[Diy_efi] Where to start...

Rick McLeod dunvegan
Sun Mar 26 13:05:22 UTC 2006

One item to make sure of when modding tpi is that you have enough injector and fuel pressure when you modify the engine, early TPI used either 19 or 23 # squirters, WOT on a modified engine may like to see more, so mechanically make sure everything is there, not just part. Lingenfelter wrote an excellent book on the injected SBC, he covers it as a system, not just add on components.
  Then, tuning 101 on the ftp/web site will give you guidance, usually starting w/ closed loop parms for drivability, then start inching up the WOT while monitoring performance against baseline/previous tune. This is an area of sneak up on it, you can't hit it first time w/out massive experience! As for hunting w/ one bin vs. another, the bins are very specific to an engne build, so that doesn't surprise me w/ a modded engine.
  Also, you might start w/ ARAP as a baseline, it was a fairly aggressive non-prod bin that was used for media events in tpi cars. It's a reasonable safe starting point.
  As you tweak idealy BLM should fall in midrange, 128 or so if I remember. Idle is simple to adjust, table for it vs. coolant temp, w/ an adder for non-PN and ACon, if an auto.
  On my '86 vette and '87 camaro, I set up all the ECM initials per the factory recommended procedures, IAC, TPS, base idle, etc using the disconnect wire and once that is set then base timing, then recheck the previous to make sure base timing didn't screw them up. The base is where you'd be looking to set up your base from 6* do 8*. The ECM/EST will only advance timing, not decrease. Once you get all that done, then start your sneak up on the tables for timing vs. load, enrich vs load, etc while monitoring data. when you get the closed loop settled down, then you can start sneaking up the WOT stuff.
  Good luck, read, read, read, and read more before tweaking, it's a system, not an add on that makes the good things happen, one simple add on is a waste of money.
  hth, -rick

Rich Rubel <rrubel at toad.net> wrote:
  I've been monitoring this list for a while, and asking one or two 
questions, but I'm now at the stage where I have to seriously start 
working on tuning my car.

What I have:

- 1986 Corvette TPI, very far from stock. Bigger heads, 52mm TB, 
Lingenfelter cam and intake, headers, more. Engine should easily 
make 400 HP, but doesn't feel like it (track numbers bear that out).
- PROMinator flash-programmable MEMCAL replacement on a 165 ECU, with 
8 slots for programs.
- WinALDL to monitor the car via the ALDL port
- TunerCat to make changes to the program
- a stock bin, an off-the-shelf MEMCAL bin (like a Hypertech), a 
first cut at a custom bin.
- laptop.
- GTech Pro (the good kind with full displays)

So far I've been limiting myself to changing simple things like fan 
temps, overdrive shift points (it's a 4+3 transmission), and things 
like that.

What I need to do is:

- bump the base idle because this cam wants 800 RPM minimum idle. I 
know I can't just change the set screw on the throttle body.
- bump the base timing from 6* to 8-10*
- figure out why my idle surges with one bin and not with another, 
and why it's so rough
- make sure the A/F ratio is correct at idle, light throttle, and 
full throttle
- keep the car able to pass MD emissions treadmill test (which it did 
even in its sad state of tune)
- get the most power I can get at full throttle.

Since I can have several programs installed at once, I have no 
problem creating an economy program and a speed program... but even 
though I've read a bunch of articles on the net and looked at a 
couple books, I have no clear idea where to begin. I haven't found a 
coherent explanation of the tables in the ECU and how changes in one 
place affect another, nor how the computer corrects for various 
conditions - so that it might override my changes if I set things too 
far off.

I realize this is a tall order, but any suggestions/help would be 
appreciated. I don't have easy access to a dyno, but I do have the 
GTech for making comparison runs.


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