So I'm curious how the ECM does this. I know for 8D that it looks at the baseline voltage initially at engine startup and then uses that for delta-TPS calcs on the AE.

But I'm looking at Tunerpro and seeing some constants that I'm curious how they play into this... also since the factory setting for the TPS voltage is .54V. I can see in TP that my ECM is seeing .57V from the TPS.

AIR FUEL Param, TPS Factor for Low Voltage => If after lag filtering, TPS voltage is lower than a calculated threshold (0x0099-see AIR FUEL Param, TPS Initialization Voltage), this factor is used to increase TPS voltage to an acceptable level before computing TPS%.
Factory Default = 0.41

AIR FUEL Param, TPS Initialization Voltage => Initial TPS voltage at key-on or if engine not running. Becomes the threshold (0x0099) against which TPS voltage is measured after being lag filtered. Factory Default = 0.94 Volts

AIR FUEL Param, TPS Initialization Voltage Filter Coefficient => Used to gradually reduce lag filtered TPS Initialization Voltage. Factory Default = 0.39%

 

So thinking about this a little more....

Is there some significance to the .41 and .94 voltages in these parameters? .94 - .41 = .53S versus the factory setting of the TPS voltage supposed to be .54V?

The ECM checks the TPS voltage after lag filtering and if it's less than .94V, it adds .41V to it for the final voltage?

So if someone has the TPS voltage set to say, .60V (which is less than .94V), the ECM will then add .41 to it which will make the default .101V?

I'm not sure what difference this makes, but I'm just curious how it works...

 

Unwritten rule, need the PROM location of the parameters. The names aren't always easy to match up with an XDF and hac.

As for the above, it is the auto-zero parameters for the TPS. The '90 - '92 TPI/MPFI/TBI don't have a 'set' factory value for the TPS base. The sensor isn't adjustable, it is what the voltage is.

Simplest explanation is that the ECM keeps track of the lowest seen TPS voltage. And uses it for the 0% TPS base line. This lowest seen voltage gets filtered into the init TPS voltage to bring the base idle TPS 0% voltage into line (hopefully that statement didn't confuse things).

The base idle 0% TPS at key-on, engine-off is the TPS Initialization Voltage. This is where it starts for 0% TPS. Then once the engine is running the ECM adjusts this value according to what the TPS reports for the lowest seen voltage.

This base idle 0% TPS voltage is what is used to calculate the actual TPS percentage (%).

Not sure about the low TPS voltage factor, maybe an assist for a malfunctioning TPS? To keep things from going totally off the wall.

Recall that the TPS is nothing more then a rheostat, like the old TV & radio volume controls. And we all know how noisy they get.

RBob.

 

Thanks RBob...

0x3E4 AIR FUEL Param, TPS Factor for Low Voltage => If after lag filtering, TPS voltage is lower than a calculated threshold (0x0099-see AIR FUEL Param, TPS Initialization Voltage), this factor is used to increase TPS voltage to an acceptable level before computing TPS%.
Factory Default = 0.41

0x3E5 AIR FUEL Param, TPS Initialization Voltage => Initial TPS voltage at key-on or if engine not running. Becomes the threshold (0x0099) against which TPS voltage is measured after being lag filtered. Factory Default = 0.94 Volts

0x3E6 AIR FUEL Param, TPS Initialization Voltage Filter Coefficient => Used to gradually reduce lag filtered TPS Initialization Voltage. Factory Default = 0.39%

 

While I have your attention..

There are a couple of other parameters too...

0x3E7 AIR FUEL Param, Coolant lag filter coefficient - There's no description on this at all. Factory default is 6.27. What happens if I increase or decrease it?

0x4A0 Loop Closed Param, SLOW o2 Coolant Temp Factor, again no description. Factory default is 60%. Again, what happens if I increase or decrease?

 

Looking back at this thread, RIP RBob.... ugh, what a tragic loss for this forum.

But, something did occur which is making me revisit this since the little over a year ago when I originally posted it.

RBob wasn't able to answer my above questions, so not knowing any better (and being more of a "trial and error" guy), I set the TPS voltage to .94V to see what would happen, since GM had this value at .94V in the code...

0x3E5 AIR FUEL Param, TPS Initialization Voltage => Initial TPS voltage at key-on or if engine not running. Becomes the threshold (0x0099) against which TPS voltage is measured after being lag filtered. Factory Default = 0.94 Volts

I didn't really notice anything different and then just left it that way. Ran fine up until a few days ago.

I started noticing the idle would start randomly getting a little erratic when sitting a stop light....couple of times would almost drop out completely before catching itself. So grabbed TP to see what was going on...

Was able to capture the event and I noticed that when the idle would go erratic, the TPS% value would be randomly fluctuating between 0 and 0.78%. 0.78% appears to be the lowest value that TP will report for TPS%.

I ended up resetting the TPS to .57V and the problem went away.

But that said....

What I'm also noticing is that with the TPS volts now set at .57V, Tunerpro will not register any TPS% increase until the TPS voltage hits .94V.

When I manually move the throttle, the TPS volts respond right away. I'm assuming that this must be some function of how TP reports because I don't see any difference in throttle response. As opposed to the ECM actually responding to this delay in % with any internal functions.

Out of curiosity, I set the value in the bin to .57V to match my current TPS volts, at which point the TPS% reacts immediately with any throttle movement.

The formula in TP for the conversion from volts to % is X * 0.392160 + 0.000000, so I'm not seeing any delay built into the formula which would cause the TPS% to remain at 0 until the TPS volts gets above .94V.

Just curious what might be happening with all this...

EDIT: So I confirmed this is a function of the ECM. I grabbed my old AutoXray and did the same test. Lo and behold... it won't register %TPS change until the TPS volts hit .94V. So then the question is, does the ECM base anything on TPS%? Or is it just looking at voltage?

I suppose the idle issues I ran into could be a reason from some buffer between actual TPS volts and what the ECM considers a % change.

Also fact that I'm not noticing anything driveability wise due to this...

But again, I'm just curious about it all, if someone knows the code well enough to say what's going on.

 

Probably not related but I always wondered if there were differences in the programming for the 88 and down and the 89 and up chip due the improved progressive cam action linkage on the 89+ throttle bodies to smooth out the off idle twitchy feeling.

 

Hard to say. The 6E xdf doesn't anywhere near the parameters that the S_AUJP 8D xdf does.

 

Had a chance to experiment with this a bit...

So it turns out with my TPS voltage set at .57, if I lower the TPS Initilization in the bin to .58V, the %TPS change is instantaneous with the the slightest movement of throttle. But it didn't make any noticeable difference in the way the car runs. Pretty much matches before when I raised the TPS voltage to .94 to match the .94 in the bin.

So I'm just leaving the bin at .94 and my TPS voltage at .57.

It must be that the ECM reacts to the voltage and this %TPS is for reporting. I can't imagine that my Miniram would maintain sharp throttle response with such a huge delay in TPS reaction.

The TPS voltage increases instantaneously as reported in TP, just the %TPS has this delay where it won't react until the voltage reaches the value in the bin... with the factory value being .94.

Any rate, interesting stuff...