Wierd Fuel Pressure - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 8 (permalink) Old 03-11-2008, 07:11 PM Thread Starter
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Wierd Fuel Pressure

Im having a problem with my 99's fuel system. I started by installing a mechanical fuel pressure guage using one of the ports on top of the filter housing. With the stock lift pump I had around 10 psi at idle and no less than 6 at WOT. After a few weeks, the guage started reading a little lower but the truck was running fine. One day, it dropped to 3psi and I got worried. After a new fuel filter the guage showed 4psi. Not wanting to chance it, and already having a Holley Blue sitting on the shelf I ordered the Vulcan Big Line kit. After installing the kit I fired the truck up and only saw 5psi. Checked the lines for the fuel pressure guage and discovered air in the guage side of the isolator. I pulled the lines apart, replaced all the compression fittings, refilled the line as best as I could and reassembled everything. Fired it up now I have 11psi. Took the truck down the road and could only pull it down to 9psi so I thought maybe I was safe. When I started it today, it was a 4psi and eventually climbed to 10. What is going on with it? Is my guage messed up? My pump? I thought the Holley was rated at 14 or 15psi so isnt that what I should be seeing? If anyone has any ideas or has had a similar problem, I need help.
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post #2 of 8 (permalink) Old 03-11-2008, 11:58 PM
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That sounds like your gauge is messed up to me. Maybe check the filter again, those can get clogged really quickly. But most likely the gauge. I would check for air in the gauge again, but either way I'd try to get it figured out so you don't smoke your IP.
Sean

2000 2500 reg. cab 4x4 auto 577hp
09 6.7L QC LB stick, 4x4.

TOTAL PERFORMANCE DIESEL 707-545-FUEL (3835)
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post #3 of 8 (permalink) Old 03-13-2008, 02:28 AM Thread Starter
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So Im right in thinking I should be seeing 14psi? Any ideas on how to get all the air out of the guage line?
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post #4 of 8 (permalink) Old 03-13-2008, 04:12 AM
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Most Pharmacys will give you syringes in either 3 cc or 5 cc. That's what I use to fill the isolator and the line running to the guage. Fill the line with a red colored anti-freeze, if you are using the clear plastic line, from the guage up to the isolator, and quickly connect it to the guage. That way you can see if there is any air and the air will come out the top. Then fill the isolator. Recheck for air bubbles. If air bubbles show, disconnect from isolator and do the finger thump you see Dr's do on TV to break the air bubble up so it will come to the top of the line. Reconnect and you should be good to go.
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post #5 of 8 (permalink) Old 03-14-2008, 12:51 AM Thread Starter
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Thanks I will try that. One more thing, why red antifreeze?
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post #6 of 8 (permalink) Old 03-14-2008, 03:25 AM
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First off I would pull the isolator out and test without it. Isolators 99% time are the cause of low pressure readings.

Second off anything under 10 PSI is asking for VP44 damage...
http://mopar.mopar1973man.com/2002%2...sure-specs.jpg

As for me I've been running without a isolator for nearly 5 years without a issue...

Gauge Write up...
http://mopar.mopar1973man.com/2002%2...icol_gages.htm

The nylon tubing I'm using is rated for 150 PSI I highly doubt that 15 PSI of diesel fuel with blow it. Second off diesel isn't gasoline. Gasoline has a extremely low flash point of -45*F and makes its extremely hazardous to have in the cab. But diesel fuel on the other hand has a flash point around 140*F. You can throw matches at diesle all day without a problem.

But back to the needle valve. The needle valve will dampen the pulses to the gauge and prevent damaging it. Also if the plumbing fails I can shut down the fuel pressure gauge and continue driving. With a isolator it can fail without warning and still have diesel fuel in the cab.

You should be seeing 14 - 15 PSI normally and no lower than 10 PSI at WOT...

Just my 2 cents to the pile...

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 8 (permalink) Old 03-14-2008, 02:04 PM
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The red antifreeze is a "just in case" you have below freezing weather, when using an isolator, and if you are running the clear plastic tubing, you can see it and any bubbles. If you aren't worried about the freeze factor, add some food coloring.
The reason I use an isolator is: The people I bought the guage from told me that if I returned the guage under warranty, they wouldn't honor it if they found fuel in the guage. Dumb me.......I do agree with MoParMan about not needing an isolator and will use his setup when/if my isolator goes.
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post #8 of 8 (permalink) Old 03-14-2008, 03:39 PM
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Quote:
Originally Posted by triker888
The red antifreeze is a "just in case" you have below freezing weather, when using an isolator, and if you are running the clear plastic tubing, you can see it and any bubbles. If you aren't worried about the freeze factor, add some food coloring.
The reason I use an isolator is: The people I bought the guage from told me that if I returned the guage under warranty, they wouldn't honor it if they found fuel in the guage. Dumb me.......I do agree with MoParMan about not needing an isolator and will use his setup when/if my isolator goes.
For what I paid for my Dipricol Fuel pressure gauge I was NOT worried about a warranty at all... It only cost me $36 bucks for a mechanical 0-30 PSI fuel pressure gauge...

Like now it even still $43 buck of a gauge... (Oh hurt me!)
http://www.dieselperformanceparts.co...fm/item_id/992

Now if it was a Autometer (which I know are spendy) I would of done the same thing too... Ran a isolator till it died...

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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