Question: Interpreting TPS Voltage

[John Robinson]

I have been chasing a number of SES issues lately and yesterday I discovered that the ground wire was broken inside the TPS plug. After repairing it I checked the TPS voltage and I have .7 at idle and 4.11at WOT. I seem to recall that the wot should be 10 times the value of the idle setting is that correct? Also I have read in the Chilton Manuel that it should be at least 5 volts at wot.(I also have the FSM but could not find corresponding information in it) The reference signal voltage is 5 volts.

Finally how Long will it take for the ECM to recognize the TPS values and adjust accordingly for performance and mileage.;help

 

[vetteoz]

I seem to recall that the wot should be 10 times the value of the idle setting is that correct?

.54V @ idle
Never had one that has shown much over 4V WOT

Corvette Action Center Knowledgebase :: 1985 - 1991: Technical Article: How to Adjust your Early C4 TPS and Idle Speed

 

[Schrade]

I have been chasing a number of SES issues lately and yesterday I discovered that the ground wire was broken inside the TPS plug. After repairing it I checked the TPS voltage and I have .7 at idle and 4.11at WOT. I seem to recall that the wot should be 10 times the value of the idle setting is that correct? Also I have read in the Chilton Manuel that it should be at least 5 volts at wot.(I also have the FSM but could not find corresponding information in it) The reference signal voltage is 5 volts.

Finally how Long will it take for the ECM to recognize the TPS values and adjust accordingly for performance and mileage.;help

Also I have read in the Chilton Manuel that it should be at least 5 volts

No. Under ANY normal circumstances, it should be AT MOST 5V.

Toss Chilton's.

TPS re-learns normal parameters after a few drive cycles CLOSED loop. In the meantime, it will string out RPMs in each gear (auto).

 

[geekinavette]

The TPS is nothing more than the wiper connection of a potentiometer with 5V and ground for the "reference" voltages. The wiper (output) voltage can not be more than 5V, and the wiper is not usually mechanically able to travel the full range, so it is normal to see just a little more than 4V as the "max" (for WOT). Usually around 0.5V is typical for idle.

 

[boomdriver]

Thats how I've always understood the TPS...its NOT the voltage as much as it is the range that it moves. 5V is the common ECM control voltage and will be the max that any ECM control will use. Set the TPS at idle to near 0.5v and the travel of the TB lever will pretty much do the rest. Thats why its set at idle because thats a "fixed" setting. Upper end is a variable depending on where the start was.

 

[TedC]

When checking WOT move the trottle body to full open and also check the throttle pedal to make sure they both reach 4V or better. I would only be concerned if you could not reach 4V. Mine is set at .54V and 4.6V. Using a DVOM works, but the best option is using a scanner which will display what the ECM actually is receiving.

 

[T.M.808]

I set mine at .54v at idle. Never have got more than 4.6 at WOT.
I remember at the track, my friend used to set his TPS to 6.5/idle when at the track, his car would idle like crap, smelled rich and set a code.

 

[John Robinson]

Fsm

Thanks everyone for your input. I have not had any codes since I fixed the TPS ground and the engine finally has learned the new TPS settings.

As for the information I was looking for in the FSM I finally found a section called Typical Tech 1 Data Definitions in section 6E3-A-19 of my FSM.

This section has some very interesting short explanations on what the data codes from a tech 1 should look like if in the normal range.

 

[Schrade]

The idle voltage for TPS is critical, because EVERYthing rests on that range (fuel trim cell, etc.).

It would be easy if range started at 0V, but that's a 'closed throttle' position, which is of course, motor OFF.

So, the base voltage figure has to come from idle reading at whatever RPM FSM calls for, AND, idle has to be as stable as can be - from a tune that's as perfect as can be.

That's why I think FSM says the idle voltage is IDEALLY .xxV. I also think TPS voltage in OPEN loop (cold) is acceptable. Most all other readings are NOT acceptable in open loop.

 

[boomdriver]

Thats correct because TPS is just a ranging instrument. Engine running or not, idle position is the same to the TB and throttle plates. How the ECM manages idle is up to IAC performance. When the TPS is set, thats a baseline for which the upper end does not matter. The ONLY reason that anyone cares is proving that the potentiometer is able to send a variable signal thru the full range of travel. Otherwise, Setting the idle automatically sets the top end value and that voltage does not matter as long as it does not somehow go past the ECM control 5v signal. Get the TPS idle set even with eng off, with TB fully closed and the TPS range will be correct.