1995 S6 Detonation (pinging) under normal acceleration

[steve52]

Recently I hear detonation (pinging) during normal acceleration between around 2500 to 3400 rpm. The car is a 1995 S6 Quattro with the turbo 5 cylinder 20 valve engine. It has only 159,000 miles the recommended major service was done at 150,000 miles. I always use premium fuel and have tried different brands but the problem continues. The spark plugs show some carbon but otherwise look good. I am also very recently noticing what seems to be an engine vibration during moderate to hard acceleration at about 4000 to 4500 rpm. Thank you for sharing thoughts about what might be causing and how to best resolve these recent problems.

[prj]

Check breather hoses.
Check MAF to turbo hose.
Check fuel pump.
Check FPR.

[x6rs]

maybe you have a bad injector? something might have clogged it? have you changed the fuel filter under the hood(feels like a longshot but check it)

shouldnt the ecu back ignition before it starts to detonate? there should be knock sensors on the car.

or is it misfiring, the oem coils on my urs4 started to behave strange under acceleration, swapped to 1.8t coils and the mystery was solved

[jimmcf]

I had the same problem on one of my old s6's never did get to the bottom of the problem, nothing showed up on vag com, it had new 1.8t coils as well. sadly a year or so after i sold it the engine wwent bang in a big way, no 5 cylinder got too hot from what i heard and melted the piston, my own conclusion was that no5 was running lean somehow. I have no evidence to suggest it was but your problem sounds exactly like what i experienced.

[prj]

shouldnt the ecu back ignition before it starts to detonate? there should be knock sensors on the car.

Well, it can only back ignition AFTER it's detonating.
But yes, it should.
After that it'll cut boost and enrich also.

Getting the injectors flowed and cleaned is a good idea as well.

[UrS4boy]

A missing and hestitation diagnostic procedure

It could be the coils. Try testing them, according the procedure in this post:

http://forums.quattroworld.com/s4s6/msgs/22611.phtml

[steve52]

Check breather hoses.
Check MAF to turbo hose.
Check fuel pump.
Check FPR.

Thanks for your help.... I should have mentioned within my initial post that this car is new to me having purchased it from a friend in September, that it is my first Audi and that it is my first turbocharged vehicle of any kind. I am also very new to the s2forum and totally impressed by the level of member knowledge and willingness to share that knowledge. That said, I do understand why you recommend inspection of the hose leading from the mass air flow sensor to ensure the ECU has the right information and I do not see any cracks or other damage to any of the hoses. As the car does have strong full throttle power, can't I conclude that the fuel pump and filter must be ok? From another post, I understand that the fuel pump regulator functions to keep the fuel rail to intake manifold pressure delta constant to help ensure accurate fuel metering; however, I am uncertain regarding how to test proper operation. Can you suggest an easy way to verify proper operation?

[newsh]

You need to do a boost pressure test to be sure that there are no leaks, visual inspection will not do. Do a search on here for the method, you'll need to make up a couple of bungs, one with a tyre valve in and have access to a compressor.

Is the ECU showing any fault codes?

[prj]

That said, I do understand why you recommend inspection of the hose leading from the mass air flow sensor to ensure the ECU has the right information and I do not see any cracks or other damage to any of the hoses. As the car does have strong full throttle power, can't I conclude that the fuel pump and filter must be ok? From another post, I understand that the fuel pump regulator functions to keep the fuel rail to intake manifold pressure delta constant to help ensure accurate fuel metering; however, I am uncertain regarding how to test proper operation. Can you suggest an easy way to verify proper operation?

Generally yes, fuel pump should be okay and FPR should be fine.
If it's really knock, then it should be caused by a lean mixture.
But the ECU should be hearing knock and pulling timing, enrichening the mixture and pulling boost.

First things first - as newsh suggested, you should pressure test the entire system using an air compressor. You need to fab up a plug with a tyre nipple which you can connect to the MAF->Turbo hose instead of the MAF.
After that block off the pipe going to the breather and pressurize the entire intake. It should hold 0.5 bar. If it doesn't, you probably will hear it, and if you hear it but can't find it, spray some soapy water over the place you hear it from.

Here is a video detailing the procedure on a different car:

http://www.youtube.com/watch?v=uixdw49Km4s

[UrS4boy]

Steve: You have a private message.

[steve52]

I had the same problem on one of my old s6's never did get to the bottom of the problem, nothing showed up on vag com, it had new 1.8t coils as well. sadly a year or so after i sold it the engine wwent bang in a big way, no 5 cylinder got too hot from what i heard and melted the piston, my own conclusion was that no5 was running lean somehow. I have no evidence to suggest it was but your problem sounds exactly like what i experienced.

Thanks. I am new to the car and the forum; but, based on the level of knowledge and the willingness of those on the forum to share that knowledge, I am confident that I will resolve the problem. For me it is a learning curve. It just may take a few weeks; but, I can drive gently for a little while longer. These cars are incredible and worth the effort to keep them on the road.

[steve52]

You need to do a boost pressure test to be sure that there are no leaks, visual inspection will not do. Do a search on here for the method, you'll need to make up a couple of bungs, one with a tyre valve in and have access to a compressor.

Is the ECU showing any fault codes?

I have not yet checked the codes although I do have the test cable and I should be able to relocate the link detailing the process to retrieve the codes as well as the code list. I see that prj has posted a link to a u-tube video illustrating the pressure test. I do have a compressor and everything else I should need for the pressure test. I will also probably try the coil test as one of the coils had failed and it was replaced by the previous owner. The other four coils are original. I will post the results in a few days, hopefully along with the confirmation of repair. Thanks again to all for coaching me along the way.

[steve52]

Generally yes, fuel pump should be okay and FPR should be fine.
If it's really knock, then it should be caused by a lean mixture.
But the ECU should be hearing knock and pulling timing, enrichening the mixture and pulling boost.

First things first - as newsh suggested, you should pressure test the entire system using an air compressor. You need to fab up a plug with a tyre nipple which you can connect to the MAF->Turbo hose instead of the MAF.
After that block off the pipe going to the breather and pressurize the entire intake. It should hold 0.5 bar. If it doesn't, you probably will hear it, and if you hear it but can't find it, spray some soapy water over the place you hear it from.

Here is a video detailing the procedure on a different car:
http://www.youtube.com/watch?v=uixdw49Km4s

The video provided the perspective needed and I plan to do the test within a few days and post an update. Thanks for all of your help.

[steve52]

maybe you have a bad injector? something might have clogged it? have you changed the fuel filter under the hood(feels like a longshot but check it)

shouldnt the ecu back ignition before it starts to detonate? there should be knock sensors on the car.

or is it misfiring, the oem coils on my urs4 started to behave strange under acceleration, swapped to 1.8t coils and the mystery was solved

The previous owner did have a total failure of coil four a year or so ago and replaced just the failed coil. I plan to test all of the coils within the next few days and I will post the update. Thanks for the help.

[steve52]

ECU Fault Codes

I have finally been able to resume the investigation. The only fault codes that blink out are 44 11/12/14/21/13 otherwise stated as fuel injectors 2/1/4/5/3. I also stepped through the output tests and the the five injector, idle stabilizer valve, carbon canister valve and waste gate valve solenoids clicked as anticipated. With regards to the fault codes, it does not seem plausible that all five injectors are at fault. Rather, I suspect that they are the symptom. Does it sound reasonable that the common denominator could be the filter (only 7,000 miles use), the fuel pressure regulator, a leaking line to the MAP sensor, or the like that the ECU reports as the fault of all five injectors?

I do hava a compressor and I am continuing to assemble some kind of leak test to better understand what the ECU is actually seeing versus what it reports. All suggestions are most appreciated.