Fuel Pressure Gauge Needle Fluctuating ?

[Mike Gaines]

Just curious as to if you have tried a non liquid filled gauge ? I here the liquid filled gauges will bounce around some. So it makes me curious if a non liquid filled gauge will read the same ? Ron

Ron, I originally bought a NON liquid filled 2 5/6" gauge to mount on my cowl (from Summit).
I installed it and it bounced so bad I couln't even see the needle.
Summit Tech told me to go to a Liquid Filled Gauge to alleviate the bounce...which I did...it bounces much, much less than non liquid filled, but still bounces.

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Maybe Im going to learn something here but having -6 feeding 2x -6 carb lines and a -6 return seems all wrong to me.
I run -10 feed -8 bypass and -6 lines to carb.

Again I might be going to learn more but I am shocked with the pump size as well. Magna fuel rate there 275 GPH pump for "up too" 750 hp . How can a 140 with -6 feed be right ? Ive been around the drags for a while (not as long as you Mike) and if I was doing the fuel system for your car Mike it would go roughly like this : -10 tank to pump, 200+ gph pump, -8 feed to hi flow reg, -8 return and -6 to carb.
Just my thoughts.

Ozy...your points are well taken, and thank you.
PS: When I was racing my 1963 Max Wedge Aluminum Nose car in 1963/1964/1965 we used 2 Stewart Warner Electric pumps mounted back by the gas tank and that was it....we knew nothing about fuel pressure and fuel pressure regulators.
In 1966 to 68 when when I was running my Funny Car I had Hilborn Fuel Injection and there was NO accomodation for fuel pressure readings. You just put the big jets in for 80% NitroMethane and then "tuned" it by the size of the bypass pill (inline jet) going back to the fuel tank.

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for carb systems if you run a # 6 supply it need an # 8 for the return, that means all fittings,no adapters.

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efi is different because it is high pressure.

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also the liquid filled gauges , when they get hot do not read correct.you have to open the little rubber cap on the side of the gauge to equalize the pressure that has developed from the oil expanding.

CDR: Thanks for your input. Everything I read says to use a bigger bypass return line (like 8an) than the supply line (which is 6an)....but I called Mallory Tech and Summit Tech and they both said a 6an return line was OK....but...maybe in real life it isn't. Thanks for the input.
And yes, I know about the little "cap" that you lift to "vent" the liquid filled gauge to equalize the pressure and I have done that...and it does "reset" the pressure...but still bounces when motor running..

 

[ozymaxwedge]

This is a good read Mike.

http://www.hotrod.com/how-to/engine/ccrp-0712-fuel-system/

 

[383man]

Ron, I originally bought a NON liquid filled 2 5/6" gauge to mount on my cowl (from Summit).
I installed it and it bounced so bad I couln't even see the needle.
Summit Tech told me to go to a Liquid Filled Gauge to alleviate the bounce...which I did...it bounces much, much less than non liquid filled, but still bounces.

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Ozy...your points are well taken, and thank you.
PS: When I was racing my 1963 Max Wedge Aluminum Nose car in 1963/1964/1965 we used 2 Stewart Warner Electric pumps mounted back by the gas tank and that was it....we knew nothing about fuel pressure and fuel pressure regulators.
In 1966 to 68 when when I was running my Funny Car I had Hilborn Fuel Injection and there was NO accomodation for fuel pressure readings. You just put the big jets in for 80% NitroMethane and then "tuned" it by the size of the bypass pill (inline jet) going back to the fuel tank.

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CDR: Thanks for your input. Everything I read says to use a bigger bypass return line (like 8an) than the supply line (which is 6an)....but I called Mallory Tech and Summit Tech and they both said a 6an return line was OK....but...maybe in real life it isn't. Thanks for the input.
And yes, I know about the little "cap" that you lift to "vent" the liquid filled gauge to equalize the pressure and I have done that...and it does "reset" the pressure...but still bounces when motor running..

Wow I did not think that would happen as alot of guys I talk to tell me their liquid gauge bounces. My non liquid gauge does not move at all. Ron

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Ron, I originally bought a NON liquid filled 2 5/6" gauge to mount on my cowl (from Summit).
I installed it and it bounced so bad I couln't even see the needle.
Summit Tech told me to go to a Liquid Filled Gauge to alleviate the bounce...which I did...it bounces much, much less than non liquid filled, but still bounces.

- - - Updated - - -



Ozy...your points are well taken, and thank you.
PS: When I was racing my 1963 Max Wedge Aluminum Nose car in 1963/1964/1965 we used 2 Stewart Warner Electric pumps mounted back by the gas tank and that was it....we knew nothing about fuel pressure and fuel pressure regulators.
In 1966 to 68 when when I was running my Funny Car I had Hilborn Fuel Injection and there was NO accomodation for fuel pressure readings. You just put the big jets in for 80% NitroMethane and then "tuned" it by the size of the bypass pill (inline jet) going back to the fuel tank.

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CDR: Thanks for your input. Everything I read says to use a bigger bypass return line (like 8an) than the supply line (which is 6an)....but I called Mallory Tech and Summit Tech and they both said a 6an return line was OK....but...maybe in real life it isn't. Thanks for the input.
And yes, I know about the little "cap" that you lift to "vent" the liquid filled gauge to equalize the pressure and I have done that...and it does "reset" the pressure...but still bounces when motor running..

Wow I did not think that would happen as alot of guys I talk to tell me their liquid gauge bounces. My non liquid gauge does not move at all. I have it mounted at the regulator. Ron

 

[actionange1]

Mine did that too. Drained the fluid (oil) out of it and its still working fine. Try it and post your results.

 

[Mike Gaines]

Mine did that too. Drained the fluid (oil) out of it and its still working fine. Try it and post your results.

Nice idea but I really do not want to drain the oil out of my gauges. But I think maybe I thought of something that could be the problem: if you look at the picture my fuel pressure gauge is mounted on a bracket on the side of the carburetor. Maybe the natural vibration of the motor is causing the gauge to fluctuate. I am going to mount the gauge over on the fender well and get it off the motor to see if that makes a difference. I will report what that does. Thanks, Mike

 

[RacerAL]

I have a gauge mounted on the cowl and one suspended in-line at the fuel block, the gauge on the cowl has always fluctuated some from 6 to 7 psi. it bounces back at forth constantly but the suspended gauge the needle is rock solid. Neither gauge is liquid filled. Ive just always figured it was vibration causing the gauge on the cowl to move around.

 

[Mike Gaines]

I have a gauge mounted on the cowl and one suspended in-line at the fuel block, the gauge on the cowl has always fluctuated some from 6 to 7 psi. it bounces back at forth constantly but the suspended gauge the needle is rock solid. Neither gauge is liquid filled. Ive just always figured it was vibration causing the gauge on the cowl to move around.
View attachment 304004

RacerAl: Thanks for the feedback....I am more and more thinking that I need to move my "carburetor bracket" over to the fender well (like Ron, 383Man, look at his picture posted earlier in this thread) has his mounted. I see most guys do have theirs mounted on the fender well like that. I guess this just might get rid of the vibration from the motor which is causing the fuel pressure gauge needle to "bounce".

 

[65 3 times]

Mike: I vibrated two of those small gauges to death mounted to the fuel rail on my carb. (They are about $30 each) I switched to a cowl mount Autometer and have had no issues. (AN-4 line from tap on regulator mounted to fender well through cowl vent to gauge) Good luck with your issue. I hate issues... Dave

 

[5.7 hemi]

My FASS lift pump on a 99' Ram 2500 TCD does the same thing. I have a gauge (liquid filled) and that damn thing bounces 15 to 20 and I cant figure out why........that is until I read the post that said something about releasing the pressure in the gauge. Gonna have to try that.

 

[dvw]

I used to use a Mallory return style regulator with a 3/8" return. Fuel pressure would always creap. We even bored out the return passage in the regulator. I never felt the return line was big enough. My current pump runs 2 relays in parallel within 12" of the batteries and the pump. Never an issue with pump voltage. There is a difference between idle and fuel requirement/ G-force going down the track. Why skimp? Run relays. As far as a return system on a drag car. Fuel doesn't have much time to heat up. My return comes right off at the pump, #8. #12 to the pump, #10 out of the pump, four #6 regulator to carbs.
Doug

 

[66Satellite47]

Mike, just thought to ask if you bled the "supply line" to the gauge. If that has air, the pulses of the gearotor could create a significant pulse at the gauge.

 

[5.7 hemi]

Wouldn't the "air" be bled out as the fuel has gone to the carb? I don't think that is the problem.

 

[Mike Gaines]

Thanks guys for all the input.

Like I said in my posting above...in the next few days I am going to re-mount my fuel pressure regulator AND pressure gauge over to my fender well to rule out the normal vibration of the engine as the culprit.

 

[hangn0ut]

That will do it for ya.

 

[383man]

Thanks guys for all the input.

Like I said in my posting above...in the next few days I am going to re-mount my fuel pressure regulator AND pressure gauge over to my fender well to rule out the normal vibration of the engine as the culprit.

Good luck with it Mike. I hope that takes care of it for you. Ron

 

[ozymaxwedge]

I would still like to hear from others about what they think of Mikes fuel system. I think it is way under fed, 140 pump with dash 6 feed ??

 

[383man]

I would still like to hear from others about what they think of Mikes fuel system. I think it is way under fed, 140 pump with dash 6 feed ??

I can tell you I use a stock gas tank and a stock type 3/8 sending unit.I use the Holley black pump and I run 3/8 line to the fuel press regulator and carb. I actually only had the Holley red pump on the car the first time I ran it with the 493 and it ran 10.70's at almost 125 even with the red pump with no fuel problem. I upgraded to the black pump to be sure it was getting plenty of fuel. Ron

 

[Yatzee]

In any return system it is always better to have the return larger than the supply ( this from Aeromotive Tech) because the return line can create back pressure which works in a negative manner on the diaphram of the regulator. A regulator controls fuel pressure forward not return. If, say, the return line were 1 inch, the fuel would literally return on it's own with out the aid of the pump to push it, and the diaphram of the regulator would only see supply pressure and regulate it to the carb. On the other hand, if the pump not only has to supply the fuel to the regulator but also has to pump it back through the return line the diaphram is going to see pressure two ways. You will get slight pressure drops at the gauge as the needle valve of the carb opens and closes but it's not really noticeable as the ball in the regulator finds a constant and slightly modulating opening. Spring pressure on the diaphram from crappy spring design will give uneven and non progressive pressure on the regulator seat and also cause the needle to bounce especially when the pressure supplied and the pressure out are seriously different. In that case, a spring with a wider range is required. Not putting in a plug for Aeromotive but I have never had an issue with their regulators that their techs couldn't resolve. Good luck!

 

[Mike Gaines]

I would still like to hear from others about what they think of Mikes fuel system. I think it is way under fed, 140 pump with dash 6 feed ??

Ozy...I hear what you are saying about bigger pump, line, etc....but....I have seen lots of 500" Mopars running 10.50's with exactly the same setup I have...in fact I have one fella that I know that runs 10.40's with a motor very similiar to mine as well as the same 140 Mallory pump and Mallory regulator with 6an (3/8") in and out with no problems.

If mounting the regulator and pressure gauge on the fender well (taking it off the carb bracket) doesn't solve the problem I will absolutely install a 10am return line.
Thanks.

 

[Jeremiah]

Mike,

Would a fuel pressure gauge isolator help with this problem?