# 2000 Audi A8 - Engine Reporting Misfire, no Misfire Happening



## 97VWJett (May 17, 2003)

I will post an autoscan tomorrow, but I don't think that it's relevant. 

I have a 2000 Audi A8 Quattro with a 4.2 liter V8. A customer brought it to me for a buyer's inspection. I did do a full scan, only engine code was 16826/P0442/001090 - EVAP Emission Control Sys: Small Leak. I did test drive the car but I did not redline it while driving. We did see that it needed rear axle seals, right front upper engine mount, valve cover gaskets, and a timing belt if it hadn't been done already. 

The customer decided to buy the car even with our $3k estimate, with timing belt. The customer called a few days later and reported the check engine light had blinked under full throttle and is now on all the time. I scanned it. I had the following: 

16689/P0305/000773 - Cylinder 5 Misfire Detected 
16691/P0307/000775 - Cylinder 7 Misfire Detected 
16692/P0308/000776 - Cylinder 8 Misfire Detected 
16684/P0300/000768 - Random/Multiple Cylinder Misfire Detected 
16826/P0442/001090 - EVAP Emission Control Sys: Small Leak. 

First thing I noticed was that someone labeled all the coils and they were not in there prospective positions. First thing to check was spark plugs. They looked okay, not old, not new. I then replaced the engine left bank of spark plugs, cylinders 5 - 8. Test drive, still misfiring with same codes. So I swapped coils on the left bank, no change. Swapped all coils from left to right in order, no change. Swapped injectors, left to right, no change. Checked compression, left bank was roughly 180psi give or take 10psi. Right bank was 150 give or take 10psi. Thought that was strange. Checked with another shop, they suggested I check to see if the cam gears had paint marks on them, someone at an Audi dealer didn't bother to use the locking tool and used paint marks. Cam timing was one or two teeth off. Replaced timing belt (again), damper, camshaft oil seals, and crankshaft oil seal. Started to bleed the cooling system and the check engine light was flashing, not at redline, but at 3k. I will say that it doesn't feel like it's misfiring on three cylinders or at all. Check for codes, same cylinders are misfiring. I decided to move on and check the crankshaft position sensor physically, there were a few burs on it. Removed burs and reinstalled. I then rotated the engine by hand an inspected the flex plate/flywheel teeth to see if there were any missing or damaged teeth, checked out okay. Ran the engine in the air, at idle, the flex plate/flywheel has lateral run-out. 

Things I intend to do or try in no particular order: 
Check signal from crankshaft position sensor on a graph 
Replace ECU (used ECU, not new) 
Replace flex plate/flywheel when there is another reason like engine/trans. removal for whatever reason. 
Check fuel pressure 
Check timing chains between camshafts 
Check for intake leaks 

I am kind of at a loss on what to do though. Since I don't have the car until Thursday I thought I'd reach out and see if anyone else has had anything like this before and what it was and how they found it. 

Seems like I get one of these weird ones at least once a month :screwy:


----------



## jetta 971 (Jul 25, 2009)

When you have these two codes : 
16684/P0300/000768 - Random/Multiple Cylinder Misfire Detected 
16826/P0442/001090 - EVAP Emission Control Sys: Small Leak. 
Most likely you have vacuum leak . Most common problem with Audi/VW cars is crank case vent system. I would check that.


----------



## 97VWJett (May 17, 2003)

Alright so I got a chance last week to check this car again. The customer stated that it was truly running a lot worse and making a funny noise. I confirmed the way it was running and the noise. I checked fuel pressure and it was good. I smoke tested it and found a leak at the bottom of the PCV valve or vent control valve and the source of the noise was the PCV valve. We removed and capped of the bottom part of the valve and found no leaks. We replaced the PCV valve and it ran great!

So the final solution was incorrect timing and a bad PCV valve.

In essence jetta, 97 was right. I still think there are some other issues like a leaky gas cap and na bad O2 sensor heater but it runs without misfiring.


----------



## jetta 971 (Jul 25, 2009)

He drove it like that for 2 months. Tell him good luck with CAT. Vacuum leak makes lean condition in the engine and if you drive for long time it will burn catalyst converter .


----------



## 97VWJett (May 17, 2003)

Same codes are back with a Cat efficiency code for bank 2 hahaha!!


----------



## mwebb (Apr 19, 2008)

*MB 094 is intake cam timing test*

if you suspect cam timing
look at measuring block 094 - test runs at every startup 

is it a pass or a fail ? 

what is intake vacuum measured at hot idle ? at the fuel pressure regulator OR the purge valve vacuum line 

what is / are MB 032 values all 4


----------



## 97VWJett (May 17, 2003)

I ran checked MB 094 in Basic Settings and both passed. I also verified LH head cam timing was good by removing the valve cover and checking the marks and they were nuts perfect.

Regarding the vacuum at idle. I don't have a vacuum gauge. I just ordered one. I feel like I should have had one all along.

I don't have the scan tool/data in front of me but I cleared the data/codes and it erased MB 32 values.

We did however find that the intake manifold gasket is leaking between cylinders 7 and 8. This was verified with brake clean, engine at 2000rpm, and watching MB 15, 16, and 17. If you sprayed brake clean near those two cylinders, the misfire count would hit zero for a moment and then start climbing up again. The other way I was going to test was with propane. I did smoke test the engine and the only leak was at the dipstick. Don't always trust the smoke machine to tell you everything!


----------



## 97VWJett (May 17, 2003)

More updates:

We replaced the intake manifold gasket, part number: 077 129 717Q

We retested for the misfire and both cylinders were still misfiring. We put 3-5psi of regulated shop air on the intake manifold, capped the intake boot and a few other spots, and pressurized the intake. We spray soap and water all around the manifold. The manifold is leaking between the upper and lower halves!! We are going to try and separate the upper and lower halves and put silicone on it and reinstall to see how it goes.

Audi does NOT offer an intake "plenum" gasket...


----------



## [email protected] Parts (Nov 27, 2006)

SMOKE 

Are you smoking yet?


----------



## 97VWJett (May 17, 2003)

Okay so we removed the manifold and separated the halves. We resealed the intake and reinstalled it. We did noticed one of the intake manifold runners doesn't move freely. Anyway, we rechecked for the "misfire", and it was still there  

We removed the connectors at the ECU and found moisture/condensation/water on the ECU. We dried and it out and rechecked, no more misfire!! 

Now the only thing left is to replace the bank 2 cat.


----------



## [email protected] Parts (Nov 27, 2006)

Cause/effect. 

Fix the water leak.


----------

