Aagghhh! It's pinking!

[hogweed]

My 325 has gradually started to pink slightly under hard acceleration, over the last couple of weeks maybe.

Does this indicate a cattled anti-knock sensor, or what?

Thanks...

[Andy_magic]

Do the motronic cars have a knock sensor?

I've just checked the engine and accessories wiring diagram and can't see one.

[randomdave325]

no knock sensor on the m20 m8. chuck some optimax in it see if it still does it! could be poor fuel. thats what is was on my old 16v gte. that or it's running a bit weak for some reason.

[johnono]

is pinking when the timing is off? as i found some site that said it is the fuel uԚ´re using or the distributor is knackered or the rockers need resetting

[Andy_magic]

Poor quality fuel, excessive carbon build up, weak mixture, overheating, incorrect ignition timing, mechanical binding in the drivetrain can all lead to pinking.


I would go with the easiest first and fill up with quality fuel, then check the fuelling and cooling side of things. Motronic cars don't have adjustable ignition timing as far as I'm aware (apart from a chip) make sure the cooling system is topped up and bled properly.

Can you push the car by hand?

Carbon build up on the pistons and combustion chanbers can cause pinking but it would have have to be pretty severe and I dount it would just start doing it, it would normally build up over months.

[vernon77]

Hey,

mine is doing the same thing it sounds awful, glad to hear it could be the fuel as I usually use BP Opti but just filled her up with Texaco prem.

It happened to me a couple of months ago, I checked all the cooling system (changed engine sensor) and changed the breather elbow and it stopped. Since them I've had the timing belt changed and rockers reset so I'd hope it's nothing to do with them!

If the BP fuel doesn't improve it them I guess the fuel filter and d/cap are my next option?

cheers

ps. typical, it's been running excellently for the past month and the weekend I want to sell it this happens

[hogweed]

..for all the input guys. I suppose it could be shite fuel, I kind of assumed they were all the same, and the rest was just hype...

Points -

Timing - as far as I'm aware Motronic has no provision for adjustment. But the way I read the Motronic manual, it is controlled by an anti-knock sensor which keeps it jsut the right side of pinking, yet you think there isn't one... typical, I haven't got the books here right now.

Friction etc - yeah, I can push her along easily enough, and she'll hit 135 on a good day.

Cooling system... hhmmm. Possibly....

[Andy_magic]

I've just re-checked the schematics for the motronic engined 325i (1989) and there appears to be no knock sensor.

There is a cylinder identification sensor which is the inductive loop thingy that goes round the No.1 plug lead and plugs into the loom under the ICV mounting bracket. I guess if this was faulty it could possibly cause ignition timing problems as the ECU wouldn't know where No.1 is.

In my experience cars fitted with engine managment come in 2 flavours. Those with ignition curves and fuelling hard coded in the ECU chip and those taht max out the advance based on info from knock sensors and air intake temp/density.

For a while Saab turbos used knock sensors and you could vary their sensitivty via an adjustment inside the ECU which gave excellent results when fed decent fuel

[randomdave325]

best bet is take the plugs out and see what they look like. should be a light brown. white is too weak. may even be shafted plugs.

[hogweed]

...it MIGHT be a bit weak, the rolling road guy said so. I asked him what he woudl do, and he said use injector cleaner. well I have, not sure it made any difference. Plug test is a good idea, if I can be arsed. Maybe I'll finally get around to fitting the E36 M3 injectors that've been lying on the shelf for over a year... they should darken the plugs a bit