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Old 10-08-2007, 10:25 PM   #1
DRW
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TPS adjustment idea

I have an idea, but I don't have an auto tranny to try it on, so I thought I'd post it here for you guys.

I know the newer computer controlled auto trannies use the Throttle Position Sensor (among other things) to gage load so it knows when to shift up and when to hold a lower gear. How about adjusting the TPS so it reads slightly lower? Wouldn't that trick the trans into shifting earlier while still letting you accellerate with a more open throttle? I know that shifting early while using heavy throttle works for MT cars, why not A/T's?
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Old 10-08-2007, 10:35 PM   #2
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acctually i believe i have a button that does it for me! i have normal drive and a power drive button.
using the power drive, i shift later and have higher rpms for faster acceleration.
it is a 1989 isuzu trooper 2.
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Old 10-08-2007, 10:59 PM   #3
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Wouldn't that also mess with the engine as it thinks it might be getting more or less air then what the throttle actually is at?
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Old 10-08-2007, 11:12 PM   #4
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Quote:
Originally Posted by Red View Post
Wouldn't that also mess with the engine as it thinks it might be getting more or less air then what the throttle actually is at?
I know on my car (and the A/T version too) the TPS is not used for fuel calculations, except for when the ecu sees a rapid change in TPS, then it gives an extra squirt of gas known as accelleration enrichment. So it only looks for a rapid change, not specific values. No problem there.
The TPS is also used to know when to go into open loop mode, so adjusting the TPS lower will keep the ecu in closed loop, which will help, too.

Other cars use engine rpm and manifold pressure to calculate fuel and ignition timing needs.
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Old 10-09-2007, 09:57 AM   #5
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Neat Idea

Nice idea, DRW. I'll have to check the shop manual to see how the TCU thinks -- I think it factors-in TPS for a variety of decisions. As far as fuel-injection, I believe it takes other factors into more consideration than the TPS -- so little concern there...

I may try this soon...

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Old 10-09-2007, 02:44 PM   #6
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May not be related to OP but any time someone mentions tps adjustment I have to post this
I know this works for Dodge 3.9 5.2 and 5.9 . Obviously works well for Fords too .The voltage reads are slightly different but the basic priciple is the same.
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Old 10-09-2007, 08:13 PM   #7
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OK, so what's the "Best Guess Estimate" on adjusting the TPS output signal -- it messes with the PGM-FI system and the Transmission Control Unit, so...

Any hypotheses?

+ Voltage = ?
Reduce V = ?

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Old 10-10-2007, 02:11 PM   #8
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Every car I've done this to is pretty close to 1v (performance junky !) . Before you do any tweaks , check the voltage as stated in the letter for a factory baseline. I can tell you that tuning it with less will give a stumble - but the ecu should think the throttle is further closed than it actually is (meaning it will adjust the mixture lean, it could also lock/unlock the torque convertor sooner/later -among a few other things) drop v read in .1 - .15 v increments and test the results.
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