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Discussion Starter · #1 ·
I have a 2000 NB 2.0L and I can’t shake the P0304 cylinder 4 random misfire code. The coil pack, lead and sparkplug all check out and it has good spark. There are no vacuum leaks, the fuel pump is active and primes, and the #4 injector sounds good and just like the others using a stethoscope. The plug looked good and a nice chocolate color, no soot or oil. I replaced it anyway and put dielectric grease on both ends of the lead.

Any suggestions as to what I should check next?
 

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The link, lists all the common issues; things we see are: cracked coil packs (spray water testing; can help diag, remove the coil, look for hairline cracks on the back of the module), there is a service bulletin, on rewiring the ground to the coil pack and sometimes, a bad ecu, will consistently, have just one cylinder misfire.

 

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Older thread with good links and discussions:


 

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Discussion Starter · #4 ·
Older thread with good links and discussions:


Many thanks and lots to work through. I'll get started at the top of the list and let you know how this turns out or what I find...
 

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Discussion Starter · #5 ·
So, it's been a while, but I've been working on this as time permitted, more so over the Christmas break.

After a ton of work, I'm still getting this misfire on cylinder 4.

So far:
  • Pulled spark plug - wet with gas
    • Replaced spark plug - no change
  • Swapped #3 and #4 leads - no change
    • Replaced coil pack anyway to eliminate that
    • Replaced spark plug leads anyway to eliminate them
  • Did compression and leak-down tests on #4
    • Did compression test, but got good 110 psi and bad 0-20 psi at different times, so pronounced compression tester suspect
      • Calling #4 compression good as a faulty tester could give low reading but couldn't give a "false" high compression (see video below)
      • Adding a little engine oil to cylinder also didn't change/increase compression when reading low
    • Decided to do leakdown test - reads "acceptable" at 60%
      • Barely audible "hiss" coming from crankcase
        • Air intake and exhaust silent
  • Visual inspection inside cylinder with borescope
    • Looks nice and clean
      • Cylinder walls shiny
      • Top of cylinder shows no damage and is clean
      • Valves and head show some carbon, but not excessive buildup
    • Both valves look seated at TDC, not bent
  • Removed air intake plenum
    • Inspected back of intake valve with borescope
      • It is wet but in good shape
      • Looks just like the others except they are dry
  • Tested injectors
    • #4 sounds good with stethoscope
    • Blinky tester shows good signal (you can see tester light in video below)
    • Pulled injectors
      • All injectors seemed to work well when exercised with an injector tester
  • Out of options and ideas - purchased a set of new injectors and prayed for a miracle
    • Installed new injectors - exact same result
    • Rough idle, smooths out with acceleration
    • P0304 comes back after a couple of minutes
    • 🤬 prayers not answered
I'm really stumped and seem to be spinning my wheels trying to identify the issue, having eliminated the usual suspects. I'm not getting any other code, just the P0304 (starts with a P0300, which becomes the P0304 in minutes).

I don't have any indications that there's a head gasket issue, good compression, no cross-contamination of any fluids, not leaks, no bad exhaust, no overheating.

I need to get to the bottom of this one soon or I'll have to call it quits, and REALLY don't want to give up on her.

Here are some pics:

Back of #4 intake valve


Back of other intake valves


Inside #4 cylinder (oil is from me, was clean before I dropped some in)


Valves inside cylinder


Here's a video of the compression test on #4 cylinder:
2000 VW Beetle 2.0L P0304 #4 Cylinder compression test

Any and all suggestions are very welcome. I do have VCDS Lite, but not sure if that will shed any additional light.
 

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Ok, you have done some solid testing and posted the results, this is really helpful. Thanks! :)

After so many parts changes, testing; have you cleared codes or a hard reset of the ecu and do a fresh auto scan with vcds, see if any codes have changed?

You seemed to indicate; the misfires, were intermittent, is there any difference of a cold, warm or hot engine?

We have a long history of 2.0L misfire issues; typically things narrow down to fuel delivery or ignition related issues.


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Known ignition issues, that you might try (you have replaced everything ignition spark related but the ecu); is the ground to the coil pack, vw issued a tech bulletin on this.


This may or may not be your issue but it is a easy wiring harness update to perform.

As to replacement parts, we have found it critical to use high quality oem parts; aftermarket Chinese stuff, are known to cause problems. What brands did you buy and replace them with?


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As you diagnose the misfires; you might hook up vcds and view the misfire counter, so you can see when they are happening, in real time.


This could help, to see, if the misfires are intermittent and vary with different thermal or other conditions.

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Fuel:

While, things seem to be pointing towards ignition/spark related issues; there are other fuel issues i would check.

A quick check would be fuel trims; long term and short term, should be in the + or - 10% range.


I would want to rule out fuel pressure as well: (pressure @ idle, residual, dead head, volume, etc):


A bit of a less possibility for a specific cylinder misfire but we have seen high mileage dirty throttle bodies cause, rough idle misfires, stalling, fuel mixture off, etc (especially, on the 2.0L).

Clean, do the tba procedure with vcds; as shown in the video:



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Lastly, on the discussion i linked to above; we have seen a ecu with a defective ignition spark driver chip on the circuit board, end up being the issue with a consistent cylinder specific misfire, (when all testing of things come back ok).

For some reason the onboard ignition signal Bosch driver chip on the circuit board has a history of failing. This is a common repair and the chips still seem available as a service part.

You could ship it out for repair; keeping the immo intact, plug and play solution.

I was working on a 2.0L Jetta with a persistent misfire; i used a ecu misfire repair service, i found on ebay and it worked out fine.

Here is vw ecu specialist; members have been using with good results (including myself). Contact him and see what solution he recommends, if you exhaust all testing, feel like the ecu is the culprit.



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Discussion Starter · #11 ·
Ok, you have done some solid testing and posted the results, this is really helpful. Thanks! :)

After so many parts changes, testing; have you cleared codes or a hard reset of the ecu and do a fresh auto scan with vcds, see if any codes have changed?

You seemed to indicate; the misfires, were intermittent, is there any difference of a cold, warm or hot engine?

We have a long history of 2.0L misfire issues; typically things narrow down to fuel delivery or ignition related issues.
Thank you @billymade for the comprehensive reply. The misfire is consistent, predictable, always there from cold startup. After clearing the codes it will come back in a few minutes of running. I haven't done a "hard reset" of the ECU - how do I do that?

I will register the car this evening with full VCDS (I have the direct-from-Ross-Tech HEX device from a while back) and do a thorough dump and analysis of codes. Hopefully that will inform next steps, and at least help map out if the misfire is there throughout the rev range. The injectors are Bosch and the coil pack and leads are from Amazon with the highest feedback rating, but manufacturer unknown. I think if I had a failing aftermarket part I'd see changes in the code/results, unless I stumbled upon a major coincidence. Regardless, the full VCDS scan should help with this too.

I think I might have a spare ECU in my shop. I got my son an '03 1.8t Beetle last year and the PO was messing around with the ECU trying to put a 2.0L in the 1.8t and left the 2.0L unit in the trunk. I'll check part numbers but I think it may be the right one and, if so, worth a quick swap-in to see if it changes anything (unless it is also bad). That would indicate a faulty ECU. I know the IMMO security functions are in the instrument cluster but don't know if an ECU swap will trigger an immobilization lock-out without it being reprogrammed to my cars VIN....? Still worth a try if the part number checks out. The ECU-to-coil wiring issue is intriguing and worth cechking out. I would think it would bring down all coils, or cause random missfires, rather then consistently #4, but I'll check it out.

Let me see what VCDS reveals and I'll check back in.

Thank you!
 

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If the used ecu is the same, then pulling the secret key code, from the original ecu; you could use vcds to code the old skc to the new/used ecu.

The 2000 year is immo 2 but the matching process is probably similar:


Here is a overview of the vw immo system:


Hopefully, the full autoscan; gives us some more clues as to possible reasons for the misfires.

As noted, even if you don’t match the new/used ecu; i would compare a full autoscan with vcds, from both and compare them, to see if the trouble codes are different.

Pulling the skc/pin code; would require a tool, like vagtacho, a auto locksmiths scan tool or one of the many knock off vag scanners with this capability.


The vw ecu specialist is i linked to; could swap the eprom/hex data info or do a immo delete for you as well (another option).


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Discussion Starter · #14 ·
Thank you. So I setup full VCDS and did a scan. Apart from an ABS sensor code everything else is OK except for this misfire. Here's the cold scan:

Code:
Monday,23,January,2023,19:29:07:39323

VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64

VCDS Version: 22.3.1.4 (x64)  HEX-V2 CB: 0.4615.4

Data version: 20220407 DS337.0

www.Ross-Tech.com



VIN: 3VWCC21C4XM474143   License Plate: 

Mileage: 268740km-166987mi   Repair Order: 



Chassis Type: 1C - VW New Beetle (1998 > 2010)

Scan: 01 02 03 08 15 17 19 25 29 35 37 39 46 54 56 65 75

 

   Mileage: 268740km-166987miles

-------------------------------------------------------------------------------

Address 01: Engine        Labels: 06A-906-018-AEG.lbl

   Part No: 06A 906 018 JE

   Component: MOTRONIC M5.9.2  AT V01  

   Coding: 00001

   Shop #: WSC 00066  

   VCID: 6E85C8FCF98E9CCB2D3-4B3C


2 Faults Found:

16684 - Random/Multiple Cylinder Misfire Detected 

            P0300 - 35-00 - 

16688 - Cylinder 4 

            P0304 - 35-00 - Misfire Detected

Readiness: 0110 1101


-------------------------------------------------------------------------------

Address 02: Auto Trans        Labels: 01M-927-733.lbl

   Part No: 01M 927 733 EN

   Component: AG4 Getriebe 01M    4386  

   Coding: 00000

   Shop #: WSC 65316  

   VCID: 00598644D31A9ABBCFF-0962


No fault code found.


-------------------------------------------------------------------------------

Address 03: ABS Brakes        Labels: 1J0-907-37x-ABS.clb

   Part No: 1J0 907 379 G

   Component: ABS     20 IE CAN  0001  

   Coding: 03504

   Shop #: WSC 00066  

   VCID: 35372790DC58EF132C9-4B00


2 Faults Found:

00283 - ABS Wheel Speed Sensor; Front Left  (G47) 

            35-00 - -

01276 - ABS Hydraulic Pump (V64) 

            16-10 - Signal Outside Specifications - Intermittent


-------------------------------------------------------------------------------

Address 15: Airbags        Labels: 1J0-909-60x-VW3.lbl

   Part No: 1J0 909 609 

   Component:  D AIRBAG VW3 SG   0002  

   Coding: 00068

   Shop #: WSC 00066  

   VCID: 6C81C2F4CF926EDB037-4B9A


No fault code found.


-------------------------------------------------------------------------------

Address 17: Instruments        Labels: 1C0-919-95x.lbl

   Part No: 1C0 919 951 

   Component: KOMBIINST.      M73 V23  

   Coding: 02242

   Shop #: WSC 131071  

   VCID: 6695B0DCD17E548B553-4B1E


No fault code found.


End----(Elapsed Time: 04:04, VBatt start/end: 11.9V/11.9V. VIgn 11.7V)-----
Some interesting observations:

As can be seen in this video I made of VCDS monitoring the #4 cylinder misfires

  • Misfires are consistent warm or cold
  • If revs are held steady between 2k and 3k rpm the misfires stop (according to VCDS monitoring)
  • Accelerating or decelerating from or within that rev window brings back misfires.
  • Idling, the misfires just keep accumulating
Computer Font Rectangle Gadget Display device


I pulled the plug to look at it after about 20-30 mins running. I was surprised it wasn't wet (like it was before). I also think I must have put the old one back or moved it during the diagnosis over the last few months, because it wasn't the new one I thought it was. I put in a shiny correctly-gapped new one in this time. No change to misfires.

Here's the plug removed:
Automotive tire Motor vehicle Automotive lighting Automotive exterior Automotive design


Inside the cylinder looked just as before. There were weird "scratches" on the piston that weren't there before. I got very concerned that perhaps something dropped in there, but nothing visible on the borescope.
Landscape Slope Road surface Asphalt Soil


After some deep thought and head-scratching, I realized these marks are from the long small socket extension I used in the spark plug hole as an indicator to see piston rise and find TDC in prior diagnosis. What a relief :)

After running for 20-30 mins I turned it off and ran another scan. It looks like I picked up additional related codes and an oxygen sensor issue (unlikely it would effect only #4 and contribute to the misfire) that might help identify the culprit here. I'll only paste below the Engine module results (nothing changed elsewhere).

Code:
-------------------------------------------------------------------------------

Address 01: Engine        Labels: 06A-906-018-AEG.lbl

   Part No: 06A 906 018 JE

   Component: MOTRONIC M5.9.2  AT V01  

   Coding: 00001

   Shop #: WSC 00066  

   VCID: 6E85C8FCF98E9CCB2D3-4B3C


5 Faults Found:

16684 - Random/Multiple Cylinder Misfire Detected 

            P0300 - 35-00 - 

16688 - Cylinder 4 

            P0304 - 35-00 - Misfire Detected

16684 - Random/Multiple Cylinder Misfire Detected 

            P0300 - 35-10 -  - Intermittent

16688 - Cylinder 4 

            P0304 - 35-10 - Misfire Detected - Intermittent

16515 - Oxygen (Lambda) Sensor B1 S1 

            P0131 - 35-00 - Signal too Low

Readiness: 0010 1101
More research needed...

I didn't get a chance to search for that spare ECM to see if it's a MOTRONIC M5.9.2. Hope to do that tomorrow after work. If it's a close-enough match I'll swap it to see if it makes any difference and go from there.

Another funky thing, the dash vents started wafting vapor into the cabin as the motor heated up. I'm pretty sure it was from condensation warming up in the cold night air (35F tonight). You'll see that also on the video. Creepy...

Onward and upward...
 

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The gap on the old plug looked very large (worn out or incorrectly gapped?); scratches on the piston makes sense and the vents, you may have coolant leak from the heater core?

Seeing, some test results for the fuel trims and fuel pressure, would be good to rule out as well.


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If the bank 1 sensor 1 oxygen sensor is bad; that can definitely affect things, damaged wiring or grounding out wires to the 02 sensors, have been known to damage the ecu.


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So, you might inspect the plugs and wires going to the bank 1 sensor 1 (before the cat); before replacing the ecu.

Here is the testing info:



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