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2004 V8
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Discussion Starter · #1 ·
Been reading through several forums on this and figured I'd start an updated one for wisdom and possible alternate ideas.

Here is my VCDS after a few days of driving. It will often start with only the first couple and then add on as the days go by.

16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 001 - - MIL ON
16689 - Cylinder 5
P0305 - 001 - Misfire Detected - Intermittent - MIL ON
16688 - Cylinder 4
P0304 - 008 - Misfire Detected - Intermittent - MIL ON
16537 - Oxygen (Lambda) Sensor B2 S1
P0153 - 002 - Response too Slow
19711 - Oxygen (Lambda) Sensor B1 S1; Heating Circuit
P3255 - 001 - Regulation at Upper Limit - MIL ON
16685 - Cylinder 1
P0301 - 001 - Misfire Detected - MIL ON
16692 - Cylinder 8
P0308 - 002 - Misfire Detected - Intermittent
17538 - Fuel Trim; Bank 2 (Mult)
P1130 - 001 - System too Lean - MIL ON
16687 - Cylinder 3
P0303 - 001 - Misfire Detected
16686 - Cylinder 2
P0302 - 001 - Misfire Detected - Intermittent
17536 - Fuel Trim; Bank 1 (Mult)
P1128 - 001 - System too Lean - Intermittent - MIL ON
17546 - Fuel Trim: Bank 2 (Add)
P1138 - 001 - System too Lean - Intermittent

These have been consistent. This is the first time Cylinder 8 was listed. I never had any problems on Cyl 6,7,8. Swapped coils all over, swapped plugs on a couple. Finally after the plug change on 8, got the error. I have NGK Iridium plugs, not sure how old.

Today, cleared codes, swapped coils on 4 & 5 with 6 & 7 to see what happens.

Here are the codes after the swap.

16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 001 - - MIL ON
16689 - Cylinder 5
P0305 - 001 - Misfire Detected - MIL ON
17536 - Fuel Trim; Bank 1 (Mult)
P1128 - 001 - System too Lean - MIL ON
17538 - Fuel Trim; Bank 2 (Mult)
P1130 - 001 - System too Lean

Still no problem with 6&7.

Calling all geniuses. Just thinking how to diagnose and choose the cheapest ideas to try first.
Thank you in advance.
 

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I'd start with those fuel trim codes. There are a few things that can cause this, but first I would check for vacuum leaks. Easiest way is to watch fuel trims as the engine is idling. If they're quite high, usually more than +10-15 and higher, and then they drop as you raise the RPM, then you likely have a vacuum leak.

You could well have more than one issue, but this would be best to start with.
 

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2004 V8
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Discussion Starter · #3 ·
Might you go into a few more details on how to check this? Do I get a reading at idle or under RPM? It is something I get on the vcds or a different reading somewhere? Sorry, early on the diagnostic experience.
 

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2004 V8
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Discussion Starter · #4 ·
I'd start with those fuel trim codes. There are a few things that can cause this, but first I would check for vacuum leaks. Easiest way is to watch fuel trims as the engine is idling. If they're quite high, usually more than +10-15 and higher, and then they drop as you raise the RPM, then you likely have a vacuum leak.

You could well have more than one issue, but this would be best to start with.
might you share more detail on this? How do I check the fuel trims at idle and under RPM?
 

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Discussion Starter · #6 ·
This is awesome. Some crazy lessons in there. I hope it's my vacuum leaks somewhere. It seems easier to fix than trying to deal with trims on the programming side.
 

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Discussion Starter · #7 · (Edited)
@Kiwikev I can't visibly or audibly hear any vacuum leaks. I searched through the lines and they're all quite clean, supple (where they need to be) and plugged in. I haven't looked at the VCDS to see if anything changed... not sure I would notice without the gaping hole like the video.

Next suggestion?
  • The plugs are NGK Iridium, doubt they need changing, they seem clean and good (I don't know when they were changed last).
  • All the coils seem original except one that has an NGK logo on it.
  • It might be the injectors. Not sure when they were changed, if ever.
  • Clean or replace the MAF?
  • There is a definite point in driving where you can feel it start to misfire and run rough. The power drops and it has a nice dragster feel at the lights (haha)
  • Read that the fuel pumps might be an issue. Is there a way to test these (although running lean doesn't sound like a fuel pump issue)
  • I see that my vacuum actuators in the front aren't doing anything (they turn by hand but are not inflating, deflating when starting). could cleaning those so they operate solve some of this?
I'm about to do my timing belt because I don't know when it was done last.

Getting it running smooth would make doing the timing belt worth it.
 

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Ignition coils are pretty well known to fail at higher mileage. You could swap them around with the cylinders that aren't misfiring and see if it follows. Pretty quick and easy way to see if the coils are faulty.
 
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