5mt stall revisited.

[Trevor]

Originally Posted by oab_au

This problem of the manual stalling has been a real bug. So I decided to start from
scratch, and look at the problem.

The Idle speed is controlled by the ECU by adjusting the Idle air By-pass solenoid valve.
This valve is an electromagnetic solenoid that is operated by a Duty Cycle, the same as
the rest of the gear box, power steering, Air conditioning, EGR, and Canister Purge
control solenoids. The valve is held in the open position by a spring, and the ECU applies
a Duty Cycle to pull the valve up to reduce the amount of air that is passed by the closed
throttle, to control the idle rpm.

The By-pass valve here.


The good book tells us that the ECU uses inputs from; Throttle sensor, No. 1&2 crank
sensors, water temp sensor, Park/Neutral switches and the Vehicle speed sensor 2.
The way the ECU controls the Idle speed, is to read the engine rpm from the crank angle
sensors, compare this against the rpm that is written in the “look up tables”. The ECU
then sends the necessary Duty Cycle to the By-pass solenoid to bring the idle rpm, in line
with the “written” rpm.

To see what goes wrong with idle when the manual is fitted, we must first understand
how the by-pass valve operates with the auto fitted. The prime input to control the valve
is the throttle sensor, as when the ‘closed throttle signal’ is received by the ECU, the
engine rpm will have to be controlled by the by-pass valve. Input from the Water temp
sensor, will cause a higher rpm, as will the Air con, and the Park signal. These speed
increases are produced by the ECU, so they are set value speeds, so that the ECU can
increase the speed, before turning on the AC or selecting a gear. This prevents the sudden
drop in speed, that has to be recovered by opening the idle valve a bit more. Other
happenings that would cause a drop in the idle speed, like the alternator, power steering,
and the brake booster, would be covered by the feedback loop of ‘ check rpm, check
tables, send correction to idle valve’.

Looking at how it would have to operate on the road. When you first start the engine the
valve would be open, as the engine runs the valve would start closing, till the ‘tabled’
speed was achieved. You pull it into gear, the valve opens the ‘tabled’ amount, to
maintain the speed. You push the throttle to go, the closed throttle signal has gone, so
there is no need for the idle valve to control the engine speed, it is allowed to return to the
fully open position. The same happens when it is idling and you just rev it up a bit, as
soon as the ‘closed throttle’ is lost, the valve is returned to full open, you let it the
throttle come back to idle, the closed throttle signal returns and the valve is pulled back
up, to bring the last few hundred rpm down to a smooth idle. That’s why the rpm never
drops down quickly to the idle speed, its always gently ‘lowered down’ to idle.

To prevent the idle valve from operating every time you back off for a corner, the vehicle
speed sensor, signals that the car is in gear and moving, so there is no need to respond to
the closed throttle signal, while it is where, the valve just stays in the fully open position.

With such a fool proof system, why does it stall? When the auto is removed, the inhibitor
switch is removed also, so the Park/Neutral signal is not sent to the ECU. With neither
connected, the ECU assumes that the transmission is it gear, so it sends the valve the
speed up signal, the result is a high idle. If we ground the N, the ECU assumes that the
box is it Neutral and sets a normal idle speed, but tends to stall when slowing or stopping.

What I think is happening, when the Neutral pin is grounded the idle is good but when
you are driving, and close the throttle the ECU is trying to control the idle speed down to
the ‘tabled’ speed, as it has been told “its in Neutral”. So it keeps closing the By-pass
valve, till it is fully closed. When we push the clutch in to stop, the engine speed now
drops like a stone, the valve was fully closed and has to open, to save the stall, too
slow,,,,,,,,, engine stalls.

What we have to do, is to simulate the auto procedure as far as possible. We have to tell
the ECU that the car is it gear and moving, so that it won’t keep trying to set the idle
speed every time the throttle is closed. If it is in gear and moving the presence of the
signal from the vehicle speed sensor, will prevent the By-pass valve from closing and it
will be fully open when we push the clutch in to stop. This will have the engine running
at high idle speed, dropping as the By-pass valve closes to set the idle speed.

This will stop the stall as it does when neither the P or N are not connected, but we are
left with the high idle speed that the ECU sets when the auto is in gear. I think what is
needed is a ground signal from the gear box, to the Park pin, when it is in Neutral and a
ground signal from the clutch switch when it is pushed, . With this arrangement, when we
start the car, it is in Park, we push the clutch down, pull it into gear, still idles OK, let the
clutch out and the Park pin is now open circuit, the ECU thinks it is in gear so the idle
By-pass valve is left in the open position, ready to control the idle speed as soon as the
clutch is pushed in to stop, and the idle speed settles down to a normal idle.

To connect it up, a relay with normally open contacts is needed, and can be connected
like this.


Alternatively a change over relay with two poles could be used, with one pole switching
the ground to the park pin, and the other switching the ground to the Cruse Control to turn
it off, when park is selected, by pushing the clutch in.

What do you reckon, do the job OK,?

Harvey.

The above convoluted screed could have been judged to have comic content, if it were not a sad indictment of one who claims to be superior in both knowledge and class status. In fact it falls within the realms of bad fiction and sheer fantasy. It is stated that a conglomeration of signals as fed to the ECU are processed in myriad ways to provide idle control, all described in suspect technical terms in an effort to impress. In fact none of this is true.

The idle control system is based on the same simple principle as the classical governor fitted to numerous stationery power plants, but uses the facility afforded by electronic control. When the engine speed rises, the operative throttle is moved towards closed and vis-à-vis and this process continually governs engine speed. As a result all engine loads and all parameters affecting engine speed are catered for with only a single input being required, i.e. engine RPM. This signal is available from within ECU data processing and a modulated signal is developed accordingly to control the By-Pass Air Control Solenoid Valve.

The idle system in fact incorporates two auxiliary throttles in the form of the Auxiliary Air Control Valve and the By-Pass Air Control Solenoid Valve.

The AACV supplies extra air for starting when the engine is cold. This valve is purely mechanical in operation and incorporates a bi-metal element and rotary valve. The AACV with its rotary valve is capable of superior airflow when compared with the BPCSV. Harvey’s claim that the Water Temperature and BPCSV are the active components in this area is wrong.
.
The BPCSV valve is most certainly NOT, as Harvey claims, “ the same as the rest of the gear box, power steering, air conditioning, EGR and Canister Purge control solenoids. How many more stupid statements have to be corrected here.

The BPCSV provides what amounts to a vernier control and comprises a dual coil, PW modulated proportional solenoid valve, which requires complex control circuitry. One coil is supplied with a steady current and provides a feed back signal. The other receives a modulated signal and the two are balanced on the basis of current, so as to allow the valve to be adjusted towards open or closed. I can explain further if anyone is truly interested.

With the correct facts on hand there may be some chance of this thread proceeding logically. At the moment it is hard to work out where it is going.