Over Revving

[Guest]

The GSI estate does this sometimes, what would be the likely cause of this?

would it be the stepper motor

[Jumturbo]

Sounds like the stepper motor. You can check quite easily. When it starts overrevving take a look at the stepper motor pushrod to see if it's decided to come out. When the engine is at normal temp it should be fully in. My car has the usual problem when cold. The pushrod has a mind of it's own. In and out until engine at running temp. Does anyone know how to cure disobedient stepper motors?

[TLC]

lubricate it or change it.

[Guest]

ah i thought it might be that, i will check it tommorrow, thanks for the heads up

[Guest]

Sounds like the stepper motor. You can check quite easily. When it starts overrevving take a look at the stepper motor pushrod to see if it's decided to come out. When the engine is at normal temp it should be fully in. My car has the usual problem when cold. The pushrod has a mind of it's own. In and out until engine at running temp. Does anyone know how to cure disobedient stepper motors?

i thought that if the rod is out (ie long) it closes the throttle bypass, so at normal temperture the rod should be longer

[G Force]

The GSI estate does this sometimes, what would be the likely cause of this?

would it be the stepper motor

HI, there are a number of different types of stepper motors fitted to our cars and all types seldom go wrong. The stepper motor often gets a bad press when all it is doing is what it is told to do by the rest of the system.

The cause of the over-reving on your car will depend on which fuel injection system is fitted. Let us know whether it is fitted with MEMS (Silver ECU under bonnet, square air filter box) or Lucas Hot Wire (Black ECU under bonnet + ECU in passenger footwell, cylinder shape air filter box).

Gary

[G Force]

My car has the usual problem when cold. The pushrod has a mind of it's own. In and out until engine at running temp. Does anyone know how to cure disobedient stepper motors?

Your problem is either incorrect idle and fast idle settings, or a faulty wiring connection between the engine bay harness and the fuel management ECU above glovebox lid, or a faulty ECU its self. Have you noticed any irregularities with the temperature gauge reading whist the engine is warming up?

Gary

[G Force]

i thought that if the rod is out (ie long) it closes the throttle bypass, so at normal temperture the rod should be longer

Depends on whether hot wire or MEMS fuel injection is fitted. Hot wire is an air valve type, MEMS has a push rod type similar to a carburettor equipped engine.

Gary

[Guest]

HI, there are a number of different types of stepper motors fitted to our cars and all types seldom go wrong. The stepper motor often gets a bad press when all it is doing is what it is told to do by the rest of the system.

The cause of the over-reving on your car will depend on which fuel injection system is fitted. Let us know whether it is fitted with MEMS (Silver ECU under bonnet, square air filter box) or Lucas Hot Wire (Black ECU under bonnet + ECU in passenger footwell, cylinder shape air filter box).

Gary

Hi the car has lucas hot wire (black ecu & cylinder air filter)

[G51 NAV]

Gary is correct (nothing new there!) but I'll also add that this can be caused by a build up of crud in the manifold. I've had two EFis show this symptom and in all cases it was cured by flushing everything out with carb clearner.

Stepper-motor doesn't half take one HUGE mf of a spanner though. It laughed at my spanner-set and even poked fun at my biggest monkey wrench. I had to buy an industrial sized one from a plumber's! If the fuzz ever find it in the car they'll pull me for possession of a offensive weapon!

[Jumturbo]

yeah, I attempted to remove one once and ended up cracking the stepper motor casing! Ouch! never again!

[G Force]

Hi the car has lucas hot wire (black ecu & cylinder air filter)

Hi Patrickingham there is one normal condition where the engine is sometimes reported as over-revving which will not be cured by the following procedures, so I think it warrants a mention. If the car is started from cold and driven for “any” distance, the engine revs will hang around 1100rpm (or slightly higher in the first 2 miles) each time the clutch is depressed to change gear, the engine revs will not return to controlled idle speed until the first time the car comes to a full stop.

If you are having problems with erratic idle speed over revving etc. with a Lucas Hot Wire fuel injection system you should reset the base idle, CO, and most importantly the throttle pot setting. You can just try set the base idle and throttle pot but for best results its best to go through the following full procedure. It looks very long-winded I know, but if you break it down into small sections it isn’t anything like as complicated as it first might seem.

I, like G51 NAV says, would normally recommend cleaning the throttle body out before you do anything as the gunk that accumulates is part of the problem. To avoid all the gunk going into the engine the best way is to remove the throttle body first, and then if you don’t have a big enough spanner you can use a vice to help unscrew the stepper motor. Give everything a good thorough clean with carb cleaner to remove all the gunk that accumulates. Clean all the deposits from all around the throttle butterfly disc and large breather port, and you will probably find the small crankcase breather port needs unblocking as it is nearly always blocked.

To set the base idle the engine needs to be hot. Then you need to ensure the stepper motor is fully closed (there is a special tool for this) but you can do it by using the following method.

Turn on the ignition and wait 10 seconds then remove the stepper motor plug, then turn off the ignition and wait 30 seconds or until you hear the main relay click out. Then replace the stepper motor plug and turn on the ignition and wait 10 seconds, and then remove the stepper motor plug again. Turn off the ignition and wait 30 seconds etc. Then repeat once more this will ensure the stepper motor is fully closed. With the stepper motor plug disconnected start the engine and set the idle speed to 650rpm with the throttle stop screw. Then replace the stepper motor plug.

After setting the base idle you will need to reset the throttle potentiometer with a voltmeter to read 325mv output with the throttle closed with ignition on. To set the throttle potentiometer you will need a suitable multi–meter and an allen key or angled pozi–drive screwdriver.

There are three wires going to the potentiometer from the fuel injection ECU The harness wires are coloured as followed: pink with black trace, pink with purple trace and a third which varies from model to model and is either green with red trace or green with yellow trace.

With the ignition switched on and the throttle potentiometer harness connected push the probe of the black wire of the multi – meter into the pink and black wire of the vehicle harness throttle potentiometer connector. Then push the probe of the red with of the multi–meter into the green and red wire of the vehicle harness throttle potentiometer connector. If your harness has a different colour wire always remember that the pink and purple wire is never connected into with the meter.

With the multi – meter set to the mv setting measure the voltage reading. The reading should be 325mv +/-10mv with the throttle fully closed. If the reading is incorrect then the two screws holding the throttle potentiometer to the throttle body can be loosened enough to move the potentiometer to obtain the correct reading. Take care as when the screws are re tightened the setting can alter. Open and close the throttle butterfly a few times to ensure the reading stays constant when the butterfly is closed. I find that sometimes it is easier not to loosen the screws of the potentiometer and just tap the potentiometer body gently with the handle of a screwdriver to obtain the correct reading, obviously sometimes loosening the screws is the only option if more force would be needed.

Once you have done this with engine at normal temperature set the CO to 2% with the screw on the throttle body nearest the stepper motor, that’s if you have access to a gas analyser of course. The mixture screw is on the throttle body just in front of the stepper motor. It is an air bleed and only affects idle mixture so don’t expect it to make a big difference to performance. To richen the mixture you will need to turn the screw clockwise, it will probably take a full turn to take the CO setting from 0.75 up to the 2.5 max.


If the engine stalls when coming to a halt it could be a faulty road speed transducer. To test the transducer disconnect the harness plug and connect a multi-meter set to read Ohm’s across the transducer wires. Then jack up one wheel and rotate the wheel observing the reading on the meter, it should fluctuate between 0 Ohm’s & open circuit.

Regards Gary

[Jumturbo]

Your problem is either incorrect idle and fast idle settings, or a faulty wiring connection between the engine bay harness and the fuel management ECU above glovebox lid, or a faulty ECU its self. Have you noticed any irregularities with the temperature gauge reading whist the engine is warming up?

Gary

No problem with temp gauge. ECU is the later ERIC item fitted to Montego Turbos (combined fuel and ignition). When the engine is warming, I can see the little pushrod doing its own thing - out increases revs, in makes the revs drop. My White montego had a similar fault but that car would stall. I ended up fitting a manual choke which of course cured the problem. My green monty doesn't quite stall as the pushrod toys with the revs at will!

[G Force]

No problem with temp gauge. ECU is the later ERIC item fitted to Montego Turbos (combined fuel and ignition). When the engine is warming, I can see the little pushrod doing its own thing - out increases revs, in makes the revs drop. My green monty doesn't quite stall as the pushrod toys with the revs at will!

It sounds like the coolant temperature sensor may be faulty or a poor connection between the sensor and the ECU. It is possible to test the sensor for abnormal readings as the engine warms up, by connecting the sensor to a multi-meter and observe the resistance readings. The resistance reading should gradually fall with no big jumps up or down, until it settles around the 150 to 200 Ohm's when the engine reaches full temperature.

For the cost of a coolant temp sensor it might just be worth renewing it to rule out any problems with it though.

Another reason for the idle speed to fluctuate would be that the base idle and controlled idle settings are so far out that the ECU struggles to control the idle. Setting the base idle and controlled idle on ERIC systems is not as straight forward as turning a few screws, you need to have special tool 18G 1560 or make your own.

The full instructions for how to make the special tools and how to set the base idle speed and controlled idle speed and CO on your ERIC system see here.

http://www.maestro.org.uk/forums/showthread.php?t=4754

[Jumturbo]

Thanks for that, will give these a go