Cat light / misfire on cylinder 8 problem.
 

Hi.

Hit a problem with my S8 and I have done some basic fault finding to try and solve the problem.
The car had been running fine, with no indication of any problems. Then came to start it up warm and the CAT light came on. The car is running lumpy and does not want to rev, as you might expect.

I scanned it with VCDS and it came back with these faults:

17604 - Oxygen (Lambda) Sensor Heater Circuit: B1 S1
P1196 - 35-00 - Electrical Malfunction
16518 - Oxygen (Lambda) Sensor B1 S1
P0134 - 35-10 - No Activity - Intermittent
17616 - Fuel Injector for Cylinder 8 (N86)
P1208 - 35-00 - Electrical Malfunction
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 -
16692 - Cylinder 8
P0308 - 35-00 - Misfire Detected

The Lambda errors have been there since I got it and to date, not caused any issue.
To try and diagnosed or fix the problem, I swapped a coil pack from cyl 8 for cyl 5. I inspected the plugs and could not see anything to cause concern (dark golden brown in colour, electrode not damaged). Not sure when they were changed last, so ordered another set anyway.
After the swap, the same errors were returned, so clear the codes again, let it cool and swapped spark plug 8 for spark plug 5 and swapped the coil packs back to their original cylinders.
It then ran fine, so took it for a spin around the block. No problem, no fault codes and the Lambda errors did not return (presumably as the engine was warm). However as soon as I turned it off then on again, the CAT light reappeared and the fault codes returned.
I supplied the codes to my local Audi specialist, who have ordered another injector, but can't look at it until next Wednesday. However it's VOR back order so is likely to take 7-10 days.
I am posting this up in the hope someone has seen this before and can advise. Would a completely knackered CAT give these errors? I guess a second hand injector is out of the question as it will need a new seal, which is likely to be just as long on order.

Thanks

Sometimes you should believe the error codes :)
When were your Series 1 (pre-cat) Labmbdas last changed?
In my experience after roughly 10years/100k miles they are usually due for replacement. Pre-cat Lambdas tell you nothing about the cat (unless its completely collapsed and blocking the pipe), that's what post-cat Lambdas are for, and you don't have those on a PF car (lucky guy!)
Since the car is telling you the injector is at fault, you could have swapped injectors with the nearest cylinder to see if the missfire moves. Personally I wouldn't be confident enough to swap injectors I have never taken one out before. There are other resistance and continuity tests you can do on injectors and Lambdas detailled in ElsaWin.

No need to swap injectors, fault code is for injector electrical malfunction. Get out multimeter and test injector resistance. Not sure what it is supposed to be on 8 but somewhere 10-30 ohm should be OK, you can always compare resistance to another injector. If the injector reads OK check wiring between injector and ECU. Faulty injector or wiring will cause all of those fault codes apart from the top one.

Hi it's really easy to do a quick test of the injectors. Touch the injector body with a long screwdriver and put your ear against the handle. Check they all click!
Dave

Thanks for the replies guys.
@Goran - I have no idea - the car has a stamped history book but no bills, so I presume never. Thanks for the info on the cats - as a pre 2001 car, the cost of replacing the cat using a non type approved type is more bearable as well. A new lambda is between 40-70 quid depending on whether it's bosch or pattern part. I am not going to attempt doing an injector swap as I know my limits too.
@ainarssems I am trying to borrow a multimeter this weekend as found my aged old MM has died a death due to being packed underneath something heavy in our house move years ago. It is going into my trusted specialist Tuesday morning.

It started fine just now with CAT light on. No lumpiness. A stop/start saw it start fine with the CAT light going out. Without getting it upto temp, I am about to go swap the plugs and coil packs around anyway. I doubt this will make any difference. NGK -R plugs, same as whats in there now. At least I will have removed the possibility of failing coilpacks or plugs from the equation.

Hi had a similar fault a few years back - the car would start and run on 8 cylinders then develop a misfire whilst driving. VCDS revealed an identical error message (injector x electrical malfunction). Replaced the injector and the fault never came back. Injector part No:077133551L to suit AHC engine, an eye-watering £175.36 from Harrogate Audi.

@Nuisanceneighbour - Thanks - 185 quid is what I have been quoted as main agent only.

At the risk of being premature, I am now optimistic that the problem is fixed.

Since replacing the plugs and swapping the coil packs around, the problem has gone. I have given it a fairly brisk test drive, driving around 25 miles in 3 seperate small journeys since yesterday afternoon and it's been perfect. Just checked for codes again and there are none except for the lambda's.
The gap on the new plugs was 0.30 whereas, due to wear no doubt, the old ones were between .45 and .50, so I left them as they were out the box.

I am going to take it in to the specialist Tuesday anyway, so that the state of the cats and possible replacement of the lambda's can be assessed.
But so far, so good....

Update a week on. So far so good. The problem has not returned....

The specialist had the car up on the ramps and said the cats were fine as far as visually inspecting them and tapping them permit. They ran the tests as I did but the fault did not returned and the suspect injector was showing the correct impedance.
The faulty lambda is still showing and is on the drivers side, sitting directly under the air intake hose joining the throttle body and airbox, so I am looking to replace it myself.

Has anyone used Bosch lambda's on their A8/S8? I suspect they are probably the same as OEM, which are £133...
I have found several on Eurocarparts, with the Bosch unit (see link) looking like it's correct @ £68.
http://www.eurocarparts.com/ecp/c/Au...sor/?710442005

Thanks

I had to have a post-cat lambda replaced (with the cat) recently as, though it was still working, it was stuck in place.
Bosch one they got from ECP was identical in every respect and the OEM one was Bosch anyway.

Many thanks for that confirmation HPsauce