M42 backfiring, running rough, help! solved

[E30 Wagen]

To begin with, my m42 was starting hard and running rough. When I tried starting it was like the engine didn't want to turn, would make horrible a squeak noise, backfire, and then die. I was getting code 1271 (I think). I tried a different set of coils with same results. Checked the coil ground and the ground from the engine mount to the frame rail, both seemed fine .

So, yesterday, after discovering a bunch of cracked vacuum hoses, I went through the process of deleting the unnecessary TB coolant plate mess and rerouting the vacuum hoses as pictured in that diagram that's floating around. However, my M42 wasn't equipped with the coolant spacer between the TB and the manifold - instead it just had a contact plate on the bottom. My throttle body also lacks the vacuum port on the bottom in front of the valve. So, when I rerouted the vacuum lines, I utilized both of the holes in the intake boot - I connected the hole closest to the throttle body to the front of the valve cover and the hole closest to the AFM to the ICV. Make sense? I also had to reuse all the intake gaskets. When I had everything apart I also noticed that the cam sensor wire had gotten damaged so I replaced it with a good one.

After I had everything back together, it started up and idled better! It wasn't perfect but I figured it would get better once I put fresh gas in and let the engine breathe some more. I let it idle for only 15 seconds or so because I was satisfied it was all good and it was like 11:30pm.

But then today it's like I'm back to square one. I go to start it and I'm getting the same symptoms as before - runs rough, misses, backfires. I thought I would change the ignition wires with a better set and now I'm thinking I may have messed the order up. I thought you matched the number on the coil to the cylinder, but I also tried matching the coil number to the firing order, but got the same result. Anybody want to clear this up for me because I feel like I'm losing my mind with this now...

Once I'm sure I've got good ignition wires I'm going to check the crank position sensor and another ecu. But if that doesn't work I think I'm out of ideas. Even if the intake gaskets that I reused were leaking just a tiny bit it should still start and at least idle, right?

[E30 Wagen]

Ok, tried a different crank position sensor, different ecu, and still the same problem. Getting code 1444. What else should I try?

[dude8383]

try to find a good AFM to swap yours out with.

[ahlem]

Do a quick search for firewall plug or running rough when hot.
There's a little plug that sends a bad message to the ecu (USA version) if it's plugged in.
It is counterintuitive to have something dangling that seems obvious that it needs to go together. It's on the firewall just to the passenger side of the heater fan cover. I believe it only has 2 wires. It should be unplugged.

[E30 Wagen]

I did find a connector that I had plugged in, so I unplugged it (it was only one wire). I don't know if it was my imagination but the engine seemed to fire up easier, but it's still really rough and if I give it some gas the engine will pop. It definitely sounds like it's not running on all cylinders. The engine has sat for a long time and I worry that the fuel injectors are questionable. I think I just need to try some new manifold gaskets, new wires and spark plugs, and I will try using the injectors from my other engine since I think those might be in better condition.

[ahlem]

Performance Diesel on 54th (?) Street just east of 131 in Grand Rapids cleaned and checked injectors for about $20-$25 each recently for us. Did you check the quality of the spark at each plug? You can use a stethoscope or a long screwdriver or a fiberglass driveway marker section and put the end on the injectors individually to see if they are receiving a signal. I made a smoke tester to check for vacuum leaks that is available if you need it.

[roguetoaster]

If ever you're confused about coil/plug order there is a little metal plate that sits on the stack of coils under the plastic cover which indicates which coil to which plug (1-4 F-B). The coil wiring has by this point pretty much set in position so that it's unlikely that you'll plug the wrong one in if you're not forcing the connector. So, take a few minutes to rationally examine the routing and assembly order if you still think that might be the problem.

[E30 Wagen]

Yeah i just couldn't remember if the number on the coil was for the cylinder number or the firing order. The answer I found online was to connect it by cylinder number.

[ahlem]

Old bad gas can cause lots of these issues as well.

[E30 Wagen]

solved, kind of

Ok, installed some new intake gaskets, and switched out the injectors for some better looking ones. I kept the same throttle body and vacuum hose routing but still got the same rough running condition. Before, I was sure that I was getting spark from each coil, but when I checked coil 1 again I discovered I wasn't actually getting spark, which also explains why the engine wouldn't struggle when I unplugged it while the engine was running. I decided to recheck the coil harness connections, then figured I'd try switching the 1 and 2 coil connections. This seemed to fix the problem as now I was getting spark and the engine ran better, but not great. So, I decided to try another set of coils, and this seemed to fix the issue because now it runs and idles great! Sits right at 700ish rpm and responds to throttle inputs without any stuttering.

Now I just gotta replace the clutch slave cylinder which decided to self-destruct. Anybody in west michigan have a spare?

[ahlem]

If only we knew that yesterday. Sent you a PM. Glad to hear you got the problem solved.