14 replies to this topic

[Sprocket]

The operation of the stepper motor. The theory of this should be very similar for the MPi if not the same, though the MPi stepper is an air bypass valve and not a 'throttle kicker' as in the SPi.

The stepper moror consists of four windings. All the windings are commoned together at one end, this is the 12+ve supply, Brown/Pink wire. The other four ends of the windings connect to the ECU. The ECU then grounds these in a certain sequence to drive the motor in steps, each one of a predetermined angle of rotation. The max number of steps of the SPi motor is in the region of 180

When you turn off the engine, you should hear an audiable clicking, this is the ECU driving the stepper fully closed. It drives it for 180 steps and a few more to make sure its closed, in doing this it knows where it is, zero steps, and can then count the steps open. After it has driven the steppper full closed and before the ECU switches off, It then opens the stepper to a point determined by the engine temp, ready for the next start. Once the engine is started it motors in relation to the engine temp and idle load of the engine. Idle speed is not directly controled by the steppper.

I normaly set the stepper up to show about 30 steps at warm idle with no load on the engine, IE no electrical devices on.

If one of the windings has not been working correctly, it misses a step in every sequence, but the ECU does not know this, so, say the ECU drives the stepper 40 steps from closed, what would hapen in reality is the stepper would move 30 steps. The engine will not respond as it should so the ECU will drive it some more, resulting in the Service tool showing a high step count. the control will become unsteady.

I have found a couple of the steppers to have dry soldered joints on the small connection PCB on the motor terminals. Its a simple fix, remove the stepper motor from its housing an re solder. Aslo worth checking that the winding resistances are all the same, if not, bin it and find another.

Corossion on the plug terminals is also an other possible, as you have seen. Id check the solder joints just to be sure.

[mk7cooper]

The operation of the stepper motor. The theory of this should be very similar for the MPi if not the same, though the MPi stepper is an air bypass valve and not a 'throttle kicker' as in the SPi.

The stepper moror consists of four windings. All the windings are commoned together at one end, this is the 12+ve supply, Brown/Pink wire. The other four ends of the windings connect to the ECU. The ECU then grounds these in a certain sequence to drive the motor in steps, each one of a predetermined angle of rotation. The max number of steps of the SPi motor is in the region of 180

When you turn off the engine, you should hear an audiable clicking, this is the ECU driving the stepper fully closed. It drives it for 180 steps and a few more to make sure its closed, in doing this it knows where it is, zero steps, and can then count the steps open. After it has driven the steppper full closed and before the ECU switches off, It then opens the stepper to a point determined by the engine temp, ready for the next start. Once the engine is started it motors in relation to the engine temp and idle load of the engine. Idle speed is not directly controled by the steppper.

I normaly set the stepper up to show about 30 steps at warm idle with no load on the engine, IE no electrical devices on.

If one of the windings has not been working correctly, it misses a step in every sequence, but the ECU does not know this, so, say the ECU drives the stepper 40 steps from closed, what would hapen in reality is the stepper would move 30 steps. The engine will not respond as it should so the ECU will drive it some more, resulting in the Service tool showing a high step count. the control will become unsteady.

I have found a couple of the steppers to have dry soldered joints on the small connection PCB on the motor terminals. Its a simple fix, remove the stepper motor from its housing an re solder. Aslo worth checking that the winding resistances are all the same, if not, bin it and find another.

Corossion on the plug terminals is also an other possible, as you have seen. Id check the solder joints just to be sure.

hi sprocket, how do you index the stepper motor? - just wondering if it would cause the car to hunt at idle (about 300rpm up and down) - its a 98 spi - cheers

[mk7cooper]

The operation of the stepper motor. The theory of this should be very similar for the MPi if not the same, though the MPi stepper is an air bypass valve and not a 'throttle kicker' as in the SPi.

The stepper moror consists of four windings. All the windings are commoned together at one end, this is the 12+ve supply, Brown/Pink wire. The other four ends of the windings connect to the ECU. The ECU then grounds these in a certain sequence to drive the motor in steps, each one of a predetermined angle of rotation. The max number of steps of the SPi motor is in the region of 180

When you turn off the engine, you should hear an audiable clicking, this is the ECU driving the stepper fully closed. It drives it for 180 steps and a few more to make sure its closed, in doing this it knows where it is, zero steps, and can then count the steps open. After it has driven the steppper full closed and before the ECU switches off, It then opens the stepper to a point determined by the engine temp, ready for the next start. Once the engine is started it motors in relation to the engine temp and idle load of the engine. Idle speed is not directly controled by the steppper.

I normaly set the stepper up to show about 30 steps at warm idle with no load on the engine, IE no electrical devices on.

If one of the windings has not been working correctly, it misses a step in every sequence, but the ECU does not know this, so, say the ECU drives the stepper 40 steps from closed, what would hapen in reality is the stepper would move 30 steps. The engine will not respond as it should so the ECU will drive it some more, resulting in the Service tool showing a high step count. the control will become unsteady.

I have found a couple of the steppers to have dry soldered joints on the small connection PCB on the motor terminals. Its a simple fix, remove the stepper motor from its housing an re solder. Aslo worth checking that the winding resistances are all the same, if not, bin it and find another.

Corossion on the plug terminals is also an other possible, as you have seen. Id check the solder joints just to be sure.

hi sprocket, how do you index the stepper motor? - just wondering if it would cause the car to hunt at idle (about 300rpm up and down) - its a 98 spi - cheers

yup it was the stepper motor - cleaned it out and no more hunt

[mikkosan]

The operation of the stepper motor. The theory of this should be very similar for the MPi if not the same, though the MPi stepper is an air bypass valve and not a 'throttle kicker' as in the SPi.

The stepper moror consists of four windings. All the windings are commoned together at one end, this is the 12+ve supply, Brown/Pink wire. The other four ends of the windings connect to the ECU. The ECU then grounds these in a certain sequence to drive the motor in steps, each one of a predetermined angle of rotation. The max number of steps of the SPi motor is in the region of 180

When you turn off the engine, you should hear an audiable clicking, this is the ECU driving the stepper fully closed. It drives it for 180 steps and a few more to make sure its closed, in doing this it knows where it is, zero steps, and can then count the steps open. After it has driven the steppper full closed and before the ECU switches off, It then opens the stepper to a point determined by the engine temp, ready for the next start. Once the engine is started it motors in relation to the engine temp and idle load of the engine. Idle speed is not directly controled by the steppper.

I normaly set the stepper up to show about 30 steps at warm idle with no load on the engine, IE no electrical devices on.

If one of the windings has not been working correctly, it misses a step in every sequence, but the ECU does not know this, so, say the ECU drives the stepper 40 steps from closed, what would hapen in reality is the stepper would move 30 steps. The engine will not respond as it should so the ECU will drive it some more, resulting in the Service tool showing a high step count. the control will become unsteady.

I have found a couple of the steppers to have dry soldered joints on the small connection PCB on the motor terminals. Its a simple fix, remove the stepper motor from its housing an re solder. Aslo worth checking that the winding resistances are all the same, if not, bin it and find another.

Corossion on the plug terminals is also an other possible, as you have seen. Id check the solder joints just to be sure.

hi sprocket, how do you index the stepper motor? - just wondering if it would cause the car to hunt at idle (about 300rpm up and down) - its a 98 spi - cheers

yup it was the stepper motor - cleaned it out and no more hunt

Noob question, where do I find the stepper motor? I've been having idling and bucking problems and want to check and clean the stepper motor. Thanks!

[TimC]

anyone know if the stepper motor in a rover 100 /Metro 1.4 AT is the same as the SPI mini?

I have a new injection assembly from one, and the throttle potentiometer is the same, and possibly the stepper motor...not real sure.

curious what parts i can salvage off of it and use on a mini.

Thanks!

[mc1]

Hi sprocket,

I have had an engine rebuild done by a reputable engine builder. They removed and installed it but having put it back they said the stepper motor was faulty and changed it. The car had been reliable up to that point having changed the stepper motor for used one last year. However when I collected it they told me it had cold start difficulty but showed no faults on the diagnostic tester! I went to give it my first run out and the engine is turning with very little indication of wanting to start. Incidentally the car seemed to drive back home ok, and before I put the car away I turned it off and it restarted. Could this be a stepper motor issue? Thanks mc1

[leroy26]

cant find the stepper, wots it look like?

The operation of the stepper motor. The theory of this should be very similar for the MPi if not the same, though the MPi stepper is an air bypass valve and not a 'throttle kicker' as in the SPi.

The stepper moror consists of four windings. All the windings are commoned together at one end, this is the 12+ve supply, Brown/Pink wire. The other four ends of the windings connect to the ECU. The ECU then grounds these in a certain sequence to drive the motor in steps, each one of a predetermined angle of rotation. The max number of steps of the SPi motor is in the region of 180

When you turn off the engine, you should hear an audiable clicking, this is the ECU driving the stepper fully closed. It drives it for 180 steps and a few more to make sure its closed, in doing this it knows where it is, zero steps, and can then count the steps open. After it has driven the steppper full closed and before the ECU switches off, It then opens the stepper to a point determined by the engine temp, ready for the next start. Once the engine is started it motors in relation to the engine temp and idle load of the engine. Idle speed is not directly controled by the steppper.

I normaly set the stepper up to show about 30 steps at warm idle with no load on the engine, IE no electrical devices on.

If one of the windings has not been working correctly, it misses a step in every sequence, but the ECU does not know this, so, say the ECU drives the stepper 40 steps from closed, what would hapen in reality is the stepper would move 30 steps. The engine will not respond as it should so the ECU will drive it some more, resulting in the Service tool showing a high step count. the control will become unsteady.

I have found a couple of the steppers to have dry soldered joints on the small connection PCB on the motor terminals. Its a simple fix, remove the stepper motor from its housing an re solder. Aslo worth checking that the winding resistances are all the same, if not, bin it and find another.

Corossion on the plug terminals is also an other possible, as you have seen. Id check the solder joints just to be sure.

hi sprocket, how do you index the stepper motor? - just wondering if it would cause the car to hunt at idle (about 300rpm up and down) - its a 98 spi - cheers

yup it was the stepper motor - cleaned it out and no more hunt

Noob question, where do I find the stepper motor? I've been having idling and bucking problems and want to check and clean the stepper motor. Thanks!

[firstforward]

http://www.southlake...or-p-77816.html

[JonnyBMX]

^{its the part that sits under the air filter to the right hand side of the throttle body, there is a black connector going into it which plugs directly onto the stepper motor, it is held down by 4 torques screws, do not undo the phillips screws these hold the internals of it to the base. you will have to disconnect the fuel lines and then remove the top part of the injector unit (the actual injector itself and the plate it sits on) to get access to it, also the accelerator cable needs to be discconnected}

[Manuel B]

This about a friends '97 MPI, two problems, which is causing what ?

 

  On the ACR4 on the stepper motor adjustment is there a number that is a desired goal or is it different for each engine ? it was idling real high, but when I squeeze the rubber hose going to the Idle Air Control Valve I can slow the idle down to normal, my friend said the Idle Air Control valve is bad, he cleaned it out but it didn't help so he put a carb jet inside until we figure out a plan of attack.

 

When I click on the stepper motor adjustment mode on the ACR4 I see a row of little squares across the bottom of the screen, and a marker above them, but the marker is ALL the way to the right of the screen, sort of like this,
                                        x
[] [] [] [] [] [] [] [] [] [] [] [] [] []

But while checking another page on the ACR4 it just shows a number for the stepper motor, it does not start cold at higher RPM (1000/1100 RPM like my SPI) then slow down to 850 as it warms up, it starts like a carbed car with no choke, at around 400/500 RPM, hit the throttle and it rises, a minute later it's around 850 RPM and acts normal the rest of the day.
       He has spent so much already, I explained it and showed him what it did at first startup, and he was ok with it, but it's been in the 90's F here,  and I wonder how it will act in the cold next Winter ?
                Manuel

Edited by Manuel B, 29 July 2013 - 01:57 AM.

[tmsmini]

I cannot really answer your question Manuel but I have always had this question.

 

Although this is for the MPi engine, the ACR4 has this information embedded in it which I never completely understood:

 

  Stepper motor position in steps, depends on idle control requirements, more steps indicate greater level of control

 

So if the range on an MPi is 16-24 steps, does having more steps than 24 and a  "greater level of control" mean it is way out of adjustment?

 

Terry

[FlyingScot]

Manuel B I think you have just proved to yourself that the IAC valve is no good. It is stuck too far open or you have a leak, since the idle speed reduces when you squeeze the hose (and when you out a restriction in it ) this indicates it is unable to seal properly and excess air is going into the system. A replacement should cure this. The ACR unit is showing that the control MEMS is flat out trying to reduce the idle speed by sending out the max positioning for the valve ( to cut the air flow)

FS

[tmsmini]

So a high number of steps listed on the ACR indicates that the ECU is attempting to close the stepper or reduce the airflow?

And a low number would indicate the inability to increase airflow?

I believe the ACR indicates the range should be 16-24.

Terry

[FlyingScot]

Terry I believe the information the ACR is reading is the signal being sent to the stepper, so when the reading is large either on the graphic or the steps it is trying to index the stepper to reduce the airflow. I don't have the MPi stepper to hand and for the life of me I can't remember if it starts closed with a low step or open. The wording about level of control is in relation the the IAV effecting the idle rather than the ignition advance I believe. Of course I could be completely wrong with this understanding and information as you know is scarce or contradicted.

FS

[Wizzalong]

I am completely rebuilding a  '93 spi 1275 after having select aluminium parts aqua blasted I stripped stepper motor casing to make sure everything was dry, in the process removed motor drive from spline, Is there a specific position this should be replaced or does it matter? i.e. does the motor find the correct position itself according to sensors?

Thanks, Mike.