TPS Adjustment mod.... myth?

[gijoecam]

I was just stumbling through the PC/ED info and stumbled across this section:

Idle Speed Control Closed Throttle Determination
One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start. This lowest learned value is called "ratch," since the software acts like a one-way ratch. The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values.

All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum.


If I read this correctly, is there really a need to adjust the TPS voltage? Won't the engine re-learn the lowest voltage setting every time you re-start the engine and simply set that as its lowest point?

I dunno.... I'm not very smart.... just a resourceful idiot.

-Joe

 

[Runnin'OnEmpty]

I don't think adjusting the TPS will help on the OBD II models, especially after reading your post, Joe. That's the way the PCM compensates for ongoing wear, as the miles pile up on the vehicle. Many people seem to think the TPS adjustment helps on the earlier models, however......

 

[gijoecam]

Hmmm... that's a possibility.... I'll have to dig into it tomorrow a bit and see. Makes sense though....

It was all just brought on by a thread somewhere where someone made reference to needing to adjust the TPS to smooth out the idle on a second-gen. Never thought that it might apply to a first gen only....

-Joe

 

[Doug]

This mod was done by jamest on a 96 5.0. I'm sure it works, Jamest is a sorry Country Bumpkin he isn't smart enough to make stuff up. Do a search there is a large thread about this topic.

 

[Creager]

ok, but what if you remove the negative on the batter and all that yadda to reset the computer... it would have to relearn those values... and it read .96v as its lowest for the new array of learned values? then it would work...

 

[Runnin'OnEmpty]

It takes about 70 start cycles for the PCM to learn new values, at least on the gen II models. Whether it starts 'learning' with a .96v on the TPS, or adjusts for a different voltage, I don't think it matters much. Bear in mind, this is only on the later models.

I forget the terminology that Ford uses, but it's some sort of "relearning strategy" that the PCM uses to compensate for engine wear. It can even compensate for piston ring wear, and change timing and mixture to get the best engine performance. I suspect it's something to do with the 100K miles/no tune-up Federal regs that new vehicles must adhere to.

 

[gijoecam]

It takes about 70 start cycles for the PCM to learn new values, at least on the gen II models. Whether it starts 'learning' with a .96v on the TPS, or adjusts for a different voltage, I don't think it matters much. Bear in mind, this is only on the later models.

I can't say I have any specific experience to the contrary.... all I know is what I'm reading here:

The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values.

All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode.

The way I read that is that it resets the voltage for the closed-throttle position (and subsequently the idle point) after every start. No?

I forget the terminology that Ford uses, but it's some sort of "relearning strategy" that the PCM uses to compensate for engine wear. QUOTE]

That's called the Keep Alive RAM. It adjusts the fuel trims (i.e. the individual duty cycles for each cylinder's fuel injector). You can clear the KARAM yourself, at which point it's just going to re-learn the values it had in there to begin with.

Disconnect the battery ground cable for a minimum of 5 minutes. Resetting Keep Alive RAM will clear learned values the PCM has stored for adaptive systems such as idle and fuel trim.

After Keep Alive RAM has been reset, the vehicle may exhibit certain driveability concerns. It will be necessary to drive the vehicle to allow the PCM to relearn values for optimum driveability and performance.

More useless info....

Idle Air Trim
Idle Air Trim is designed to adjust the Idle Air Control (IAC) calibration to correct for wear and aging of components. When engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The Idle Air Trim values are stored in a table for reference. This table is used by the PCM as a correction factor when controlling idle speed. The table is stored in Keep Alive Random Access Memory (RAM) and retains the learned values even after the engine is shut off. A Diagnostic Trouble Code (DTC) is output to indicate that the Idle Air Trim has reached its learning limits.

Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that Keep Alive RAM be cleared. This is necessary so the idle strategy does not use the previously learned Idle Air Trim values.

To clear Keep Alive RAM, refer to PCM Reset in Section 2A. It is important to note that erasing DTCs with a scan tool does not reset the Idle Air Trim table.

Once Keep Alive RAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes. The modes are shown in the following table.

I'm still not convinced that adjusting anything to do with the TPS on an OBD-II equipped Ford makes any long-term difference.... I'm running the search right now for the other thread....

-Joe