Re: [Amc-list] TBI fuel injection tuning...

[Wrambler242@xxxxxxxxxxx]

TPI shortens transport time and, the big thing is it makes all cylinders equal.
Well, not exactly but probably not very measureable!
With TBI you inject and mix in the center of the intake.
You have long runners and short runners, then cylinders then, exhaust ports to mix it back together and measure it.
So some cylinders are probably rich and some lean.
Oxygen sensor only sees the blend going out.

With TPI it still only sees the blend but you take the intake and mixed up runner lengths plus fuel drop out of the equation.
 
  They actually have made and maybe still do batch fire port injection.
They just shoot fuel at the back of the valves, open or closed.
I never have got a handle on how that works without creating a gas hog, but it does.

--
Mark Price
Morgantown, WV
1969 AMC Rambler, 4.0L, EFI, T-5
2004 Grand Cherokee Laredo, 4.7L, Quadratrac II
" I realize that death is inevitable.
I just don't want to be around when it happens! "

 -------------- Original message ----------------------
From: Tom Jennings <tomj@xxxxxxx>
> This weekend I plan on driving around with the system in open loop to 
> tweak the tables into 100% perfection. It's awful close now. Air temp in 
> the morning yesterday was 80 (sorry, I don't mean to offend you cold 
> weather people) and the BLM (fuel trim) indicated rich (like 1%). At 
> night, air temp in the 60's, it was spot on. TBI is one hell of a good 
> carburetor!
> 
> 
> But I can now see TBI's limitations. Since the oxygen sensors are so 
> stupid (they say only lean/rich, basically) the exhaust gas oscillates 
> rich/lean/rich/lean/rich/... a tiny bit, all the time, even at steady 
> cruise. It's something like 1 - 4 excursions per second, so mixture is 
> off-perfect most of the time. This is "transport time", how long it 
> takes for a change in fuel at the manifold (your foot, or software 
> adjustments) to get detected at the O2 sensor.
> 
> So does TPI basically shorten transport time, a lot?
> 
> 
> I have "highway mode" disabled now, where it runs extra-lean under 
> highway conditions. That's the next project in there I think. I have a 
> trip to Tucson coming up in December, so it all better be done then!
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