Throttle Problems

[harasn]

you guys must remember that we here at the track are the test dummys! They try all these different things when a system dies like the throttle on us first! what we see may not be what ended up being produced! Stopping the car at the engine RPM I spoke of was not hard but you certainly noticed something was up! thanks FORDTECH for the propper explanation!

[Turbo6man]

FORDTECH, and others, I don't mean to be pedantic BUT Dammit I am going to be pedantic - So what happens if the fault that develops in the accellerator position sensor is that the sensor sees the pedal at full throttle when in fact it isn't? This scenario can arise (as reported) and neither of the "failsafe" modes described will detect this as a problem. So there will be no overriding action brought to bear by the PCM.

[FORDTECH]

  Turbo6man said:

FORDTECH, and others, I don't mean to be pedantic BUT Dammit I am going to be pedantic - So what happens if the fault that develops in the accellerator position sensor is that the sensor sees the pedal at full throttle when in fact it isn't? This scenario can arise (as reported) and neither of the "failsafe" modes described will detect this as a problem. So there will be no overriding action brought to bear by the PCM.

There are 3 potentiometers in the accelerator pedal sensor that are monitored by the PCM at all times while the engine is running as well as monitoring the ETB throttle plate position.The reason there are 3 when technically it only needs 1 is for this exact reason.Unfortunately I have to question the validity of the claim about the ETB going to full throttle by itself. I have watched an XR8 throttle that developed a mind of its own with a WDS attached and monitored the results. You can monitor 2 PID's(parameter identification data) on the ETB that show you in real time what the ETB should be doing and what it is actually doing.They are throttle position demand(ETB_DMD) and throttle position actual(ETB_ACT). With the engine running at idle both readings were approx 1.5 to 2 deg(Both readings should mirror each other). Then suddenly the ETB_ACT reading started to increase by itself(Hence the engine started to rev up).When it got past 7 deg(Failsafe default)it started shutting cylinders down.When it got to 10 deg it went back to 7 deg and the throttle light came on.The whole time it was doing this the ETB_DMD read 0.

To sum this up and answer your question, Yes they can develope a mind of their own but there are failsafe strategies in place (and they do work) to prevent it from getting out of hand and you really have to question the source of the claim(Oh I dont know what happened officer.The car just stuck flat out and left that 150m tyre mark all by itself).

And by the way,the fix for the above mentioned vehicle was a new throttle assy and the re routing of some missplaced wiring that provided the PCM with some nice back emf (electro magnetic force) and made it think it needed to accelerate when it shouldnt.

Hope this makes sense.

[Turbo6man]

FORDTECH, Thanks for the detailed explanation - I do understand what you have described and agree that the "failsafe" mechanism will work as you have described it when the vehicle is operating in neutral. However I am still not 100% convinced that while the vehicle was being driven in a "normal" driving cycle, that a fault could not occur which could "fool" the system and allow full throttle. After all, full throttle is a normal (for some of us) situation during a drive down to the supermarket etc.

How does the PCM decide that we don't really mean to be at full throttle if it is a fault that causes full throttle and not the driver? E.G. Is it linked to the braking system so that if it detects braking and full throttle at the same time then it realises this is not a normal situation?

Or, are you saying that the three pots are monitored and measured against each other's values constantly in order to determine if one develops a fault - and if one becomes out of sync then the PCM goes to one of it's default modes?

[Ford_Power]

  Quote

Or, are you saying that the three pots are monitored and measured against each other's values constantly in order to determine if one develops a fault - and if one becomes out of sync then the PCM goes to one of it's default modes?

I think that's exactly what hes saying.

[FORDTECH]

  Ford_Power said:

  Quote

Or, are you saying that the three pots are monitored and measured against each other's values constantly in order to determine if one develops a fault - and if one becomes out of sync then the PCM goes to one of it's default modes?

I think that's exactly what hes saying.

Exactly.

[Guest LOK@ChipTorque]

FORDTECH,

While we're on the subject, the last time I looked at WDS data (might have been a while ago) the TPS values seemed to all read 32Volts. Was this just an old version of software or something?

LOK11

[FORDTECH]

  LOK11 said:

FORDTECH,

While we're on the subject, the last time I looked at WDS data (might have been a while ago) the TPS values seemed to all read 32Volts. Was this just an old version of software or something?

LOK11

that's right. Up until version B24 of the WDS software you were unable to monitor the APP(Accelerator Pedal Position) sensor.You were also unable to montior the ETB(electronic throttle body)control function.If you now have a look with your WDS(Latest level software is B27. you should be able to monitor them all.

You will also notice that they are the normal reference voltage of 5v.