B8 a4 misfire

[Bkscooby]

Hello everyone,

So i got this car which I thought felt like it was misfiring. The CEL was not showing. It is tuned to stage 2 around 23 PSI. Upon hooking it up to a scanner, a p0300 (multiple cylinder misfire detected) and p0303 Cyl 3 misfire detected popped up. The car is only misfiring on idle. The following was done as an attempt for a remedy to no avail.

- Compression - Good in all 4
- PCV Valve swapped from another car
- New plugs NGK BKR7EIX
- Swapped coils - Misfire in 3 still popped up
- Swapped injectors around - misfire in 3 still popped up
- Cleaned intake ports - Misfire in 3 still popped up
- Swapped to an unchipped ECU - CELs is not coming back, but scanner still logs intermittent misfire
- Vacuum is -20 at idle, which appears normal for these motors

After swapping back to the stock tune the car started to drive slightly better, but still the misfire is there. Any ideas?

[STA4]

Sorry to hear. If you did a search, you would've found some existing threads:

http://www.audizine.com/forum/showth...sue-In-Low-RPM

http://www.audizine.com/forum/showth...-Misfire-Issue

[Bkscooby]

Sorry to hear. If you did a search, you would've found some existing threads:

http://www.audizine.com/forum/showth...sue-In-Low-RPM

http://www.audizine.com/forum/showth...-Misfire-Issue

Appreciate the help, but the 1st thread says that his compression on cyl 3 was low which was assumed to be a bad valve guide. In my case compression is good in all 4. Thread #2 is irrelevant to my problem as well. Investigating on more possible causes.

[Fburg A4]

Any info on your fuel trim values? And have you looked at the misfire counter to see what the actual number of misfires is? Like is Cyl 3 way higher than the others, cyl 3 and cyl 1 both missing but cyl 3 more so, etc

[Bkscooby]

Any info on your fuel trim values? And have you looked at the misfire counter to see what the actual number of misfires is? Like is Cyl 3 way higher than the others, cyl 3 and cyl 1 both missing but cyl 3 more so, etc

Thanks for chiming in Fburg A4. I'll check the misfire count and the fuel trim and will report back.

[inv3rtig0]

Regular coils or R8? I had misfires with stage 2 until I did the R8 coils. I did plugs at the same time, same ones you got, so I can't say for sure if it was coils or plugs or both that solved it for me.

[Bkscooby]

Update CEL misfire in CYL 3 popped up again. P0303
Torque app shows :Misfire cylinder 3 Data misfire counts for last/ current driving cycles (calculated) - 121 Count. Don't know how to log the fuel trim value, but I'll log it once I get the vcds cable on Monday.
inv3rtig0 - Wouldn't switching a bad coil to another cylinder not switch the misfire cel to another cylinder?

[van462]

On the torque app you can see fuel trim by bringing up real-time info. Go to set up a new gauge and when it gets to the values to pick from you should see fuel trim in the list.

[van462]

http://www.audizine.com/forum/showth...ing-Torque-app here are some baselines I ran in torque app if you want comparables.

[Bkscooby]

http://www.audizine.com/forum/showth...ing-Torque-app here are some baselines I ran in torque app if you want comparables.

Below are the readings logged by the torque app today. I don't understand what half of it means, but I thought I'd log everything I saw. P.S. Misfire occurs in not only Cyl 3 but cyl 1 as well. Today, the misfire counted for the past drive cycle was 66 for cyl 3 and 4 for cyl 1. The check engine light did not come back, but it feels that the warmer it gets, the less misfires I get. Can it be the fuel filter, rail, line, pump?

Fuel flow 12.0cc/min
Fuel flow 0.7l/hr
02s1eq:1.0
COMEQR: 1.0
AFR(m): 14.2:1
AFR(c): 14.7:1
R THR: 1.2%
A THR2:11.4%
Pedal D: 14.9%
Pedal E 14.9%
Fuel flow 13.4cc/min
o2 1x2 0.6v
Air temp: 15.0C
Baro 14.5 PSI
LTFT1: 11.7%
Fuel Rail 559.8psi
Cat B1S1 525.2C
Volts (CM) 13.4V
Boost: -11.6psi
Coolant 105.0C
MAF: 2.1g/s
Revs idle: 692.5rpm
Load: 9.4%
STFT1: 0.8%
Intake: 42.0C
Timing Adv:0.0
Throttle 11.0%

[Allowencer]

Have you ever done a carbon cleaning?

[Bkscooby]

Yup. I did clean the intake ports

[Bkscooby]

Yup, in my original post by cleaning intake ports that is what I meant. They were not even that dirty. The previous owner cleaned them not too long ago I guess. Nonetheless they were thoroughly cleaned and nada.

[Allowencer]

my bad, guess I shouldn't skim read

Only thing that is left is valvetrain or maybe even the coil connector?

If you're getting good compression then the valves are seating properly; however, doesn't rule out a bad spring or bad valve guide.

[RW12]

You've done compression, but did you do a leakdown test?

[van462]

Below are the readings logged by the torque app today. I don't understand what half of it means, but I thought I'd log everything I saw. P.S. Misfire occurs in not only Cyl 3 but cyl 1 as well. Today, the misfire counted for the past drive cycle was 66 for cyl 3 and 4 for cyl 1. The check engine light did not come back, but it feels that the warmer it gets, the less misfires I get. Can it be the fuel filter, rail, line, pump?

Fuel flow 12.0cc/min
Fuel flow 0.7l/hr
02s1eq:1.0
COMEQR: 1.0
AFR(m): 14.2:1
AFR(c): 14.7:1
R THR: 1.2%
A THR2:11.4%
Pedal D: 14.9%
Pedal E 14.9%
Fuel flow 13.4cc/min
o2 1x2 0.6v
Air temp: 15.0C
Baro 14.5 PSI
LTFT1: 11.7%
Fuel Rail 559.8psi
Cat B1S1 525.2C
Volts (CM) 13.4V
Boost: -11.6psi
Coolant 105.0C
MAF: 2.1g/s
Revs idle: 692.5rpm
Load: 9.4%
STFT1: 0.8%
Intake: 42.0C
Timing Adv:0.0
Throttle 11.0%

A few numbers look a little off. It looks to me as there may be a slight vacuum leak. Your MAF signal appears a little low indicating that the air is being pulled in after the MAF. Your long term fuel trim is at 11% (adding fuel to match the extra air) and your A/F(m) 14.2 is still a bit lean but the primary O2 has a lamba reading of 1 (perfect) so it satisfies the ECU enough to not trigger a lean code. I ran my baselines again today and had a lower idle this time at 700 but still had 2.44 g/s. Brooklyn and Bremerton are both sealevel cities. So there there shouldn't be huge atmospheric differences. I had hoped more would post their baseline values on that thread. to create with more data from different altitudes and problems to see what causes the numbers to shift.

I would start by inspecting the plug on the intake manifold http://www.audizine.com/forum/showth...ntake+manifold
If that looks good then you can disconnect the hose that goes from the intake manifold to the PCV and cover the intake manifold with a thick ziplock bag and reinforce it with tape. If this fixes the rough idle and codes then the PCV is leaking too much air into the intake. Even if the PCV is good; a failing front or rear main seal (very hard to diagnose without seeing an oil leak from these seals) can allow more air into the intake. On the plus side likely your injectors aren't leaking.

[Fburg A4]

yeah van is on to something, that fuel trim is high. makes sense since it is missing only at idle (or when the vacuum is high) when a vacuum leak would be most prevalent and cause a misfire. interesting the misfire is isolated to one cylinder, or at least that is what the computer data shows. like perhaps the intake gasket around cylinder 3 may be bad on a cold start, but when the engine warms up and expands it may close the vacuum gap between the head and the intake gasket. or a crack in the intake runner as well could lead to an isolated cylinder 3 vacuum leak. not sure how much faith you want to put into the isolated cylinder issue, but it very well could be correct and lead you in the right direction.

not sure if you have a buddy for a smoke machine, but if you do now is a good time to buy a 6-pack of his favorite beer. or maybe looking into a place that mey rent smoke machines to help diagnose. otherwise, the good ol' water spray method works pretty well

[Bkscooby]

Once it gets a bit warmer, I'll figure out a way to smoke test it. Don't have a buddy with a smoke machine, so I'll figure out a way to create some ghetto smoke machine using an air pump and incense lol. Can the fuel trim be possibly that high also because the car has no cats? It has turbo back and it is now on a stock tune.

[Bkscooby]

And so. Did the smoke test and nada. Replaced a new PCV and it idles a bit better, but still misfires. Not too much to trigger a code, but still enough to feel it. When you unscrew the oil cap, it gets sucked in, so you have to apply a little pressure to pull the oil cap off. Any other ideas that I should investigate? At this point, if I can't figure it out, I'll just sell the car.

[lostkeyz]

And so. Did the smoke test and nada. Replaced a new PCV and it idles a bit better, but still misfires. Not too much to trigger a code, but still enough to feel it. When you unscrew the oil cap, it gets sucked in, so you have to apply a little pressure to pull the oil cap off. Any other ideas that I should investigate? At this point, if I can't figure it out, I'll just sell the car.

Check for carbon build up. I have 2013 with 35k and there is a lot of carbon build up. Need to get a carbon cleaning. I replaced my pcv because it was no good. It idles a little better but not as smooth stills misfires at idle


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[Bkscooby]

Been there, done that and more.


- Compression - Good in all 4
- PCV Valve swapped from another car
- New plugs NGK BKR7EIX
- Swapped coils - Misfire in 3 still popped up
- Swapped injectors around - misfire in 3 still popped up
- Cleaned intake ports - Misfire in 3 still popped up
- Swapped to an unchipped ECU - CELs is not coming back, but scanner still logs intermittent misfire
- Vacuum is -20 at idle, which appears normal for these motors

[helldriver]

Did all this also, we're into the valve train now, lifters looked ok, cyl 3 misfire saga continues, right now waiting on apr valve springs since its apart why not?, I'll keep this updated..

Been there, done that and more.


- Compression - Good in all 4
- PCV Valve swapped from another car
- New plugs NGK BKR7EIX
- Swapped coils - Misfire in 3 still popped up
- Swapped injectors around - misfire in 3 still popped up
- Cleaned intake ports - Misfire in 3 still popped up
- Swapped to an unchipped ECU - CELs is not coming back, but scanner still logs intermittent misfire
- Vacuum is -20 at idle, which appears normal for these motors

[Bkscooby]

Did all this also, we're into the valve train now, lifters looked ok, cyl 3 misfire saga continues, right now waiting on apr valve springs since its apart why not?, I'll keep this updated..

Fuck my life. I did think it was the head. The only thing I didn't do was a leak down test, but I've had it. I think I'll just sell it. I wasn't planning on keeping it long anyway.

[Bkscooby]

Let me know how the valve springs pan out.

[Bkscooby]

And I am bumping up the dreaded misfire code for cyl 3. P0303 AND NOTHING ELSE. Took it to 3 mechanics. No one seems to be able to know wtf is going on.

- Compression - Good in all 4
- PCV Valve – New
- New plugs NGK BKR7EIX
- Swapped coils - Misfire in 3 still popped up
- Swapped injectors around - misfire in 3 still popped up
- Cleaned intake ports - Misfire in 3 still popped up
- Swapped to an unchipped ECU - to no avail

Negative suction on the oil cap and it goes through 1l of oil between oil changes.

It's getting worse. Sometimes EPC light comes on and you can feel that cyl 3 is not firing at all. It goes away after shut the car off and on.

[jjvwg]

There's your next clue to work off of. Your oil cap shouldn't have suction on it. Sounds like your block is under too much vacuum.

[TJet1.8]

Ok...so I have 2 A4 2.0T's in the family (2011 A4 - Mine, 2012 A4 - Wife).
I got my A4 first (obviously) and after ~70000Km...she starts shaking like it's misfiring.

Things I did to remedy?
1.) New Plugs gapped @ .026 (I have APR Stg 2 Tune)
2.) New R8 coilpacks

This fixed "most" of the misfiring...but she was still misbehaving.
My dealership scanned the ECU and found no apparent issues.
Next on the dealerships checklist was to replace the MAF sensor.
After the MAF was replaced...she ran smooth as butter.

My Wifes A4 started the same issues @~77000Km.
I replaced the Plugs gapped @ .026 (She also has APR Stg 2).
Replaced the coilpacks.

Again...this fixed "most" of the misfiring.
So I then replaced the MAF sensor...and again, runs smooth as butter.

www.europaparts.com
Get yourself a new MAF sensor.

Hope this fixes it for you.

GL.

[Bkscooby]

What is the likelyhood of it being the maf since it only shows misfire in a single cylinder?

[TJet1.8]

...forgot to mention...

I "was" get misfire codes before replacing the plugs/coilpacks, after replacing I got no more codes...but it still felt like it was misfiring, especially under mild to moderate acceleration.
Replacing the MAF was the final fix for that.

If you are still getting codes "after" replacing the plugs/coilpacks...then I would agree that the MAF is likely not your issue.

Since you are also on a Stage 2 tune, have you shrunk the plug gaps to ~.026 to .028 (smaller is better on APR Stage 2) ?
Which Tune are you using?

[helldriver]

Have it scoped, same issues here with cyl 3, found a burnt valve. Good luck.

[Bkscooby]

Have it scoped, same issues here with cyl 3, found a burnt valve. Good luck.

Interesting. Wouldn't a compression test show a burnt valve?

[mecg]

You need 4 things for that cylinder (and all cylinders) to fire. You need fuel, air, compression, and spark. You're not in space, so there is air. So one of the other 3 is missing. You've swapped everything around that you can (plugs, injectors, coils) so fuel and spark seem to be OK. That only leaves one thing it can be....

[helldriver]

Interesting. Wouldn't a compression test show a burnt valve?

My compression was and still is checking good, its not burned all the way around, they rotate around while running and seat and not seat from the puffs of carbon then go away, cyl 3 has always been a problem, done everything required, it goes away for a month then back again, head will come off then upgrade valves next. cheers.....

I forgot to add my car runs strong, it just misfires at idle..

[van462]

This sounds like a leaking rear /fwd main seal or intake manifold. Is your LTFT long term fuel trim still above 2. At idle intake manifold vacuum is at its highest. Any air leak in the intake manifold or the engine block will allow extra air in. Even partial throttle greatly reduces manifold vacuum. You could scan data on short and long term fuel trims at idle and then hold the throttle at 2500 rpm. If the values change likely you have a vacuum leak.

[Bkscooby]

This sounds like a leaking rear /fwd main seal or intake manifold. Is your LTFT long term fuel trim still above 2. At idle intake manifold vacuum is at its highest. Any air leak in the intake manifold or the engine block will allow extra air in. Even partial throttle greatly reduces manifold vacuum. You could scan data on short and long term fuel trims at idle and then hold the throttle at 2500 rpm. If the values change likely you have a vacuum leak.

I smoke tested/ waterspraid for vacuum leak. Doubt it. Will check the ltft and sltf and let you know.

[d3signz]

Any news ? I have exactly same on audi s5 v8 4.2L

[2004s4stk]

Any update on this?

[Bkscooby]

Ended up being a bad intake cam.

[helldriver]

My compression was and still is checking good, its not burned all the way around, they rotate around while running and seat and not seat from the puffs of carbon then go away, cyl 3 has always been a problem, done everything required, it goes away for a month then back again, head will come off then upgrade valves next. cheers.....

I forgot to add my car runs strong, it just misfires at idle..

The culprit to my misfire problem ended up being a a bad roller rocker arm, bearing was worn out, they all were not so good. But the cyl 3 set was the worst, turns out in usual audi fashion there's an updated version, but at less than 80,000 miles at the time on the odometer come on!

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[Nick4929]

Did you take it to a shop or pull the valve cover n stuff off to diagnose?