Engine/Transmission (1998.5 - 2002) fuel pressure

[63shult]

the fuel pressure gauge on my truck fluctuates back and forth real fast about a 1/4 in.,it also makes loud vibrating noise. I have about 20psi at idle, 15 psi at 60 mph, 10 or 12 at wot i have a FASS 95 on the truck the question is, is the problem in the gauge, fuel pump or injection pump. I have a mechanical gauge on it.

 

[RonaldLarson]

the fuel pressure gauge on my truck fluctuates back and forth real fast about a 1/4 in.,it also makes loud vibrating noise. I have about 20psi at idle, 15 psi at 60 mph, 10 or 12 at wot i have a FASS 95 on the truck the question is, is the problem in the gauge, fuel pump or injection pump. I have a mechanical gauge on it.

Sounds like the Fass is not regulating pressure. Try switching your pressure pickoff to the opposite side of the filter, and see if there's any change. Could be the filter is clogged intermittently. If the inlet side of the filter reads normal pressure, it's your filter element.

 

[63shult]

i should clarify something when i say the pressure fluctuates its more like a flicking back an forth like blur

 

[VolsFan]

Is the gauge new? Has this always happened or just started? I have an isspro on mine and did the same thing you describe, had a bad ground.

 

[SnoKing]

the fuel pressure gauge on my truck fluctuates back and forth real fast about a 1/4 in.,it also makes loud vibrating noise. I have about 20psi at idle, 15 psi at 60 mph, 10 or 12 at wot i have a FASS 95 on the truck the question is, is the problem in the gauge, fuel pump or injection pump. I have a mechanical gauge on it.

That is the normal pulsing of the pump. You need a snubber valve in the line.

http://www.amazon.com/GlowShift-Diesel-Snubber-Cummins-Pressure/dp/B007SYGRBW

http://www.xtremediesel.com/autometer.aspx

A section of rubber hose also helps. Some just install a needle valve and turn it down to the point that gauge smooths out.

Do you have an isolator in line? I have a rubber hose from the button of the filter to the isolator, and anti-freeze in the line from the isolator to the gauge. The white plastic line is inside a black tube for addition protection.

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SNOKING

 

[63shult]

I have been running a mechanical gauge for 3 or 4 years and the FASS a couple years. It started doing it this past summer i wonder if it would be something in the pressure regulator in the lift pump? If i need the snubber valve why is it acting like till recently?

 

[SnoKing]

I have been running a mechanical gauge for 3 or 4 years and the FASS a couple years. It started doing it this past summer i wonder if it would be something in the pressure regulator in the lift pump? If i need the snubber valve why is it acting like till recently?

Got rid of an air bubble in the line????? SNOKING

 

[63shult]

Got rid of an air bubble in the line????? SNOKING

So what i am hearing is that i had air in the line up to this point and that worked as a shock absorber keeping the needle on the gauge steady?

 

[JR]

The VP indeed will hammer your gauge to no tomorrow. Why it hasn't done it up until now is only speculation but you need a snubber of some type to dampen it or depending on the quality of the gauge you will trash it in short order. I've got a needle valve and open it just enough to allow the gauge to come up to pressure. It also pulls double duty As an isolation gauge in the event one is needed.

 

[63shult]

is it only mechanical gauges that have this problem? that do you use for a needle valve?

 

[JR]

Electric gauges have a sending unit threaded into the fuel port or spliced in line and the gauge will not pick up the fluctuation in pressures.

 

[klcammie]

Electric gauges have a sending unit threaded into the fuel port or spliced in line and the gauge will not pick up the fluctuation in pressures.

But snubber is still needed. Thrashed two sending units till I learned about snubber.

 

[KATOOM]

Any fuel pressure monitoring system on these trucks need at least one snubber to reduce or eliminate the hydrodynamic fluid pulses coming from the VP. You can pick up dedicated snubbers at places like Genos or you can get a needle valve at the hardware store. I personally prefer the dedicated snubbers since I dont want to have to adjust something else but its to each is own.

 

[RonaldLarson]

But snubber is still needed. Thrashed two sending units till I learned about snubber.

My Westach electric , purchased from Genos 12 years ago has no external snubber. My sending unit is connected to the filter nipple with a grease gun hose. I have no needle oscillations.

 

[63shult]

i finally got around to putting a needle valve on last week all is well thanks for the help