I have installed 32lbs injectors (old 24lbs were partly dead) and the engine is running rich as expected. It drives like hell though and is quite greedy on fuel but I have a problem of passing MOT yearly test due to emissions as CO is over the allowed limit (more than 3.0%) - will it help to install custom made fuel pressure regulator to lower the pressure thus lowering emissions? Reprogramming of PCM is the very last option as I am at the other side of the world (PCM was tuned by Fastchips by mail order years ago) and I need to solve the problem now.

 

You must tune for the larger injectors. There is no other way around it. You also run the risk of washing down your cylinder walls with the excess fuel and causing possible engine damage. You either need to have your 24# injectors rebuilt (FIC is a good place to go), replaced with another set of 24# injectors (used ones can be found for cheap) or get a tune.

 

Forgot to mention engine mods:

LT4 heads and intake
GMPP Hot Cam kit
BBK 58 mm TB
K&N Cold Air Intake
LT4 knock module
1LE air intake bellow
!EGR, !AIR, !TB

and PCM was reprogrammed by Fastchips (mail order).

 

Well, if it was tuned correctly it shouldn't be rich, unless there is another problem. But you can compensate for injector size by changing fuel pressure. We do it all the time as a rough way to get the tune close. Of course, you need an adjustable FP regulator.

Rich

 

If Ed tuned it for 24's, run 24's. To turn down the 32's to 24's, you would have to drop the fuel pressure to 25psi (1.72 bar), rather than the stock 43.5 psi (3 bar). That would probably reduce the fuel atomization and affect the spray pattern negatively.

 

Ed is really easy to work with. give him a call. He will probably fix you up with another mail tune for extremely cheap or even free (minus shipping costs) I know what I had to go back with an injector change he didn't charge me.

 

just curious, if you have tunercat or something do you still need an adjustable fp regulator to change fuel pressure?

 

Cars with returnless fuel systems typically have a FP senor and a variable speed pump controlled by the PCM. The PCM regulates the pressure, so it can be changed by tuning. The LT1 has a more conventinal return-type system in which the FP regulator is mechanical and controls pressure by restricting the return line (the pump output is constant). With that kind of setup you need an adjustabe FP regulator to change pressure.

Rich