Those will have to work for now.. Im tapped out.. unless someone has too much injector and is willing to trade for some bosch injectors.. I heard its hard to get the car to idle right with 50# injectors.. is this true? what about with a higher # injector?

 

You will probably need to raise the fuel pressure to get the 42# injectors to flow enough fuel. The larger high impedance injectors (50# range) do seem to have a bit of a problem operating properly at very short pulsewidths, but it's not terrible. Larger injectors are almost always low impedance and don't have a problem. A buddy has 160# injectors in his Mustang and it idles decent (albeit at ~1,300rpm). He is using an Electromotive TEC3.

Rich

 

My idle I would like to be about 700.. The injectors I have are bosch and was told they flow very well.. What should the fuel pressure be around at idle? At WOT? What are High Z injectors? I have seen those go up pretty high..

 

high Z = high impedance, largest you usally see are ~50lb/h
low Z = low impedance, readily available up to ~160lb/h

Unfortunately, you can't use low-z injectors with a stock PCM (without a converter box). The FP you need will be determined by your AF ratio at WOT.

Rich

 

If you are really gonna see 18-19 psi, and run no intercooler, I would run 104ul and 60 lb Mototrons. If you try to do stuff in a hurry and on the cheap you will blow it up.

 

My 84's idle fine - with LJ's impedence converter box.

When you raise the fuel pressure, you also have to raise the injector constant in the ECM, else the computer will eventually cut pulse width and negate the effect of the increase. Use this formula:

Injector constant = injector size * (new fuel pressure / old fuel pressure)^.5

For example:

Injector constant = 42 * (50/40)^.5 = 47

So, the 42's at 50 psi will flow 47 lb/hr, but you have to program the computer for 47 lb/hr.

Fuel pressure should be checked at idle with the vacuum line off the regulator. At full throttle, it should be base fuel pressure + boost pressure. If it isn't, you don't have enough fuel pump or the regulator isn't working right.

Mike

 

please explain this to me... How do I know what the fuel pressure is with that line off? I have a fuel pressure guage in my car.. How do I know if I need more pressure or not? How do I know what Lb to program the comp to? Lets say im running 15 lbs of boost.. lets just use that as the boost so i can get the formula down

 

You remove the vacuum line from the regulator, start the engine, then check the pressure. It should be ~40 psi.

You need more pressure if it runs lean. But, you have to change the injector constant in the ECM if you raise the pressure or it will cut the pulse width and run lean again.

You figure out the injector constant using the formula I posted above.

Check the fuel pressure at full throttle / full boost. At 15 psi boost, you should have 55 psi fuel pressure (assuming 40 psi base). If you don't, the regulator is faulty or the fuel pump is inadequate.

Mike