TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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I was on the "______ 4x4 boards"....yeah my big 3rdgen has a t-case and stuff. This is TBI related though This guy was running a 383 stroker, with with a holley 670, stock fuel pressure, vortec heads, and a 268h cam ( the cam i have in the short block ) with a stock chip, and he's asking why at idle it surges back and forth from 1200-1800 rpm and driving it stumbles at 1800-2100 rpm. The people vaguely hinted at needing a chip, mostly said to get the hypertech stage 2 offroad chip lol, or replace tps, or iac, or EGR is bad, or ignition is bad. He said he swaps the original 350 tbi system back on and it drives better, but still has the same problems, just not as bad. Someone who sounded like they were from here finally chimed in and posted step by step how to set the idle and tps and said he seriously needed to modify the fuel injection and tune chips, and he got a steady idle pulling 14 or 15" of vac. but even with the surging gone, I can't imagine much from a 383 with vortecs with a decent cam for tbi and a stock 350 tbi and injectors with stock fuel pressure, plus stock chip still..... then the thread end.
You are right with the stock fueling he ishn't doing very good on power, probably less than stock.
Really all that needs to be changed is go to 454 injectors, calculate and change the Injector Constant, dial in the VE table, redo the spark table, set the comanded idle, and change the PE fuel to 12.6:1. I like to set the open loop table to 12.6:1 all the way across as well. (That is what works best for me). Basically at 100 map and open loop I want 12.6:1 air fuel mixture. Below that map the Air/Fuel to Map table takes up and leans the mixture as vacuum increases(much like the power valve or power piston and metering rods in a carb). I treat the thing just like a carb but more exact and changes easier and less time consuming to make. Heck, to tune a TBI I don't even have to open the hood!
shoot, what do I need to do you get you down in NW side of SA once I get the motor and trans in? help me tune a little lol
Oh also, for headers, if I have a 94 chassis, with vortec heads, do I need headers for vortec heads, or will headers for my 94 chassis headers meant for 193's work? I didn't check the differences, since I didn't have the 193's and vortecs at the same time
Last edited by z71stroker; 03-12-2005 at 02:32 AM.
Headers for the 193 should bolt to the vortecs fine. I know the cast iorn manifolds will bolt over because I have helped a friends stick a pair of 305 vortecs on a 400 in a caprice. Those bolted on fine. If I am not mistaking I believe that the manifold on the passenger side is the same between vortec and non vortec but I could be wrong.
I will see if I can send you a copy of my latest BIN file sometime this weekend or next week, just so you can use tunerpro to see what I have done. Be warned it is for 454 injectors in a TBI headed 350 with a LT1 cam and is not compatible with your ecm. It is based off of a late 80s ASDU 350 calibration, just changed from there. I will also PM you the injector constant math if you are interested.
sounds good to me. so by 454, they are 70/80lb'ers? I am trying to find some GM 17084304 *RPD 80lbers, and I'm supposed to use turbolink4 or TTS to look at my ecm, i have the memcal stuff, is that right? is a 50-100kpa fuel curve a big alteration from 30-100? I'm coming along slowly, I think.
) with a stock chip, and he's asking why at idle it surges back and forth from 1200-1800 rpm and driving it stumbles at 1800-2100 rpm. The people vaguely hinted at needing a chip, mostly said to get the hypertech stage 2 offroad chip lol, or replace tps, or iac, or EGR is bad, or ignition is bad. He said he swaps the original 350 tbi system back on and it drives better, but still has the same problems, just not as bad. Someone who sounded like they were from here finally chimed in and posted step by step how to set the idle and tps and said he seriously needed to modify the fuel injection and tune chips, and he got a steady idle pulling 14 or 15" of vac. but even with the surging gone, I can't imagine much from a 383 with vortecs with a decent cam for tbi and a stock 350 tbi and injectors with stock fuel pressure, plus stock chip still..... then the thread end. 
