Struggling through pages of meaningless "EPROM talk", I found that there was at least one definition of %TPS. That was "3.23volts = 65%". That computes 100% at 4.97volts. But it doesn't end there. Later in the file, I find that the default TPS = .96. That corrects the maximum default TPS to be 4.77volts.

I did get a code 21 with WOT at 5volts, and then at 4.8.

To my untrained eye it appears that the current TPS can get corrected from the default TPS, if need arises and as time goes on, but that mechanism is too hard for me to follow.

Before anyone gets worried that their TPS is set low, the highest %TPS that I could find that means anything is 69.9%, or 3.23 volts with the default TPS definition. At 69.9% PE is allowed with no delay. If the TPS is set to a higher voltage than 3.23, full PE will come on a little sooner using the %TPS vs RPM vs PE table. However it appears that you do not want to be any lower than 3.3 volts, or you risk loosing some PE in an engine that clearly wants it.

So my guess is that the highest possible TPS expected by the ECM on a 1985 700R4 'Vette is 4.77 volts. This number can get fudged if a new TPS definition is warranted. The highest meaningful voltage (that is, one that causes action) on a 1985 700R4 is 3.23 volts, using the default TPS definition.

Maybe I will set it back to 4.7 volts - See!! I can't leave it alone! This thing will never run right if I cannot keep my hands in my pockets!!

Of course, I can be totally incorrect in my uneducated interpretation of the code.

Heck, it's raining anyway. Perhaps I will leave it at the healthy sounding .62 - 4.48 that is set for now. Going to 4.7 cannot possibly help anything. Let's see how it runs by tomorrow.

Ouch! My brain hurts!

Just ramblin' on,
George

 

Hello all,

According to Service Technology Group publication # 16030.02-3 (granted, this is an OBD2 text but OBD1 very similar) comments on the throttle position sensor function:

"The TP sensor signal is used to determine idle, Wide Open Throttle (WOT), deceleration enleanment and acceleration enrichment."

When using a scanner, I typically switch to "percent throttle" vs voltage. I ususally check voltage just to make sure it's within a general range, then switch to "% throttle" reading. As long as the ECM recognizes 0 % and 100% throttle positions, I am not sure 4.58 volts is really any better than 4.34 volts at WOT. As long as the ECM recognizes 100%, I am not sure the ECM cares about the higher voltage, as long as it is within the acceptable range. Clearly, ECM uses the TPS signal for trends, ie, enleanment or enrichment and this can make a difference. I would SPECULATE earlier ECM's, with slower processors, are more likely to cause probems when voltages are near the limits. As expected, during WOT or enrichment, the cylinder mixture is likely very rich, guessing around 12.0 to 12.4. Remember, engine design people really want to avoid detonation and build in several layers of safety. It's AIR and FUEL, more fuel with the same air doesn't do much beyond 12.5 to 1 A/F ratio.

As long as the voltages are within acceptable limits(low and high voltages-value vary's slightly among years) and the ECM is getting the correct throtlle angle position information to determine rate, (sweep check), my vote goes to set it and forget it.

For a better understanding of the acceleration enrichment mode, head for page 177, paragraph 3.3, "Corvette Fuel Injection", by Probst(likely available at Barnes and Noble). This may help with a better understanding of closed loop and open loop enrichment.

BTW, darned OBD2 software includes a TPS sensivity check. Good stuff that OBD2.

Keep the greasy side down.

dlmeyers 90 coupe zf6 3 speed shocks


[Modified by dlmeyers, 10:29 AM 11/29/2003]


[Modified by dlmeyers, 11:14 AM 11/29/2003]

 

In case anyone was wondering why my TPS had such a large range (I colud get 5.0 volts) - I found that the idle stop had backed way out. That gives the throttle plate shaft close far more than usual.

The IAC was driven full open - that is why the car could still idle.

After setting the idle stop properly, I can only get 4.7 volts max. That is closer to what others report.

George

 

TPIS claims that some ECMs learn faster than others (sorta like my kids), but GM engineers scoff at this saying "ain't no way".

TPIS stands behind their position, though, based on feed-back from numerous customers' accounts.

85 ECMs are notorious for being sloooooooow.

Jake