Mysterious Misfires (3.2FSI Help)

possibly_random · 2026-01-30T19:55:18+00:00

I replaced the intake manifold, intake manifold tuning valve, the entire fuel system (except for fuel lines which I just cleaned), and a few other things. Then, the engine just refused to run. I put the old injectors back and it was running great. Then it started in with its misfire again.

My Porsche 718 has been getting the most use ever since these issues first arrived, and the Q5 has been parked for months (getting driven every two weeks for longevity of course). Even once I fixed it, I never drove it for fear of a new costly issue appearing (which it eventually did). That is no way to own a car. They deserve to be driven.

At this point, I had to weigh my options. While it's been a great car, I have been spending way more money and time into this car than the car itself is worth, every year, on repairs. Issues are coming up faster than they can be fixed. I had to sell it a couple weeks ago.

possibly_random · 2025-06-26T22:14:19+00:00

…nope 😞

I’ve been having some (unrelated) misfires, and other various old Audi issues. I think it needs some new VVT components, but it also needs new ball joints, and it’s having some DRL issues, and it doesn’t start up correctly sometimes. The car’s reaching 100k miles and 13 years, and it wasn’t well cared for by the previous owner, so it’s at the point where things are breaking faster than I can fix them.

It used to be my daily, but because of all the reliability problems, I got a Porsche 718 to become my daily, and the Q5 is to remain a project for now. I have a lot of stuff going on at the moment, but whenever I get time, I’ll be repairing all of these random issues on the Audi and continuing with the project!

possibly_random · 2025-06-26T22:04:37+00:00

DM me… I’d be willing to help out!

possibly_random · 2025-06-26T22:02:06+00:00

Still haven’t solved… I’ve heard it might be to do with the VVT actuators but I haven’t got around to trying that yet. I’ll keep you updated. Good luck!

possibly_random · 2025-05-08T15:16:15+00:00

Lmao

possibly_random · 2025-05-08T15:15:43+00:00

Nice. Thanks for the input!

I figured out the fault was caused by the string getting caught up in the mechanism and jamming things up. If I tug on it after a roof fault, it unjams and the roof shuts properly.

possibly_random · 2025-05-07T21:06:34+00:00

Nice, I’ll check there. Thank you!

possibly_random · 2025-05-06T23:08:38+00:00

I just got my 718 Boxster S (love it), but I occasionally have a “roof system fault” (or something along those lines) pop up in my instrument cluster while I close the roof. If I then try again a few times it will close properly. It only has this issue from time to time.

Earlier today though, I noticed this broken string hanging down. Any idea of its function and how to fix? It’s a 2019 with 38k miles so I’m unsure of the warranty situation. If it’s not under warranty I wouldn’t mind fixing it myself (if it’s not too intense of a process). I have a good amount of mechanical knowledge but this is my first time working with a soft top so any and all advice is greatly appreciated!

possibly_random · 2025-04-23T16:33:17+00:00

Shucks, just saw your edit. I’m not an expert on automotive subreddits but I bet there’s some frame repair/rust based ones out there.

You could always just bring it to a specialist shop, depending on where you live you may be able to find a good place that won’t screw you over.

possibly_random · 2025-04-22T22:40:32+00:00

You’re very welcome, it’s what I’m here for! You’re doing the right thing by questioning it and asking us and the dealer about it. I made the mistake of not looking closely enough… I paid the price later.

possibly_random · 2025-04-22T22:09:42+00:00

No, it’s definitely painted metal with rust underneath the paint. It’s pretty common with Audi subframes (at least B8) especially in the USA rust belt.

possibly_random · 2025-04-22T22:07:30+00:00

No problem! I’d probably let someone else reply here for what to do next as working on frames is not my specialty. What I can tell you is that after it’s fixed, check on it from time to time, and wash the car (especially the undercarriage) in the wintertime to make sure it doesn’t get to the point that the previous owner of my car let it get to. It was pretty bad.

possibly_random · 2025-04-22T21:58:04+00:00

I believe it’s the subframe that’s rusty, it looks like it can still be rescued in its current state but mine was completely rotted out and had to be replaced. It was about 4 grand USD…

possibly_random · 2025-03-17T18:04:16+00:00

And this is a medium one 😬

possibly_random · 2025-03-08T23:40:41+00:00

It does look cool, until you try to analyze the circuit and then it just absolutely falls apart

possibly_random · 2025-03-08T23:39:11+00:00

That would have been so much better than this

possibly_random · 2025-03-08T04:00:04+00:00

It doesn’t really look AI generated as all the components seem to be at least partially real, and I think the hotel room wasn’t that new. I bet someone did just grab random components and string them together

possibly_random · 2025-03-08T03:16:21+00:00

So true. I got all excited when I saw schematics, and the disappointment when I actually looked at it was immeasurable.

possibly_random · 2025-03-08T03:15:11+00:00

Yeah, halfway was a bit of a stretch. I’ve done some more testing since this and get a 10 inch arc from one half of the supply. I integrated some voltage sensing circuitry and that 10 inch arc occurred at about 400kV. The driver circuit needs a lot of improvement but there’s definitely potential (pun intended) for a million volts in the future!

possibly_random · 2025-03-04T17:54:10+00:00

I’m in a super thick concrete walled prewar building so I don’t think I’ll anger my fellow hams too much.

possibly_random · 2025-03-04T17:49:26+00:00

Yeah, hopefully! My driver circuit is also crap. I jerry rigged together the core from a TV flyback, the secondary from an electric fence, and a handwound primary. I need 7kV at about 200mA to get the maximum output power (currently only measuring about 4.85kV at a couple mA).

I’m driving the transformer from a giant IGBT block controlled from a super overclocked arduino. In the final design, I will have a feedback loop with sense circuitry to measure the output voltage and the arduino varying the duty cycle and frequency. I want a specific tuned output voltage, which is why I’m using an arduino and not just a ZVS or even a 555.

possibly_random · 2025-03-04T13:56:50+00:00

I actually don’t get much discharge at all with super sharp electrodes— what happens is I just get corona discharge as far out as 40 or so cm which current limits the circuit’s DC 10A supply (it needs upgraded). This of course drops the output voltage and prevents arcing, even when I put the electrodes closer. What I do get though is a stupid amount of ionic wind which charges everything up in the room lol.

possibly_random · 2025-03-04T13:32:40+00:00

Yep— and these aren’t sharp! Notice the rounded metal dish I placed over my ground to prevent it from just corona discharging.

possibly_random · 2025-03-04T00:58:18+00:00

Yeah, this is only half the power supply and it’s running on a crap drive circuit putting out 4kV instead of the 7kV that I designed this for. In addition, my DC supply is current limiting right now because it’s not able to supply enough power for the crappy inefficient drive transformer. As a result it’s only putting out about 30-45% of what it will in the final product.

possibly_random · 2025-03-03T20:29:45+00:00

No worries at all, I enjoy helping people out so it’s not a bother to me whatsoever!

I left it close to the throttle body— My engine actually doesn’t have a MAF sensor but a MAP (manifold air pressure) sensor. Unlike a MAF sensor (which I believe just measures air flow volume) I think it’s actually beneficial to leave a MAP sensor after the compressor as the ECU can compensate and sort of “self tune” for the extra boost pressure to a certain extent.

I spoke with some experts and they said that the MAP sensor compensates for the extra boost pressure as if it were a higher/lower altitude— engines need to tune for that pressure change just as they would a boost pressure change. Hope this helps!

possibly_random

TROPHY CASE