Is it worthwhile to have a fuel pressure gauge or just set it and forget?

[rsimoes]

Is it worthwhile to have a fuel pressure gauge on the fuel line or just set it and forget?

[petek]

I'm running Holley Projection FI and figured the gauges (in the engine compartment) were cheap enough that I could put one on the feed line and one on the return line. The only time that I've used the gauges so far is when I set the line pressure.

I'd guess that a dash mounted gauge might tell you if your fuel pickup was dry while you went (quickly) around corners.

[Roscoe]

Dash mounted fuel pressure gauges are nice but make sure you have an isolator so you do not have gas running into the cockpit. I also have found them to be a bit tricky and hard to bleed. Best is to put a non-liquid filled gauge on your fuel log or regulator.

I recently (yesterday) had a problem where I was pumping anywhere from 6 to 15+ pounds of fuel into the carb. The carb was flooding and gas was coming out of every orifice on the carb. Turned out there was a round 1/4" burr inside my pressure regulator that got stuck in the ball check valve. I noticed the fuel pressure going nuts so that was where I looked for the problem.

Roscoe

[Tom Wells]

Hi rsimoes,

I endorse the dash-mounted gauge as a diagnostic tool.

Engine quit! Since I had a fuel pressure gauge, I could watch it, and discovered it went to zero right before the engine stopped! Turned out to be a loose wire on the fuel pump. Without the gauge I wouldn't have had a clue whether it was electrical or fuel.

Also, cornering. I have EFI so it is important not to uncover the pickup in the tank during cornering. I can now tell when I need to stop and add some gas! A hard corner can cause the fuel pressure to drop - gotta get a fuel cell one of these days

I got a marine unit - electrical - from Nisonger. Easy to install, no worries about leaks

Tom

[Back in Black]

They are only useful (in the dash) if you have fuel injection...that way you could spy why your motor was sputtering, if that be the cause, matey... ditto to the ABSOLUTE need for an isolator unit... the problem there is that the Autometer isolator was like $350 !

The gauge itself was cheap... if mounted in the motor compartment it would not cost much, but then you can only view it with the hood up, kinda hard to drive that way

[rsimoes]

I'm running a Holley 4150 4 bbl double pumper carb. . . I was actually asking about the inline fuel pressure gauge in the engine compartment.

But if diagnostics is the only use, that easy enough to check with a diag gauge if something goes wrong. . . I have too many guages in the dash already. . .

Do you think it is still important to have with a carb?

[Roscoe]

I think it is good to have one in the engine compartment. Make sure you use a NON-liquid filled gauge.

Roscoe

[rsimoes]

Why non liquid filled?

[Roscoe]

Liquid filled gauges in an environment where there are severe temperature changes will effect the readings on the gauge. I believe it has to do with the expansion and contraction of the liquid. I have done comparisons with both. I have a liquid filled on my regulator behind the block and a dry one on the fuel log. After the engine warms up the liquid reading drops and the dry one stays on mark.

I have been told by BG and Aeromotive to stay away from them. Also, if they are filled up with little air there is a chance they can burst. nuff said?

Roscoe

[rsimoes]

amen!

Thanks!

[Cobra20646]

Started with a liquid filled one under the hood. Lasted about two months then wouldn't read accurately any more...... had it replaced with another liquid one....... thought they sent me the bad one back!!! Now using the simple "air" filled.... no problems.

Had a vapor lock problem once...... no gas getting to the carb. Didn't know what the problem was :-( Put the gauge on so I see what's going on ..... if it ever happens again.

- Jim -

[JAM1775]

I have an in-line BG dry gauge from Jegs right in the Holley DP carb line by front port. All is AN fitted in a braided line. It looks good, it helps me if/when the rare ocassion is I have a carb problem..just another factor in considering causes, helps with float adjustment and I believe it will fluctuate if there is a drop in fuel pump pressure or clogged filter. I have never had a leak but would hate that to happen under the dash.

[ToyCollector]

BIB, that seems like a real high price. I bought an autometer isolator from Kirkham and it was somewhere in the $50 range, maybe less, maybe more, but less than a hundred.

Does anyone know if the Smith's fuel pressure guage can be bled?

[Hal Copple]

I am a compulsive modfier of cars, starting back with my dad's '59 Anglia. So when i was up at the used NASCAR place up in NC a year ago, picked up a used VDO fuel pressure gage for a few bucks. Then, ran an AN four line to the gage (no isolater at first), put it in a black autometer cup, mounted in under the dash, passenger side, aimed up at me. But found the fluctuations of the mechanical Carter pump made the needle fluctuate so much it was useless. I ran the fuel off an AN adaptor at the end of my braided SS fuel lines.

So, i got a short AN female/female adaptor, put a 22 gage hypodermic needle (about the size of a large human hair) in it, and filled the adaptor with fuel proof JB weld. Since then it responds very quickly, and without any needle fluctuation . Basically, nice dampening of the needle fluctuations.

For those who cringe about not using a pressure isolater, if i crash, my engine i am sure will die, (mechanical pump), and the only gas that may get into the cockpit is via a 22 gage needle, i doubt more than a thimble at most. If i crash hard enough to tear off my gage, i have lots of things to worry about. An isloater would be appropriate for an electric pump, and larger lines into the car.

Anyway, i think next to fuel level, and oil pressure, a working in-cockpit fuel pressure gage is the most useful instruement in the car!

I refer to it all the time, when i start the car, especially when it is after a "heat soak", making sure sure the pressure continues to rise, because it it falters at 3 psi, I need to blip the engine immediatly to get some gas to the carb. When my fuel filter is becoming clogged, i can watch my fuel pressure drop down under WOT (wide open throttle), and know it is time for a fuel filter change. When i am idleing in hot traffic, i keep an eye on it to see if my carb is about to boil over.

So an in-cockpit gage is very useful and helpful to me. My Carter runs a steady 7.4 psi pressure, by the way.

[Rodney]

I've been doing some research and this is what I've discovered.
Temp fluctuations during shipping and in the process application cause the liquid filling to expand and contract which in turn increases or decreases case pressure. As a result, accuracy can be decreased and the pointer may not return to zero properly until the gauge is vented to atmosphere.
To vent a liquid filled gauge, simply cut the top part of the rubber nipple plug on the back side of the gauge. This allows the case pressure of the gauge to be equal to atmosphic pressure. Also make sure the gauge is installed in the upright position ( nipple at the 12 o'clock) to prevent leakage of the glycerine or silicone.
Give this a try and your liquid filled gauges will work as intended! Hope this helps. Rod

[cobrashoch]

A fuel pressure gauge is almost as important as a oil pressure gauge IMHO. In both injection or blown engines it will warn you of a "leanout" condition before you milt down your engine. Cheap
insurance, when you also look at the reasons Hal listed above too.
cobrashock