question about checking fuel pressure

88_GT_5_oh

Sportin' a turbo 5.0 in Canadistan

Jul 4, 2004

1

0

1

WPG/MB/CA

Sep 30, 2004

#1

• Sep 30, 2004

• #1

this is kind of a dumb question, but when your reading your fuel pressure, should it be at 39 psi with the vacume line on or off? i looked in the haynes manual and searched here but no luck.

 

D

Daggar

New Member

Jul 19, 2004

3,902

5

0

Sep 30, 2004

#2

• Sep 30, 2004

• #2

Mine sits at 39 at idle with vac lines connected.

 

88_GT_5_oh

Sportin' a turbo 5.0 in Canadistan

Jul 4, 2004

1

0

1

WPG/MB/CA

Sep 30, 2004

#3

• Sep 30, 2004

• #3

cool thanks....... just wanted to be sure

 

S

Stang717

New Member

Sep 22, 2004

25

0

0

Jamesburg, NJ

Sep 30, 2004

#4

• Sep 30, 2004

• #4

To adjust fuel pressure..

Take vacume line off, plug with finger, and adjust to the # you want.. normally 38-42 psi with your set-up.. When you put the vacume back on, the pressure should go down about 6 psi.. this is because there is a lot of vacume at idle.. When you hit the throttle, the psi will go back up to about the point where you set it.. good luck..

Mike

 

88_GT_5_oh

Sportin' a turbo 5.0 in Canadistan

Jul 4, 2004

1

0

1

WPG/MB/CA

Sep 30, 2004

#5

• Sep 30, 2004

• #5

so right now it's been around 39 psi with the vacume on..this is probably why it seems like its running rich

 

S

Stang717

New Member

Sep 22, 2004

25

0

0

Jamesburg, NJ

Sep 30, 2004

#6

• Sep 30, 2004

• #6

possibly.. while just driving aroung, it'll be ok, when you hit it, the pressure will jump up, to around 44-46 psi..

best thing you can do is to pay 75 bucks, hit up a dyno, and fine tune it..

i went to get dyno tuned, after just screwing with the fp and my timing, i bumped my rwhp up by 12..

Not too bad for under 100 bucks

Mike

 

88_GT_5_oh

Sportin' a turbo 5.0 in Canadistan

Jul 4, 2004

1

0

1

WPG/MB/CA

Sep 30, 2004

#7

• Sep 30, 2004

• #7

k thanks man... i'll play with it a bit cause winter is coming (suposed to get snow tonight, probably will melt by noon) i don't wanna pay for a tune right now cause i'm parking it for winter

 

HISSIN50

"How long does it take to get help in here?

15 Year Member

Nov 29, 1999

31,179

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Oct 1, 2004

#8

• Oct 1, 2004

• #8

if you set it a little too high, the adaptive strategy will shorten the injector pulsewidth a smidge to compensate so you keep the A/F stoich correct.

 

giddyup306

Founding Member

Oct 22, 2002

3,041

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Oct 1, 2004

#9

• Oct 1, 2004

• #9

To a certian degree yes.

 

HISSIN50

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#10

• Oct 1, 2004

• #10

giddyup306 said:

To a certian degree yes.

Click to expand...

the EEC can adapt ~ +/- 25%. you dont think it will adapt!?

 

giddyup306

Founding Member

Oct 22, 2002

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Oct 1, 2004

#11

• Oct 1, 2004

• #11

Don't get me wrong it will but with aftermarket AFPR's around you can have pressure as high as 120 PSI of fuel pressure. That's the exception I was talking about.

 

HISSIN50

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#12

• Oct 1, 2004

• #12

giddyup306 said:

Don't get me wrong it will but with aftermarket AFPR's around you can have pressure as high as 120 PSI of fuel pressure. That's the exception I was talking about.

Click to expand...

ok, i gotcha. - i think that might fall outside the adaptive strategy parameters. LOL.

i was thinking in terms of the numbers 88 GT 5 oh posted - he might be 5-6 psi high. i think we would both agree that the puter will adapt to that.

(you threw me for a loop with your post as it would pertain to this thead).

 

giddyup306

Founding Member

Oct 22, 2002

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Oct 1, 2004

#13

• Oct 1, 2004

• #13

HISSIN50 said:

ok, i gotcha. - i think that might fall outside the adaptive strategy parameters. LOL.

i was thinking in terms of the numbers 88 GT 5 oh posted - he might be 5-6 psi high. i think we would both agree that the puter will adapt to that.

(you threw me for a loop with your post as it would pertain to this thead).

Click to expand...

OIC. I thought you were asking a question. I thought you meant to type a ? instead of a . Sorry about the confusion. Carry on

 

HISSIN50

"How long does it take to get help in here?

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#14

• Oct 1, 2004

• #14

giddyup306 said:

OIC. I thought you were asking a question. I thought you meant to type a ? instead of a . Sorry about the confusion. Carry on

Click to expand...

as you were.

 

Michael Yount

Mustang Master

Apr 10, 2002

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Charlotte, NC

Oct 1, 2004

#15

• Oct 1, 2004

• #15

It should be checked with the vacuum hose off and plugged, the engine idling and warm. It should be set to 38-40 psi under those conditions. Depending on how much vacuum your engine (cam) makes at idle, when you hook it back up, pressure at warm idle with the vacuum line on should drop to 32-36 psi. When you "hit" it, you kill the vacuum in the intake and it should jump back up to the "no vacuum line" set point - 38-40. It won't go any higher than the reading you had with the vacuum line disconnected.

 

Gearbanger 101

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#16

• Oct 1, 2004

• #16

It shouldn't matter whether you've got the hose plugged or not once you've got it off, should it?

 

Michael Yount

Mustang Master

Apr 10, 2002

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#17

• Oct 1, 2004

• #17

Practically - it probably wouldn't make a big difference; but without it being plugged (just hold your thumb over it) you've got a pretty good vacuum leak which impacts idle speed - that impacts alternator output which might impact fuel pump performance; and reduced idle speed impacts how the engine's using fuel. How big will those impacts be? Probably not big - but why wouldn't you cover the vacuum line with your finger while you're taking the reading?

 

HISSIN50

"How long does it take to get help in here?

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#18

• Oct 2, 2004

• #18

Michael Yount said:

Practically - it probably wouldn't make a big difference; but without it being plugged (just hold your thumb over it) you've got a pretty good vacuum leak which impacts idle speed - that impacts alternator output which might impact fuel pump performance; and reduced idle speed impacts how the engine's using fuel. How big will those impacts be? Probably not big - but why wouldn't you cover the vacuum line with your finger while you're taking the reading?

Click to expand...

man Michael, you think of everything.

 

Gearbanger 101

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#19

• Oct 2, 2004

• #19

Michael Yount said:

- but why wouldn't you cover the vacuum line with your finger while you're taking the reading?

Click to expand...

Cause I was using one hand to adjust the pressure and the other to hold up the hood (no prop rod).