Fox T-Bird/Cougar Forums

My guess would be the pcm was in a "flooded engine" mode due to the shorted 5.0v reading it was seeing, thus killing injector pulse. It could start and run without a tps in fmem and possibly only affect thottle tip in and tip out which might not be noticeable when driving.
 Maybe someone with more knowledge of the pcm's strategy could describe what exactly happened.

This is what happened. The TPS has a "failure mode" that will let the car run without an operating TPS, but when stuck in 5V range, it thinks you're trying to clear a flood and cuts duty cycle (I'm not 100% sure of this, maybe 95%).

I understand there was a TPS hanging from the wires - even better as it wasn't out of range to start the car & warm it up with.

Would my knowledge improve if I started using a tweecer?

 Thanks,
  Mike

Cougar5.0 and t.birdsc - trying to shorten my post one just for you all.


-truck cranked but no start
-I had fuel and spark
-found 5v on the green tps wire (bad reading, open tps)
-unplugged bad tps
-plugged in spare leaving spare just hanging to the side
-cranked and truck started.
Not only did it start but it responded to throttle normally as though it were mounted. I was able to drive without any problems.
Later i pulled the trottle body and changed the tps so i could actually mount it.

Also, i had to oblong the mounting holes with a chainsaw file to make the TPS adjustable in order to get .6v on the green wire.

I want to know why did the truck run and respond to throttle when it had nothing that I know of deciding what my trottle position was?

CRKFLG = 1 ----|
------------------|AND ------------| BGFUL1 = BGFUL2 = 0
APT = 1 --------|
(Wide Open
Throttle)
-------------------------------------| --- ELSE ---
...

FAILURE RECOGNITION

The FMEM strategy checks the "Continuous Self-Test Code" Filters to ascertain
whether a sensor has failed. If the sensor failure lasts long enough to
trigger a Self-Test Code, the FMEM strategy will substitute an alternate
value and strategy. Until the Self-Test filters exceed their fault
thresholds, the strategy continues to use the last known valid value.

The TP sensor Update logic substitutes a function of MAF for a failed TP
sensor. This action permits recognition of the various throttle modes
(Closed, Part or WOT). However, AE fuel will be disabled due to lack of TAR
signal.

He also has no MAF...

I don't know what ECU he is using,.

1990 351 EFI per post 1.
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The reason this bugs me is because of a very old response i posted to someone that claimed they just hook thier tps up but didnt mount it. 

I told them it wouldnt work.  Obviously it will and I have no idea why. 

I didnt test my 20th, had second thoughts on inserting a code and the "if it aint broke , dont fix it" theory".

im not shooting the messanger, i just dont use enough emotions off to the side when i post.  Since Daboss says it worked on one of his 5.0's, maybe that catch code will be a template for you.  I have no idea what eec # i have other than eeciv.

Daboss...........
your dead on what happened.  This is what i am tring to figure out.  what signal is telling the eec that the trottle plate has moved.  without a tps mounted,, it would almost have to be map related.

I had NO acceleration issues at all, no power issues and no signs that it was richer than normal although the 351 does like its go juice.

daboss, doesn't the LSC have a 5L HO engine with a MAF - just like the Mustangs?

I had NO acceleration issues at all, no power issues and no signs that it was richer than normal although the 351 does like its go juice

The EEC-IV system is capable of storing both ongoing ("hard'') and intermittent ("soft'') faults. As a result, it is possible to monitor irregularities which may not be immediately present.

While the EEC-IV system is capable of recognizing many internal faults, certain faults will not be recognized. Because the computer system reads only electrical signals, it cannot sense or react to mechanical or vacuum faults affecting engine operation. Some of these faults may affect another component which will set a code. For example, the PCM monitors the output signal to the fuel injectors, but cannot detect a partially clogged injector. As long as the output driver responds correctly, the computer will read the system as functioning correctly. However, the improper flow of fuel may result in a lean mixture. This would, in turn, be detected by the oxygen sensor and noticed as a constantly lean signal by the PCM. Once the signal falls outside the pre-programmed limits, the engine control assembly would notice the fault and set an identification code.

Additionally, the EEC-IV system employs adaptive fuel logic. This process is used to compensate for normal wear and variability within the fuel system. Once the engine enters steady-state operation, the engine control assembly watches the oxygen sensor signal for a bias or tendency to run slightly rich or lean. If such a bias is detected, the adaptive logic corrects the fuel delivery to bring the air/fuel mixture towards a 14.7:1 or "centered'' ratio. This compensating shift is stored in a non-volatile memory which is retained by battery power even with the ignition switched OFF. The correction factor is then available the next time the vehicle is operated.

If the negative battery cable is disconnected for longer than 5 minutes, the adaptive fuel factor will be lost. After repair, it will be necessary to drive the car at least 10 miles to allow the processor to relearn the correct factors. If possible, the driving period should include steady-throttle open road driving. During the drive, the vehicle may exhibit driveability symptoms not noticed before. These symptoms should clear as the PCM computes the correction factor. The PCM will also store Code "19'' indicating loss of power to the controller.

Failure Mode Effects Management (FMEM)

The engine controller assembly contains back-up programs which allow the engine to operate if a sensor signal is lost. If a sensor's input is seen to be out of range-either high or low-the FMEM program is used. The processor substitutes a fixed value for the missing sensor signal. The engine will continue to operate, although performance and driveability may be noticeably reduced. This function of the controller is sometimes referred to as the limp-in or fail-safe mode. If the missing sensor signal is restored, the FMEM system immediately returns the system to normal operation.

Hardware Limited Operation Strategy (HLOS)

This mode is only used if the microprocessor fails to operate, or if the fault is too extreme for the FMEM circuit to handle. In this mode, the processor has ceased all computation and control, and the entire system is run on fixed values. The vehicle may be operated, but performance and driveability will be greatly reduced. The fixed or default settings provide minimal calibration, allowing the vehicle to be carefully driven in for service.

I find it odd that there isnt a code that tells the us that the engine is in / was in limp mode.

If you want some cheap neons, just run the engine with the MAP vac disconnected... The area around your car will glow brightly just before the catalytic converter burns up(along with the car)...

I've never had a properly working TPS. I have started the car without it hooked up before too. As far as I can tell, I think the TPS is only for idle. It seems to idle okay without one as well.

But, a tps can be all wacked out , the engine will still run.
It should through a code and drivability may suffer.

LOL! Nice!

It dosen't glow. It burns out your cat really fast though. It will also leave big black marks near the exhaust and on the ground. Make a killer weed killer if you park by weeds and let it run.