10 replies to this topic

[lewoof]

Please help! i have a 1995 Rover Mini Sprite. When the engine has warmed up the idle gets higher and higher untill we have to turn the engine off. We also have to charge the battery every couple of days because the battery is draining itself, but i have replaced the battery and alternator. i was advised that the ECU may be faulty but diagnostics place just have just called to say the ECU is fine........can anyone help???

Is the engine over revving to componsate for the battery losing its charge somehow???

Edited by lewoof, 02 April 2009 - 04:00 PM.

[oldskoolracer]

alternator goosed?

[lewoof]

goosed?

[DaveRob]

sorry if this sounds pedantic.... but batteries dont drain themselves...... well ok.... on a flooded cell system using lead plate construction they actually have a VERY low internal resistance... thats why they can start the car.

BUT...... in answer to your question. we actually need a bit more info to go on.... so bear with me.

An increase in idle?...... over how long a time does it rise.... is it a few mins or does it start going up quite quickley. Either way it sounds stepper motor related... does this idle speed vary from cold or ONLY when up to temperature?.....When you switch the ign on but dont start the car do you hear any clicking noise from the stepper motor, ( try to ignore the fuel pumo priming ), ..... 2 people are needed for this test you wont be fast enough to get round or you will need VERY big ears...lol. Is the ' lost motion gap' adjusted to be mid point..... if you dont know what this is bu a Haynes manual and find out..... its IMPORTANT. Have you checked the basics.... ie is the vacuum tubes from the back of the throttle body connected to the right places... IE left side( as you look at the engine).... to the oil trap then from their to the ECU...... thier must be ZERO leaks..... if in doubt replace all of it..... right side to the air filter sensor. Have you checked for any other air leaks.... this is essential...... no manifold leaks or blowing exhaust etc etc...... are all of your breather pipes connected to the right places...... You say but diagnostics place just have just called to say the ECU is fine. Im interested to know where you sent it and what they did to test the MEMS ECU..... its rare to find anyone who actually can test this system. Did they test it off car or in the engine bay all connected up...... What is the part number of the ECU... its on the lable on the side of the unit and starts with MNE......... have you done anything recently to disturb ANYTHING under the bonnet.... what work have you done before this happened..... was it working fine one day then like this the next.... the latter is unusual .... but possible.

Re the battery....... if its fully charged when you start..... measure the voltage with the car not running and ign off..... start the car and keep an eye on the meter..... it should creep slowly upward toward 13.8-14 volts.... switch the lights on..... it should drop a little then you should get the stepper kicking in to correct the load .... so the alternator pumps in more charge.... so the result is a gradual increase in volts to 13.8-14 volts.

Report back when you can answer these few questions..... I know its a pain ..... but information about everything above is needed to work out a logical sequence to find your problem.

Hope this helps

Rob

[lewoof]

thanks for your in depth advice Rob....i will investigate further.

when i say battery losing its charge i mean something is draining it! When we fully charge the battery, the mini starts and runs well but if we go on a journey for say an hour, the idle increases to drastic proportions......sometimes to the point where we have to turn the engine off. When this happens, the engine doesn't restart straight away. we wait a few minutes and then it starts, sometimes. If we then start the mini a few hours later, it starts but with not with so much 'umf' as previously. After a couples of days the mini wont start at all.

i will investigate the possible causes you suggested.

cheers.

[Sprocket]

The MEMs sometimes suffers a failure which causes the main relay to stay energised and this drains the battery.

[xrocketengineer]

The MEMs sometimes suffers a failure which causes the main relay to stay energised and this drains the battery.

This is easy to detect. Wait for the car to cool down (or overnight). If the relay module feels warm to the touch, the relay is active.
There is another trick to detect this that worked well for me. Pin/terminal number 3 of the smaller connector on the relay module, white wire with pink tracer, provides the ECU ground (earth) path to activate the main relay. Use a pin or needle and push it into the back of the connector parallel to the that wire until it touches the terminal inside the connector. The pin/needle will slide in between the wire insulation and the weather seal in the connector. Use a voltmeter and connect it to the needle and an earth point. With the ignition switch in the OFF position there should be 12V. With the ignition switch in the ON position it should read ideally 0V but it will be approximately 1.5 V. If you have that low voltage with the ignition OFF, your relay is active all the time draining the battery.
In my case, just disconnecting the relay connector and reconnecting it, would reset the ECU output. I had no need to disconnect the battery to prevent the drain.
I am still waiting for my repaired spare ECU from APT.
So, good luck with your troubleshooting!

[Avl_Paul]

One addition to above advice: disconnect the electrical connector to the stepper motor and see if the engine still does the idle runaway thing. That should tell you if it is a stepper motor / Engine Control issue or something else like an Air Leak.

(Ps. I had the problem with the battery draining in a couple of days and it was the main relay staying closed like Sprocket mentioned due to a BAD ECU in my case. Easy to check for by disconnecting the connector to the Relay Module and listening for the main relay click).

[lewoof]

thank you all for your advice......i will check the relay and stepper motor at the weekend and will let you know the outcome.

[wardy23]

we have the same problem with our mini over reving there was a fault on the ecu which was sent away and repaired but its now started over reving again when warm its fine when cold but once up to temp it can rise to 2000rpm and 3000rpm and quickly sometimes we turn the engine off and it can go away for a while but then can come back again in the same journy also it sometimes seems to happen when you go above 50mph any help on this would be great as if i cant solve it i think i will be looking to convert it to carb

could it be the throttle body thats sticking???? are these easy to replace???

cheers
paul

Edited by wardy23, 08 April 2009 - 05:58 PM.

[xrocketengineer]

For high rpm idle check for vacuum leaks. The number one suspect is the line going to the Thermac valve on the air filter. Check the thread. Good luck.

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