Running 42 lb injectors, is a PCM reprogram necessary to get it to run right?

So I just got done rebuilding the engine while adding forged pistons and other goodies. I also put in some 42 lb Lucas injectors so I could ditch the FMU......I was under the impression that the PCM could compensate for them and run them at least "OK" for awhile.

I currently have a CC306 program in the PCM, designed for the stock injectors. But I can't seem to get it to run right. It is running WAY rich right now. I thought it was the rocker arms, but damn, I've adjusted and re-adjusted all of them and I can't find one that's off. It's running so rich that it seems like a few of the cylinders are misfiring badly.

Do I have to reprogram to get it to run right for sure? I thought these were "plug and play" things. Should I just keep messing with the rocker arms and hope that's the cause? All plug wires are in order, all plugs tight, cam and crank gear were lined up correctly.

Thanks for any help.....

You need to change the injector constant to 42lb/hr. Of course it is running way to rich! The computer uses the injector constant to figure out the injector pulsewidths. It thinks it has 24#ers in there when it actually has 42#ers. The pulse of fuel is 75% larger than the computer thinks it is. The computer will try to compensate but as soon as the BLMS reach 108, which they will very quickly, its compensation is done and your left with a pig rich, barely running motor.

So in answer to your question, yes you have to change the program.

Where is your tune from. Changing the injector constant in the LT1 edit or Tunercar programs is about a 2 second operation. (minus dumping in the program) Either pick up Tunercat or LT1Edit or send back the PCM to whoever tuned it and ask for the injector constant to be changed.

Bill

It's a program that was on Brent Franker's website (I think), it was supposedly a professionally designed program for that CC306 cam.

A friend of mine had used TunerCat to put it on there.

Well, guess I'll be getting LT1_edit sooner than I originally thought.......

If your friend has tunercat and programmed your computer then he posses the necessary tools to fix your tune. Just have him go into the ECM Constants and change the injector constant.

Bill

He lives in Arizona now. I'm hosed. :)

Just ordered the editor this morning though. :)