[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[2 Svo] How to adjust Throttle Body



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