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[3 Svo] How to adjust Throttle Body



Mike,
 Thanks for responding,I'd can't belive someone questioned the S.V.O. GOD
                                          Neil


At 11:20 PM 10/7/97 -0600, you wrote:
>I always set the value to less than 0.90 VDC at closed throttle and
>greater than 4.50 VDC WOT - new TPS's will alwyas make that range unless
>they're defective, so return them (1 year warranty). The EEC processor
>uses a 10-bit A/D (actually 8-bit with the other two bits being
>extrapolated thru some capacitors). Since the range is 0-5.0 VDC
>(approximately, the A/d will never convert to 0 (minimum) or 1023
>(maximum) cause it only sees say 0.8 to 4.7 VDC of a range.  On the PE
>SVO calibration, the threshold transition between closed and part
>throttle is very near 0.92-0.95 VDC - you can check this with a timing
>light: idle the engine and loosen the TPS (an advance-tyoe light is most
>useful). Rotate the TPS until the timing jumps - it will increase 15-20
>degrees when part throttle is detected - and drop nack to the base
>timing (30 degrees BTDC in Premium setting) when closed throttle is
>detected again.
>
>The problem of setting it too high is the engine will maintain a high
>idle if closed throttle is never detected - this is what the major
>symptom is when the TPS goes defective.  The original software premise
>was that the EEC could keep track of what the min and max throttle
>settings were for the entire cycle and "decide" a floating lower and
>upper end and adjust automatically. That theory went away by the end of
>MY (model year) 84 cause it flat out didn't work - couldn't compensate
>for driver characteristics and defective parts at the same time (suppose
>the drive never used full throttle - what happens to the three ranges
>then??). Notice that all original TPS's had no adjustment and ALL
>replacements do have an adjustment range - this isn't accidental.
>
>If you set yhe TPS on the hairy edge of closed-to-part throttle, the
>throttle response will improve cause there's not much pedal movement
>before the timing jumps and the fuel map changes but if you're off my a
>few millivolts you'll be dogged [intermittently if your throttle body
>shaft and linkage are worn] by the high idle thing cause the plate/shaft
>won't return to the exact same position every time. This also can effect
>parking lot driveability. I usually don't go for the hair cause I just
>leave with a louder pedal. Effect on fuel consumption is insignificant,
>in my experience. 
>
>It's difficult to differentiate between how it was originally designed
>to work and what it actually does. I live in the world of software
>testing and see this alot.
>
>-Mike Fleming
>----------------------------------------------
>Cory Erickson wrote:
>> 
>> On Tue, 7 Oct 1997, Gary Morrell wrote:
>> 
>> > I'd like to know the reason for this as well.
>> >
>> > For most calibrations, 0.9V is above the threshold where the base tables
>> >  transition from idle -to- part throttle. I would expect this to improve
>> > driveability a bit, as richer mixtures almost always improve
driveability, but
>> > there is extra fuel in the part throttle tables, and this will put
extra load
>> > on the catalytic converter and could result in elevated HC's and a
flunked
>> > emissions test.
>> 
>> I always worried about which was _the_ correct setting for the TPS...until
>> realizing that the TPS voltage is run through an ADC (analog to digital
>> converter). Talking to Mike Flemming, he told me that the eec relies on
>> the _relative_ values (or counts) of these ADC's....like 555 relative
>> counts of the TPS is WOT. Relative means that when the circuit is
>> initialized, if the voltage by the TPS is within "range", a relative 0
>> count is assigned to the eec. So to make a long story short, I don't think
>> it matters a whole bunch. Everything is relative to the initial voltage of
>> the TPS...I just set mine to about .990 and say "good enough."
>> 
>> Cory
>
>