I hate to put a damper on things in there, but is anyone here concerned about carbon buildup on the 991's direct injected engine? I've heard rumors that people have had problems with the DI 997.2, but my dealer says they haven't seen any in service (no surprise) and a quick search on the boards isn't showing a lot of talk about it.

I'm currently driving an Audi RS4 that is direct injected and I've needed numerous carbon cleanings because of the problem. It's a bit of a pain to have to have the dealer (or outside shop) remove my intake manifold and manually clean off the intake valves every 10-15k miles.

I'm planning on ordering a 991 C4S when they are announced, but I'm a bit worried about going from the frying pan into the fire. Maybe Porsche did something to prevent the problem with the design of the new model?

Thanks for any input / insight you guys can give.

 

Hi brianja,

I don't have an answer for you, but this worry has entered my mind a little as I went through the same thing with my RS4. My dealer pleaded ignorance to the issue as well, but I knew of other RS4 owners who had been to that dealer with the same situation. I remember after the first cleaning my car felt like a supercharger had been installed - so drastic was the power loss due to the carbon buildup on the intake valves.

I've been out of my RS4 for a bit, but what I remember is that the problem was EXTREMELY common. It seemed that either you had the issue, or you didn't yet know you had the issue!. I had my intake valves cleaned for the first time around 15,000 miles, and I recall that being about the time most were noticing a problem. I would guess, in general, most 911s don't get driven as many miles per year compared to most RS4s. Hopefully, this issue is not common with the 911 engine, but maybe only time will tell?

Excuse my ignorance, but was the 997.2 the first 911 with Direct Fuel Injection?

Either way, I can't wait for my 991 to arrive - dirty intake valves or not.

 

I drove my 997.2 for 21k miles and didn't notice any power loss

 

This is going to be pretty interesting going forward. I do know that diesels have this direct injection stuff for a long time and do not seem to have any averse effects but then.... as one of the responses state.... it happens slowly and the driver may not even feel the change.... perhaps until some CEL light gets triggered. Hopefully we get some good input and discussions on this board...

 

The RS4 was very well known for this issue. On the other hand there are PLENTY of Direct Injection gas engines on the market. Let's hope that issues on early generations were the exceptions. I can not imagine that Stuttgart engineers have not checked this...

 

There are new fuel injectors in the 991 which are 6 hole rather than 1 hole in both engines. The hole pattern for the 991 is 1 in the center with 5 around. The old one tried to produce a swirl pattern and the new one does not. Hopefully if there was a problem, this will cure it, although my 997S has 27,000 on it and I don't have a problem.

ChuckJ

 

I don't think the design of the injectors will have any impact on a carbon build-up problem since the injectors are downstream of the intake valves on a DFI engine.

 

You may be right, but these squirt directly in line with the injector and the other is shown to have a lot of swirl and flame at the injector. The normal model gets two squirts per ignition and the S gets up to three, depending on RPM.

ChuckJ

 

As a weak data point, my car is a 997.2 Carrera with DFI and is about to turn 50k miles on the odometer. I haven't noticed any loss of power, excessive oil consumption (based on owner's manual) but just a bit of sooty exhaust tips. Everything seems good so far.

I'd love to see the intake valves to know for sure but otherwise, none of the Audi-like symptoms here.

 

You seem very knowledgable to me! I am reasonably sur the 997.2 was the first DI system and came in on the 2009 cars. That, plus a boost in power on the S (at least), a crank shaft fix, and more up to date electronics (blue tooth, sat. NAV. Instead of DVDs) were some of the biggest changes from the 2008 997.1.

 

Thanks AG991! I'm going to show this to my wife.

 

Happy to help. I wish you better luck than such posts would bring me!

 

My 997.2 had about 44k on it when my 991 arrived and I can't say that I noticed any power drop. Lots of soot on the exhaust though.

 

I have a 997.2 S with 26K miles on it; I am about to put the X51 power kit on - I will obtain empiric data when they take the intake manifold apart to see what it looks like inside. I know that Audi has blamed US gas on the DFI problem, BMW denies it whilst M5 V10 owners sue, and Porsche has been silent on the issue. I am very curious.....and as some on this board state, there is no empirical information yet....

 

Thanks for the input. Were you active on any of the RS4 boards while you owned? I'm pretty active on Quattroworld (Audiworld before that) and I check in on a lot of the others. I organized the NYC Spring RS4 drive for a few years.

15k seems pretty normal for the RS4s to need a first cleaning. I made it almost 30k the first time, but it has been 15k and 10k miles between cleanings since. It's getting annoying. Thankfully, my dealer has been very good to me on the issue and I haven't paid for any of these cleanings out of pocket like a lot of people.

I agree that the relative lower usage of 911s in general will make it harder to notice the trending problem (if it exists). I guess it will just take longer. While in the RS4 it may take 1-2 years to hit that 15k mile range, it may be 3 or 4 years for a lot of the 911s. That won't be true in my case, though. I'm going to rack up miles like crazy. lol

I'm really hoping that they have addressed the problem somehow. I believe that a few manufacturers (Acrua?) were adding an additional injector into the intake to spray just enough fuel to wash down the backs of the valves and keep them clean.


Both of you guys have a nice number of miles on your cars. That's very encouraging! Any problems with a rough idle on cold starts (especially in low ambient temperatures)?

The problem with Audi's carbon buildup is that it happens so gradually that you really don't notice the power loss. I have a series of dyno plots I made with a friend's car over the first few years of ownership. We dyno'd it a few times as he racked up the miles. He didn't feel any difference in driving it, but the numbers don't lie. After a carbon cleaning we re-dyno'd to see a bump of 40whp. It felt like a different car.


Please report back and let us know what you see. I'm very curious.

Audi did blame the gas for a while and in order to have a cleaning done under warranty it was a whole production. You had to bring it in once, have them put in a bottle of injector cleaner and drive around for a while. That usually got rid of the CEL for a while (2k miles maybe?). When the light came back and you brought it back in with more misfires they would then do the cleaning. At least they are willing to do something about it while you are under warranty, though.