2012 4.2 FSI startup/idle single cylinder misfire questions
#1
2012 4.2 FSI startup/idle single cylinder misfire questions
2012 4.2 FSI startup/idle single cylinder misfire questions
I have a few questions for the 4.2 Engine forum.
I am not new to Audi. I had a B6 A4 with a 2.0T petrol engine.
I own VCDS for at least 5 years and leveraged that to diagnose and fix every issue on my A4.
I now recently acquired a 2012 A8 D4 A8L with a 4.2 petrol engine and 110,000 miles.
I have been diagnosing and repairing everything from the sun roof to the GPS to several other deficiancies, but most of all, a major misfire on cylinder #6. Here is the initial VCDS autoscan, and a more recent autoscan:
I have swapped the number 5 and 6 plug and coil, and the misfire persists on #6.
Compression check yielded good compression ( at least on these 2 cylinders) #5=175psi #6=185psi
So now I am looking to remove the intake manifold and replace fuel injector #6 for this misfire, some details below.
I am prepared to do a carbon cleanout on all cylinders while I have access since I do not know the real service history of this car. If it needs it, I will perform it.
I have a new injector on hand: 079906036AD. As best I can tell, this is the correct injector. I believe that the "as built" revision was 079906036C, and that has been superseded by revision AD.
The real issue I have in front of me is:
#6 misfires when the car is started, only after it idles down as it comes out of Open Loop. While its in Open Loop, the car seems to not misfire, but of course idles higher than normal. After driving a while, the misfire is gone (but the car really has no performance, which I attribute to carboned up valves, but we will see about that shortly). If I shut the car off, run into the supermarket, come back out and restart the car, it is misfiring again at idle. If I drive for let's say 20 minutes on the interstate and pull into a parking spot in a parking lot and sit there idling, talking on the phone or something, there are no misfires.
Any of these startup/idling misfires can, and many times do, can cause the EPC to shutdown cylinder #6 if I sit idling for a while after startup. Im driving around with a handheld scantool plugged in, just in case I need to clear the EPC code so I can actually drive around. I've also been driving around with VCDS computer connected graphing and recording data. Yet the car is still getting 25 mile per gallon combined normally, but the performance on acceleration and the aforementioned misfires are driving me crazy. I know this can be solved, I just need some help.
So I am wondering a few things about this particular D4 with a 4.2L gas engine and the misfiring #6 cylinder.
1. My B6 A4 2.0T had full Canbus diagnostic so when I went to the Engine Module, I could read Measuring Blocks and they were very useful. On this D4, I only have UDS connectivity and there are no Measuring Blocks available. I can understand the two architectures, but not the lack of fidelity. It seems to me that I do not have, under Advanced measurement values, the same fidelity that is there in a CAN connection. For example, I know that there are high pressure fuel sensors on the two (2) high pressure fuel pumps, but when I go to Advanced Measurements, I only see one actual High Pressure fuel pressure value. Am I missing something? I wanted to monitor both bank's high pressure individually, because I am also occasionally getting a lean condition on Bank 2, which I am attributing to a weak or bad #6 injector. I wanted to monitor Bank 2 high fuel rail pressure independently, but I cant really see that.
On the mechanical side of things, it looks like somebody has been under the intake manifold before I got this car because a couple of screws around the low pressure fuel distribution block are missing. I hope I don't get under there and find out that somebody already replaced the #6 injector. As I explained to my brother recently, these cars are not for the faint of heart, and with the cost of parts, you don't want to just throw parts at a problem and hope it fixes it. With all the diagnostics and expertise available, we all should be able to come to a "confirmed kill" of a diagnosis before we buy and change a part.
2. I was reading on some Audi World forums where guys were talking about lean conditions and, and aside from looking for vacuum leaks and bad intake gaskets (which I will soon be inspection and replacing) they were talking about bad Teflon injector gaskets at the combustion chamber. My question on this topic is: If that base injector gasket were bad, wouldn't the compression be down as well? I can't see having good compression on a cylinder and a bad seal causing an air leak on vacuum. Any comments on that are welcomed.
3. I was reading about injector adaptation for IQD. These forum discussions were in the TDI engine forums. I was wondering is there any kind of adaptations for FSI fuel injectors for this 4.2. I did unlock the engine module with a security code and opened the injector adaptation and it declared an error. I assume that there is no adjustment for FSI injectors. Can somebody please confirm this. I know a friend had a small misfire on a Toyota, and the tech changed a bias on the injector pulse, and bingo, misfire gone. (Sorry, I may have some of this nomenclature wrong without connecting back up to the car)
4. The main question here is: Is there any other diagnostic that I can perform regarding the prominent misfire on #6 before I remove the intake and examine and replace the #6 injector? And furthermore, do I in fact have the correct injector for this 2012 A8 4.2L petrol engine, 079906036AD?
5. Are there any other tests I should perform that could confirm some other issue that could be causing a #6 misfire that is not the fuel injector? Id like some ideas before I delve into the mechanical work of replacing the #6 injector and potentially performing the carbon cleanout.
I am also attaching some data recordings of me driving around looking at the O2 sensors and Lambda values, because as I said, I have received a lean code on Bank 2, and I have seen widely disparate vales of these measurements between Bank 1 and Bank 2, which again I have attributed to (based on my novice interpretation) of #6 injector not behaving properly.
I hope that someone could give me a few ideas of things to check before I delve in. I am willing to record a bunch of VCDS data if requested because I want to know as much about this issue before I open up the engine. As always, I will be eternally grateful for the expert advise.
Kind regards!
I have a few questions for the 4.2 Engine forum.
I am not new to Audi. I had a B6 A4 with a 2.0T petrol engine.
I own VCDS for at least 5 years and leveraged that to diagnose and fix every issue on my A4.
I now recently acquired a 2012 A8 D4 A8L with a 4.2 petrol engine and 110,000 miles.
I have been diagnosing and repairing everything from the sun roof to the GPS to several other deficiancies, but most of all, a major misfire on cylinder #6. Here is the initial VCDS autoscan, and a more recent autoscan:
Spoiler
Compression check yielded good compression ( at least on these 2 cylinders) #5=175psi #6=185psi
So now I am looking to remove the intake manifold and replace fuel injector #6 for this misfire, some details below.
I am prepared to do a carbon cleanout on all cylinders while I have access since I do not know the real service history of this car. If it needs it, I will perform it.
I have a new injector on hand: 079906036AD. As best I can tell, this is the correct injector. I believe that the "as built" revision was 079906036C, and that has been superseded by revision AD.
The real issue I have in front of me is:
#6 misfires when the car is started, only after it idles down as it comes out of Open Loop. While its in Open Loop, the car seems to not misfire, but of course idles higher than normal. After driving a while, the misfire is gone (but the car really has no performance, which I attribute to carboned up valves, but we will see about that shortly). If I shut the car off, run into the supermarket, come back out and restart the car, it is misfiring again at idle. If I drive for let's say 20 minutes on the interstate and pull into a parking spot in a parking lot and sit there idling, talking on the phone or something, there are no misfires.
Any of these startup/idling misfires can, and many times do, can cause the EPC to shutdown cylinder #6 if I sit idling for a while after startup. Im driving around with a handheld scantool plugged in, just in case I need to clear the EPC code so I can actually drive around. I've also been driving around with VCDS computer connected graphing and recording data. Yet the car is still getting 25 mile per gallon combined normally, but the performance on acceleration and the aforementioned misfires are driving me crazy. I know this can be solved, I just need some help.
So I am wondering a few things about this particular D4 with a 4.2L gas engine and the misfiring #6 cylinder.
1. My B6 A4 2.0T had full Canbus diagnostic so when I went to the Engine Module, I could read Measuring Blocks and they were very useful. On this D4, I only have UDS connectivity and there are no Measuring Blocks available. I can understand the two architectures, but not the lack of fidelity. It seems to me that I do not have, under Advanced measurement values, the same fidelity that is there in a CAN connection. For example, I know that there are high pressure fuel sensors on the two (2) high pressure fuel pumps, but when I go to Advanced Measurements, I only see one actual High Pressure fuel pressure value. Am I missing something? I wanted to monitor both bank's high pressure individually, because I am also occasionally getting a lean condition on Bank 2, which I am attributing to a weak or bad #6 injector. I wanted to monitor Bank 2 high fuel rail pressure independently, but I cant really see that.
On the mechanical side of things, it looks like somebody has been under the intake manifold before I got this car because a couple of screws around the low pressure fuel distribution block are missing. I hope I don't get under there and find out that somebody already replaced the #6 injector. As I explained to my brother recently, these cars are not for the faint of heart, and with the cost of parts, you don't want to just throw parts at a problem and hope it fixes it. With all the diagnostics and expertise available, we all should be able to come to a "confirmed kill" of a diagnosis before we buy and change a part.
2. I was reading on some Audi World forums where guys were talking about lean conditions and, and aside from looking for vacuum leaks and bad intake gaskets (which I will soon be inspection and replacing) they were talking about bad Teflon injector gaskets at the combustion chamber. My question on this topic is: If that base injector gasket were bad, wouldn't the compression be down as well? I can't see having good compression on a cylinder and a bad seal causing an air leak on vacuum. Any comments on that are welcomed.
3. I was reading about injector adaptation for IQD. These forum discussions were in the TDI engine forums. I was wondering is there any kind of adaptations for FSI fuel injectors for this 4.2. I did unlock the engine module with a security code and opened the injector adaptation and it declared an error. I assume that there is no adjustment for FSI injectors. Can somebody please confirm this. I know a friend had a small misfire on a Toyota, and the tech changed a bias on the injector pulse, and bingo, misfire gone. (Sorry, I may have some of this nomenclature wrong without connecting back up to the car)
4. The main question here is: Is there any other diagnostic that I can perform regarding the prominent misfire on #6 before I remove the intake and examine and replace the #6 injector? And furthermore, do I in fact have the correct injector for this 2012 A8 4.2L petrol engine, 079906036AD?
5. Are there any other tests I should perform that could confirm some other issue that could be causing a #6 misfire that is not the fuel injector? Id like some ideas before I delve into the mechanical work of replacing the #6 injector and potentially performing the carbon cleanout.
I am also attaching some data recordings of me driving around looking at the O2 sensors and Lambda values, because as I said, I have received a lean code on Bank 2, and I have seen widely disparate vales of these measurements between Bank 1 and Bank 2, which again I have attributed to (based on my novice interpretation) of #6 injector not behaving properly.
I hope that someone could give me a few ideas of things to check before I delve in. I am willing to record a bunch of VCDS data if requested because I want to know as much about this issue before I open up the engine. As always, I will be eternally grateful for the expert advise.
Kind regards!
#2
I have heard of the carbon causing 100% of your symptoms. I would just do that and send off the injectors for cleaning while you have it all apart along with anything else in the area that's otherwise unreachable.
#3
Thanks for the feedback. I didn't want to take the car down for the extended period to get the injectors cleaned. I know some guys swear by that rather than replacing injectors with Hitachi (for cost concerns) .
I ended up taking it all apart to inspect and repair. I didn't have any history on this car because I bought it used, so I didn't know what to expect and I was prepared for the worst.
First, the lower intake flap on Bank 2 was stuck. I guess the last person in there didn't follow the manual and apply vacuum to that assembly when it was re-installed.
Next, the carbon buildup was minor, so clearly it was done before at some point because the car has 110,000 miles on it. I was prepared to do the cleaning, but deemed it not necessary at this time.
Also, when I had the lower assembly out, I tested potentiometer while articulating the flap with vacuum, and there was no change in the resistance. It was reading half the value at all times. That potentiometer, and the Bank 1 piece also, is going to be replaced as soon as they arrive from the parts vendor.
With all the other troubleshooting, I was convinced that the #6 fuel injector was bad, and that's why I opened it all up in the first place. I had a brand new OE injector on hand, and replaced it. Honestly, if the carbon was extreme, like I've seen on YouTube videos, I might have done a thorough cleaning and just reassembled it to see what happened. But because the valves were mostly clean, I just replaced #6 injector and all the seals, cleaned everything up, including the throttle body, did an adaptation of that, and fired it up. No misfires at idle!
I drove this around with VCDS on my laptop and monitored the O2 sensors and there is little to no variation between Banks. That's far different than the 'before' capture.
Problem solved. I replaced #6 fuel injector and it runs like a new car. I've driven it for about a week and there is no relapse of symptoms. In my book, that's a confirmed kill! I am going to replace those intake manifold flap potentiometers when they come, and also replace the PCV / Oil separator (the lower coolant connection is cracked and leaking slightly) and this thing will be good as new.
Again, thank you for reading my post and replying!
I ended up taking it all apart to inspect and repair. I didn't have any history on this car because I bought it used, so I didn't know what to expect and I was prepared for the worst.
First, the lower intake flap on Bank 2 was stuck. I guess the last person in there didn't follow the manual and apply vacuum to that assembly when it was re-installed.
Next, the carbon buildup was minor, so clearly it was done before at some point because the car has 110,000 miles on it. I was prepared to do the cleaning, but deemed it not necessary at this time.
Also, when I had the lower assembly out, I tested potentiometer while articulating the flap with vacuum, and there was no change in the resistance. It was reading half the value at all times. That potentiometer, and the Bank 1 piece also, is going to be replaced as soon as they arrive from the parts vendor.
With all the other troubleshooting, I was convinced that the #6 fuel injector was bad, and that's why I opened it all up in the first place. I had a brand new OE injector on hand, and replaced it. Honestly, if the carbon was extreme, like I've seen on YouTube videos, I might have done a thorough cleaning and just reassembled it to see what happened. But because the valves were mostly clean, I just replaced #6 injector and all the seals, cleaned everything up, including the throttle body, did an adaptation of that, and fired it up. No misfires at idle!
I drove this around with VCDS on my laptop and monitored the O2 sensors and there is little to no variation between Banks. That's far different than the 'before' capture.
Problem solved. I replaced #6 fuel injector and it runs like a new car. I've driven it for about a week and there is no relapse of symptoms. In my book, that's a confirmed kill! I am going to replace those intake manifold flap potentiometers when they come, and also replace the PCV / Oil separator (the lower coolant connection is cracked and leaking slightly) and this thing will be good as new.
Again, thank you for reading my post and replying!
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