Fuel Pressure

[WhtTA1995]

Does anyone know what the the OE pressure is for a 95 T/A?? If I install an adjustable regulator what should it be set at??

[Injuneer]

Stock fuel system operating pressure for all LT1's is 43.5psi. GM specs will accept anything in the range of 41-47psi. That's measured with the vacuum compensation line disconnected, or at WOT when there is no (or little) vacuum.

Set your AFPR at 43.5psi. Unless you have some valid reason for changing it, and have corrected the injector flow constant in the PCM to reflect the changed pressure.

[94formulaLT1]

could that be the reason that my motor is having a hard time starting? i checked my pressure and it was at, maybe a little below 40psi. i also have 30lb injectors..is this a problem?

Stock fuel system operating pressure for all LT1's is 43.5psi. GM specs will accept anything in the range of 41-47psi. That's measured with the vacuum compensation line disconnected, or at WOT when there is no (or little) vacuum.

Set your AFPR at 43.5psi. Unless you have some valid reason for changing it, and have corrected the injector flow constant in the PCM to reflect the changed pressure.

[fastTa]

could that be the reason that my motor is having a hard time starting? i checked my pressure and it was at, maybe a little below 40psi. i also have 30lb injectors..is this a problem?

Yes, you need to update your injector constants. It's called "Injector Size" in most LT1 tuning software. The more accurate the flow rate constants the better. You should contact the manufacturer of your injectors and ask them what the exact flow rate is and at what pressure.

Until you get your mildly low fuel pressure resolved, you can make some minor tweaks to your Inj Offset vs. Volts table......BUT I remember you said your battery was so low that it would barely turn over the motor. That could very easily cause a low pressure reading because your pump is not getting the proper voltage.

[Injuneer]

could that be the reason that my motor is having a hard time starting? i checked my pressure and it was at, maybe a little below 40psi. i also have 30lb injectors..is this a problem?

40psi with the vacuum line connected or disconnected?

[fastTa]

40psi with the vacuum line connected or disconnected?

He told me the line was disconnected.

[Kevin - Blown 95 TA]

Jeff, If you have 30# SVO injectors, I believe those were flowed at 39 psi. When I had those in my car, my injector constant needed to be 31.X to get the fueling to be neutral.

If you have some other brand, you just need to see what pressure they were flowed at and either set your FP to suit, or adjust the constant to line up the BLMs.

[94formulaLT1]

well the injectors i got were ford racing, i was told they fit into f bodys quite nicely and they are a good brand. i know, i dont like the "ford" name in my engine, but hey, no one has to know..oopps..i did get my pcm reprogrammed for the bigger size. explain to me what you mean by constant..i am guessing it is where the fuel is flowing constant without change? lol just a guess..i just really want my car back..i miss it so much, you guys know how that goes..im calling up a friend tomorrow that has a lt1 and see if he will come over. he rebuilt his a couple times before so he knows how to do it. i will keep you UTD with everything..mean while, keep giving me some possibilities..thanks a lot

Jeff, If you have 30# SVO injectors, I believe those were flowed at 39 psi. When I had those in my car, my injector constant needed to be 31.X to get the fueling to be neutral.

If you have some other brand, you just need to see what pressure they were flowed at and either set your FP to suit, or adjust the constant to line up the BLMs.

[Kevin - Blown 95 TA]

What I was trying to explain is that with the 30# SVO Ford injectors which are flowed at 39, if you run the stock fuel pressure 43.5 you will have excess fuel so you need to fool the PCM into thinking you have larger injectors than you really have so it will give you less fuel, otherwise you're BLMs will be low (PCM taking out fuel due to richness) So you do that by giving it an injector constant larger than 30. Clear as mud?

Otherwise, you can achieve the same thing by setting your fuel pressure lower to 39.

[Injuneer]

Some Ford/FMS/SVO injectors are flow rated at 2.7bar (39.15psi). When operated at 3bar (43.5psi), they will flow 5.4% more than rated.... i.e. a "30#" injector would in fact flow 31.62 #/HR and should be programmed at that value.

(43.5 / 39.15)^0.5 = 1.1111^0.5 = 1.0541

40psi with the vaccum line off would be on the low side of acceptable, and worth investigating further.