12 replies to this topic

[Jackman]

Right odd one here.

Car runs fine, no problems with running, smooth and how it should be.

However every so often the car skips a beat and the stepper motor sticks at the revs it was at, so if i was cruising at 2k if it skips a beat the idle will be 2k. If i drive a bit at between 200-500 revs higher the stepper goes back to normal.

The odd occasion (especially if it did it when coming to a stop) i need to turn the engine off, wait awhile then restart and its fine again.

Any ideas where to start looking, code reader brings up no faults and everything reads correctly.

Ta

Jackman

[DaveRob]

Sounds like a winding in the stepper is going intermitant open cct...... maybe temp or fatigue related. If it is intermittant then its going to be hard to identify without taking the stepper and its PCB and driving it continuosly on the bench with a scope monitor. The ACT code reader has a facility to drive the stepper manually.... have you tried driving it in and out for a while and seeing if it sticks at any point? especially after getting the underbonnet temp hot..... Their isnt an absolute encoder output from the stepper so their isnt any feedback to the ECU confirming position relative to idle or bas.... this means if it loses some steps it dont know where it is...... of course if you switch off the whole thing resets to zero... in The ECU sense and you get back to normal operation or at last somewhere inside the lost motion gap. The odd bit isyou say driving for a bit at higher revs gets it back in sync..... but this might be a winding cooling and reconnecting at roughly the place where it when open cct.... this would give you roughly the right stepper position.... but might be out by just a few positions so it appears in the correct place.

Just my thoughts

Rob

[Jackman]

Ta Rob.

Didnt think about the stepper thing on the code reader
Good having a brainstorm with someone about it. Strange thing is it always happens after a skipped beat.

Shall check it out tonight if i get chance, if not will be next week now as im away at weekend.

[DaveRob]

The skipped beat could also be a clue.... maybe. Just thinking about it if thier was a spike to the ECU or transient that it didnt recognise it might throw the ECU into thinking the stepper was somewhere it wasnt....... although if its been ok for as many years as it has it should have had enough thrown at it to suggest the suppression is ok. This also wouldnt be the case if it resetts itself without being switched off.... at least I dont think it would. My bet for starters is that one winding is going open intermitantly...... from temp or vibration....... try the stepper driver on the ACT first then shout when youve tried the test.

Rob

[Sprocket]

Chris, check the air gap on the crank sensor. I am also sure there is something amiss with the stepper motor on your engine with that cold start.

I would be sure to tune the stepper so that it is about 40 steps at warm idle speed. What is the stepper at, at the moment when its idling warm?

The stepper motor follows the throttle movement, to catch the throttle on release of the accelerator pedal, and lowers the engine speed gently to idle without over shooting and stalling. A low step count at idle can and does cause the stepper to hold the throttle and engine speed above the threshold for idle codition, the ECU mistakenly thinks that the throttle input is by you. The stepper just sits there and the revs dont drop. if the revs dont drop, the stepper will not retract.

you need to watch the stepper motor count to see what is actualy going on. I would check the crank trigger, make sure it is still tight and in the right position

[El Chibro]

Hi Jackman,

I had a problem that looked like yours a few month ago, it was due to the idle control valve. I forgot to plug it and it gave the same symptoms.

Edited by El Chibro, 27 March 2009 - 08:01 AM.

[Jackman]

Well ive just done a few hundred miles this weekend while i was away, the problem happened on one day 3 times and since then nothing at all. Its been sweet as a nut.

Will give it a full check over tomorrow though, air gap of the crank sensor seems to be ok still.

[Jackman]

Stepper count 40 when warm at idle.

On warmup the stepper goes to 72ish then drops and sits at 60 steps. Tested the range of the stepper, it goes all the way out then goes back in freely.

See how it is tomorrow, i used the tune stepper function and it seemed to be ok.

[DaveRob]

could be wrong but I thought the stepper count at idle should be about 25-30 steps.....

Rob

[Sprocket]

IIRC the tollerance is 20 - 40 at full warm idle with no load.

to be honest it doesnt really matter as long as its not below 20 and above 40 which would indicate either an air leak or a mal adjustment

[Jackman]

Right, its still doing it

I think its a dodgy cable somewhere Everything else is perfect.

[DaveRob]

Everything else is perfect..........

Are we talking car here or life in general....lol

its rare to find someone with a PERFECT A series so dont feel isolated in this respect...lol.... so you must be talking life...... and it cant be perfect unless you have a girlfriend like mine....lol...... so I have a perfect life and an imperfect A series... how good can it get......

Sorry if this is a bit off topic...... might see you at Minis Vs Beetles

...... good luck with the ' dodgy cable '..... they arnt easy to trace.... not without a scope and some time..... and especially with the stepper function......

Keep us updated

Rob

[Jackman]

Everything is perfect, idle well, drives great. All sensor readings are withing tollarance but there is just this problem. It started randomly and keeps doing it randomly, all i can think of is a cable fault. Ive had a few already with the coil and other things so i guess when i re-wire my dash i shall look at the engine loom too... but im doing that the minis vs beetles weekend but if its done for then ill see you there, if not see you another weekend.