Can someone describe to me how the LT1 might feel if its running low fuel pressure. And what do you guys think the pressure should be set at with 30# injectors / LT4 hot cam, headers ec....

Thanks,

 

If you have 30# injectors and a HOT cam, you had the PCM reprogrammed - correct? What pressure did you tell the programmer you were going to run with the injectors? That's where you set it. You needed to tell him the capacity of the injectors, the brand/model, and your fuel pressure, so that he could input the correct flow rate and offsets for the injectors.

Lacking any other info, if you feel you are making enough HP to run out of fuel with 30# injectors (480-500HP), it will be possible to increase injector capacity by increasing the pressure. A 20% increase in pressure, for example would give you a 9.5% increase in injector capacity. Now they will support 525-550flywheelHP.

In general, you tune by putting the correct info about the injectors into the PCM, tweek the PE tables, and look at the results. You don't start playing with fuel pressure to tune, because is doesn't work unless you totally disable the PCM's learning ability = run only in open loop.

In order to determine that your injectors are not delivering enough fuel, you need to look at the duty cycle, and measure the exhaust with a wide-band sensor.

 

I did have the PCM tuned to the new motor I just installed. My problem is, that the car runs fine when its cold but as soon as it reaches normal operating temp it feels sluggish and seems to shutter a bit. I am nor using a adjustable fuel pressure regulator as of yet and I think thats the problem. The car is in closed loop when its cold correct? Therefore running richer? The car feels alot stronger when cold.

My current set up includes brand new short block, LT4 hot cam, Crane Valve springs, Comp 1.5 RR's, Ported intake, pocket ported heads, Accel 30# injectors, Custom tuned PCM, Accel 300+ ign, Pace Setter coated headers, Flowmater cat back with no cat, TSI 2400 Stall, Brand new TCI street fighter tranny and 323 gears. I'm also running a NX 150 wet shot (soon to be 175)

 

No, its the other way around. When the engine starts, it is in "open loop". It is using long term fuel corrections stored in Cells 16, 17 and 18. It is not getting any feedback from the O2 sensors. It is targetting a "richer" A/F ratio, based on coolant temperature... the colder the engine, the richer the target A/F ratio... just like a "choke" on a carb.

When your engine reaches the correct coolant temp (~120-140degF), the O2 sensors heat up and are active, and a timer times out (about 3-4 minutes in cold weather), the PCM switches to CLOSED LOOP. Then the traget A/F ratio at part load is set to 14.7:1 and the O2 sensor readings are used to adjust the fuel calculations and keep it PRECISELY at that value. When you go WOT, the PCM ignores the O2 sensors, and targets a richer A/F ratio, that is calculated by a formula using RPM and CLT temp. That usualy nets you about 11.7:1.

When does your engine feel like it is sluggish and shutter.... at part throttle, at WOT, or at all times? I can't see those injectors running short on fuel running without the spray.

Have you checked your fuel pressure?

 

When does your engine feel like it is sluggish and shutter.... at part throttle, at WOT, or at all times? I can't see those injectors running short on fuel running without the spray.

Have you checked your fuel pressure? [/B][/QUOTE]

The sluggish feeling is mostly at part throttle like when I'm in onerdriveat 60mph. It also shutters any time when I hit the gas at a lower RPM. It almost sounds like I cant here a real faint miss inside the motor. Like I said it mostly happens after warm up. I have not tested fuel pressure as of yet but plan to this next week. I have also added an ATI inline hi flow pump that I left out earlier. I called the Summit tech line to ask them what they thought and they told me I need a adjustable fuel pressure regulator for proprer operation. They said it doesnt matter how big the injectors are, if their not getting the proprer fuel pressure they say I need for the bigger injectors and cam then I'll be starving the engine of fuel.

I did pull the plugs out after 250 miles to see what they looked like. Just about all of them were white. I don't know, I just cant seem to figure it out.