what should my fuel pressure be?

[stang5011]

i have an 89 5.0L GT i have made several mods onto the car which include, 24llb injectors, 190lph fuel pump, fuel pressure regulator, trickflow twisted wedge heads,1.6 roller rockers trickflow efi manifold, 75mm throttle body, 73mm mass air sensor.

i am trying to get the car to run right it is running a little rich with open headers i was wondering if that had anything to do with it.

what should my fuel pressure be??

 

[90mustangGT]

The computer makes it run rich. If you lower fuel pressure the computer is just going to compensate with a longer pulse to the injector.

 

[331 stang91]

Is it normal for the fuel pressure to go down when I give it some throttle?It goes from about 39 to 35 or so?

 

[stang5011]

what should the fuel pressure be?

ok i got you on that but at idle what should my fuel pressure gauge read? right now my car is starving at higher rpms, should i have a higher gauge then 0-30?

 

[DMAN302]

idle vac line disconnected=39-40psi...pressure SHOULD NOT DROP when throttle is applied.

 

[stang5011]

ok thank you that answered my question.
i have one more to ask, with all these mods that i have done will it take a little while for the computer to adjust or it will adjust right away?

 

[DMAN302]

Provided your MAF is calibrated for your injector upgrade, pressure is set as indicated above..your car SHOULD fall into good idle and somewhat reasonable fuel curve (timing also may be an issue..I like to keep it around fourteen to sixteen). More tuning may be required...a dyno tune may help, but my combination works quiet well with above mentioned settings. Good luck and keep us updated.
Derek.

 

[stang5011]

when you do a lot of modifications is it a good thing to burn a chip for the computer or keep the computer original?

 

[DMAN302]

Depends...I have not gone the burnt chip route..but no doubt there is some power left in my combination that a dyno tune/chip tune would find for me. That method is probably the BEST to make the most of your cars performance..but if the package is working well with you current settings then you'll be fine without the tune...really up to you. Should a dyno session become available to me, I would definately go for it.

 

[jrichker]

At WOT, the air/fuel ratio is a function of fuel pressure, RPM, airflow through the MAF (mass air cars only) and the TPS. The O2 sensors don't have any control input into the computer's program at WOT.

Therefore you can use the SOP meter...

Get one of your buddies to ride along with you. Find a level stretch of road where you can do some testing. Don't choose a speed range that will make you shift gears, the shift quality & speed will affect your results. Use 2nd or 3rd gear and do a run from 2000 RPM to 5800 RPM. Call out the RPM as it increases and have you buddy record it and the elapsed time. If you have one of those cheap digital watches like I do, a stop watch is built in. Start the fuel pressure at 36 PSI, vacuum off and make a run. Turn it up to 37 and make another. Be sure to reconnect the vacuum every time you set the pressure. Keep turning up the pressure and making runs until you notice a drop off in time. If your bud was careful to record the results, you'll have a nice chart to use to find the optimum pressure.