Engine/Transmission (1998.5 - 2002) Fuel Pressure Gauge Install, Bleed Air Needed?

[rakm]

Is it required to bleed the air from the lines on a FP install for accuracy? I know air is compressable and fluids are not so would it matter to leave air in the line? The reason I ask is this:



I bought a cheap FP gauge and hooked it up about a month ago. Had 14 idle, 11-12 cruise, 7-8 wot. Seemed good but I hated the gauge. It stuck occasionally on the way back down and was loud. So I removed it and bought a Dipricol 0-30# White (very nice gauge imo) and hooked it up yesterday. My readings are now 9-10 idle, 6-7 cruising, 2-3 wot. I did change the location of the gauge from the previous install from below dash to steering column but wouldn't think that should matter for mechanical gauges. I guess I'm just a little hesitant to believe the LP is already going out at 6800 miles and don't want to get charged by the dealer if it's not.



So should I demount the gauge and bleed the line or is that a waste of time?



Would the mounting location matter on the pressure readings? If so how much difference between below dash and steering column?



Thanks for any advice...

 

[Thomas]

Actually air is a fluid. Liquids don't compress. Air should not cause inaccurate readings. Air in the line can buffer any hammering that your gauge might see from the injection pump. I intentionally trapped air in eighteen inch lines between the banjo bolts at the transfer pump and the two senders for my dual fuel pressure gauge. As far as vertical position influencing the reading, it's kind of like checking the air pressure on your tires. Do you see different pressures with the valve stem at the top of the wheel versus the bottom of the wheel? Any pressure loss due to mounting the gauge higher would be unmeasureable with the gauge you are using. I think the only thing that you can conclude with the reading differences on your two gauges is that at least one of the gauges is not accurate.

 

[BillH]

It is very possible your LP is going out, mine had to be replaced at 4000 miles, injection pump at 5000 miles.



BillH

 

[rakm]

That makes sense. Not real sure how to determine the accuracy of the gauge so I'll assume I've already got a bad LP. I figure a brand new Dipricol FP gauge is pretty bullet proof as far as accuracy goes.



Thanks for the quick response.



Ron

 

[rakm]

Well I changed the Fuel Filter just to make sure and no change in pressure. It was a little hard to get it going again priming but I managed. Hooked the old gauge up and it read, you guessed it 14 psi idle. So one of the gauges is inaccurate, now just to figure out which one...

 

[Thomas]

GFoley - I won't argue with your statement. However, I don't believe I ever stated that air was a liquid. I'll stand by my statement that air is a fluid.

 

[RobbyRam]

I have a Westach f/p gauge with the sending unit attached to a bracket on the inside fender with a 5 foot A/C charging hose(Briar Hoppers) fed via the Banjo connection after the fuel filter.

There is mostly air in the hose but the gauge works great with a new lift pump that gets: 15psi idle, 13 psi @ 70 mph, and 11psi at W. O. T.

 

[rakm]

Don't really have any friends. Just joking but don't have any with a CTD. Thinking about getting a cheap oil pressure gauge and comparing. Which-ever it matches is the accurate one. My luck and it'll read something like 11-12 psi and I still wont know. I have a hunch the one thats reading low is the inaccurate one as my truck has so few miles. That's wishful thinking also.



Yes, air does flow so is considered a fluid. I did mean liquids don't compress when I actually said fluids in my original post but if you want to get technical, liquids do compress a little, just MUCH harder to do so.



I should have also thought about the question before asking as I really could have answered both of those questions with some common sense. Just got in a hurry and ask before thinking. I should be ashamed

 

[monkeyman]

I wonder......................

Just reading old threads. Air is a Gas, Simple as that.

Gases flow.

Rick

However there is a liquid form of oxygen, but air is not pure oxygen