heinzboehmer's 2002 Topaz 6MT Coupe

[Obioban]

Ha, that's the most modern DIYer cover. CAD, lasered parts, 3d printed brackets/feet. You just need to work a Pi into there somewhere, and you'll have it all.

[heinzboehmer]

Also, found the datasheet for this sensor (attached to this post). Looks like it's almost entirely self contained and requires very little supporting bits. It's very likely that all that's inside the BMW box is the orange sensor itself and a resistor. At least this is what the example circuit that the manufacturer included in the datasheet looks like.

They're everywhere on eBay for cheap, but most of them ship from China, so no idea about quality/genuineness. I did find a seller in the US with a bunch of NOS parts, so ordered a couple to add to the stash in case the sensor on the car ever fails.

[heinzboehmer]

Fun bit of electrical debugging today.

Car has been ultra stinky in the cabin lately and after some sitting-in-stop-and-go-traffic experimentation, I started to suspect that the auto recirculation wasn't working correctly. I mean, root cause of the smell is definitely the shitty SSV1 headers -> section 1 interface, but if the AUC sensor is faulty, then the A/C will always pull (stinky) air from outside. Read codes on the IHKA and yep, the sensor was apparently bad. INPA read 0V from it, so decided to investigate further.

Turns out the thing comes apart fairly easily. Here's how to take it apart for future reference:






Unfortunately, the electronics are fully potted, but I guess that's to be expected of something that is fairly exposed to the elements.

Anyway, plugged it into the harness and probed with a multimeter just to see if it was reacting at all. Turns out the sensor was working just fine, so the issue must have been something with the connector or harness.

Fired up INPA again and to my surprise, it was reading it now. Here's me testing the sensor by spraying some isopropyl alcohol close to it:

Put the sensor back together and INPA was once again reporting 0V. Hmmm

Finally discovered that I could get INPA to read it if I removed the weather seal from the connector. This thing:



Seal was pretty dirty, so I cleaned and lubed it up. Aaand INPA reads it! Guess the dirty seal wasn't letting the connector fully seat.

I did also slightly bend all the inner connection tabs on each of the pins in case they were a bit worn, but I don't think that did much. Pretty sure the issue was the seal.



I do wish the IHKA somehow communicated the issue (not letting you use the auto recirculation feature, for instance), but glad it was a quick fix. Will periodically check for codes, but hopeful that this will fix the issue.

[heinzboehmer]

This is only tangentially related to the M3, but thought I'd document/share cause, sometimes, living in the future is pretty cool.

Only took 3 days to go from designing this in CAD to having it fully assembled and in service. That includes the time needed to have sendcutsend laser cut and ship all the parts, as well as the time needed to print all the internal reinforcements.

For context, a small section of my workbench is dedicated to electronics. I figured dust and grime from working on the cars would be an issue for those types of projects, so I designed an 18th century slidey door thing to cover the whole thing up:



Started work on it and got about 90% through before I lost all motivation. Remaining work involved routing the channel for the door and I just really didn't want to deal with the mess. Don't have proper dust collection in the garage, so doing anything wood related really sucks. Thing sat like this for an embarrassingly long time:



Anyway, back to living in the future. Finally decided that it was stupid to be wasting so much workspace, so I switched strategies and decided to build a cover for it instead:






Structure is just some laser cut 1/8" MDF with printed ABS reinforcements bonded in. Also added rubber edge trim to the sealing surface and printed TPU feet around the locating pins (not pictured).

Happy with how it came out and amazed at how little effort and time it required. As per usual, should have done this a long time ago

[heinzboehmer]

RPM (2600-3000ish), but it seems louder and more unbearable at higher speeds. I think adding the updated rear bench insulator would help reduce it.

Interesting. Maybe something in the clutch assembly? Can't think of anything that would make that noise and be related to RPM. Especially if it sounds like it's coming from the rear of the car.

[SQ13]

My car has the wheel hop issue too in wet conditions. Recently noticed it in the Cayman as well.

Is yours RPM or speed related?

RPM (2600-3000ish), but it seems louder and more unbearable at higher speeds. I think adding the updated rear bench insulator would help reduce it.

[heinzboehmer]

Yeah you're not the only one who has told me that they experience the same thing. Guess it's just inherent to the rear suspension design. Oh well, at least it only does it in a straight line.

[maupineda]

My car can get wheel hop too in the dry. B8 dampers. It was a bit worse with the H&R shocks original to the coil over kit.

[heinzboehmer]

Wheel hop was starting to get pretty bad, likely exacerbated by all the rear biased weight savings that has happened over the past year or so. Turned down the rebound on the rear dampers by quite a bit (it's at a half turn from full soft now) and it feels pretty good now. More testing to come.

Update: Still wheel hops like crazy when losing traction in a straight line, in the wet. Damn.

Seems fine if I initiate a slide in the wet and in all conditions in the dry. Granted, I didn't go and do burnouts when it was dry, but still. For sure an improvement over how it was before though.

[heinzboehmer]

Don't forget the rear deck speakers

Pre-facelift, so no logos on those from the factory

[Obioban]

Ha. I, too, unbranded my speakers-- even without the fabric peeling. I just don't like logos everywhere.

Don't forget the rear deck speakers

[heinzboehmer]

The fabric on the front tweeter covers was starting to peel off, so got some non-HK covers to replace them:




It's a stupid detail, but I do like the all black cover more.

Since the door cards were off, I took the opportunity to fix a rattle inside the passenger door. Sounded like the clip that holds the window regulator cable in the middle of the door had broken off, so was prepared to zip tie it. However, I found that the cable just wasn't clipped in. Clip still felt nice and pliable, so I just clipped the cable back in. We'll see if it pops back out or not.

Also, found no witness marks on the door from the bavsound speaker Bry5on. Must be a coupe vs wagon difference.

[heinzboehmer]

No way, my car makes this noise too, and I don’t even have the Slon wall!! I’m guessing it’s the Supersprint Sport muffler. 😂😭😭

Is yours RPM or speed related?

[SQ13]

Resonance is gone! I'm so glad this was an easy fix, it was driving me crazy on the highway. If you want to feel my pain, type 201 Hz into this website and just let it play for a while: https://www.szynalski.com/tone-generator/

No way, my car makes this noise too, and I don’t even have the Slon wall!! I’m guessing it’s the Supersprint Sport muffler. 😂😭😭

[heinzboehmer]

Alright flimsy racecar seat backs made a couple things very obvious.

First up, the way I had attached my plywood barrier was fine for stopping sharp objects from cracking the carbon wall, but not for actually stopping heavy objects from entering the cabin.

I wanted to attach it to as many stock structural points as possible, but with the seat latches gone, I had nowhere to attach the barrier latches. Dug through the stash and found a couple nuts that fit the stock seat latch bolts:



The captive nuts in the seat latches aren't in line with each other, so I was only able to get one bolt through my latches. Decided to add a couple rivets to keep them from rotating:




I would have preferred to use both bolts, but these top latches aren't what's gonna be seeing most of the load in a crash, so it should be fine. What will be seeing significant load are the bottom two points that attach to the frame tie down brackets:



I had previously used wood eye screws for this. They would have 100% ripped out under any significant load, but I was fine with that cause the stock seat backs were still in place. That is no longer the case, so I got some proper bolt through eye bolts and big fender washers:



Did a similar thing up top:



First issue fixed, onto the next one.

The Slon wall has acted as a giant speaker that amplifies all the annoying noises/vibrations that get to the the rear subframe/RACP since I installed it. However, the seat foam absorbs the majority of that, so hasn't really been a problem. Turns out the stock seat backs were contributing to the attenuation and absorbing a very specific resonance from the panel as well. Poked around and found that if I put pressure on two specific points on the panel, I was able to get rid of the resonance completely.

Following video shows my testing for this. I'm hitting the panel with my fist where the green circle is and am placing one finger with very light pressure where the red x is:

Headphones encouraged, but you can hear the resonance right at 201 Hz. You can even clearly see it in the waveform of the audio in that video. Notice how much longer the decay of each hit is when I'm not damping the left/right sides with my finger:



Printed some modified sections for my seat backs and added some adhesive window foam seal to put some pressure on the panel at the two dampening points that I identified:





Resonance is gone! I'm so glad this was an easy fix, it was driving me crazy on the highway. If you want to feel my pain, type 201 Hz into this website and just let it play for a while: https://www.szynalski.com/tone-generator/

That's what I had to listen to constantly whenever I went above 60ish mph. So glad it's gone.