fuel pressure question

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noslow1986

New Member

Mar 25, 2006

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oswego Il

Oct 16, 2008

#1

• Oct 16, 2008

• #1

today i started the car and the fuel said 25psi when it should be at 39 to 40. now if i had the adjustable fuel pressure reg on there for almost a year why would the pressure change all by it self. its a aeromotive with an autometer gauge. i put the pressure back a 39 to 40 but my question is why would it drop to 25 to 30.

 

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1/4mile_runner

New Member

Jun 1, 2008

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Oct 16, 2008

#2

• Oct 16, 2008

• #2

Was the tightener loose? I run mine at around 28lbs in the summer. It seems to be good for a tenth in the 1/4. But in the winter time it has a tough time starting up when it's cold out so I put it back up to 40lbs. for the cold months.

 

MY 85 GT

10 Year Member

Mar 7, 2008

1,852

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104

New Jersey

Oct 16, 2008

#3

• Oct 16, 2008

• #3

Do you guys have any pictures of how your regulators look and were you putting the pressure gauge?

 

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1/4mile_runner

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Jun 1, 2008

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Oct 16, 2008

#4

• Oct 16, 2008

• #4

MY 85 GT said:

Do you guys have any pictures of how your regulators look and were you putting the pressure gauge?

Click to expand...

I don't use a permanent gauge. I just hook one up when I want to adjust it. I "have" one, just havent put it on yet.

 

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noslow1986

New Member

Mar 25, 2006

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oswego Il

Oct 16, 2008

#5

• Oct 16, 2008

• #5

its on the fuel rail and a autometer gauge pod on the cowl

 

Vipersix

Founding Member

Feb 25, 2001

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Clarksville, TN

Oct 17, 2008

#6

• Oct 17, 2008

• #6

1/4mile_runner said:

Was the tightener loose? I run mine at around 28lbs in the summer. It seems to be good for a tenth in the 1/4. But in the winter time it has a tough time starting up when it's cold out so I put it back up to 40lbs. for the cold months.

Click to expand...

How long have you been doing this? You run a good possibility of causing lean conditions in your chambers. While this will yield a performance increase in the short term, it wreaks havoc on your internals if you get excessive.

noslow1986, unless your pump is taking a **** on you, the most likely candidate is the adjustment bolt backing out during operation.

 

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noslow1986

New Member

Mar 25, 2006

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oswego Il

Oct 17, 2008

#7

• Oct 17, 2008

• #7

the fuel pump is only a year old i just dont understand why one day it would run at 25 psi. now i adjusted as far as it would go which is 39 psi. if u turn it the other way it brings the pressure down. i used an allen wrench and adjusted it at the top. i adjusted it with the vacuum line attached and got it 39 psi is that how u do it

 

Vipersix

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Feb 25, 2001

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Clarksville, TN

Oct 17, 2008

#8

• Oct 17, 2008

• #8

No, you'll want to set the base pressure with the vacuum line disconnected. The purpose of a regulator is to adjust the fuel pressure with changes in atmospheric pressure and engine airflow in order to maintain a constant pressure at the injectors.

How old is your regulator? Most of the cheaper units have a rubber diaphragm inside, which is used to alter the pressure, and these have a habit of degrading in hot temperatures.

 

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noslow1986

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Mar 25, 2006

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oswego Il

Oct 17, 2008

#9

• Oct 17, 2008

• #9

just started it a little bit of go and everything looks good the idle doesnt drop and idle at 1000 rpms doesnt jump around. i thouht u had to set it with vacuum off i did it with vacuum on seems alot better, dont know why it drop fuel preesure like it did. anyways its a autometer fpr just about a year old and the fuel pump is bbk 190lph just over a year and a half old. i think my car has issues. beat it til it runs right

 

1

1/4mile_runner

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Jun 1, 2008

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Oct 17, 2008

#10

• Oct 17, 2008

• #10

Vipersix said:

How long have you been doing this? You run a good possibility of causing lean conditions in your chambers. While this will yield a performance increase in the short term, it wreaks havoc on your internals if you get excessive.

noslow1986, unless your pump is taking a **** on you, the most likely candidate is the adjustment bolt backing out during operation.

Click to expand...

Pretty much every year. What kind of havoc?

 

NIKwoaC

中國製造

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Oct 31, 2006

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Chengdu Province

Oct 17, 2008

#11

• Oct 17, 2008

• #11

You set the fuel pressure with the vacuum line disconnected because it simulates WOT condition, where manifold pressure is essentially atmospheric. If you are setting the pressure with the line connected and the engine running at idle, the manifold is under vacuum, and therefore, the fuel pressure will read lower, in proportion to the amount of vacuum the manifold is seeing.


1/4mile_runner, could this be why your car runs well at "28psi"? I've never heard of anybody running that lean and getting better performance. The only way I can see this making sense is if you are running over sized injectors, and in that scenario, its really just a band-aid fix.

Anyway, unplug the vacuum line, crank it to 40 psi, and sleep better at night.

Edit: Don't forget to plug the vacuum line back in after the change. the car will run pig rich at idle if you don't!

 

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noslow1986

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Mar 25, 2006

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oswego Il

Oct 18, 2008

#12

• Oct 18, 2008

• #12

i think im going to leave the fuel pressure where it at right at 39 to 40 it doesnt go any higher or lower just stays at 39 to 40. the only thing is it ok that i did it vacuum attach the. fuel stays where i set it 39 to fuel

 

NIKwoaC

中國製造

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Oct 31, 2006

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Oct 18, 2008

#13

• Oct 18, 2008

• #13

If the fuel pressure is at 40 when the car is idling with the vacuum line connected, it is set waaaaay to high. You need to set the FP to 40 with the car idling and the vacuum line disconnected. Then, you will see a lower FP reading once the vacuum line is plugged back in; the drop in FP you see is the equivalent to the amount of vacuum in the manifold. I'm sorry if I'm beating a dead horse here, but I'm not sure that I was clear enough before.

 

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noslow1986

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Mar 25, 2006

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oswego Il

Oct 18, 2008

#14

• Oct 18, 2008

• #14

I don't understand it stays at 40 psi doesn't go any higher.

 

66sprint6

Member

Oct 5, 2005

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Dec 20, 2008

#15

• Dec 20, 2008

• #15

noslow1986 said:

I don't understand it stays at 40 psi doesn't go any higher.

Click to expand...

Did you put the vacuum line back on? If not, then the fuel pressure will stay the same always and forever regardless of RPM and the likes. Read slowly and go do it, trust me, it works and will make your headaches go away.

1)pull vacuum line OFF of regulator
2)pug or clamp said vacuum line
3)start car and let idle
4)set fuel pressure to 39-40psi
5)PUT VACUUM LINE BACK ON REGULATOR
6)enjoy :o)

Trust us, this is the way to do it and it has cure plenty of my problems in the past and is hopefully fixin to solve another one for me here shortly lol.
Good Luck
Matt