What could be causing a misfire when warm - 325i

[Endless325]

Hi all,

What could be causing a misfire when warm, on a 325i?

Around 2,500rpm, but you drive through it fine?

Cheers!

[dilo_attax]

check the plugs + leads? or a lose earth?

[Endless325]

Will do mate, am I right in thinking that the worse case scenario, it's the loom, or ECU?

I'm just worried that it may be something internal, or serious, could it?

Thanks for the reply

[Endless325]

Serious yay or nay?

Cheers

[Brianmoooore]

Check distributor cap, rotor arm and plugs for a start, and consider giving it a good service.
A lot of these problems can be solved by simple servicing!
Won't be your ECU or anything serious with the loom, although there's a plug and socket under the inlet manifold that can give trouble. Can be removed and hard wired if beyond repair.
Next on the list with be the air flow meter.

[Endless325]

Cheers mate, as always!

The hose from the AFM to inlet has some holes, it's taped up very well until I get a new one, could this cause a misfire?

Also when you first start it, it starts with a misfire, and then settles to a normal idle after a few seconds, and then while ideling at standstil, if you stab the throttle it misfires and sounds like it's about to stall, but it does'nt.

The misfire is very low down

Cheers for all the help guys, damn misfires!

[Brianmoooore]

Sounds like yo may have more than one fault, but the hesitation when you stab the throttle is typical of the effect of an air leak between AFM and throttle body. I.e. Split hose.
Check out the distributor cap, rotor arm and plugs as well, as a weak mixture is hard to ignite.

[Endless325]

Cheers mate, will do, could it be a duff ignition coil?

[Brianmoooore]

, could it be a duff ignition coil?

Only if you are in America! Most of their faults seem to down to dud lambda sensors and faulty ignition coils, according to the E30 forums I watch!
Personally, I've never seen a dud E30 ignition coil.

[Endless325]

Must be the food!

Mine seems a little damaged, could it cause the misfire I described?

[Brianmoooore]

Damage to the plastic like that isn't going to cause a misfire, but what it will do is encourage a flashover from the HV connection to the ECU connection (black wire), and ECUs don't generally appreciate 40,000 volt pulses.

[Endless325]

Cheers Brian, another thing for my list!

What's this lead? Because it has a split in it, which was neatly taped over, could it cause a misfire?





Thanks

[Brianmoooore]

On some (early) versions of Motronic, this wire just connects to the diagnostic connector, but on other versions it's the M20's equivalent of a cam position sensor, and tells the ECU which of the pair of pistons that are at TDC at any one time is at the beginning of its firing stroke and which is just beginning it's intake stroke.
Engine will run happily without it though, but at a slightly reduced efficiency.
Sorry, it's another thing to sort out, but I don't think it's the source of your problem.

[Endless325]

The list is ever-growing!

Thanks for the explanation too, even an idiot like myself can understand it!

Is there anyway you could help me find out if mine's an earlier motronic? as mines a 325i conversion, and I don't know what year car the engines from!

Cheers

[Brianmoooore]

Is there anyway you could help me find out if mine's an earlier motronic? )

ECU number will indicate what motronic version you have.
I think the version that doesn't use the pulse from the plug lead has a two wire idle control valve and a 35 pin ECU.

[Endless325]

Thanks mate, will check and report back! If I find out what motronic version I have, would this tell me what year car the engine came out of, roughly?

Also, on the misfire front, crank sensor was changed not so long ago by the previous owner.

[Endless325]

OK, changed the plugs, rotor, and dizzy cap, but the misfire's still there.

What else could it be? What sensors/connectors shall I clean out?

Please guys, list every possibilty, I'm trying to source an AFM in good working order to try.

Thanks