Audi Q7 (2012) Misfire with cylinder 4,5,6 only, please help to diagnose

I changed several catalytic converter on 3.0TFSI egines in different cars. Like audi S5, audi a6 4g, S4.

I would say missfires on TFSI engines, always injectors, if no extreme carbon build up on the intake valves, good coils and plugs, but yours on one side only, so that's why I would bet it is the cat.

First they cause random missfires, you didn't notice anything else, one car which i did ,was so bad, one side of cylinders couldn't even run.

When removed, you can notice cracks in the matrix of the cat, and broken part melted to everywhere. Later I may post some picture if I find it.

You can remove the o2 sensors, and use a cheap chinese usb phone camera to inspect the engine facing side of the cat.

Aitrui said:

I changed several catalytic converter on 3.0TFSI egines in different cars. Like audi S5, audi a6 4g, S4.

I would say missfires on TFSI engines, always injectors, if no extreme carbon build up on the intake valves, good coils and plugs, but yours on one side only, so that's why I would bet it is the cat.

First they cause random missfires, you didn't notice anything else, one car which i did ,was so bad, one side of cylinders couldn't even run.

When removed, you can notice cracks in the matrix of the cat, and broken part melted to everywhere. Later I may post some picture if I find it.

You can remove the o2 sensors, and use a cheap chinese usb phone camera to inspect the engine facing side of the cat.

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Hi Autrui,

Thanks for your kind suggestion. I really appreciate if you can post a few photos of the cat as well as guideline of how to analyze and replace it.
I am searching for a sparse part of catalytic converter and it is quite expense ($400-700) so I'd like to know how to check and replace the affective part.

Thanks,

I wouldn't search for cat yet. If you have the tools and knowledge, remove the front O2 sensor on the left side of the car from the cat. In a q7 engine bay, it might be an easy job, I don't remember how it looks there.

You can buy a cheap USB phone camera, which has diamater of 5-9mm, so you can use that camera to inspect the cat over the O2 sensor hole.

Check this picture, it's not from q7, but the locations are the same, remove that sensor which i marked with an arrow, and look up with the camera towards the CAT.

https://imgur.com/QCGNT8l


If you don't repair cars, don't have the tools, just ask a service to do it for you, there s a chance they will have a bore scope camera.

Aitrui said:

I wouldn't search for cat yet. If you have the tools and knowledge, remove the front O2 sensor on the left side of the car from the cat. In a q7 engine bay, it might be an easy job, I don't remember how it looks there.

You can buy a cheap USB phone camera, which has diamater of 5-9mm, so you can use that camera to inspect the cat over the O2 sensor hole.

Check this picture, it's not from q7, but the locations are the same, remove that sensor which i marked with an arrow, and look up with the camera towards the CAT.

https://imgur.com/QCGNT8l

If you don't repair cars, don't have the tools, just ask a service to do it for you, there s a chance they will have a bore scope camera.

Click to expand...

Thanks a lot, Aitrui.

I am not a car mechanic guy but I understand the basics of combustion as well as electronics thanks to my background. Moreover, I like to explore and fix the car myself because I can learn and gain my knowledge through technical problems.

As I shared in the previous email, I bought new O2 sensors and changed it by myself, so it is not a problem to inspect the cat as you said.

I'm going to order an camera from Amazon https://www.amazon.ca/TAOPE-Waterproof-Inspection-Megapixels-Smartphone/dp/B07B92KL7J/ref=sr_1_6?keywords=USB%2BEndoscope%2BCamera&qid=1553475148&refinements=p_85%3A5690392011&rnid=5690384011&rps=1&s=gateway&sr=8-6&th=1

I will take some photos as well as videos and post it here for your further advice. On the other hand, if you have any examples about what a defective cat is, please share with me.

Thanks,

Hello,

I got the Camera so I opened up the upstream O2 sensor to put the visual probe through it. Here are photos:







In addition, I also opened and took some photos of the spark plugs which look very bad after 15km. Note that the spark plugs are completely new and I changed it a few days ago but the engine light was up after 10km.





A short video:

Do you think the cat has any issue? It does not look like defective to me. I do have a short video which I will post on later if necessary!

I also tried to come back with the suggestion of MAF sensor but I could not find it on Audi Q7 (2012). Please advise how to check the MAF sensor (if existing) as well as Air Leak!

Thanks,

While waiting for advice from you, I am doing some research with the Audi Q7 3.0 TSFI engine.

– Charge air pressure sensor 2 G447 (cylinder bank 2)
– Intake air temperature sensor 2 G430 (cylinder bank 2)

On page 25 on the V6 TFSI engine

" Signal Utilization
The signal generated by the manifold absolute pressure sensor G71 upstream of the throttle valve control module is used to determine the nominal position of the bypass valve.
This information is required to set the required charge pressure. This nominal position of the bypass valve depends largely on the pressure level upstream of the supercharger module.
Charge pressure sensors G31 and G447 have two purposes. First, they are used to adjust the charge pressure to the required nominal value. Second, the air mass is calculated from their output signal during each working cycle. This air mass is a key input variable of the torque-based engine management system, which determines the injection rate, injection timing and ignition advance angle.

Effects of signal failure
In case of signal failure, the malfunction indicator lamp K83 (MIL) is activated. Failure of the manifold absolute pressure sensor G71 will result in less precise adjustment of the charge pressure, which may result in uneven acceleration.
If charge air sensors G31 and G447, fail this will result in an incorrect air-fuel mixture throughout the load/speed range because of an incorrect air mass calculation.
This will in turn cause an incorrect quantity of fuel to be injected, resulting in higher exhaust emissions and loss of power (and even misfiring). In charging mode, a fault in this sender can result in wrong charge pressures, causing irreparable damage to the engine.
For this reason, all senders are validated after the ignition is turned on. If irregularities are detected, an entry will
be made in the fault memory and the system switches over to an equivalent sensor or the backup sender. This allows the system to operate normally from the driver's viewpoint and consequential damage will be avoided.
"
I am wondering whether you have any experience with those sensors causing misfires?

Cat looks kind of shitty at certain angles to me.

Be careful CAT's like oil sump screens can appear as if looking okay to naked eye & when they are not, but the only real way to inspect & get a good observation is to shine a light from other side to grant the perspective or measure a distilled water gravity time flow test to compare new to volume flowed over time.

Someone got the similar problem but did not receive a proper answer

https://www.audiworld.com/forums/a6-c7-platform-discussion-194/4-5-6-cyl-misfire-3-0t-2896131/

Hello All,

After I changed O2 sensors of Bank 2 as well as brand-new spark plugs, the misfire of Cylinder 4,5,6 were still happening. I also looked into the CAT and think it looks not too bad (although shitty as Jack said). I still keep the CAT faulty chance open but wanted to look into other angles to out what could cause misfire issues of only Bank 2.
Yesterday, in order to clean up the injectors, I bought an STP fuel injector cleaning so it is still on the way.

In this morning, I decided to go back our conversation from the first post until now, especially about the fuel trim analysis with possibility if air leak/vacuum leak. I did some online measure and experiment this morning, which I'd like to share with you and ask for your advice of the next step.

In short, I decided to look into long-term fuel trim (032) and short-term fuel trim (033) and misfire counter of Bank 2 (016) vs. misfire counters of Bank 1. No misfire was observed on the Bank 1 at all while the random misfire was still observed on the Bank 2.

Since one of the error code is System too Rich (not enough air), I remembered that we can pull the oil dipstick up to get some air. I decided to do this experiment. I pulled the dipstick up and I cleared the DTCs. Surprisingly, the misfire counter showed that misfire are also 0 (only 1 times on cyl 5 but disappeared quickly). I put the dipstick down and cleared DTCs again, I observed on misfire counters and number of misfires were back on Cyl 4,5,6. It seems the air leak is truly an issue - which is also well recognized as the first reason of misfire on Q7.

Here is 7-min video clip of my experiments.



Could you advise me what should I do to check the air/vacuum leak? Note that, I am super-amateur with auto reparation so please give me some basic info with detailed guidance which can be done by an amateur!

Thanks,

Hello All,

After I changed O2 sensors of Bank 2 as well as brand-new spark plugs, the misfire of Cylinder 4,5,6 were still happening. I also looked into the CAT and think it looks not too bad (although shitty as Jack said). I still keep the CAT faulty chance open but wanted to look into other angles to out what could cause misfire issues of only Bank 2.
Yesterday, in order to clean up the injectors, I bought an STP fuel injector cleaning so it is still on the way.

In this morning, I decided to go back our conversation from the first post until now, especially about the fuel trim analysis with possibility if air leak/vacuum leak. I did some online measure and experiment this morning, which I'd like to share with you and ask for your advice of the next step.

In short, I decided to look into long-term fuel trim (032) and short-term fuel trim (033) and misfire counter of Bank 2 (016) vs. misfire counters of Bank 1. No misfire was observed on the Bank 1 at all while the random misfire was still observed on the Bank 2.

Since one of the error code is System too Rich (not enough air), I remembered that we can pull the oil dipstick up to get some air. I decided to do this experiment. I pulled the dipstick up and I cleared the DTCs. Surprisingly, the misfire counter showed that misfire are also 0 (only 1 times on cyl 5 but disappeared quickly). I put the dipstick down and cleared DTCs again, I observed on misfire counters and number of misfires were back on Cyl 4,5,6. It seems the air leak is truly an issue - which is also well recognized as the first reason of misfire on Q7.

Here is 7-min video clip of my experiments.

Click to expand...

The miss vacates slightly due to more air being made available to burn fuel.

See if you pull dip stick and this creates more air to allow for the fuel to burn that is hence "RICH"?

It is more likely that a HPP or injector are leaking and the LDP and N80 circuits can indeed be bifurcated from the system by crimp to isolate.

Misfires are the kiss of death for the CAT!

Jack@European_Parts said:

The miss vacates slightly due to more air being made available to burn fuel.

See if you pull dip stick and this creates more air to allow for the fuel to burn that is hence "RICH"?

It is more likely that a HPP or injector are leaking and the LDP and N80 circuits can indeed be bifurcated from the system by crimp to isolate.

Misfires are the kiss of death for the CAT!

Click to expand...

Thanks Jack. I will look into leaking of injectors today but still learn how to do it. Please advise if possible.

Regarding LDP and N80, I should come back to my logical thinking that if there is any issue with N80 or LDP, it should cause misfires on all the cylinders rather than one side only. Does it make sense to you?

Anyway, there are three MAF sensors on Audi Q7 3.T (please see http://www.vaglinks.com/vaglinks_com/docs/ssp/VWUSA.COM_SSP_925803_3.0L_V6_TFSI_Engine.pdf). I am wondering whether one on the bank 2 is defective and whether I can swap MAF sensors of Bank 1 and Bank 2?

Thanks,

Thanks Jack. I will look into leaking of injectors today but still learn how to do it. Please advise if possible.

Click to expand...

As always using RTFB

Regarding LDP and N80, I should come back to my logical thinking that if there is any issue with N80 or LDP, it should cause misfires on all the cylinders rather than one side only. Does it make sense to you?

Click to expand...

Not always....

Anyway, there are three MAF sensors on Audi Q7 3.T (please see http://www.vaglinks.com/vaglinks_com...FSI_Engine.pdf). I am wondering whether one on the bank 2 is defective and whether I can swap MAF sensors of Bank 1 and Bank 2?

Click to expand...

Yes........

Hello,

To follow up what we have discussed as well as to share with you what I have done so far, so you can help to diagnose the random misfire.

- To verify the MAF sensors (three sensors on Audi Q7 TSFI 3.0T), I swapped two MAF sensors of Bank 1 and 2 this morning. Random misfires are still there and I did not feel the difference in the engine sounds. I could not take the sensor at the back of the engine because it is quite complicated but I don't think it could be an issue. In short, we can eliminate issues of the MAF sensors.

- I used soap water to check the hoses around N80 but did not see the leak. Of course, I don't think I can check all the hoses by this way but that was what I have done.

Here are some snapshots of the long-term fuel trim and short-term fuel trim as well as the misfire counters on the cylinders of Bank 2 (cyl 4,5,6).









You can find the misfire counters on the cylinders of Bank 1 (cyl 1,2,3) which looks perfect.



Note that I added STP fuel injector cleaner into the gas in order to test whether the N80 can hold mechanically as suggested by Jack. However, I don't think it truly affected to the engine run as well as misfires, to my witness

I bought a new N80 and plan to change it tonight so I can eliminate this issue. If N80 is not the issue, I guess there are only two issues I should look into it.

- Injectors built up by carbon or HPP leaking
- Leak detection pump (LDP)

Both seems hard to DIY!

Any advice?

First you can't see leaks with soapy water when it's a "vacuum".

Crimp tests and use mighty vac to isolate leaks while using carb spray and trims plus misfire observation IN VCDS blocks.

Thanks, Jack. I will try what you said when I have the tools. However, I could not find the location of the N80 on this car, at least with my looking down! Probably, it is located around or under the CAT so I must lift the car up, which I cannot do at home. If you have any photo with 3T engine, kindly share with me!

Anyway, a short update of what I looked into last night so you can help to diagnose:
- I double-checked all the ignition coil connectors as it may cause misfires. However, all seem good so we can eliminate this issue.
- I also checked the fuses, which may also cause misfires as said by someone. All are good!

We can eliminate the electric connection now!

I spent a hour to test with the mess block again and found an specific situation. In short, I monitored at the misfire counters of bank 1 (cyl 1,2,3) and bank 2 (cyl 4,5,6). No matter what I did, no misfire found on cyl 1,2,3 (super stable) but there are the following situations on cyl 4,5,6:

- Idle: misfire happened randomly on 1,2,3. I saw misfire counters increased randomly on cyl over second!
- Lift the oil dipstick up to get more air but did not clear DTCs, misfires reduced significantly.
- Kept the dipstick up and cleared the DTCS, misfires came back as usual.
- Cleared DTCS, let the engine run at 3000rpm and above, almost no misfire appeared.

It seems random misfires only happens with the Idle mode. What should I learn from this?

Thanks

It seems random misfires only happens with the Idle mode. What should I learn from this?

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Do you have RTFB yet?

No, I don't have it. Do you have RTFB? If yes, kindly share with me.

Thanks,

RTFB is not possible to share...........

Go to ERWIN, subscribe and print to PDF to archive.

Jack@European_Parts said:

RTFB is not possible to share...........

Go to ERWIN, subscribe and print to PDF to archive.

Click to expand...

Listening to the video it sounds like you have a noisy cam follower/ followers . If that follower/ followers isn`t opening one or two valves enough wouldn`t it run rich on one bank ?

I brought the car to the Audi service. After an hour, they told me that the car has a problem with timing chain and leaking of fuel injectors on the bank 2, mostly based on the sound of the engine.

To my knowledge, there are two separate timing chains for the bank 1 and 2 and the timing chains should last as the life-time of the car, thus I guess the problem is about the tensioners of the timing chain. However, I am wondering whether timing chain issue could cause random misfire on a bank (e.g. Bank 2 in this case)?

Note that I drove for 700km from my town to the Audi service and back but there was no engine light during the trip. I was very surprised with this issue because the engine light was up after 10-20km last months. I am wondering whether the temperate could be the main reason because the temperate is above 10 degree at the moment.

Thanks,