Well, i got my PCM reflashed and tuned after my PCM failure last week. Got it down to the shop and got it tuned back up. Seems now with my 7lb pulley i have maxed out my injectors... . I was suprised to see my 43lb injectors were at 106% @ 4900rpm's. I redline at 5K anyway so its not like i will be up there that much, but it may be time to start looking at some 60lb'ers. Seems kind of crazy to me that my 43lb'ers are maxed out and i still see 68psi of fuel pressure on my stock pump. Another thing that was a little bothersome was we could not for the life of us get all the knock out of this thing. Even pulling back to 12* at WOT it was pulling some timing out, about the same as it was at 14*, so we left it there. A/F was good at about 11.4 but just could not get the knock all the way out. Cleared out the burst knock table and even lowered the sensor tolerance a little and it still remained. If anyone has any suggestions im all ears. Im not really all that knowledgable about tuning but i can relay any suggestions to the shop guy. Truck is running strong again, now back to my intercooler quest..

 

I know you don't like to hear it, but meth will fix both your problems and let you run more timing. Just an idea. I got a Devils Own kit and it works great. Price was right too.

 

Thats funny, As I was reading his post I was thinking the same thing, METH
it will help with your knock and also if tuned for the meth will help ease the load on your injectors

 

Oh, yeah......and i have just about maxed out my MAF...LOL. Maybe I should not have put the 7lb pulley on.

 

I'm not surprised you're maxing out the injectors. My 4.8 w/ 10 lb. boost is hitting 86% at WOT and about 5500 rpm. I would go with the 60 lb. injectors if I were you. Meth injection (or an intercooler) will help with the knock, but would just be a band-aid over the lean condition, which could haunt you later (just ask mjhoward ). Does the 8.1 engine have iron heads? If so, that can also be a factor. Do you actually hear the knock, or is it just pulling timing? If the latter, how much was it pulling? It is normal to see 1° or 2° of knock retard, even when everything is OK, just the pcm probing the limits.

 

How can you have 106% duty cycle? At 100% they are static. 68 psi is a good bit of fuel pressure too.

 

Hey, im just tellin you what the EFILive map recorded. My gauge may be of +/- a pound or 2 but its pretty close.


Yes, it has iron heads. I can't hear the knock, but its pulling out about 4*-5* sometimes, and sometimes it pulls none at all. Its very odd because we cant duplicate it on any regular basis. It generally does it when i get on it from a dead stop, but not all the time. Rarely does it when i get on it from a roll. I think i will enjoy it the way it is till i save up enough money for a water to air I/C and some 60lb'ers. Bad part is, i will have to remove the blower, space out my fuel rails, and change connectors for the injectors. Unless someone knows of a 60lb injector with the correct GM connectors on it.

 

So did you re-dyno it? If not, how does it "feel" powerwise, any noticeable difference?

 

About the 106% duty cycle, yes that is possible. That is the commanded value, i.e. what the pcm would like to inject to meet the calibration. Of course that value is not possible in the real world, hence the lean condition.

 

I see now. The sensor might picking up some other noise and pulling the timing. I've seen loose fittings and brakets cause that.