Engine/Transmission (1998.5 - 2002) where is air in fuel press gage coming from?

[Jim Ross]

I am having an on-going problem with air getting into my fuel pressure gage and causing needle bounce. It is easy to bleed the air from the sending unit, but it's a pita to have to do it almost every day!

I believe this problem started shortly after the original lift pump was replaced, but maybe that's only coinicidence.

Recently, I had to replace the lift pump again... . this time I had a FASS pump (the one w/o the filters) installed. After the FASS pump was installed, my problem was greatly reduced... but not altogether cured, so I am scratching my head now trying to figure out where the air is getting into the system.

Help?

 

[CCutshaw]

If it's an electrical gauge you need to install a snubber.

Calvin

 

[Jim Ross]

The gage is a DiPricol... . it has a ss braided hose running from the schrader valve (on the injection pump) to a sending unit on the firewall (which is where I bleed the air out of it). From the sending unit there is a small plastic line filled with anti-freeze that goes to the gage on the A-pillar..... so I don't believe this would considered an electric gage. What is a snubber?... . I never heard the term before.

BTW, the gage shows the FASS pump to produce 15psi at idle, 13psi running down the road, and never less than 10psi under a load.

 

[steved]

Sounds like you have air getting into the system... having the FASS mounted further away (and probably a little more pressure) is preventing as much aeriation of the fuel.



IMO, that's what I'd start looking for... somewhere the air is getting in.



steved

 

[lil red cummins]

jim:



the air in the line is not causing the needle bounce and should not be a problem. the air actually provides a cushion or snubber effect of its own.



the "snubber" as mentioned in a previous post is basically a shutoff valve put at the point where you are reading your fuel pressure.



open the valve ONLY enough to get a pressure reading. this will help reduce the pulsations coming from the fuel system and snub (where the term comes from) the vibration. you can tell when it is open enough by the way the gauge responds when the key is turned on. it should not snap up to pressure, but come up a little slower than normal. a two to five second delay in reading "true" is about right.



good luck



jim

 

[CCutshaw]

The gage is a DiPricol... . it has a ss braided hose running from the schrader valve (on the injection pump) to a sending unit on the firewall (which is where I bleed the air out of it). From the sending unit there is a small plastic line filled with anti-freeze that goes to the gage on the A-pillar..... so I don't believe this would considered an electric gage. What is a snubber?... . I never heard the term before.

BTW, the gage shows the FASS pump to produce 15psi at idle, 13psi running down the road, and never less than 10psi under a load.

Go to www.mcmaster.com do a search for snubber. On page 527 Porous-Disc Medium-Pressure Snubbers 10 microsize they work great on electric guages. My Autometer FP went out after 2 weeks. They told me to install a snubber on the end of the SS line.

Calvin

 

[Fishin Guide]

Is your isolatar mounted above or below the lowest point in the fuel system?



If it is above, it is simply draining out of the line. and being replaced with air.



There is a bleed orifice in the VP44 overflow valve. This allows all pressure to bleed off when the engine is off. I think the true intent is to allow the electric fuel pump to push out air after fuel filter changes. And to possibly stop hard start issues due to pressure.



Most electric pumps do not have the ability to keep the fuel from draining back. Add this to an overflow valve that is open to a fuel tank with air in it, and it's no wonder what's going on. Not to mention the fact that there may be an additional air leak elsewhere in the system.



Mount those isolators lower and you will never see air in them.



Dave

 

[RAJohnson]

If it's an electrical gauge you need to install a snubber.

Calvin

My electric gauge would bounce allot when I had it tapped at the schrader valve. I then added a snubber and it reduced it by about half, so I them relocated it to the bottom of the OEM FF and it is now rock solid. Distance from the VP is what you need.