328i cylinder 1 & 3 misfire

[HardTrackz]

Dearest fellow Beemer enthousiasts

I have run into another little issue with my 328 coupe build.
The car still misfires and runs very rough while idling. I have worked out that the problem is my first and third cylinders. Obviously, it wouldn't be as simple as just replacing the spark plugs... those are brand new.
I measured the resistance on my coils, they appear to be fine too. The wiring is okay too.
When I swap the plugs on the 2nd and 1st cilinder, the first cylinder does fire, so in conclusion, it's the plugs on cil 1 and 3 that don't get any power. Swapping another DME into the car doesn't help either.
What could be the problem here? The crankshaft sensor will be replaced, but will that fix the problem? No idea what else it could be.
Any help would be appreciated!

[ed323i]

It's very probable this isn't related to the crank position sensor. If the DME gets a good signal from the crank position sensor, then it should fire all coils.
What you can try is buy a sub-wiring-harness for the ignition coils at the junk yard (shouldn't cost much) and replace that..
This is what it looks like:
s-l300.jpg

You can also use a multimeter to measure resistance to the DME connector for each coil. I'm not sure if your M52 has been converted to OBD1 (as your chassis is from 1993). You'll need the DME pinout for the specific DME you're using (either OBD1 Bosch Motronics or OBD2 Siemens MS41)..

Also check if the coils gets proper ground (probably brown wire). Using a multimeter in the 0-100 Ohm setting you can measure between the coil connector and a know-good ground point (I often use one of the three bolts on the shock tower). Resistance should be 0-2 Ohm max.

With ignition on you should also see +12V on one of the three pins of the coil connector. Using a multimeter in the 0-20V DC setting you can measure between the coil connector and a know-good ground point. Voltage should be +/- 12.5V with a charged battery (might register a bit higher if the car was running just before).

Good luck!

[HardTrackz]

It's very probable this isn't related to the crank position sensor. If the DME gets a good signal from the crank position sensor, then it should fire all coils.

I'm pretty sure the cps is dead, or at least on it's last legs, so is it possible that it sends a wrong signal to 2 of my cylinders? Or will it just stop working entirely when it's broken?

What you can try is buy a sub-wiring-harness for the ignition coils at the junk yard (shouldn't cost much) and replace that..
This is what it looks like:
s-l300.jpg

I have a full, second harness at my disposal, but like I said, I checked with the beep-resistance thingy on my multimeter and none of the wires were interrupted so I highly doubt the harness is cur somewhere.

You can also use a multimeter to measure resistance to the DME connector for each coil. I'm not sure if your M52 has been converted to OBD1 (as your chassis is from 1993). You'll need the DME pinout for the specific DME you're using (either OBD1 Bosch Motronics or OBD2 Siemens MS41)..

My engine has an M50 head with an aluminum M52 block, but it runs like it should, save for those 2 down cylinders

Also check if the coils gets proper ground (probably brown wire). Using a multimeter in the 0-100 Ohm setting you can measure between the coil connector and a know-good ground point (I often use one of the three bolts on the shock tower). Resistance should be 0-2 Ohm max.

With ignition on you should also see +12V on one of the three pins of the coil connector. Using a multimeter in the 0-20V DC setting you can measure between the coil connector and a know-good ground point. Voltage should be +/- 12.5V with a charged battery (might register a bit higher if the car was running just before).

Good luck!

This is some solid intel, I checked everything with the beep thingy mentioned earlier but I didn't know the values of everything so I'm def gonna give all this a go tomorrow

[Eric93se]

Wire harness is not usually the culprit. You should know that coils can 'leak' and a basic resistance check is not sufficient. High voltage can jump right through the coil. Also injectors fail and can clog. When buying Cam and Crank sensors you have to stick to OEM and that is Siemens and VDO. Ebay has some good prices for true OEM there is a seller "partscontainer" also I've seen RMeurpean.com with good prices for oem. You should do a compression test, but in this case the compression might be low because the cylinder wasn't firing. Sometimes an inspection camera might be helpful but you cannot see the valves

[ed323i]

I'm pretty sure the cps is dead, or at least on it's last legs, so is it possible that it sends a wrong signal to 2 of my cylinders? Or will it just stop working entirely when it's broken?

Normally the CPS either works or it doesn't.. It can also be intermittent and for example stop working correctly above a certain RPM, or just cause intermittent ignition/injection errors. But it being related to specific cylinders, though theoretically possible I guess, would seem very improbable. The crank wheel doesn't have specific teeth that indicate when it's TDC for a specific cylinder. It just syncs to a missing tooth (which I think indicates TDC for cylinder 1 or 6, or perhaps a few degrees before or after, but at least it's only 1 fixed reference) and then goes on to count the teeth. Even if it fails to read a couple of teeth, it will interpolate (using current rpm/flywheel speed) and calculate when it should fire a coil or inject fuel. So, what I'd expect is it might stop firing completely for all cylinders if it fails to find the missing tooth for 1 or more revolutions, then resync itself (by finding the missing tooth again) and then continue to fire for all cylinders. Specifically failing to fire for 2 specific cylinders is, I think, virtually impossible.

If it's not the coils, and it's not the DME, then it must be that either the specific coils don't receive proper 0-2 Ohm ground, or don't receive +12V, or there is a problem with the wiring between DME and coils (remove DME connector and find the connection to each coil connector and verify it's below 2 Ohm; a lot easier with the DME pin-out table). Coil connector has three pins. Ground, +12V and DME signal (not sure of the exact order, but if I remember correctly ground is pin 2).

Update: I remember some cars have a resistor between ground and the coils, so then you won't find 0-2 Ohm ground, but a few hundred Ohms between the coil connector and ground. At least make sure all six coil connectors have identical ground resistance values.

[HardTrackz]

Sorry for reviving this thread but due to work I barely touched the car all winter. I have done a few things so far;

- Swapped out the crankshaft sensor just to be sure, as you guys pointed out, that didn't work, but at least I'm sure now

- I measured the 3 pins on the coil connectors: all 6 of them have around 12V (a little less but the battery ain't 100% anymore) but they're all the same around 11,60V with ignition on, they all have good ground I think (around 240ohm, I don't know if that is any good but it's the same for all 6 of them) and there are no interruptions between the DME connector and the coil connectors.

I'm seriously running out of options now, so now what's left imo is either;

- the DME is bad, which seems unlikely seeing as it did the same thing with another DME which is known to be good

- the coils are bad, which seems unlikely as well because I have 6 others from the old engine which, same as with the DME, are known to be good, and I have swapped them already, didn't help either

- the sparkplugs are bad, which would be weird because they're brand new, but when I think about it, they were the only things I changed after the swap and the engine came out of the other car running. It had been sitting still for a while but that shouldn't have caused the problems I'm facing now. Idk what could have gone wrong with the plugs but I'm gonna check those tomorrow.

- and lastly, if they're not to blame, then it has to be something else and I would have absolutely no clue what it might be.

Any further input would be greatly appreciated, you guys have helped me out heaps already!