Major help needed

[Audi_Rafa]

Hello Iam an owner of a 2005.5 Audi S4. I have been experiencing a major problem with random misfires. I have changed the coils along with the plugs and the misfire continues to show up. The check engine light also begins to flash once I hit high rpm's. The codes the car is reading are

1.) PO300 , multiple misfires detected
2.) PO305- cylinder 5 misfire,
3.) PO308- cylinder 8 misfire,
4.) PO306-cylinder 6 misfire
5.) PO304-cylinder 4 misfire

1.)I have had the audi dealership tell me I need to have my timing chain fixed and this is what is causing the misfire.
2.)However, I also know a guy who works for audi and tells me that I need to replace the cats because they are torn apart and this is what is causing the misfire.
3.) Another mechanic says it cant be the cat because the car has low pressure on the spark plugs

If anyone has experienced this similar problem and knows the solution. Any help would be apprecited by the audi community.

[jakeoboy67]

when did it start misfiring ? (after a particular modification or not )

does it misfire under 2000 rpm too, or only at high rpm (high exhaust flow) situations ?

no timing related codes ?

compression test ? (I assume you have enough compression)


when my cats were falling apart I started having slight misfires at over 5000rpm( WOT)
it quickly became worse , ( couldn't get the revs over 3000 or so , exhaust also had a muffled sound and all)

[Audi_Rafa]

The car started misfiring after having the plugs and valve cover replaced at some shop. It does not misfire at low rpms the car misfire at high rpms such as 4000 or 5000.
There are no timing codes thus far.
Did you fix your issue by replacing the cats?

[Audi_Rafa]

@jakeoboy67

[IslandHydro]

I wouldn't be doing any high rpms until you get this sorted out, hell I wouldn't drive it at all.

[Juncura1]

What kind of load condition?

[2004B6S4]

3.) Another mechanic says it cant be the cat because the car has low pressure on the spark plugs

I assume this means this other mechanic did a compression test and found low #'s on the side that's misfiring?

[Juncura1]

I assume this means this other mechanic did a compression test and found low #'s on the side that's misfiring?

From his post it looks like it's misfiring in both banks. I'd like to know what kind of load condition. At the very least check the plugs. Those can tell you a lot.

[2004B6S4]

From his post it looks like it's misfiring in both banks. I'd like to know what kind of load condition. At the very least check the plugs. Those can tell you a lot.

oops, you're right. I just thought when he said "low pressure on the spark plugs" that sounded like possibly a misinterpretation of the mechanics explanation of a compression test.

[VinnysS4]

Sounds like Cam Adjusters. I'm no expert, but i would try to fix anything and everything thats not related to the Timing Components first. Timing Chain R&R is not cheap

[Audi_Rafa]

I assume this means this other mechanic did a compression test and found low #'s on the side that's misfiring?

correct

[2004B6S4]

are you sure you didn't mean to say cylinder 7 instead of cylinder 4 in your first post?

[badger.]

The car started misfiring after having the plugs and valve cover replaced at some shop. It does not misfire at low rpms the car misfire at high rpms such as 4000 or 5000.
There are no timing codes thus far.
Did you fix your issue by replacing the cats?

are you sure they put the correct plugs in?

[Audi_Rafa]

are you sure you didn't mean to say cylinder 7 instead of cylinder 4 in your first post?

Nope there was no mistake made. It is in fact cylinder 4

[Audi_Rafa]

are you sure they put the correct plugs in?

I had more than one mechanic check the plugs so I’m positive it can’t be that

[A4Maine-iac]

The car started misfiring after having the plugs and valve cover replaced at some shop. It does not misfire at low rpms the car misfire at high rpms such as 4000 or 5000.
There are no timing codes thus far.
Did you fix your issue by replacing the cats?

This pretty much tells you something was done wrong. I'd have it redone and inspect everything that they did. Make sure all connections are done.

[VinnysS4]

Might be a long shot...but have you checked the fuel system? a leak that is letting in air could in theory cause a misfire. I ran out of gas once in my S4(stupid sending unit lies!) and right before it died it was misfiring at higher RPM's. Only reason i noticed was because i had the cruise control on and the computer tried to keep the car moving at the same speed and raised the engine RPMs. it started misfiring like hell until i hit the brakes. Ran ok at lower RPMs. ( for a minute until it died) i had the same codes you did. Might be worth a look?

[S4quattro2015]

Had a similar problem on my previous car (S3) and it was cracked insulation on the coil pack wiring loom. may be worth a check if everything else fails.

Nige

[Audi_Rafa]

Might be a long shot...but have you checked the fuel system? a leak that is letting in air could in theory cause a misfire. I ran out of gas once in my S4(stupid sending unit lies!) and right before it died it was misfiring at higher RPM's. Only reason i noticed was because i had the cruise control on and the computer tried to keep the car moving at the same speed and raised the engine RPMs. it started misfiring like hell until i hit the brakes. Ran ok at lower RPMs. ( for a minute until it died) i had the same codes you did. Might be worth a look?

Ill take another look at the fuel system but I had that checked as well and was told everything regards to the fuel system was okay. The fuel injectors are functioning okay.