'84 tps
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Safety Car
Joined: Sep 2004
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From: Mission Viejo CA
'84 tps
The adjustment specs for the Throttle Position Sensor (TPS) say 0.525 v +/- 0.075 v for my '84 CFI. That's 0.45 v min. to 0.60 v max. Even if I set this to 0.40 v or 0.65 v, I can't tell the difference. How does this adjustment affect the ECU? I presume it's got something to do with the fuel mapping, but what?
Le Mans Master
Joined: Sep 2013
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From: near the thumb in the mitten
The tps setting 0.50v signals ECM that the throttle plate is closed / engine is at idle. As long as it is within the proper range you won't notice whether it's .45 or .60 unless you are using base idle screw to adjust it., which is altering min idle speed. When setting TPS volts the engine needs to be at minimum idle speed or idling a the specified rpm with out the aid of the IAC device. With Cross-Fire it is very important the the throttle bodys be in "sync". At that point the TPS should rotated and screws tighten verifying setting didn't chance. The TPS has more to do with IAC, EGR, A.I.R., & clear flood. If TPS value is too high ECM can turn egr on at idle, not reduce IAC counts to slow engine speed, A "sail on" condition where car won't coast down and may maintain speed unless brakes are applied. The MAP sensor is more in tune with fuel mapping. The TPS, O2, Tach signals all are inputs to the fuel map. If MAP sensor hose is off ECM will supply excess fuel regardless of TPS volts.
Thread Starter
Safety Car
Joined: Sep 2004
Posts: 3,953
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From: Mission Viejo CA
Everything is normal on the engine: throttle bodies balanced, idle screws not touched from factory, IAC's connected and working, idle speed normal, EGR working fine, MAP sensor connected and good, O2 apparently okay, starts good, runs good. TPS can be about anyplace! What's it doing?
Pro
Joined: Jan 2003
Posts: 706
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From: Denver Colorado
Everything is normal on the engine: throttle bodies balanced, idle screws not touched from factory, IAC's connected and working, idle speed normal, EGR working fine, MAP sensor connected and good, O2 apparently okay, starts good, runs good. TPS can be about anyplace! What's it doing?
Team Owner
Joined: Aug 2004
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From: Park City Utah
with the above 100%. IME, the actual min setting/voltage doesn't matter that much. As long at it's AROUND .5v, it's fine. I laugh when folks say you have to "set it to .525v". .525. WTF.
What the TPS supplies the ECM that is meaningful, is throttle position change, and rate of change and that is what's necessary for the ECM to supply the correct "pump shot" for enrichment during accel and enleament/fuel cut during decel.
An interesting thing to play with, is w/the engine running at idle, manually move the TPS open slowly, while throttle stay closed. What happens? Nothing. You may get a little surging of the inj spray pattern if you move the TPS too fast, but you can move it all the way to "WOT" and the engine should continue to idle mostly normally. Mine did, in the past. Now, do the same experiment again, but move the TPS fast. What happens? Injectors DUMP fuel for a brief moment, as you stroke the TPS. The TPS, during this "testing" should work very similarly to an accelerator pump in a carb.
.
Last edited by Tom400CFI; Feb 22, 2016 at 11:06 PM.
Thread Starter
Safety Car
Joined: Sep 2004
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From: Mission Viejo CA
Tom and 1984, that's exactly what I'm seeing! I couldn't believe it was so non-critical, after all the information I read tells me it's VERY critical! Thought I must be doing something wrong. Thanks for verifying that I'm not quite crazy (yet)!
Last edited by Hot Rod Roy; Feb 23, 2016 at 02:20 AM.
Pro
Joined: Jan 2003
Posts: 706
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From: Denver Colorado
It is as you noticed. The "start/stop" voltage is not that important as long as they are in the range. What really matters is the change in voltage, the rate of the voltage change and that the variable resister in the TPS is in good shape so the voltage changes smoothly with no dead spots.
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Why I love this forum in a nutshell - practical answers for impractical engineering & specs. I've certainly searched for reasoning before, which ultimately wasn't there 
Last edited by 84Z51J; Feb 24, 2016 at 09:11 AM.
Thread Starter
Safety Car
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From: Mission Viejo CA
Advanced
Joined: Apr 2021
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From: Northern Neck Va
New TPS question. So I replaced my TPS and have had to re-ajust the new TPS several times. The bolts are tight and the part is not moving around, though am wondering if maybe the new Chinese made TPS voltage is fluctuating once the engine is warmed up? The latest, after re-adjusting to the perfect .525 voltage, ran the car a week and it through code 21, TPS voltage high. Checked it while hot and the voltage was at .542. Has me thinking that my new TPS part is bad. Any brand to recommend?