Acceleration Misfires

[jtlund]

Hey guys,

2006 A4 Tiptronic Quattro with 95k on the clock. Recent services include:

Timing belt, water pump, tensioners and rollers
Carbon cleaning and injector cleaning (Cam follower done at same time)
All 4 injection coils replaced (F revision, by dealer)
Oil changes at least every 5k and never had any oil consumption issues

I have still been experiencing acceleration misfire shudder issues. If I'm on the highway and use the slap stick to keep it in 5th gear and get it up to 3k rpms and punch the gas I get repeated misfires. I wasn't getting any codes so I took it back to the dealership and had them replace the ignition coils again. After having it for almost two days... they too could not get any codes thrown and ensured me that the ignition coils were not the issue. All this was free of charge and they asked if I wanted them to diagnose further and I said no way. Knowing they would charge me for something they probably couldn't resolve considering they initially thought the car just needed a carbon cleaning. Other than the services I have already completed, any ideas what else I could look in to?

Thanks!

[RakkCity]

You didn't mention it, but did you change the plugs and gap them correctly? Sounds like it's misfiring under heavy load which would lead me to believe it's fuel or spark related.


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[jtlund]

If the dealership has been replacing the coil packs wouldn't that entail new plugs and they should know the gaps? I'm leaning towards fuel. Any ideas?

[vce1232000]

They dont have to the plugs to change the coil paks. So there is no reason for them to check the gaps if they dont remove plugs unfortunately.

[Wharfbanger]

Could be an O2 sensor. Just changed mine at 93k after misfires under load. It was triggering the check engine electrical system light so I downloaded the Dash Command App (about $19). The App allows you to check fault codes and monitor the O2 sensor via a wireless ODBII connection dongle ($12 on Amazon). The fault code indicated a faulty O2 sensor.

Plenty of info on the webs how to monitor the O2 sensor to verify it is faulty - mine clearly was. So I ordered a new sensor ($100) online an fitted it using a borrowed O2 sensor removal tool from Autozone. The job took about an hour.

[Low and Behold]

Sounds fuel related to me. Have you checked your cam follower?


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[RakkCity]

Sounds fuel related to me. Have you checked your cam follower?


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OP mentioned cam follower was changed. Fuel he'd be likely to see a code, no?

[Okedokey]

Scan your car mate. It will help.

[Rulty]

May just be plug blow out as well, Id swap in step colder plugs if your stage 1 or higher

[Low and Behold]

OP mentioned cam follower was changed. Fuel he'd be likely to see a code, no?

Gah I suck at reading.

He wouldn't necessarily get a code. You can blow straight through a cam follower without getting a code (and fuel pressure would definitely be down). Scanning would tell us the most.


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[engineerjet]

Most has already been covered, check plug gaps, cam follower, coils.

From personal experience I've experienced most of them and then some. When it comes to misfires, maybe also see if your valves need a cleaning, and possibly your in tank fuel pump may be on its way out.

I replaced my in tank fuel pump and the misfires never came back.

[80sGuy]

Not everything installed by the dealer is fine and dandy. Have them recheck/reseat the plugs/coils again.

[doughboy17]

Definitely check all the plugs and gaps ... "mind the gap"

[adam044]

Plugs

[jtlund]

Update -

Changed out the spark plugs. Dealer told me they looked good and they looked like absolute shit. Swapped with OEM Bosch and made sure they were gapped correctly. Did not fix issue.

Took the car an indie performance shop and drove with the tech to show him the issue. He hooked up the laptop and took it for a good drive and still could not get any thing to pop up in the logs. There is a metallic grinding/buzz noise that happens at the top end of the gear, which is when the "misfire" feel happens as well. We both thought that it might be the waste gate, but he inspected the waste gate and turbo and he said it looks great. Told me to wait until something breaks and that I have done all maintenance to have this car run for a long time and sent me on my way.

Now let's introduce this metallic grinding/buzz noise - http://www.audizine.com/forum/showth...T-Rattle-Noise - I know it's tough to hear but you get the point.

It takes about 15 mins of driving for the car to warm up before any of these symptoms start happening (i.e. what feels like misfires/shudder, and grinding noise). It happens most frequently when you slowly get the car up to speed in any gear and then 3-4 seconds before the car shifts into the next gear, you get what feels like misfires and this metallic grinding/buzz noise.

The tech said it could be the motor mounts, but I don't understand why the car would have to be warm for those to start failing? And those most likely wouldn't cause a metallic grinding/buzz noise?

Any idea guys? Thanks!

[miA4]

I wanna say the metal sound may be coming from your drive shaft. You'll have to put it in the air while someone is driving it to pinpoint where the noise is coming from.

[jtlund]

That's what I was thinking. CV joint or the center support bearing. Does this sound right?

[jtlund]

Update -

Turns out that both the shudder and grinding noise were caused by a bad torque converter (incase anyone else is experiencing these issues). 6 months later and a good amount of $$$ the problem is fixed.