405 stepper motor connector

My 1995 petrol 405 cuts out at low revs. But it's very
intermittent so I'd like to check that it's not a bad
connection on the wiring to the stepper motor.

So does anyone know where on the engine, or whatever, I
might find the stepper motor connectors. I have the
Hayes book, but they don't show that piece of info.

Thanks.

 

Tim wrote in message ...

Tim, You don't say which engine you have but on my 1995 405 with XU7 engine
the stepper motor is right on top of the engine just to the left of the coil
pack. It has two hoses about 1" diameter connected to it and the electrical
connector is on the rear of the unit as mounted.

HTH

Bob

 

Could this be the same for my N reg 405 auto estate ( petrol) ?

just cuts out at low revs, restarts ok, then may cut out again and again ,
lasting for anything from 10 minutes to a day, but then will not return for
2 to 3 months ?

David

 

Interested because I once had a 405 petrol (now have diesel) that
sometimes cut out for no apparent reason: what is the stepper motor and
what does it do? Thanks

 

Bob - many thanks. The car is a 405GTX estate and the engine
is an XU10 (1998cc.) The connector you mention doesn't seem
to want to come out so I've given it a good wiggle and we'll
see if that fixes it.

Just in case there is a connection, I should mention that the
car also shows a couple of other faults: the STOP light comes
on, with the temperature guage red light on, even when the car
is just about stone cold and the temp guage is reading minimum
- the fix is an emergency stop! And the flasher 'ticker'
sometimes goes nuts when the car is cold. These could be
independent faults...

 

Tim wrote in message ...

Tim,
Are you familar with removeing the engine elctrical connector on your
Pug?You will see a metal wire spring loop around the connector which need to
be compressed to withdraw the connector.

I doubt if your temp light/ stop problem is related to the flasher
observation.

I recently had cause to remove the thermostat housing from my engine only to
find thet not only did it have three separate temp sensors but also it had
provision for a fourth. I looks like at least three systems need to know the
temp and do not talk to each other!!
I think I'm correct is say that the temp gauge sensor becomes lower
resistance as the temperature increases. I could well be that you have an
intermittent short circuit in the wiring or gauge thus indicating very hot
irrespective of the actual temperature.
Any one of four events will light the STOP light
Over temp water.
no oil pressure
and two other things I cant recall

I strongly suspect your fault is an intermittent short which is 'cleared' by
the deceleration when you slam on the anchors.

As for the flasher problem, I don't know but several posters to this NG seem
to have flasher oddities and I suspect they are also intermittent
connections.Try a wiggle and clean up of the relay contacts.
Pugs generally have a poor record of electrical connections.

hth


Bob

 

A stepper motor is a motor that rotates a small fraction of a revolution in
one direction or the other when a small electrical pulse is sent to it. When
no pulses are sent, the moter is held stationary by the act of the magnetic
field
In this application, the stepper motor adjusts the amount of air that is
allowed to bypass the throtte. ie it allows the ECU to control the idle
speed of the engine once you have taken your foot off the accelerator.
By sending pulses from the ECU to the stepper it can make small changes in
the amount of air allowed into the engine, measure the engine speed and then
check if it needs to make a further adjustment and so on until the idle
speed is just right.

This link http://209.41.165.153/stepper/Tutorials/UniTutor.htm
will probably give you more information than you want/need about stepper
motors.

HTH

Bob

 

Just adding to the explanation Bob gave... My 1952 BSA Bantam
had an adjustable screw on the carb which would set the tickover
speed. Quite probably this was also used on cars until emission
control regs came in. My understanding is that the stepper motor
(in reality just one of many stepper motors in a modern car) is
an automated version, controlled by the ECU, of the screw on my
Bantam.

 

Hi,

No, the stepper motor brings an extra amount of air to the engine, this
replaces choke. AFAIK (correct me if I'm wrong) it doesn't act once the
engine is warm.
You're talking about the idle screw here, if I understand correctly.
The idle is automatically managed by the ECU. and is a different thing (you
can consider the stepper motor as a bypass on the air intake / throttle body
assy - where the idle settings are). At least it was the case on older ECUs
(Bosch Jetronic series. Ok, I know we're talking about Motronics or some
crappy Marellis here).

 

Because this will be archived, I should add the final diagnosis...

The connector is where Bob described and plugging and unplugging
had no effect. The dealer cleaned out carbon dust from inside
the stepper motor and, so far, that has done the trick. Didn't
cost much.

Of the other problems I raised in a follow-up post, the temp
warning light seems to have been caused by a slightly low
coolant level (!) and the tick.tick.tick from the flasher
unit remains undiagnosed - it went away when taken to the
garage ;-)