In short, how can you get big injectors to run decently at low rpm while not at WOT? The 75#ers in the Red 95 Z28 (see sig.) run great at WOT but make the car pig rich during normal driving and cause the spark plugs to foul.

Now some details & observations: I had a tuner over and we were trying to solve the issue. A/F ratios at a bit less than 13 at idle and going way lean (11.5) up to about 4krpm causing the car to sputter. For clarification the is not at WOT. 1.3 MS pulse widths. Changes were made until the PW's were at .9ms but the A/F ratios were about the same. Fuel pressure set at 43psi at idle jumps to about 60 psi at times. (Aeromotive APR installed)

Now the big question: Should I run smaller injectors or is there a way to make it happy and not foul the plugs?

Thanks in advance,

Dave

 

Rise the idle, oure car runs perfect at 15 a/f at 1350rpm at idle in park (1200 in drive), under that it just dies, no vacum at all beacuse of the cam... Thats widh 150lbs injectors

 

Mine idles fine with 84's. You just have to decrease PW enough. I think the stock LTx ECM has a minimum pulse width that only the most recent version of TunerCAT will let you reduce.

Mike

 

We did use turnercat (not sure what version) to make the reduction to .9ms. The problem with that was when you mash the throttle it would go WAY lean (18:1) and cough before it could catch up with the change.

 

150's???

 

Are you running it in MAF or SD mode? CL or OL?

 

MAF

Closed loop.

 

Have you tried playing with the MAF calibration tables?

 

Yep we did dable with that and I think that gave us the best results but it wasn't much better.

 

What MAF sensor are you running? If it's not stock, then you should be able to install the stocker, complete with screens, and the stock MAF calibration table, put in an injector constant of 75, set the fuel pressure back to stock, and it run just fine.

Mike

 

If it were only that easy. LOL!!

Stock MAF installed. MAF table has been altered to account for High RPM short commings. 43 is stock pressure but the after market pressure regulator bumps the pressure up when certain conditions are present. With all that you have suggested the PW's stay at 1.3ms. We took about 50% out of the maf tables at low rpm and it helped but only very slightly. The PW's were at .9 but it didn't change the A/F much because I don't think the injector can respond that fast. And that's when it would go crazy lean until the fuel pressure jumps. Easing into the throttle the engine would rev ok but a/f ratios were still about 11.5/1 at 2500 to 3krpm even with a .9 pw. This is observed without a load. I've also tried starting with really low fuel pressure but it doesn't like that either. I'm looking into the latest tunercat and possibly some smaller injectors. I just thought somebody might have a trick I didn't think of yet. Thanks for the help.

 

It sounds like you have something else wrong then. My 84's weren't that difficult to get running right. I'll bet you have a bad sensor or injector.

Mike

 

I have thought about that but what is the most likely one it could be?

It could also be the FPR is bumping the pressure too much and the PCM can't keep up with the changes????

 

You could run an experiment by installing the stock 24's, set the injector constant back to 24, then see how it runs. If it runs fine, then I'd be suspect of the injectors themselves.

Mike

 

Not a bad idea but I don't have a set of stockers. I've got 36's, 50's, and the 75's. Any best guesses? I'm pretty sure all the sensors are original and the car is 12 years old. What would go out first?