Audi A4 1.8T B6 Avant - EPC & terrible banging idle

fanta

Registered User
Hi All,
I'm having some serious issues with my a4, the EPC light was coming on when getting to 2000rpm then if I ignore it and push through it goes into limp mode and eventually ultra limp (nothing there at all, but doesnt conk out).
If I drove it below 2000rpm it was usable most of the time but no doubt not doing it any good!

The car has a custom turbo (K04 internals) but hasn't been mapped in yet (probably caused some of this!!)

I did scans and 17579 kept coming back when clearning.
I've lived with 17535 for a while awaiting the remap (too rich).

I've now;
  • Changed Crank Sensor - this seemed to make it start far quicker, but not fix the issue.
  • Cleaned TB flap and internal electrical bits - made no difference.
  • Replaced TB with one from a friend - made idle far worse but feels more responsive (circuit better perhaps).
  • unplugged the N75 - This obviously gave me practically no boost but was driveable, it didnt fix the issue as its only when pushing a bit more.

The codes and assumptions are;
Missfires
  • 16686 - Cyl 2
  • 16688 - Cyl 4
  • 16684 - Cyl 3
(no idea why Cyl 1 is not coming up...)
These I guess are a result of the actual issue, so can pretty much overlook them.

Remaining codes
  • 17705 - N75/Throttle pedal switch?/VAC leak
  • 16497 - Air intake sensor/Fuse (is this the one beside the TB?
  • 17956 - N75
  • 17950 - Wiring to throttle angle sensor/battery ground/02 Sensor wiring
  • 17579 - Same as above...

So I'm about to go out and work through these, clearing codes each time and staritng car;
  • Check wiring to throttle angle sensor, pull sensor out and give it a quick drying electrical spray
  • Check battery earth
  • Change all Spark plugs - Havent changed them for 2 services so worth doing anyway.
  • Swap N75 with one I know is good.
  • Remove all PCV pipework from turbo area and inspect for issues.
  • swap electrical bits from newer TB to old.
If you have any tips, tricks or help I would hugely appreciate it and will continue digging around but from my searching the above seem to be logical.

I'll post progress here so a future me in this situation doesnt give up on their struggling engine.

Thanks.
 

fanta

Registered User
Hi All,
I'm having some serious issues with my a4, the EPC light was coming on when getting to 2000rpm then if I ignore it and push through it goes into limp mode and eventually ultra limp (nothing there at all, but doesnt conk out).
If I drove it below 2000rpm it was usable most of the time but no doubt not doing it any good!

The car has a custom turbo (K04 internals) but hasn't been mapped in yet (probably caused some of this!!)

I did scans and 17579 kept coming back when clearning.
I've lived with 17535 for a while awaiting the remap (too rich).

I've now;
  • Changed Crank Sensor - this seemed to make it start far quicker, but not fix the issue.
  • Cleaned TB flap and internal electrical bits - made no difference.
  • Replaced TB with one from a friend - made idle far worse but feels more responsive (circuit better perhaps).
  • unplugged the N75 - This obviously gave me practically no boost but was driveable, it didnt fix the issue as its only when pushing a bit more.

The codes and assumptions are;
Missfires
  • 16686 - Cyl 2
  • 16688 - Cyl 4
  • 16684 - Cyl 3
(no idea why Cyl 1 is not coming up...)
These I guess are a result of the actual issue, so can pretty much overlook them.

Remaining codes
  • 17705 - N75/Throttle pedal switch?/VAC leak
  • 16497 - Air intake sensor/Fuse (is this the one beside the TB?
  • 17956 - N75
  • 17950 - Wiring to throttle angle sensor/battery ground/02 Sensor wiring
  • 17579 - Same as above...

So I'm about to go out and work through these, clearing codes each time and staritng car;
  • Check wiring to throttle angle sensor, pull sensor out and give it a quick drying electrical spray
  • Check battery earth
  • Change all Spark plugs - Havent changed them for 2 services so worth doing anyway.
  • Swap N75 with one I know is good.
  • Remove all PCV pipework from turbo area and inspect for issues.
  • swap electrical bits from newer TB to old.
If you have any tips, tricks or help I would hugely appreciate it and will continue digging around but from my searching the above seem to be logical.

I'll post progress here so a future me in this situation doesnt give up on their struggling engine.

Thanks.
None of these helped and putting old throttle back in with a manual realign hasn't taken it back to drivable. Now I'm stuffed. Guess I need

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fanta

Registered User
Actually after another code clear it's back to its drivable under 2k.
One of these I didn't do is n75...

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fanta

Registered User
Have tried another N75 and issue is not fixed.
I'm going to do a full scan tomorrow to see whats left, hopefully some of the above are gone! Then at least we'll be nearer the issue.

I'll keep this updated.
 

QuattroCalum

Registered User
Also check map controlled thermostat and throttle body connectors haven’t been swapped ( has happened before)
Inlet air temp sensor is on the side of inlet manifold.


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fanta

Registered User

fanta

Registered User
It's now off road until this is fixed. The issue has got worse and the MAF change didn't help.
Thankfully we have bought a cheap vw polo 1.4 as a runner while we're fixing the A4.

The rain really isn't helping things and it's not exactly motivating me!

I have a fuel rail and set of injectors to swap over next.

Then it's electrical wiring and ECU!

Looking through the list from the link above:

Cylinder misfires - result of issue
Spark Plugs - DONE
Old or worn out plugs - DONE
Incorrect type for engineFuel -DONE InjectorsLeaking - TODO
Dirty, poor spray pattern -TODO
Weak ignition system - ??
coil(s), plug wires - RECALLED LAST YEAR
Fuel Pressure - TODO
Boost leak - SMOKE TEST TODO
EVAP Purge Valve (N80) - TODO
MAF (G70) - DONE
O2 Sensor(S) - TODO
 

fanta

Registered User
Replaced all injectors today and still no joy.
I've uploaded a video for what its worth.


ECU and electrical stuff next.

Driving it around the block was noisy! The brakes sound like they've rusted together!
 

QuattroCalum

Registered User
That definitely doesn’t sound good, sounds like actual engine damage. I don’t understand how it comes and goes though.


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QuattroCalum

Registered User
Does it make the noise if you hold the clutch down?


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QuattroCalum

Registered User
I’d take the sump off and check the big ends and main bearings.


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fanta

Registered User
That definitely doesn’t sound good, sounds like actual engine damage. I don’t understand how it comes and goes though.


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It seems to have stuck now, its boost or power related.
Perhaps its the turbo thats toast. It is a Chinese jobby, perhaps its done its time...

The rattle could be catalytic converter too perhaps, so the shaky engine and running lean could kill it.

So many things to try, such little money :(
 

QuattroCalum

Registered User
It seems to have stuck now, its boost or power related.
Perhaps its the turbo thats toast. It is a Chinese jobby, perhaps its done its time...

The rattle could be catalytic converter too perhaps, so the shaky engine and running lean could kill it.

So many things to try, such little money :(

Try disconnecting the cat and down pipe spring mount this will allow you to pull the cat back and off the turbo then start the engine and see how it sounds. Then take off the turbo inlet pipe and check the turbo with engine off obviously.


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fanta

Registered User
Does it make the noise if you hold the clutch down?


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It's only when lettimg off throttle so at first I thought it was something loose rattling with the engine shake.

An AA bloke said it could be the Cat as they die if running too rich, the precious metals knacker or something.

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fanta

Registered User
Try disconnecting the cat and down pipe spring mount this will allow you to pull the cat back and off the turbo then start the engine and see how it sounds. Then take off the turbo inlet pipe and check the turbo with engine off obviously.


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I'll give this a go! Thx

My gut is that the turbo is toast.

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QuattroCalum

Registered User
Hopefully it’s the cat, a broken turbo won’t make any noise, you’ll just have no boost.


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QuattroCalum

Registered User
A broken cat would cause back pressure and play havoc with fuelling.


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fanta

Registered User
I finally managed to spend some time on this today. I lifted the battery out and there is a very deep puddle! It runs under the battery and ecu. God knows how long it's been there but I'm guessing it's caused some the bigger issues.
The cat is definitely the rattle on deceleration and everything else seems to point to Ecu or wiring ssues.

I now need some damn light! The wiper arms are being a bitch and I only had 40 mins to look at it. Next step is to pull the arms off, scuttle and then get the ECU out and inspect. I'll get videos for others facing this in the future.



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QuattroCalum

Registered User
There’s not enough water in there to reach the Ecu, replace the cat first and go from there.
There are rubber bungs at the bottom of the plenum chamber, just push them through and the water will drain away.


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QuattroCalum

Registered User
What you could do for now is remove the cat, gut it then refit with an 02 spacer for the rear 02 sensor. Clear all codes you have in the ECU then run the car and see which codes come back. It's obviously up to you whether you keep/run the car this way but at least it will help with the diagnosis.
 

fanta

Registered User
I've managed to get a replacement cat for £50 so gonna swap them over. I'm hoping to jump on it at 4pm! Getting things off is always the delay!
I did get into it eventually and clear it out, the bungs are not visible but I found a youtube video that helped me find them. I've grabbed a video myself and will post it for others on this 'journey' in the future.
I'll take your advise and leave the ECU as it then, after lifting the lid it looks clean as a whistle and no signs of water. Better to know I guess...

I very much appreciate your advise Calum and will keep you posted.
 

QuattroCalum

Registered User
For removing the lower bolt on the cat I cut a 17mm spanner in half and used the ring end. There's no room for a normal spanner in there. Remove the cat at the turbo end first, then remove the bracket at the downpipe then tackle the three bolts at the downpipe/cat joint.
 

QuattroCalum

Registered User
I think it also helps to remove the driveshaft guard, giving you more room.


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ANDYMC_TQS

Registered User
I got the bottom but from underneath with a ratchet and a couple of extensions. Had to remove driveshaft seal to get it out. It did help that my exhaust had snapped off at flexi so took it out with cat
 

QuattroCalum

Registered User
So easy with the “half spanner” put it on the nut and hook a 19 mm ring spanner over the end and pull up, when tightening push down on it with the shaft of a hammer.
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jimmcgee

Registered User
or the next time Aldi have the wee dumpy spanner sets in , grab a set ,7 quid and perfect for that bottom bolt . anyhow , let us know if you run it without the cat , when mine ,eh, fell off , it was like a whole new car :racer:
 

QuattroCalum

Registered User
or the next time Aldi have the wee dumpy spanner sets in , grab a set ,7 quid and perfect for that bottom bolt . anyhow , let us know if you run it without the cat , when mine ,eh, fell off , it was like a whole new car :racer:

But I have the only one I need now lol


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