Misfire until warm

[Morat]

Folks, my 325 is playing up when cold. When I first start her up, especially on frosty mornings, she'll run on 4/5 cylinders. As the engine warms up to the mid point on the temp gauge, I get 6 cylinders and all is good until the next cold start.
The car had a new blue temp sender a couple of months back which cured the madly rich running and constant misfire, now it only runs properly when hot.
I've checked for air leaks with carb cleaner and I can't find any.
I've also tried to check which cylinders are missing but it doesn't seem to any specific ones (the engine sounds the same no matter which lead I remove at any time).

Does anyone have any ideas? I'm wondering about injectors but I'm too tight to do them unless it's likely to help.
Cheers,
Morat

[DaniTD]

Check HT leads. Mine was doing something similar so I went to check the lead with the multimeter (mine is a 4 pot) and guess what? 3 of the leads show 6k Ohms which is right, but one of them was jumping from non-continuity to 120k Ohm to 6k Ohm and so. Replaced it and no more V8 sound

[Morat]

Fair play... now where did I put my meter ...

[pukar]

i have a 325i and had this exact same problem and it turned out to be a HT lead and dodgy ecu....give that a go if all else fails

[parkin10]

mine was tracking out between the weather sheld and the dizzy cap

[Morat]

Hmmm, so basically we're looking for a weak spark? That would make sense.. I forgot to mention that i replaced the spark plugs which helped for a short time. The old ones were all a healthy colour but the electrodes had all eroded back so the gaps were too big.

[DaniTD]

Problem is we don't give the same importance to sparkplugs and HT leads (me first) and we often overlook them and our cars have some years over them check them and tell us the results!

[parkin10]

i could never find a miss fire on any one cylinder but it was miss firing mostly when cold
then when i saw a spark jump between the back of the cap and the weather sheld i took the sheld off all to gether its been lots better but why would it ark out on plastic?

[DaniTD]

i could never find a miss fire on any one cylinder but it was miss firing mostly when cold
then when i saw a spark jump between the back of the cap and the weather sheld i took the sheld off all to gether its been lots better but why would it ark out on plastic?

That's because the cap is broken and there was humidity between the cap and the dust cover you removed.

[Brianmoooore]

I'm wondering about injectors but I'm too tight to do them unless it's likely to help.

May or may not be relevant to your current problem, but injector performance is of fundamental importance to how an E30 engine with no mixture trimming feedback loop performs.
Unless you get free fuel, you can't afford NOT to get them rebuilt.

[Morat]

I hear you Brian... Maybe next month :/

Anyway, I've taken readings - they're all coming out at 1. Which would indicate I know SFA about multimeters.
I'll be back once I've read up a bit on the net.
Also, the leads are all marked BBL rather than BMW - are they aftermarket?

[Morat]

I've checked I'm using the meter properly, and I think I am. The probes were in the right holes and selector was at 20k Ohms.

More worryingly, I can't even get continuity. Tapping the probes makes a tone, sticking them down the two ends of an HT lead gives nothing.
I've tried every single plug end of every lead, no joy.

Also, although the dizzy end is nice bright copper, the plug ends all look nasty and corroded - like this:



Just for my sanity, could someone tell me which leads I've unplugged from the dizzy in this photo? It would help me if I didn't have to check all six each time
Thanks

[Grrrmachine]

Left-Right (so top-bottom in your pic) it goes 2 - 4 - 6 - Coil - 3 - 1 - 5.

So you've got 2 and 4 unplugged there.

[Morat]

Thanks Grr.
I think it's time for new leads. There's absolutely no way my multimeter can get a signal through the rust and crap on those cables, so I guess that is hurting the spark as well. Resistance is infinite, continuity 0.


The leads are BBT which look to be aftermarket shite.

[jonny323i]

I have a full set inc cap and support rail in my for sale thread if you want to try them

[DaniTD]

Thanks Grr.
I think it's time for new leads. There's absolutely no way my multimeter can get a signal through the rust and crap on those cables, so I guess that is hurting the spark as well. Resistance is infinite, continuity 0.


The leads are BBT which look to be aftermarket shite.

OEM HT leads are supposed to be Bosch. That (no continuity) is what I got on one of my HT leads. Maybe if you put the selector on a bigger scale of the multimeter you could get some readings but anyway they are shot. If you can, replace them. After all, on this kind of injection systems it is part of the maintenance and all of our cars are of age

[Morat]

I've just tested my new (second hand) leads, and they're coming out at between 6200 and 6400 ohms each, apart from the king lead which is much lower. Are they OK? I'd rather know before I go out and fit them in the b&&&y snow :/
Oh, and they're Bremmi which isn't Bosch... has anyone got any experience of this brand?
Thanks all.

[Grrrmachine]

BREMI are the OEM manufacturer of the distributor cap and rotor, so they probably do pretty good HT leads too

[jonny323i]

Just worth a mention my car had recently been running rough when cold not as bad as yours by the sounds of it, but this weekend after doing some jobs I found I had drained my battery which I was surprised at so I checked the voltage being supplied when running which was very low 13v enough for everyday running but not enough for extended use without the engine running.
Iv since fitted another alternator with a healthy 14v and it does run better.

[DaniTD]

6200-6400 Ohm is right for the spark plug leads (about 6000+-500 Ohm aprox). If the king lead you mention is the coil to distributor lead, it should be around 2000 Ohm

[Demlotcrew]

A good stable voltage is a good as six new injectors! Anything lower than 14v and you've got issues (even with the voltage compensation table in the eprom).

[Morat]

Well, I fitted the leads this morning and despite it being -2 degrees overnight she fired up straight onto 6 cylinders like a little champ
The car feels much smoother overall, so perhaps she was missing now and then without it being obvious. Or maybe not. Anyway, I'm now happy with the engine (for now) and it's time to move onto the PAS which has drunk a litre of ATF in the last 1000ish miles.
It could be time for an E46 rack... except I just changed DanThe's avatar to Justin Bieber
Let's hope he's a forgiving type

[Speedtouch]

I've checked I'm using the meter properly, and I think I am. The probes were in the right holes and selector was at 20k Ohms.

More worryingly, I can't even get continuity. Tapping the probes makes a tone, sticking them down the two ends of an HT lead gives nothing.
I've tried every single plug end of every lead, no joy.

Most continuity testers on multimeters will only work on resistances of up to around 200 ohms, so with a typical HT lead measuring in at 6000 ohms, it won't sound the buzzer.

[jonny323i]

Well, I fitted the leads this morning and despite it being -2 degrees overnight she fired up straight onto 6 cylinders like a little champ
The car feels much smoother overall, so perhaps she was missing now and then without it being obvious. Or maybe not. Anyway, I'm now happy with the engine (for now) and it's time to move onto the PAS which has drunk a litre of ATF in the last 1000ish miles.
It could be time for an E46 rack... except I just changed DanThe's avatar to Justin Bieber
Let's hope he's a forgiving type

Glad to hear itB-)

[Morat]

Thanks for that, it confirms what i had begun to suspect....I know nothing about electronics