really weird issue

[bmwman91]

Crazy. Try popping the cover off and getting a peek inside. You might be able to fix it by cleaning the track and adjusting the radial position of the wiper. If there's any definitive damage, I would be curious to see a pic of it.

[ThatOneEuroE30]

turns out its my AFM its not getting any continuity through the veins range of motion i ran the car with it unplugged the idle was great and the lights went off i did it 3 times to be sure. it does fall on its face at 1500 rpm but Im willing to bet that's from the chip and lack of fuel mixture reading

[ThatOneEuroE30]

Wondering if i shouldnt order this lab scope to try and diagnose the issue. Seems like it could help rule things out.

https://www.aeswave.com/uScope-with-...ead-p9493.html

[ThatOneEuroE30]

really weird issue

Is there any way that the muffler got clogged somehow? Like a loose baffle, or chunk of cat core?

I have checked the muffler and it looks clear. Its a brand new Strömung unit. From what i can tell when i gutted the cat it was all intact and nothing came apart and got lodged in the piping. I have a scope i can shove down the muffler and see if there is anything


Is it possible a faulty AFM could have the engine running full lean?

[bmwman91]

Is there any way that the muffler got clogged somehow? Like a loose baffle, or chunk of cat core?

I say pull the cat back and see how it runs. I will tell you from experience that it sounds...amazing (?)! And that was WITH a functional cat! Your neighbors will thank you...

[ThatOneEuroE30]

Ecu looked fine. board had a little discoloration but nothing that indicated a short or anything or so i think. I'm done with this thing for the day or week.

[ThatOneEuroE30]

put one lead on the junction box and touched it to the main engine ground strap and got nothing. I touched it to the box and the grounding point on the battery tray and got nothing. I touched it to the box and alt ground and got nothing to make sure i was getting through I touched my main battery terminal to the fusible link and got continuity

[ThatOneEuroE30]

so I unplugged the o2 sensor and still had same result. I moved to the fuel pressure test and at idle my gauge read 36-38 psi unload it bounce around from there to 44 psi. So that leads me to believe its got good fuel pressure? next thing on the list is it check the power to grounds and then pull the ecu

[squidmaster]

Yep! Test out the grounding areas against a battery lead wire and see if any give you a beep (or have a very low ohm rating).

There was another thread with a member that had a burnt-out driver recently, but I can't find it in my subscribed. If it pops up again, I'll post it here.

[ThatOneEuroE30]

Hey bud,

you may want to do a continuity test between some positive terminals and the ground terminals-- the grounds may be well connected, but a loose positive terminal/wire may be making contact with a grounded area as well.

Another thing to note is that I've seen a few of these M42 ECUs blow out their coil driver in the ECU. You can usually see some white and/or black discoloration around the up-right heat-sinks on the sides of the PCB.

Let me know!

so your saying to take the ecu apart and make sure nothing is burnt up in it and to take the DMM and put one lead onto the positive terminal on the junction box on battery tray and then the engine ground straps?

[squidmaster]

Hey bud,

you may want to do a continuity test between some positive terminals and the ground terminals-- the grounds may be well connected, but a loose positive terminal/wire may be making contact with a grounded area as well.

Another thing to note is that I've seen a few of these M42 ECUs blow out their coil driver in the ECU. You can usually see some white and/or black discoloration around the up-right heat-sinks on the sides of the PCB.

Let me know!

[ThatOneEuroE30]

There are some (small) alternate ground paths between the engine & chassis. With a multimeter they would not show up as being significant, but when the full current of the running engine is passing through them they can be a big problem.

Yeah, might as well try resetting the ECU too. Are there any stored error codes?

No stored error codes the CE light hasnt came on except for when it stalled once. I was talking with an instructor at school this morning he told me to check my fuel pressure and to try and unplug the 02 sensor and see what happens. He thinks it could be stuck in full rich and even at first start up so the DME is taking all the fuel away. Also told me to check the AFM. I really need to buy a lab scope to see what things are doing.

[bmwman91]

There are some (small) alternate ground paths between the engine & chassis. With a multimeter they would not show up as being significant, but when the full current of the running engine is passing through them they can be a big problem.

Yeah, might as well try resetting the ECU too. Are there any stored error codes?

[ThatOneEuroE30]

really weird issue

Verify the installation and condition of the alternator ground strap.



Between which CPS pins did you read 0.561 Ohms? I agree that it seems like the car should not run at all if that sensor was toast since the timing would basically be random, and I think that the DME would cut fuel+ignition if it saw more or less than 58 teeth between the 2-tooth gap.



This is a weird one. I could see the headers heating up like that from lean running due to a bad chip, but obviously that is not the case. Given all of the other electrical issues that are popping up, this seems like it could be a grounding problem somewhere. Maybe a strap got damaged? If the alternator or engine straps are broken, there are other paths for all of that current to go, but they are really not good paths since they are going to pose a high resistance.



Rig up a multimeter so that its ground is connected to the battery's negative post, and then with the engine running probe around the engine bay with the positive lead. Specifically, see what the voltage is at the ground lug on the chassis ("battery tray" where the Motronic is grounded), on the engine itself (intake manifold?) and the alternator body if you can safely access it while it is running.

I have tested all the grounds in the bay and none of them have a short. I did a continuity test and they all passed. I can try and see if can make some longer leads and do a voltage drop test on all the ground but i would think if they all had continuity they would be functioning.

i tested pins 1-2 on the cps like the bentley stated. I made sure I was on 1-2 by doing 2-3 and that just read nothing not OL just contnuity


The only other thing i think i might try and do is unplug the dme and plug it back in. On my chipped m30 car i was testing the afm and unplugged it and it ran extremely lean and couldn’t recover even after turning car off and restarting it. I unplugged the dme and plugged it back in and car ran fine again. Maybe unplugging the cam/crank sensor even with the car off screwed with the chip?

[bmwman91]

Verify the installation and condition of the alternator ground strap.

Between which CPS pins did you read 0.561 Ohms? I agree that it seems like the car should not run at all if that sensor was toast since the timing would basically be random, and I think that the DME would cut fuel+ignition if it saw more or less than 58 teeth between the 2-tooth gap.

This is a weird one. I could see the headers heating up like that from lean running due to a bad chip, but obviously that is not the case. Given all of the other electrical issues that are popping up, this seems like it could be a grounding problem somewhere. Maybe a strap got damaged? If the alternator or engine straps are broken, there are other paths for all of that current to go, but they are really not good paths since they are going to pose a high resistance.

Rig up a multimeter so that its ground is connected to the battery's negative post, and then with the engine running probe around the engine bay with the positive lead. Specifically, see what the voltage is at the ground lug on the chassis ("battery tray" where the Motronic is grounded), on the engine itself (intake manifold?) and the alternator body if you can safely access it while it is running.