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chris
Dodge Dakota
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1/31/2002
00:01:38

Subject: fuel pressure
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Hi all, i have a 99' rt and i just got through installing the powerdyne supercharger and high flow fuel pump. Well in the cold weather ( around 40 degrees) the fuel gauge reads about 58psi. when its this high, the truck is amazingly fast. Well when it warms up ( about 70 degrees) the pressure drops to around 35. I live in Texas, so these random temp. changes are normal. Any ideas on why this happens, and how to keep the pressure up all the time? thanks



bernd
*GenIII*
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1/31/2002
00:41:49

RE: fuel pressure
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Factory Fuel Pressure:
At idle and cruise: 49 psi +/-5psi

Under boost (FMU plate depending): 70-90psi

It should not be falling below 44psi at all. Something else is wrong.

Testing and Inspection

Use this test in conjunction with the Fuel Pump Pressure Test and Fuel Pump Capacity Test.

Check Valve Operation: The electric fuel pump outlet contains a one-way check valve to prevent fuel flow back into the tank and to maintain fuel supply line pressure (engine warm) when pump is not operational. It is also used to keep the fuel supply line full of gasoline when pump is not operational. After the vehicle has cooled down, fuel pressure may drop to 0 psi (cold fluid contracts), but liquid gasoline will remain in fuel supply line between the check valve and fuel injectors. Fuel pressure that has dropped to 0 psi on a cooled down vehicle (engine off) is a normal condition. When the electric fuel pump is activated, fuel pressure should immediately (1-2 seconds ) rise to specification.

Abnormally long periods of cranking to restart a hot engine that has been shut down for a short period of time may be caused by:


Fuel pressure bleeding past a fuel injector(s).
Fuel pressure bleeding past the check valve in the fuel pump module.
Disconnect the fuel inlet line at fuel rail. Refer to Fuel Tubes/Lines/Hoses and Clamps for procedures. On some engines, air cleaner housing removal may be necessary before fuel line disconnection.
Obtain correct Fuel Line Pressure Test Adapter Tool Hose. Tool number 6539 is used for 5/16" fuel lines and tool number 6631 is used for 3/8" fuel lines.
Connecting Adapter Tool-Typical



Connecting Adapter Tool-Typical





Connect correct Fuel Line Pressure Test Adapter Tool Hose between disconnected fuel line and fuel rail.
Connect the 0-414 kPa (0-60 psi) fuel pressure test gauge (from Gauge Set 5069) to the test port on the appropriate Adaptor Tool. The fittings on both tools must be in good condition and free from any small leaks before performing the proceeding test.
Start engine and bring to normal operating temperature.
Observe test gauge. Normal operating pressure should be 339 kPa 34 kPa (49.2 psi 5 psi) .
Shut engine off.
Pressure should not fall below 30 psi for five minutes .
If pressure falls below 30 psi , it must be determined if a fuel injector, the check valve within the fuel pump module, or a fuel tube/line is leaking.
Again, start engine and bring to normal operating temperature.
Shut engine off.
Testing for fuel injector or fuel rail leakage: Clamp off the rubber hose portion of Adaptor Tool between the fuel rail and the test port "T" on Adapter Tool. If pressure now holds at or above 30 psi , a fuel injector or the fuel rail is leaking.
Testing for fuel pump check valve, filter/regulator check valve or fuel tube/line leakage: Clamp off the rubber hose portion of Adaptor Tool between the vehicle fuel line and test port "T" on Adapter Tool. If pressure now holds at or above 30 psi , a leak may be found at a fuel tube/line. If no leaks are found at fuel tubes or lines, one of the check valves in either the electric fuel pump or filter/regulator may be leaking. Note : A quick loss of pressure usually indicates a defective check valve in the filter/regulator. A slow loss of pressure usually indicates a defective check valve in the electric fuel pump.



1997 Dodge Dakota SLT - V6
Supercharged/Intercooled @ 10# w/Nitrous
14.55 @ 96.01mph

chris
Dodge Dakota
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1/31/2002
09:33:34

RE: fuel pressure
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Thanks for the test bernd. The weird thing is, it seems to change with the weather. It starts fine, hot or cold, and it runs fine as well. But when its cold, and when the motor is cold but running, thats when i have the most fuel pressure. Although, i have never seen the pressure go above 58-60, even under wot and boost. I really dont see how a small leak would cause that big of a pressure drop, yet not affect starting or drivability. Could my regulator, or high flow pump be bad? how would i test those as well? thanks for the post, any help is appreciated. (by the way, this is real important... i got a friend with the trans-am firehawk lt1, and he only pulled about a car on me untill about 115 (speed limiter) but that was when my pressure readings were around 35. Now that it went up again, the truck feels like its not running out of gas anymore (somewhat).



Lew360
Dodge Dakota
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2/01/2002
05:26:46

RE: fuel pressure
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Did you actaully hit the speedlimiter? The speedlimiter is actually a fuel shut-off. When you hit the limiter the computer pulls fuel to slow the truck.

99 RC DA R/T, Gibson Headers and Cat-back,APC clear tails, MSD 6a, MSD BTM, IAT adjuster. Powerdyne supercharger.



chris
Dodge Dakota
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2/02/2002
02:03:52

RE: fuel pressure
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no, this was the reading before i hit it. thats whats weird.



drtswinger
Dodge Dakota
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2/04/2002
00:19:18

RE: fuel pressure
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any ideas? anybody? It only does this when its cold outside.... the pressure goes up, and down when its warm. Its not a leak, i checked. thnaks



bassboy170
Dodge Dakota
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6/22/2002
16:25:59

RE: fuel pressure
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hi drtswinger i have the same setup in my truck when idling i have 58psi under boost i goes to 70psi never had my pressure dropped below 55psi even in 95 degree weather so something is definitely wrong. but let me make a suggestion try changing your intank pump to a high flow holley pump and i made a big difference i make 100psi of pressure now at full boost and the truck is an animal hope this helps



MACSR
Dodge Dakota
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4/03/2003
10:13:11

RE: fuel pressure
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92 Dakota has no fuel pressure. New fuel pump,filter and all lines are clear but still no fuel getting past the regulator at the fuel rail, could the regulator actualy be the problem?



Pete Groudas
Dodge Dakota
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12/30/2003
15:30:35

RE: fuel pressure
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Hi,

I am having a problem with my 2000 4.7l Dakota. I have long cranks hot or cold, if I turn crank the engine for a second or two and stop and then try again it starts right up. I checked the manifold pressure and it reads 0psi with key on, engine off, and 49psi running, but tdrops to 0 immediately when the engine is shut off. I am thinking check valve on the filter/Regulator, but I expected some pressure with key on though. Any ideas, thanks?



Dakaty
GenIII
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12/30/2003
16:55:32

RE: fuel pressure
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Many Daks are having this problem. The key is to determine if the fuel pump/check valve assembly is defective OR if the injectors are allowing the presssure to leak down.

Does anyone know of a different test to make the determination other than the one described above? I do not have access to the tools/guages required.

14.63 @ 91.8

Pete G
Dodge Dakota
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12/30/2003
19:19:36

RE: fuel pressure
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I bought the truck used in October and this started around a month later. They do not make it easy to check the filter/regulator since it looks like it is part of the pump assembly and has to be purchased as a set at $200+, plus the hassle of dropping the tank. I think I can isolate the injectors by clamping the source hose at the same time as turning the engine off, however I do not think an injector will bleed off as fast as I am seeing, so I may be wasting my time trying to test for it. I am going to see about finding the adaptor hose specified above or equivalent, otherwise just shotgun the pump assembly unless someone knows if it is servicable?



DesertCoyote
Dodge Dakota
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9/25/2004
20:23:06

fuel pressure
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What is the normal fuel pressure for an 1989 3.9 v6 Dodge Dakota Sport??? Please Help I'd, its my sister's truck and we'd like to fix our problem tomm.



rusty wyckoff
Dodge Dakota
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3/12/2010
21:34:17

RE: fuel pressure
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hi i am trying to diagnose a problem with my 1989 dodge w150 5.2 tbi, thinking the fuel pressure might be making it run bad btu can not find what fuel pressure am supposed to run. heard that the tbi is very picky about fuel pressure thanks.



pssst
Dodge Dakota
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3/12/2010
21:35:34

RE: fuel pressure
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and how bout telling us what the pressure test
showed?



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