Damaged crank trigger sensor(could this be causing missfire)

[Finny]

Hi all, as many of you may remember i have out an M20 in my 316i touring but i am having a problem with the car only firing on 5 cylinders, i have tried virtually everything and still cant seem to sort it.

I noticed the other day that the crank trigger sensor isdamaged and bent so that it is not pointing directly at the crank pully. Could this have anything to do with my problem??

I do appologise if this has nothing to do with anything as i dont even know what this component does, i assume it is something to do with the injector timming though.

Cheers

[Ant]

I doubt the pulse generator would cause only one cylinder to missfire but, you need to get that sorted out before anything else as its crucial to injection and ignition timing dude.

refit it so it is exactly over the toothed wheel centreline and 2mm away from the teeth themselves, thats one item off your maybe list either way.

[DelaneyG]

Get a new one if its damaged the ECU,s gona get the wrong signal from the sensor

[Mops]

do you know which cylinder ?

you can check by unpluggin spark plug leads... if you unplug ont one thats causing missing, engine behaviour wont change.

re crank sensor... if it was not picking up correclty your car wouldnt even start - but it's a good idea to fix it ASAP.

undo the plugs and see whats going on.

check whether you got spark on offending cylinger.

if thats all well, then hm.... well... other offending thing might be the offending cylinder injector, but you would have to pull it out to make sure and thats a bit of work....


keep us updated...

[Finny]

Hi, i have found out which cylinder it is(cylinder 6 nearest bulk head)

The plug in this cylinder is black and wet with petrol.

There is a spark i checked that too.

Im starting to get a bit fed up of it now to be honest. havent checked the injetors yet. Gonna swap the offending cylinder with another to see if the problem moves with it.

Im in the last couple of weeks of my uni degree at the moment so i aint got much time to mess with my car at the mo. Finished my dissertation now though! Any one who wants to know how too design a hydroelectric turbine give me a bell. Lol

Cheers

[DelaneyG]

mite be worth getting your local garage to do a compression check, they shouldnt charge more than half hour to an hours labour

[Finny]

Why what could be causing compression probs?

Had a new head gasket bout 1500 miles ago.

Could the inlet manifold gasket cause probs such as this?

[DelaneyG]

bunrt out valve from tight tappets, head not torqued down properly, damaged piston or rings, did u have the cylinder head crack or pressure tested an skimmed cos m20 heads are pron to warp an should always be checked, inlet manifold wouldnt cause low compression doh

[Finny]

Yeh i had the head skimmed when i replaced the gasket. Thing is it was running fine in the last car.

I took it out and it was standing for about a year then ever since i put it in the new car it has only run on five!!

[Mops]

really wierd. how come can you confirm it has the spark ? if the rotor arm is worn, you might be not getting spark on that very cylinder. might be a good idea to check out rotor arm.

dont bother checking injector. if the plug is black and wet from petrol, it means the injector is most likely right and spark is an issue. Sometimes if the connection is weak, spark will jump in free air (i.e. with plug outside the engine), but in the cylinder, where air and fuel is compressed.

it is possible the compression is lower in that cylinder because of the reasons mentioned in the previous posts....

[Brianmoooore]

inlet manifold wouldnt cause low compression doh

Would cause an idle missfire though.

[Brianmoooore]

dont bother checking injector. if the plug is black and wet from petrol, it means the injector is most likely right

Injector could well be not atomising petrol properly.

[Finny]

I checked the spark by resting the spark plug ontop of the rocker cover obviously connected to the HT lead.

It seemed to be sparking ok.

A worn rotor arm would cause probs on all cylinders surely. Would be the dizzy cap if anything.

I am baffled by this problem really cant think of anything. although my knowledge of injectors is limited(im used to my good old M10 Carb!).

Any more thoughts people? Im starting to loose faith in the M20!

Cheers

[Mops]

hm... yeah, he's right... it can possible be the injector... maybe is half burned and not opening complelty or clogged or something...

feww wat to check would be to swap offending injector with one form a good working cylinder. that will require pulling fuel rail and it's a rather tricky, but hey - it's free !!!
look up the guide for replacing injectors - its either here on this forums or e30tech i guess...