View Full Version : Tuning TBI
09-16-2006, 10:24 AM
Where can I find good info on how to read my datalogs. Im using datamaster and tunerpro. I dont have any of the stuff to burn my own chips and it seems to hard for me to learn how. I just want to know how like the fuel trim works, and how to read O2 volatage. So I can set my fuel pressure right without running too rich. Can you tell how much air your getting and the efficiency of air intake by the diffrence in the BAP and MAP or is this to inaccurate. Like on a colder day would the BAP be higher or will it stay the same? Why does the O2 volatage jump all around between high and low volts then at WOT it stays the same? One more question what should my 02 sensor be at at WOT for best power, and how much timing should I be getting without knock at 195 thermo and 93octane?
09-17-2006, 07:46 PM
Im at about 190degrees, and only getting about 21 or 22 degrees advance at WOT. Im running 93, but im getting like 1 or 2 degreese of knock retard. Im on a stock 95 TBI 350. Is this KR normal? Anyone with a stock TBI set your WOT shift points lower it seems like my truck could be faster if it shifted earlier instead of sitting at 4000rpm and no making any power?
09-18-2006, 10:13 PM
Sounds like your injector Duty Cycle is getting above 85-90% @ rpms above 3,500 or so, not at all suprising on even a stock TBI 350 with the stock 61 lb/hr injectors @ 12 PSI. Check the duty cycle. The stock long-block should have no problem turning to 4,600 RPM WOT upshifts.
At part throttle the O2 sensor jumps around because it is in closed loop. Under heavier throttle, about 85% TPS or so, the ECM will enter PE mode and dump enough fuel to bring the mixture down to 12.1:1 or so and exit closed loop.
It is hard to select an ideal voltage for PE with a narrowband O2 sensor, but I would say somewhere between .850 and .900 would be safe.
The difference in Barometric Pressure and MAP would let you know how badly restricted your intake is. The difference in Baro and MAP is known as VAC or vacuum. I have run STOCK TBI units on 350s approaching 275-300 FWHP @ 4,500 rpm and see less than 1.5 in/hg of vacuum under the TBI. I mostly run a 1" thick open center TBI spacer though. I have seen a spacer of this spec drop the intake vacuum a full 2-3 in/hg in some applications, without touching the TBI. FULLY Opening the IAC @ WOT in the programming is typically worth about 5 KPA MAP or somewere around .75 in/hg. The spacer and opening the IAC valve were worth 15 RWHP @ 5,000 on a 300 HP 350 (older 300 HP 350 GM crate engine from the 90s) utilizing the stock unmodified TBI unit.
You should be able to run 24-28* total timing all in by 2,800 RPM on most TBI 350 engines. If it is knocking before this, suspect a fuel delivery problem, lean air/fuel mixture, or carbon buildup. The later can be greatly reduced by Sea Foam thru a vacuum hose.
09-18-2006, 10:27 PM
Where can I find good info on how to read my datalogs. Im using datamaster and tunerpro. I dont have any of the stuff to burn my own chips and it seems to hard for me to learn how. I just want to know how like the fuel trim works, and how to read O2 volatage. So I can set my fuel pressure right without running too rich. Can you tell how much air your getting and the efficiency of air intake by the diffrence in the BAP and MAP or is this to inaccurate. Like on a colder day would the BAP be higher or will it stay the same? Why does the O2 volatage jump all around between high and low volts then at WOT it stays the same? One more question what should my 02 sensor be at at WOT for best power, and how much timing should I be getting without knock at 195 thermo and 93octane?If you want to learn to read datalogs and even burn your own Proms, read the chip burning writeup by Badburban in the "Tech Articles" forum and then read the Eprom tuning software sticky at the top of this forum and then follow all the links and read as much as possible. Then follow the links from the sites you were linked to and read some more. Once you have done this several times, it will all start to make sense. Then when you have more specific questions, post back here. The tuners will chime in to help. HTH
09-19-2006, 01:54 PM
I dont plan to keep my truck very long, so I dont want to buy everything to burn chips for it and just have a newer truck with ODB2. I realize that tuning my own chips could be a lot better as it takes so many to get it perfect. I had Brian from tbichips tuning my chips and ive been through about 6 or 7, but I havent heard back from him. I mainly just want to retune my shifts points back to stock so if I try to sell my truck someone wont think somethings wrong with the trans. And to have no knock and get some milage back instead of 9 and 10mpgs, but thats not as important to me as the shift points and knock retard. I might have to start learning and burn my own chips if I have no one to do it for me.
Anyway I adjusted my fuel pressure a lot higher and went thorugh about 5 chips tuning it leaner and leaner. I screwed up my fuel lines when I was cleaning my egr, so I had to take my tb spacer off. Ive also already ran seafoam thourh and I think it fixed my low throttle stumble.
Since I have no tb spacer I have no fuel pressure gauge anymore. Im going to try to get it back on. But shoudent my computer tune itself for the fuel pressure?
Sorry for the long post, but if anybody wants to tune my chip for me let me know. Thanks for yalls help.
09-19-2006, 02:07 PM
Im only getting about 13 degrees of timing at 2500 and at about 4000 im only getting about 20, and by it shifts about 21 or 22. Theres about .3 to 1.3 degrees of KR thorugh the rpm range. Can I go lower temp thermostat?
09-20-2006, 02:11 PM
On datamaster is says my INJ DC is 52.9 percent at 4225rpm and my BPW is 7.51. Is this only for one injector or is it really at only 52.9 percent dc.
09-20-2006, 05:17 PM
I never thought of this but could my base timing be off. Could it be retarded so im not getting that much timing. Or Would the datalog not show it becuase it only knows how much the spark is advanced electronically and not how much advance phsically?
09-21-2006, 02:46 PM
Sorry for posting so much. Im going to add some fuel pressure. By 3600rpm my KR is gone and it dosent come back. But from the time I went WOT at a stop there was a little less than a second where my O2 volatage was about 700. Once I get to 4000 it drops to like 814 823, but in between rpms its at 850 to 890. Ill see what this does its not getting any knock counts it just gets about under 2 degrees KR under 3600.
Sorry for posting a lot of questions and not trying to look them up myself.
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