Took the car to get dynoed today. I have the stock chip with the correct injector constants in it (SVO 24# @50.5psi). Well it started from idle really good, except it went from 14.1 the climbed it's way up to 15.5!!! and that was at 3800rpm!! He shut it down for fear of running it more lean. wtf. Is the stock chip really that bad? I am running headers, AFPR, SVO 24#, and a couple other things.

In that very short run, it managed 300ft/lbs and 205hp. Not want I wanted to see, but the stock programming is bad.

What can I do to get it a richer up top? I thought at WOT is was supposed to hit 128blms and hold it there? Shouldn't the 24# @ 50.5 be pushing enough fuel through? The injector constant is set at 27.2. This is correct right? The stock 350 injectors are 22# rated at 43.5psi, so after some quick math it came out to 27.2. I checked my math again and again to make sure that is what I was getting.

Sorry it's long, but I need some help.

 

first off no it should not hit 128 blms it should go way rich like to 11.4-12 to 1 and yes the stock chip realy dose suck that bad

 

I assume your car is MAF ?

With the headers, yes - You are going to go Lean at higher RPMS because your VE is pretty dramatically increased.

Why are you running 24# injectors at 50 PSI ?

I suggest that you back the fuel pressure down a little, and using your 02 Mv's start adding PE fuel untill you see approx 890 o2 MV across teh powerband.

Then take it back and dyno it again

 

Well I figured out a little bit of the problem, but I will answer your questions first.

When I first got the car, I didn't know about EFI. I was a carb man before. I didn't know that the injectors in the car were rated at different psi than others. I did what everyone else does and purchased the cheaper SVO injectors. Not knowing that they were rated at 24# at 39.5psi.

The reason that I am running 50psi is becuase my AFPR will not go any lower. I can take the screw out and it will still be running 50!!! That is why I am running 50.5, put the screw in just incase.

That is why I had to change the stock programming from 22# to 27.2# for the injector constant.


I found the problem to be the knock sensor. I don't know if the sensor is bad or what, but scanned the car and it hit 74 counts at wot, and then went down to 0-10. What the hell is is picking up?

TIA

 

No, the stock programming is not that bad. You should be at an AFR between 11-12:1 at WOT with the stock PROM. Something else is wrong. Is the fuel pump original? Lots of time the output will slowly degrade with time before outright failing. Check the fuel pressure during a full throttle pass. There's a decent that could be your problem (pump, clogged filter...) This would also explain the knock counts that result from running too lean a mixture.

 

Thanks, I will check that. I think that I found that the exhaust hits the subframe connectors when the engine is under torque. I need to dent the heat shield in on the CAT. I will post again after this weekend.

Anyone else have anything to chime in?

 

Do what Mark said about checking the pressure when driving the car, GM made the stock chip richer then it really needed to be and it should be close to what is needed on your car.