motorgeek.com :: Socially inappropriate motoring information.
Search this topic:
motorgeek.com :: Board index :: The Tech Lounge :: General
Post new topic Reply to topic  [ 7 posts ] 

Seeking help with a '99 A6 misfire

Author Message
 Post subject: Seeking help with a '99 A6 misfire
PostPosted: Wed May 17, 2017 4:02 pm 
Offline
I post, therefore I am
User avatar

Joined: Sat Mar 12, 2005 9:31 pm
Posts: 6989
Location: East Germany, NH
It's a 2.8 30v, picked it up with the issue but I'm chasing my tail a bit. It had the coilpack, plug wires replaced by the PO. He said the cats were clogged, so I checked and indeed they were, so I gutted them to get it running. I also replaced the plugs(gapped them properly but I don't recall exactly to what). It was still running like a bag of sh*t, wouldn't idle and seemed like more than just a bad misfire(no throttle response) . Then I remembered the battery had died, so I tried a TBA. At first it was saying error in the status bar so it didn't work, I recalled seeing in a tutorial that some times you need to disconnect the battery terminals and touch them together to erase the 'dumb memory' stored in the ecu. So I did that& tried the TBA again and it worked. It was idling good and thrilottle response seemed right.


Codes were random multiple, 'rough road something something, cyl 1& 6 misfire, and 'control module incorrectly coded'. I double checked that the misfire is isolated to the #1/6 cyl. confirmed w/vagcom ch 15&16, and it stops completely at 3k rpm. I'll check them again to get the exact codes lol.

After I gutted the cats & cleared the codes it was still misfiring. For giggles I put the old coil pack back in(w/the new wires) and it stopped for a few weeks, then came back. I also checked all the wires and coilpacks secondary resistance per the manual and all but one of the old wires (#4) were within spec. The #4 wire was open(?) and I quadruple checked it to make sure.

After reading that an incandescent test light can damage the ecu when testing that the coil pack is getting the signal, I started wondering if the PO mechanic had done just that.

The theory I'm working on is that ecu was damaged while diagnosing the misfire, which may have originated from the bad wire. Either the misfire due to the bad wire or damaged ecu could've caused the cats death, or maybe it was just from being old.

At any rate, I'm waiting on the led test light to check the ecu is sending signal. If it isn't sending the signal on #1/6 I assume the ecu needs to be replaced. But if it is sending the signal, what's next? Cam sensors? Injectors? Am I just letting the fact that it's isolated to the #1/6 throw me off, perhaps it could just be a coincidence?

_________________
Time to make the effin' donuts sucka! Image
New DD B7 06 S4
95 90q
01 S4 Avant TIPTRON BISHES!{RIP}
03 Aprilia Caponord

Image


Top
 Profile  
Reply with quote  
 Post subject: Re: Seeking help with a '99 A6 misfire
PostPosted: Wed May 17, 2017 6:15 pm 
Offline
:blog:
User avatar

Joined: Fri Jul 30, 2004 1:38 pm
Posts: 12140
Location: CT
Coolant temp sensor get one from the dealer. Can cause weird issues like you have mentioned.

_________________
Austin
90 90Q 20v 91 200 20v avant 92 urS4


Top
 Profile  
Reply with quote  
 Post subject: Re: Seeking help with a '99 A6 misfire
PostPosted: Fri May 19, 2017 6:18 am 
Offline
I post, therefore I am
User avatar

Joined: Sat Mar 12, 2005 9:31 pm
Posts: 6989
Location: East Germany, NH
Oh no shit huh? Would that throw a code? I'll replace it anyway, PO made no mention of it so it can't hurt.

_________________
Time to make the effin' donuts sucka! Image
New DD B7 06 S4
95 90q
01 S4 Avant TIPTRON BISHES!{RIP}
03 Aprilia Caponord

Image


Top
 Profile  
Reply with quote  
 Post subject: Re: Seeking help with a '99 A6 misfire
PostPosted: Fri May 19, 2017 6:19 am 
Offline
I post, therefore I am
User avatar

Joined: Sat Mar 12, 2005 9:31 pm
Posts: 6989
Location: East Germany, NH
.... Thanks!

_________________
Time to make the effin' donuts sucka! Image
New DD B7 06 S4
95 90q
01 S4 Avant TIPTRON BISHES!{RIP}
03 Aprilia Caponord

Image


Top
 Profile  
Reply with quote  
 Post subject: Re: Seeking help with a '99 A6 misfire
PostPosted: Fri May 19, 2017 7:35 am 
Offline
:blog:
User avatar

Joined: Fri Jul 30, 2004 1:38 pm
Posts: 12140
Location: CT
Don't believe it will throw a code. It has two parts one for the ECU the other for gauge. But it definitely can cause weird random misfire issues.

Just be aware there are different types of sensors an early one 059919501 with a square plug and a later one 059919501A with the half rounded plug.

O-ring N90316802 Clip 032121142

https://www.audiworld.com/tech/eng108.shtml

https://www.audiworld.com/how-tos/a/aud ... sor-423483

_________________
Austin
90 90Q 20v 91 200 20v avant 92 urS4


Top
 Profile  
Reply with quote  
 Post subject: Re: Seeking help with a '99 A6 misfire
PostPosted: Sun May 21, 2017 10:05 am 
Offline
I post, therefore I am
User avatar

Joined: Sat Mar 12, 2005 9:31 pm
Posts: 6989
Location: East Germany, NH
Ok, replaced the cts, it was the square plug type, cleared codes and it didn't change the misfire. It was worth a shot anyway. The led test light came in too so I was able to check the ecu was sending signal and + & - were good at the the coil connector.

This is the thread I used to check the coil(posts by tester123):

https://www.audiworld.com/forums/a6-s6- ... s-2810091/

Also used this which I was surprised to find on autozone lol and it's not exactly the same as the audi world thread but pretty much the same info.(wider range on the audi world thread).

http://www.autozone.com/repairguides/VW ... 52800c2a65

So at this point does that rule out the coil? I mean if the resistance is within spec, could it still be faulty? The built in pos?

_________________
Time to make the effin' donuts sucka! Image
New DD B7 06 S4
95 90q
01 S4 Avant TIPTRON BISHES!{RIP}
03 Aprilia Caponord

Image


Last edited by Alloutofdonuts on Sun May 21, 2017 11:13 am, edited 1 time in total.

Top
 Profile  
Reply with quote  
 Post subject: Re: Seeking help with a '99 A6 misfire
PostPosted: Sun May 21, 2017 11:10 am 
Offline
:blog:
User avatar

Joined: Fri Jul 30, 2004 1:38 pm
Posts: 12140
Location: CT
Maybe check the injectors and do a compression test.

_________________
Austin
90 90Q 20v 91 200 20v avant 92 urS4


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 
Search this topic:
motorgeek.com :: Board index :: The Tech Lounge :: General

Jump to:  



Information

Users browsing this forum: No registered users and 1 guest



You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum
  |  It is currently Mon May 22, 2017 8:35 am
Share |