Buzzing noise from engine

[GJR]

Noticed over the weekend that when I turn the ignition off I get a strange, short, buzzing noise from the engine around the plenum area.

The car is running fine (engine and electrics), and the engine doesn't even need to be running to cause this buzz. If I turn the ignition electrics on, the fuel pump primes as normal, all is okay. If I immediately turn the ignition back off again the buzz can be heard. I got my OH to turn the key as I listened under the bonnet and it's not the coil. I don't think it's the stepper motor or the wiper motor. The sound seems to be coming from the RH underside of the plenum area (when looking from the front of the car).

Does anyone have any ideas as to what it could be?

[K4TRV]

Get a long screwdriver and place it on the stepper motor. Place handle against your ear and switch on or off.

Pound to a penny, its the stepper motor.

Trev

[carsy]

I bet its the Stepper.

[carsy]

Disconnect the wires to the stepper and see if it still does it.

[GJR]

Thanks guys, I'll check it out tomorrow.

[blitzracing]

Its supposed to do that- its a reset sent to the stepper for next time the engine starts. There nothing wrong.

[GJR]

blitzracing said:

Its supposed to do that- its a reset sent to the stepper for next time the engine starts. There nothing wrong.

Ahhhhhh! Not sure what to do now. I'm going to check this evening whether or not the noise is actually from the stepper itself. I maybe should be clear that it is actually more audible when the car is cold and you've just turned on the ignition to open the boot, then turned it off again, then you have the buzz. It doesn't seem to happen after a journey, that I've noticed.

Over the past few days I've noticed that the engine hunts a fair bit on idle, certainly more than it did ~1 week ago. It has done this on and off in the past, at which point I'd remove and clean the stepper. It usually has some carbon deposits, but not what I'd call excessive. After cleaning the idle usually settles and is stable for another few months. I've using V-power which helps, but my commute to and from work is short ~4 miles. However, the engine fans are usually kicking in at the end of the journey.

What has concerned me more this time is the buzzing noise when you turn the ignition key off. Fingers crossed, my car has always been pretty reliable, but like most owners you do get used to the normal sounds of your car, and you do become acutely aware of anything unusual. In this case the buzz is very audible, even from the cabin sometimes.

With a new stepper at the best part of £100 it's not the sort of thing you just want to spend out on if you're not sure.

Cheers for all your advice so far, I appreciate that it's the sort of thing that is difficult to diagnose over the internet!

[GJR]

Okay, hope this works. I've added this Video Clip to youtube. From under the bonnet the buzz is obvious. From in the car the sound is less audible in the clip, it is there but very faint.

The noise is from the stepper. After recording this I disconnected the wires to the stepper and the buzz does not occur.

Question is.... is this normal? If it is, I'm staggered I've never noticed it before.

[V8 GRF]

I think there is something wrong with the stepper, perhaps it's stalling and hunting. Try giving it a clean.

[carsy]

The buzzing noise when switching ignition off is completely normal.

[V8 GRF]

carsy said:

The buzzing noise when switching ignition off is completely normal.

Yes you can hear it if you listen for it but it's quite feint and more of a gentle whirr as the motor winds itself in or out that sounds like a motor turning and gears not moving and grinding on each other.

I'd suggest seeing if you can borrow a stepper to swap over and see if that solves it.

[carsy]

IF you take it off and give the internals a good soaking with wd40 it will probably quieten it down a bit.

[Colin RedGriff]

Also worth cleaning the hole the stepper goes into as well.

Whereabouts in Hants are you. I'm up in Crowthorne so if you wanted to compare it with mine at the w/e you could.

Edited by Colin RedGriff on Wednesday 14th November 22:47

[GJR]

Thanks for all the comments guys. ColinRG, I'm down on the coast (Portsmouth way) and thanks for the offer . I think I'll give it a clean first and see if it improves, but my gut feeling is that it's on the way out. I seem to be doing this quite often though, probably not helped by my short daily commute.

[blitzracing]

The exact reason is the ECU fires 180 stepper pulses as the ignition is powered down. The noise problem is the stepper simply has not got a 180 step range- so it hits the end stops and buzzes. Its designed to do this as the ECU has no idea of where the stepper last was when the engine was running (it simply moves it in or out to get the idle right- it does not have any feedback of its physical possition) , so it simply drives it as far back as it can go, ready for the next restart. It then knows the stepper is at position "0" when it has to be moved to control the idle on restart. Its possible that simply its on the end stops for longer when the engine temp is cooler, so its louder.

[GJR]

Thanks for the information blitzracing. I'll remove it this weekend and check it's condition. I usually clean it with meths, an old tooth brush, and a bit of wire wool. But the meths is clearly going to remove any lubrication along the stepper motor shaft. A squirt of wd40 has been mentioned above, but would a little engine grease last longer?

[blitzracing]

There are some metal bearings in the base of the motor that corrode and the motor becomes noisy, but you cant get at them. You can get the shaft out if you really want to, otherwise WD40 ir the like wont do any harm. Id disconnect the motor when the car is at idle, so the shaft cant pull back when turn off the ignition. This will allow more access to the keyway that's behind the cone that carbons up.

Details on the stepper here- half way down the page:

http://www.g33.co.uk/fuel_injection.htm

[EGB]

My BMW does the same 2 minutes after switch off. Just a slight humm. Griff does it immediately after switch off. Just a slight buzz. No worries!


http://www.g33.co.uk/fuel_injection.htm

Nice one Mark.

Edited by EGB on Friday 16th November 10:03

[GJR]

Thanks for all the advice guys.

I took the stepper out today and gave it a clean. It wasn't particularly dirty, but to be honest I wasn't expecting it to be as I'd only cleaned it ~3 months ago. There was a bit of PTFE debris stuck between the spring and nose cone which could have prevented it seating properly. Anyway, I made sure the shaft was fully wound in, WD40'd and that the new PTFE was a little further back on the threads before re-installing back in the car.

The good news is that the loud buzzing is gone, now just the quiet buzz that others have suggested is normal. However, the idle is still jumping around by ~400rpm. If you rev the engine it will often hang at ~1400 - 1800 rpm when you take your foot off the throttle. It will drop after a few seconds.

If this is not the stepper playing up, what else could it be ? It's not a major issue, but it would be nice to solve.

Thanks

[blitzracing]

You need to go and read Steve Heaths ECUmate manual- it covers the idle control in depth and its fairly complex. The TVR speedo calibration unit under the dash is a good place to start for fault finding.

http://ecumate.com/docs/Ecumate%20inst.pdf