Constant Misfire

[mikeyv8]

Hi guys, my 325i has a bad misfire on idle, it smooths out as the revs increase but its still there, it doesn't smell rich from the rear which I thought it might do if it was a spark plug, the plugs are new, no visible signs of an air leak, leads aren't genuine but look quite new, where do I start with tracing this fault?

[motormanmick]

Hello mikeyv8, assuming it's an m20 - dizzy cap, rotor button and leads is a good place to start, you have new plugs, are they the right ones. I once had a similar problem once on an m30, my rotor button was arching (shorting out). Are your leads the correct ones, leads can look pretty good on the outside, but show up as stuffed when tested. Terminals on dizzy caps get a build up on them and need to be cleaned, if it's within your budget replace the lot with genuine.

[mikeyv8]

Ok, thanks for the advice so far, ill make a start today.

[mikeyv8]

Initial finds are its got the wrong plugs in, jenso or denso I think, 3 were wet 3 were dry, I guess its a good starting point to replace them 1st.

[HairyScreech]

Which 3 were wet and which 3 were dry?

The injection is batch fired so 3 fire followed by the other 3. Might still be an injection issue.

[Yeti]

where are you located mate if im near i could lend a hand if needed

[Brianmoooore]

Time to inspect the plug and socket, located under the inlet manifold, that joins the injector loom to the rest of the engine loom. Common failure, with a TIS from BMW to prevent it happening.

[mikeyv8]

May have made some progress, I took the car for a good drive, while I was out I got the correct plugs and fitted them, when I took the plugs out this time they were all equally dry and much lighter in colour, so I fitted the new ones and it made no difference, it smelt very rich from the rear like it was choking itself, anyway, I disconnected the air flow meter and immediately idled smooth with no misfire, but the car would then hardly rev with it disconnected, so I reconnected it and back came the misfire/hunting. Am I on the right track with this? Could it be a faulty air flow meter? Im certain now its a fuelling problem not an ignition one..

Ps... in im Tamworth

[aze30]

Bump...my old car
almost missing it already mike!
Guys the car has what seems to sound or feel like a hunt only at idle.
When driving under load there is no evidence at all of a missfire or any issue related to the hunting.
Im thinking possible injectors?
its not really a missfire as such, it sounds almost like an erratic idle ...bit of a 'humm humm humm' sort of sound.
Azzy

[Yeti]

possibly afm ? the car wouldnt rev as you disconnected it so the ecu doesnt know how much airflow there is. id try that get someone with a working one and swap over.

and your 1hr 40 mins away :/

[mikeyv8]

Unfortunately I don't know anyone with a spare so ill have to buy one, is it likely to be this as I don't want to waste my money if its not.

[Brianmoooore]

Unfortunately I don't know anyone with a spare so ill have to buy one, is it likely to be this as I don't want to waste my money if its not.

You could always TEST the one you have.
As I've stated on here many times, test, don't blindly swap components. You should never change a component until it has been proven to be faulty.

[mikeyv8]

How do I test it?

[markus_74]

Engine should off while you disconnect afm plug but If you disconnect the afm plug and engine still run and.smooth, it is the tps goes wrong(bad contact inside so need to clean) or if you just open your throttle body may be you have misalign the tps.

Please check the throttle adjuster screw does it has factory original setting or uou may be just change it?

Do yoi hear a sound click while you touch the throttle on the top of throttle body?

It should have sound click if not your tps is misaligned.

[mikeyv8]

When I unplug the afm it runs smooth, unplug the tps and it makes no difference, I'm inclined to think it's afm but would be interested in knowing how to test it?

[markus_74]

It is not afm but tps, you have just test it with unplug the afm. If tps good and correctly alignment engine will stall and die.

You can see a screw throttle adjuster? Check it if it has maybe someone has turn it? If yes. You can turn it back to normal position.

With engine off check the throttle lever touch it gently move a few mm you should hear a click sound and if not turn to loose the screw until you hear a click sound

[mikeyv8]

Yes, if I move the throttle slightly I can hear the tps click, so is that ok?

[markus_74]

Yes, it is OK. But may be you should check tps with ohm meter? It has continuity or not if you move the lever after hear click?

[mikeyv8]

Ok, so ill look at testing the tps and afm then,

[mikeyv8]

Tps checked and working fine, still not sure how to test afm though, the misfire isn't as bad from a cold engine but as the engine warms up and the revs drop is when it's really lumpy.

[Brianmoooore]

still not sure how to test afm though,

Just tried to find it in the wiki, but I don't think it's in there!

To test the AFM, you need to connect a 6 or 9 volt battery across the ends of the potentiometer track, and connect a volt meter (preferably analogue) between one of the battery terminals and the rotor of the AFM.
As the AFM flap is slowly opened by hand, the voltage on the meter should gradually increase, with no 'drop outs' or reduction in voltage at any time.

[mikeyv8]

Ok, update, checked TPS fine, checked blue plug at both ends hot and cold, both fine, now when I unplug the afm the car stalls whereas before it ran better, no matter when you start the car, for the first few seconds its ok then its back to being very lumpy, any ideas on what to check next? Is it still pointing to a bad AFM?

[ah]

I've had the same sort of fault for the last few years and never got the bottom of it.Ive got a horrible misfire at 1500_2000 rpm as I increase the revs it gets better but not perfect,also some times I'll show the key to the ignition and it's starts,other times I have to crank it over for approx 10 secs and it does not fire but some how jumps into life.Also mine hunts after starting and smells a bit rich.The last part of my fault is at he revs I mentioned obove it kangaroos badly.Ive never had injectors seviced and it's done 104k.I replaced countless things but to no avail.

[Brianmoooore]

Ive never had injectors seviced and it's done 104k.

And you wonder why it kangaroos??

[ah]

But would the other symptoms point at injectors.

[aze30]

I've had the same sort of fault for the last few years and never got the bottom of it.Ive got a horrible misfire at 1500_2000 rpm as I increase the revs it gets better but not perfect,also some times I'll show the key to the ignition and it's starts,other times I have to crank it over for approx 10 secs and it does not fire but some how jumps into life.Also mine hunts after starting and smells a bit rich.The last part of my fault is at he revs I mentioned obove it kangaroos badly.Ive never had injectors seviced and it's done 104k.I replaced countless things but to no avail.

while i owned the op's car i did many checks and chnaged many items trying to fix it...i had it narrowed down to either the injectors themselves or the loom leading upto it.
although the car didnt do any kangarooing lol
azzy

[aze30]

Exactly my thoughts!
On idle the car is very lumpy but on acceleration its perfectly fine.
i see what you mean by the fuel not atomising if its dribbling...it makes perfect sense ...when the car is at high revs its not noticeable at all as the fuel mixes with the higher air velocity giving a more even mixture whereas at lower rpm (slower engine) speed it just drips in....causing the hunting.
azzy