of the injection pump could cause hard
starting.


If a Diagnostic Trouble Code (DTC) has been stored


for “decreased engine performance due to high injection
pump fuel temperature”, the overflow valve may
be stuck in closed position.


DIAGNOSIS AND TESTING - OVERFLOW VALVE


Fuel volume from the fuel transfer (lift) pump will
always provide more fuel than the fuel injection
pump requires. The overflow valve (a check valve) is
used to route excess fuel through the fuel return line
and back to the fuel tank. Approximately 70% of supplied
fuel is returned to the fuel tank. The valve is
located on the side of the injection pump (Fig. 59). It
is also used to connect the fuel return line (banjo fitting)
to the fuel injection pump. The valve opens at
approximately 97 kPa (14 psi). If the check valve
within the assembly is sticking, low engine power or
hard starting may result.
If a Diagnostic Trouble Code (DTC) has been stored
for “decreased engine performance due to high injection
pump fuel temperature”, the overflow valve may
be stuck in closed position.
A rubber tipped blow gun with regulated air line
pressure is needed for this test.
(1) Clean area around overflow valve and fuel
return line at injection pump before removal.
(2) Remove valve from pump and banjo fitting.
(3) Discard old sealing gaskets.
(4) Set regulated air pressure to approximately 97
kPa (14–16 psi).
(5) Using blow gun, apply pressure to overflow
valve inlet end (end that goes into injection pump).
(6) Internal check valve should release, and air
should pass through valve at 97 kPa (14–16 psi). If
not, replace valve.
(7) Reduce regulated air pressure to 10 psi and
observe valve. Valve should stay shut. If not, replace
valve.
(8) Install new sealing gaskets to valve.
(9) Install valve through banjo fitting and into
pump.
(10) Tighten to 30 N·m (24 ft. lbs.) torque.







Michael Nelson - 2002 Dodge Cummins & 1996 Dodge Ram 5.9L Gasser
116K Miles On My VP44 - 4 Years of 2 Cycle Oil Diet! - Mixed at 128:1 Ratio - 25.3 MPG maxed out!
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post #7 of 11 (permalink) Old 02-06-2008, 03:17 AM Thread Starter
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how do I go about setting the (4) Set regulated air pressure to approximately 97 kPa (14–16 psi).
And how do I go about (2) Remove valve from pump and banjo fitting.
I'm sure that you know what you are telling me but I'm, basically a novice concerning your explainations.
I'm not a novice concerning mechanical stuff, but I'm not sure what you are trying to tell me and I do appreciate the help you are providing me.
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post #8 of 11 (permalink) Old 02-06-2008, 01:55 PM
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Quote:
Originally Posted by triker888
how do I go about setting the (4) Set regulated air pressure to approximately 97 kPa (14–16 psi).

Most air compressors have a pressure regulator that you can adjust amount of pressure...

And how do I go about (2) Remove valve from pump and banjo fitting.
I'm sure that you know what you are telling me but I'm, basically a novice concerning your explainations.

Actually the valve is the banjo bolt and the bolt passes through the banjo fitting... Like a bolt in a hole... But remember there is 2 washer. 1 on top of the banjo and one under it...

I'm not a novice concerning mechanical stuff, but I'm not sure what you are trying to tell me and I do appreciate the help you are providing me.
Here is where the overflow valve is at...



It kind of look like this... This happen to be a tapped banjo bolt though...


now you want to put your regulated air pressure at the threaded end... Then see if the air bled pass the check ball inside... That's why you need a rubber tipped air gun. Also then increase you air pressure above 14 PSI to about 16-18 PSI and see if the check ball will open up to allow flow...

Michael Nelson - 2002 Dodge Cummins & 1996 Dodge Ram 5.9L Gasser
116K Miles On My VP44 - 4 Years of 2 Cycle Oil Diet! - Mixed at 128:1 Ratio - 25.3 MPG maxed out!
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post #9 of 11 (permalink) Old 02-07-2008, 02:19 AM Thread Starter
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Most air compressors have a pressure regulator that you can adjust amount of pressure...

I had thought you were referring to the banjo bleed off valve. My mistake.
The light just came on and I can visualize what you were telling me. Thanks.
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post #10 of 11 (permalink) Old 02-07-2008, 02:29 PM
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Quote:
Originally Posted by triker888
Most air compressors have a pressure regulator that you can adjust amount of pressure...

I had thought you were referring to the banjo bleed off valve. My mistake.
The light just came on and I can visualize what you were telling me. Thanks.
Geezzz....

Someone needs anothe cup of coffee this morning... :

Michael Nelson - 2002 Dodge Cummins & 1996 Dodge Ram 5.9L Gasser
116K Miles On My VP44 - 4 Years of 2 Cycle Oil Diet! - Mixed at 128:1 Ratio - 25.3 MPG maxed out!
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