S4 Stuttering big time on acceleration

B6/7 S4/RS4
#1

Howdy folks,

So to get everyone up to speed, my delphi alternator caught on fire a while back and about a week and a half ago I finally got it all fixed up, I replaced the following:

  • passenger side motor mount
  • starter
  • alternator
  • positive battery harness (the one that goes from the battery to the alternator and starter)

After replacing all that, I filled her up with fluids and took her on a test drive. All was well. Naturally, I was babying her a bit as it had been a while that she was down so I wanted to take it easy. I put about 60 miles on her that night and nothing felt out of the ordinary so I drove her to work the next day. On the way back from work I decided to drive a bit more aggressively. Nothing too crazy just a few harder pulls here and there. Once I was on the highway, I tried accelerating a bit and I felt this crazy stutter and the car was lagging pretty bad. Pretty big loss in power. I would say it was a misfire but no codes for that so maybe lack of fuel?

Once I got home I pulled the codes and this is what I got

3 Faults Found:

19711 - Oxygen (Lambda) Sensor B1 S1; Heating Circuit
P3255 - 001 - Regulation at Upper Limit - Intermittent
16592 - Injector: Cylinder 8 (N86)
P0208 - 004 - Circuit Malfunction - Intermittent
16591 - Injector: Cylinder 7 (N85)
P0207 - 004 - Circuit Malfunction - Intermittent - MIL ON

Readiness: 0010 1000

Waited a few days, checked the grounds, changed a few things and drove her around last night. The first part of the drive in my neighborhood went well. I got on the frontage road to the highway and did a few pulls from like 20-70 and everything felt super strong. She was running tip top. Then once I was on my way home, she started stuttering really bad again. The more I accelerated and drove, the less power she could put down. Just felt terrible so I limped her home to the garage and here is where I’m at.

All the wiring on the main harness looks fine as none of it was really near the fire. Especially since cylinders 7 and 8 are on the opposite side of the motor as the fire took place. So I’m thinking once I get home from work today I’ll check the injector clips and that wiring and maybe some of the fuses. Other than that, I have no idea where to look and where to go from here to solve this problem. I’m at a pretty big loss since I’ve never seen or felt anything like this before. Any suggestions would be greatly appreciated.

#2

First off sorry to hear about the fire that sucks but its nice to hear you got most of that worked out.

The loss in power would make sense that your injectors are not working properly at certian points. if its intermittent its not going to be a fuse so I dont know that i would spend all that much time on looking there.

The B1S1 sensor code could be more than just heating so log B1 instant fuel trims and make sure the sensor is actually working. As that can give you issues as well.

It sounds like you have issues after you go WOT. It sounds like a vintage wire or electronic issue as it comes and goes. Generally if your injectors were bad they would just be bad. To check you can always move injectors 7 and 8 to see if something follows but the fact that its both those two cylinders makes me think its going to be something electronic still. Start with moving the injectors then try logging the B2 instant fuel when you go WOT and have issues see what happens. That should tell you more

#3

Sounds good. I’ll look over a few things once I get home and then I’ll start logging those fuel trims. Could you tell me which measurement blocks those are?

#4

So I ended up fixing the issue later that night but I wanted to update this for closure.

I narrowed it down to being three things and so me, being the guy that wants his car back asap, decided to try and fix all three things at once. So I called my local dealership and picked up a few things on my way back from work.

First thing I did was check the fuel injector plugs. I cleaned every one of them and made sure the pins we’re in good condition. I’m pretty much missing the clip on every plug since they’ve all broken off at some time which sucks but my dealership said they were a special order part so I didn’t want to wait on new plugs for those. Basically after the cleaning, I just pressed the plugs in and made sure they were nice and snug.

Next I replaced the Bank 1 Sensor 1 O2 sensor. I was pleasantly surprised at how easy this was to change. I was expecting a much more cramped situation. Any way, I’m not sure how to test if it really was bad. I guess I can cut the wires by the sensor and test the wires with a multimeter. Regardless it was replaced in case it was the issue. Here’s a pic of the O2 sensor. It’s a bit orange. Probably as a result of running rich because of using 93 octane on a JHM 91 tune about a year ago for a little while.

https://uploads.tapatalk-cdn.com/20170702/459e74fc1f7c9150b1a2fd0df59f3755.jpg

Lastly, I had a hunch that the motor mount resistor from 034 may have gotten some heat during the fire and gone bad. Boy was that a hell of a hunch…

https://uploads.tapatalk-cdn.com/20170702/de4d26339ec1cb1ebeed80cd343e5fc9.jpg

So I basically had to sit there with an array of pliers and flatheads to pic apart the old plug and resistor to try and get to the terminals. After some time, I got to them and they looked good so I cleaned em up a bit and threw a new universal two prong plug I got from Audi on them. And then I plugged them into the oem motor mount I’m temporarily running.

https://uploads.tapatalk-cdn.com/20170702/771e04aaa608e56f9b4ba68d00af5a94.jpg

https://uploads.tapatalk-cdn.com/20170702/67be7a69637510a4c775b92a47735505.jpg

And she’s been running super strong ever since! No codes, no lights, just pure powa! Sorry I wasn’t able to do any logging. I was planning on doing so once the issue came back but because I didn’t wait to fix it, I wasn’t able to log while the stuttering was happening.

Sent from my potato

#5

Glad to hear about the victory. Its always great getting things back in good running order. The fire did some serious damage and caused a few gremlins that it seems you have fixed what should be all of them now. good update thanks. Its always great to get closure on a issue