I'm guessing you are saying to do the same test run again, with O2 sensor connected , but with more variances in my driving? More hard throttles etc? As far as the driveability issues, I'm not sure how I could explain them other than, the truck doesn't feel as alive as it can in an overall sense.... a passenger or unfamiliar driver would never be able to tell if that makes sense. Maybe a miss here and there at idle...? Pretty sure the ses light would be blinking as it should when I were to feel any of the things I don't like if that makes sense. But I will pay closer attention...
This does makes sense. Understand that the blinking SES light is just tell you 1/3 of the story
when it comes to engine dynamic behavior. A/F ratios are 1 variable, the engine's physical
function/compression is a 2nd variable, and of course ignition timing is the third variable.
So if you were to tell me that the SES light was blinking with a 50/50 duty cycle (stoich)
when the vehicle hesitated/stuttered/stumbled/etc., then I could absolutely believe this.
Always remember that the coders of all the data points in the Open Loop tables will
be the first to tell you that they have to assume that support systems like the
Ignition System spark plugs/wires/cap/coil/etc are 100%, the dynamic functioning of
the EGR valve is to specification, the fuel filter isn't partially plugged, the connections
to the fuel pump aren't corroded, the spring in the Fuel Pressure Regulator is correct,
the valves are all seating properly, all the engine sensors are still in calibration, etc.
Saying it another way, IF you experience an anomaly while proper A/F ratios are being
reported, then that's good, for we at least know what the problem
isn't, so using the
Process of Elimination we're one step closer to the solution.
I know it's not a reliable test but if I start my truck up first thing in the morning and take off within a minute (which I hardly if ever do) , it feels really alive.... I did this today to go around the block just to see... Who knows, maybe I'm just confusing that my street's speed limit and limited room between cars is making it feel peppier..but I don't think so.....
If could be part perception. And yet this tells me that your engine's physical condition is pretty
decent if it will run strong cold. Understand that cooler, denser air is always going to give you
a stronger feel from the engine. (HP drops ~1% with every 10°F rise in intake charge temps.)
So when you first start, the engine is Open Loop, the intake manifold isn't heating up the
charge, and the TBI heated air stove is pulling air over yet to be fully heated exhaust manifold.
(We have to heat the incoming air so that the TBI throttles don't freeze up due to the fuel's latent
heat of vaporization causing the humidity in the incoming air to freeze the throttle plates. And
also the fact that we're running a wet intake. If I'm not mistaken, the engineers designed the
charge air temps to be ~90-100 degrees?
In English, a healthy motor can/do run strong on cold Open Loop tables. And once everything
comes up to temp you may feel a slight difference in go power. All depends on how conservative
the ignition timing is vis-a-vis fully warmed up engine operation.
I really do think it acts more tired as the day goes on....
This could be happening despite 50/50 duty cycle (stoich) operation.
As the entire engine bay gets heat soaked, between the higher air inlet temps
& other variables, the ignition timing that was perfect when the engine is cold
may be causing just a little bit of knocking, which the computer responds to by
pulling ignition timing out. So, no pinging/knocking like in the old days, but by
the same token the engine just feels a little soft, a little off it's feed.
But the only way we will prove/disprove that theory will be to monitor the Knock
Counts (live data) while driving.
I hope so.....
If true, any idea why my truck would decide to go rich when letting off accelerator and/or when initially coming to a stop? You mentioned possible tps? or maybe that was somewhere else...I haven't back tracked yet....
I did mention the TPS. The example I used was a TPS sensor that is misadjusted to the point
where the computer never sees the throttle at the fully closed (idle) setting. So the
computer is blocked from going into the idle (or Deceleration) routine.
Or for that matter, the MAP sensor is no longer accurate at high vacuum levels consistent
with low load/cruise/decel/idle conditions. IF the MAP sensor is no longer accurate across it's
full range of measurement, then due to it's authority/importance in a Speed Density system,
the engine's fueling will only be as accurate as the MAP sensor itself. But instead of just
firing the parts cannon, instead we want to monitor what the computer says that the MAP is
telling it. Again, another vote for live data access.
Thanks for all the details. For some strange reason, my mind absorbed it with a feeling of excitement and growth as it made complete sense... What in the world have I done? This wasn't part of the plan...
Good! Thanks to the elegant simplicity of the TBI design, we were able to get our learning model
running with just a couple of inputs, and then in order to improve it's flexibility of operation and
resposiveness to the driver, we kept adding optimizations in the form of additional inputs until it
drove as good as a Quadrajet after a fresh rebuild. The neat thing? If I dial in a Q-Jet for you in
your '74 C10 in Houston, and you hop in and drive straight to Denver, the vehicle would still drive
when you arrived at Mile High stadium, but not as peppy, nor nearly as clean, emissions-wise.
But if we did the same thing on a '94 TBI GMT400, the computer would be retuning the vehicle
~5 times/second all the way from Houston to the mile high stadium...and back. And it would drive
much better while being as clean as possible.
And that's why an old carb guy like me was so interested in learning exactly how these EFI systems
made our GMT400 TBI 350 SBC engine run
almost 90% cleaner than the same SBC in 1970...and
with better manners.
This technology really is worth learning about.
Cheers --
