thanks for your help man!! I am going to definitely give that a try when i get home... the only thing that i am not sure about is the 252cc stock ecotec injectors.... i kno its 55psi stock... i saw the gauge before i had an adjustable fpr



|Forged 8.9:1 Wiseco Pistons|Forged Eagle Rods|HPTuners|60trim|Tial Wastegate|
|Precision Intercooler|2.5" Exhaust|2.5" Charge Pipes|630CC Mototron Injectors|
|Stock: Fuel Pump, Transmission, Manifold, TB, Head, Head Gasket, Ignition, Suspension...|

So now that everyone is trained to think a 17 lb injector is a 17 lb injector, they need to be retrained to adjust 'em for fuel pressure changes, eh?

Here's something that might help.

http://go.delphi.com
Look up your injectors by make, model, engine, year. Get the specs. Flow is in lbs/hr, so to convert to cc/min multiply by 10.5. Pressure is in kPa, so to get psi multiply by .145038 .

So Delphi's information shows 252 cc/min @ 55 psi in the stock application. If your pressure is different

I won't promise that site will always be correct, but it has been every time I've used it.

GM injectors in the past were listed by flow at 43.5 psi. Ford injectors were at higher pressure. I think Shifted's got this backward. Recently GM has been increasing the pressure at the rail to improve atomization and emissions.

The injector constant represents a base amount of time the injector is on for to deliver a specific amount of fuel (I know SweetnessGT understands this). Bigger injectors mean smaller constants, or less time the injector is on. It may help to think about filling a bucket with a garden hose, which might take 2 minutes, or with a much larger fire hose, which may take a second or two.

Make sure the fuel pressure is read with the key on and engine off. If the engine's running the pressure reading will be too low.

Here's the numbers I get:

Your injectors @ 35 psi = 37.67 lbs/hr or 394.67 cc/min.
Original injectors are 252 cc/min
So 252/394.67 * .17800 = 0.11365

Part of the error in the calculations above was an incorrect scale for fuel pressure. Injector flow and pressure have the relationship new flow = old flow * (square root new pressure / square root old pressure). Obviously, this does not produce the same result as saying injector flow = 10.11 cc per psi, so new flow = 10.11 * 35. Here's an example of correct and incorrect flow ratings at different pressures with the 440 cc injectors :

New pressure	Correct flow	Incorrect flow

10	210.9638527	101.1

15	258.3768966	151.65

20	298.3479416	202.2

25	333.5631392	252.75

30	365.4001114	303.3

35	394.6772288	353.85

40	421.9277053	404.4

43.5	440	439.785

50	471.7295153	505.5

55	494.7540896	556.05

60	516.7537932	606.6

65	537.8544007	657.15

70	558.1578897	707.7

maybe it is time to put the factory tune back in and start over. Change the constant from there, if it does not start, take it out and keep it running for 10-15 minutes, your computer should make some correct adjustments. That constant can be WAY off and the car will still run.


HP Tuners | Garrett T3/T04B | 2.5" Charge Pipes | 2.5" Downpipe | 650 Injectors | HO Manifold | Addco front/rear | Motor Mounts | HKS SSQV | Spec stage 3 | AEM UEGO Wideband | Team Green LSD | FMIC | 2.3 cams | 2.3 oil pump swap | 280WHP | Now ECOTECED

if i had my laptop, i would be walking outside right now!! Its at my buddies house... i going to try this tomorrow

thanks slowolej and sweetnessGT, i will try both and see what happens...



|Forged 8.9:1 Wiseco Pistons|Forged Eagle Rods|HPTuners|60trim|Tial Wastegate|
|Precision Intercooler|2.5" Exhaust|2.5" Charge Pipes|630CC Mototron Injectors|
|Stock: Fuel Pump, Transmission, Manifold, TB, Head, Head Gasket, Ignition, Suspension...|

now is this where the short term and long term fuel trims come into play?

if i keep backing off the injector constant with small adjustments shouldnt I see my fuel trims get closer to -4 rather than -14



1989 Turbo Trans Am #82, 2007 Cobalt SS G85