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Old 11-02-2018, 01:36 PM   #1
rkneeshaw
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Stumped: Misfire cyl 6 above 6k RPM

Issue: during a series of full throttle pulls in 3rd gear the car will detect a misfire on cyl 6 above 6k RPM, it cuts fuel to that cylinder and pops the SES light. If I restart the car the SES light goes out and it runs fine, until the next 3rd gear full throttle pull to redline.

1 code was found stored in the DME:
Number of errors: 1

0x2745: Misfire - Cyl. 6
Torque current value: 336.00 Nm
Maximum speed with misfires: 6176.00 RPM
Maximum relative load with misfires: 99.61 %
Minimum relative load with misfires: 99.61 %

This code is also referenced as an OBDII code: P0306 - Misfire cyl #6

The symptom is repeatable, I can make it happen at any time by running out 3rd gear to redline.

The car exhibits no other symptoms. It idles perfectly, it drives perfectly around town, it accelerates strong, and my AFR is where it should be (between 11:1 and 12:1 under full load, which is about right for a supercharged car, and at 6k RPM its at about 11:1 when the misfire occurs).

Things I've tried:
  1. Swapped spark plugs and coil from cyl 6 to 1, no change
  2. Also replaced spark plugs with new plugs
  3. Replaced cyl 6 fuel injector and inspected the electrical connector, no change
  4. Removed the ESS manifold and pressure tested to ensure the intercooler wasn't leaking coolant into the cylinder, pressure tested good, held 11psi for over 4 hours.
  5. Compression tested: between 209 and 211 psi across all 6 cylinders

Car has about 144k miles on the odometer. Original motor.

Some context that may be helpful: This problem started happening immediately after I had my clutch replaced. While replacing the clutch I had M3 transmission mounts installed, engine mounts are stock originals (and are probably due for replacement). I notice more NVH after the clutch job. Could be a coincidence, I'm not sure.


I'm really at a loss. What could be causing this?
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Last edited by rkneeshaw; 11-02-2018 at 01:38 PM.
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Old 11-04-2018, 01:07 AM   #2
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The misfire above 6000 rpm is a blessing to avoid money sink hole.
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Old 11-04-2018, 06:50 AM   #3
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I've checked fuel, ignition, and compression. So I guess I have to question the misfire itself.

It sounds like the DME detects misfire based on changes in RPM speed picked up by the crankshaft position sensor. This sensor is located directly below the starter.

I will try replacing this sensor, as I have no other idea of what to try.
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Old 11-04-2018, 07:26 AM   #4
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Haven't seen the tune mentioned here. Which DME software is it running?
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Old 11-04-2018, 10:03 AM   #5
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Its the MS45.1 with my own custom tune on it. Minimal changes from the stock ZHP software. Adjusted fuel scaling for injectors and ignition timing.

Long term fuel trims are -0.5 and 0.04 for bank 1 and 2, respectively. The time or two I can get a full 3rd gear pull in without a misfire, the AFR is about 11:1 in that 6000-6500 RPM range.

Ignition timing stays a solid 17 degrees through to redline, even during a misfire event.

Based on the logs, when the misfire happens bank 2 suddenly goes real lean, which I can only deduce is because the car is shutting off fueling to cyl 6 as soon as it detects the misfire and pops the code. When I restart the car and all cylinders are firing, fueling looks great all around. And I replaced that fuel injector anyway, to rule out a failing injector. So I'm pretty convinced the DME cuts fuel to the cylinder it detects a misfire on.
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Old 11-04-2018, 11:08 AM   #6
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Have you tried logging all the relevant PIDs while doing the pull to look for clues? OBD Fusion or a similar OBD tool that logs might help here. Isolating what's causing the misfire seems like the first step.

Only clue we have so far is that it started right after the clutch job. Verified everything nearby whatever was touched during that job?
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Old 11-04-2018, 05:54 PM   #7
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thats one reason I suspect the crankshaft position sensor, its right below the starter, maybe it was dislodged or bumped, and maybe now it's failing. I'm not sure, still sounds like a long shot but I'll entertain anything.
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Old 11-04-2018, 08:17 PM   #8
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Does it also miss fire on a free rev? If so, throw an o-scope on it and see what the crankshaft sensor signal shows.
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Old 11-05-2018, 06:56 AM   #9
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It could be starved for fuel at 6000rpm. Is the fuel pump original? When was the fuel filter (it includes the fuel pressure regulator) last changed?
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Old 11-06-2018, 02:50 AM   #10
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Quote:
Originally Posted by rkneeshaw View Post
Its the MS45.1 with my own custom tune on it. Minimal changes from the stock ZHP software. Adjusted fuel scaling for injectors and ignition timing.
did you replace ess software with your custom zhp software?
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Old 11-06-2018, 06:48 AM   #11
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Quote:
Originally Posted by BaliDawg View Post
Does it also miss fire on a free rev? If so, throw an o-scope on it and see what the crankshaft sensor signal shows.
That's a good idea, I haven't tested a free rev to 6k

Quote:
Originally Posted by markusmarkus View Post
It could be starved for fuel at 6000rpm. Is the fuel pump original? When was the fuel filter (it includes the fuel pressure regulator) last changed?
I ruled this out because I am ONLY seeing fuel cut on bank 2 (the bank with #6 cyl) once the misfire happens. Both banks are getting fuel right up to the misfire event and aren't leaning out. See attached for a copy of the log. The misfire happens right at the thick black line. At that point only bank 2 goes lean because I believe the DME cuts fuel to the cylinder it detects a misfire on.

Quote:
Originally Posted by MadToha View Post
did you replace ess software with your custom zhp software?
Yeah, I got rid of that shitty ESS tune about 18 months ago. I've been running my own software since (which is based on the full clean stock ZHP OEM software with tweaks for fuel scaling and ignition timing). I ran the car hard including dyno pulls on my software and never had a misfire issue. So I think this isn't where the problem is. But, just for shits and giggles, I'll load up a copy of my tune from the last time I ran the car at the track and see if there's any change.

So, I'll run these tests on Thursday:
1. Free rev to 6k RPM and hold for a while and see if I can get it to misfire
2. Flash to an older proven revision of my tune
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Last edited by rkneeshaw; 11-06-2018 at 06:49 AM.
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Old 11-06-2018, 08:43 AM   #12
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Side note: many folks will want to know how/who unlocked your MS45.1 DME.
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Old 11-07-2018, 06:11 AM   #13
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Iíd still check the fuel pump. Yes, I realize that both banks arenít misfiring but Iíd still configure a fuel pressure gauge so that you can read it when driving. Also, pull the cover on the coils and make sure both ground straps have clean, tight connections.

Iím wondering if the custom tune is the culprit.
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Old 11-08-2018, 05:41 PM   #14
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Well I tried free-revving the motor to about 6250rpm and held it there for about 20-30 seconds, and no misfires.

I also installed M3 motor mounts to match the M3 transmission mounts, and I now have LESS NVH than I had after installing the M3 trans mounts. So the car feels smoother again.

I also flashed the tune that I had ran at the track earlier this year, and once again I got a misfire on Cyl 6 above 6k RPM. This tune I know for a fact ran flawlessly for a full track day weekend where I was in 3rd gear all day long running up to redline and I never had a single misfire at all before. So I think this safely rules out software as the culprit.

Markus, you made a good suggestion about the grounds on the coils. I'll check that.

Also, I have a brand new crankshaft sensor to install.

I really have no other clue what could be wrong here other than questioning the detection of the misfire itself (aka bad crankshaft sensor?).

Quote:
Originally Posted by BaliDawg View Post
Side note: many folks will want to know how/who unlocked your MS45.1 DME.
I worked with Frank Smith on my tune, he's got all the tools necessary. I also worked with Bimmerlabs.com so that I could flash files to my car whenever I made changes. And additionally, there is a tool in beta right now called ByteTuner that will read and flash MS45.1 and allow you to edit your tunes all in one tool.
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Old 11-08-2018, 05:50 PM   #15
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Updated list of things I've tried:
  • Swapped spark plugs and coil from cyl 6 to 1, no change
  • Also replaced spark plugs with new plugs
  • Replaced cyl 6 fuel injector and inspected the electrical connector, no change
  • Removed the ESS manifold and pressure tested to ensure the intercooler wasn't leaking coolant into the cylinder, pressure tested good, held 11psi for over 4 hours.
  • Compression tested: between 209 and 211 psi across all 6 cylinders
  • Free-rev to 6k RPM, held there, no misfires
  • Installed M3 motor mounts to match M3 trans mounts
  • Flashed known good tune to the car, still misfires

Only misfires above 6k RPM and under full throttle, and in 3rd gear or higher (does not misfire under full throttle in 1st or 2nd gear).
No other symptoms or misfires at any other time, car drives perfectly otherwise

wtf.

Has to be crankshaft sensor. What else could it possibly be?

I'd like more data before I try to replace fuel pump (which is only 30k miles old). That sucker is like $300.
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Old 11-08-2018, 07:09 PM   #16
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I can't imagine that it would make a difference but are you still running my 83mm pulley? That's the only other thing I can think of that you changed.

I haven't installed my Walbro pump yet and won't get to that and the injectors until I get the new heat exchanger in. I can send that to you so you can test with it...

I also have a fuel pressure gauge with a really long hose. You can connect it to the Schrader valve on the fuel rail and observe the pressure while driving. The hose is long enough to lay it on the windshield with the hood closed. The gauge is encased in rubber so it won't damage anything. This is how I found out I had a bad fuel pump under load.

Let me know if you need them and I'll be more than happy to FedEx them to you
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Old 11-09-2018, 08:31 AM   #17
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I'm thinking if it was the fuel pump then I'd start to see the fuel lean out as it approaches the misfire event. But it doesnt. At the time of the misfire the car is still running a healthy 12:1 AFR across both banks. Makes me think fuel isn't the cause of the misfire, because the logs show I have fuel.

I already ruled out a failing fuel injector cutting out, because I replaced it already.

So if fuel and ignition are good, and compression is good, I'm back to the algorithm or sensors used to detect the misfire.
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Old 11-28-2018, 10:03 AM   #18
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Ryan, I am having this exact same issue with my bone stock ZHP. It's safe to assume that your issue is not supercharger related.

Also, I'm able to reproduce my issue under part throttle as well at 6krpm in third gear.

It has to be a sensor taking a dump. Have you made any progress so far?
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Old 11-28-2018, 03:51 PM   #19
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Not yet. Its been snowing, so the car has been sleeping. I have a new crankshaft sensor ready to go in, and as soon as the weather clears a bit I can test it.
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Old 12-16-2018, 05:47 PM   #20
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EDIT: Nope, crankshaft sensor wasn't the problem. I'm still getting a misfire event under full load in 3rd+ gear above 6k RPM. ****.

New box on the left, old sensor on the right

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