Mother says clean your FSI fuel injectors

Justin suggested starting a thread about FSI fuel injectors and the potential problems caused by carbon buildup on/in the injectors. There’s not much information specific to the RS4 available on the subject so this is a good place to start.

I’ll start with my recent symptoms and the diagnosis that led me to cleaning the fuel injectors.

Surging idle - Idle was constantly fluctuating
Rough cold start - The cold start cycle was extremely rough with RPMs approaching 2000

Other possible symptoms:
Engine misfire
Performance loss
Increased Fuel consumption
Engine damage - Possible in the event of a fully clogged injector. There have been a few documented cases of this.

In our cars the fuel injector heads are exposed to the combustion chamber so they can get carbon on/in them just like our intake valves. Fortunately the buildup is not near as dramatic as the on intake valves. However, when you have a tolerance of 1 micron any amount of carbon buildup can affect the injector flow in a big way.

When I had my injectors cleaned, the guy said he found sludge inside the injector filter baskets. I’m still not sure on the cause of that or if it should be expected on our injectors.

Fuel trim data is a good place to start if you think your injectors might be clogged. Look at VCDS measuring block 032, which shows your long term fuel trims at idle and load. Short term fuel trim can be monitored in block 033.

A clogged fuel injector will inhibit optimal fueling in the motor. The ECU will see this lack of fuel over time using the O2 sensors and call for a permanent fuel trim correction. Looking at measuring block 032, a clogged fuel injector will cause a positive number to show up in the Partial field(Partial means at load). In my case it was showing between +5% and +6%. While these numbers are in spec, we really don’t want to be running lean. Lean is bad for performance.

If you have positive long term fuel trim at load(block 032 Partial field), you can be fairly certain your fuel injectors are not flowing optimally if your car meets the following conditions:
Good O2 sensors - Bad O2 sensors can cause inaccurate fuel trim readings
Good fuel rail pressure on both banks - Check measuring block 106
No vacuum leaks - Check the Idle field in block 032, it should be slightly negative.
Normal short term fuel trims - Your short term fuel trims need to be within +/- 10%.

Clean your damn injectors! Like with soap and water dummy. I wish it was that easy.
You’ll need to either:
Buy a new set of injectors, which is a minimum of $800. Part number 079906036D
Send your injectors off for cleaning, should be around $200 + shipping. Look for someone with an ASNU machine. I used but it’s best to find one in your region to minimize shipping time.
If you opt to buy a new set you will minimize down time and have the option of reselling the old ones after having them cleaned.

Here’s a data sheet showing injector flow results before/after cleaning. Two of the injectors were pretty bad off. I’m guessing those were both in bank 1.

Please share data. I would like to see long term fuel trim data from other RS4 owners. If you have any of the symptoms listed above, please consider servicing or changing your fuel injectors during your next carbon clean. If you have a positive LTFT >10% on either bank you might not want to wait that long.

Technical gurus, please add to the topic.

good find and good read !

So apparently our injectors are made by Hitachi. I found part number 079906036D for $57.79 on Rockauto. Meem’s motor failed with these injectors, but who knows if the proper part was sourced or if they just got a bad batch.

The OEMs MSRP is $200 and can be gotten for $134.40 on Jim Ellis Audi’s site.

My plan is to have my injectors cleaned every 2 carbon cleanings, or 40k. At $57.79 it would be worth it to buy a bunch of them and have them flow matched to within 2% for optimal performance.

Hitachi part is FIJ0008. Some ebay sellers are as low as 50 bucks.

Have 8 of these lying around for months already but not installed yet. Meem’s car blew shortly after supercharging which makes it somewhat less likely the injectors were the cause I reckon.


Excellent information!

I’ve read read several posts in the forums regarding engine damage as a result of adding superchargers. Just by looking at the information you posted I have to think that poor performing injectors could be a direct cause. For example - where a cylinder runs lean under boost. If you are spending the money on a power adder I would think for reliability sake and, at the very least, you should clean your injectors or have them flow matched. Komseh had idle issues in NA but exaggerate this differences under full boost and I can envision damaging lean conditions within the engine. It takes only a second or two to destroy an engine.

To follow up on the OP’s info I found an article which I’m cutting and pasting below to preserve. It basically describes the exact issue that Komseh was experiencing and elaborates a bit more on the theory behind the issues.

[i]EVEN THE LONGEST journey begins with a single step’ is an often heard saying used in the context of motivating folk whom are finding it hard to begin a big task. During my feature job this month, a 2007 Audi RS4 V8 FSi with 60,000 miles on the clock, this phrase kept repeating in my mind. In my case though, I was soon wondering how I’d managed to get myself involved with this repair. Well, it started with a fault code.

The initial customer complaint was that the engine warning MIL was coming on and the vehicle was intermittently suffering from rough running – it was hesitating as well as misfiring and it had a flat spot on acceleration. The fault codes related to multiple cylinder misfires and an air flap implausible position. The driver had owned earlier versions of this vehicle type and was prepared for the ‘cost of ownership’. We discussed a few different scenarios and agreed a budget for initial assessment.

The FSi system has its fans and undoubtedly the technology used is top quality. However, there are inherent design flaws in the way it is implemented on this vehicle. In fact, there are three distinct areas for concern. Firstly, is the triple vortex oil separator design used in the crankcase ventilation system. This uses a vortex ‘swirl affect’ to throw oil particles out of the crankcase gasses prior to allowing them into the intake system. In theory this is brilliant but in practice, it doesn’t really work. The oil vapour reaches the relatively hot intake port and valves and makes a ‘nest’. It is not unusual to see the intake restricted to less than half of its original ‘clean’ size. This restricted breathing leads to flat spots in the performance of the engine.

Secondly, there were the problems with the EGR system. The direct fuel injection (FSi) system, when running in lean burn (stratified) mode, suffers from high combustion temperatures, due to the lean cylinder mixture. EGR is required to ‘pad’ the cylinder volume out with inert exhaust gasses rather than air. This means that a lot of hot exhaust gas and combustion particles re-enter the intake system; this bakes the intake system oil residue onto the inlet system. Also the direct petrol injection FSi system does not allow the fuel to act as a detergent on the ports as it is injected, unlike a more conventional system.

Thirdly, the direct in-cylinder fuel injectors face the harsh environment of the combustion chamber. This means that they can suffer from a build-up of carbon on the tips and, due to the higher than normal injector temperatures, lacquer or varnish is said to occur inside the internals of the injectors restricting fuel flow. Direct petrol injection is a great way of ensuring maximum utilisation of the fuel injected with characteristics like great atomisation, precise metering and excellent mixture formation. However, you’d be right if you are starting to think that the FSi engine has the potential for some real issues.

Actuator test

I used the Autologic to run an actuator test on the intake manifold flaps, both sides of the ‘vee’ seemed to be moving. On closer inspection though, the right hand bank wasn’t quite as it should be. Using the borescope, I could see that the flange attaching the actuator to the flap shaft had a large crack which prevented proper movement (access in situ is a real problem). It looks as though the manifold would have to come off to progress the repair.

Next, were the intermittent running problems of misfire/flat spot/hesitation. The plugs had been replaced on a recent service but I chose to remove these and check the coils and plugs for serviceability and signs of mechanical cylinder malfunction issues. All looked good. I used the pressure transducer in the cylinders whilst I was examining the coils and plugs, running a compression test, to rule out valve train malfunctions (sticking valves). The MAF sensor also checked out fine when tested on the scope.

I used the diagnostic smoke leak detector to flush out any minor manifold air leaks, which may cause similar issues, but this test passed O.K. as well. On scoping the ignition system on roadtest, the firing lines were quite high and the spark line voltages were kicking up at the end, indicating a lean mixture even during non-lean burn mode.

Misfire counting

Using the live data cylinder misfire counters, I could see random cylinders incrementing the counter. At the same time, the oxygen sensors were reporting excess air. The gas analyser didn’t show a significant increase in HCs (of course, these may have been cleaned by the cat converter if there were any). At this point, I considered mixture problems (intake coking/injector poor flow) to be the root cause, so I had to take the manifold off after all, just to access the injectors. On removing the manifold, I could see that the intake ports were extremely clogged; they needed remedial cleaning as well as an in-situ de-coke to enable the engine to breathe properly (Figure 2) . I updated the customer and he sanctioned the work.

The fuel injectors were removed and tested on the ASNU fuel injector service machine. The spray patterns from the injectors were uneven; the final flow test (Figure 3) highlighted a large imbalance between injectors. A 40 minute session in the ultrasonic bath, followed by a reflow (with new filter baskets) showed that the flow was much more even (Figure 4) .

Following the intake flap diagnostic trouble code, I inspected the underside of the manifold and could see more clearly where the control rod had detached from the arm. These were not available separately as they come assembled as part of a new manifold, which costs an unbelievable £1,900+vat!

Once the V8 was back together, I reset adaptations and ran through a throttle re-learn. Idle was nice and smooth and there was no misfire. The owner commented that the vehicle pulled much better and was a nicer drive altogether.

Customers often want to know the cost of the repair upfront. This is never easy to do. A staged approach is considered by many to work the best. It is easy though to see how a ‘simple’ fault can end up in a complex repair and communication is the key to maintaining customer confidence. The Audi’s fault was larger than the initial diagnosis but the cost ‘vs’ value equation still balanced, however, it’s easy to see how either lower value vehicle could be easily written off or a higher value vehicle, as the owner who can’t really afford to run it. [/i]

Leads to several questions:

Are there any newer better injectors? Updated spray patterns? Does that even matter?

Per the article is the EGR hot air injection preventable?

Is there a better oil separator design?

Great article there, just reinforces the importance of validating proper fueling for this motor. Some people may be overlooking dirty fuel injectors as the potential cause of common driveability and performance issues. If you rush into a forced-induction modification with a pre-existing lean condition, you’re gonna have a bad time.

My car went ~85k miles before showing symptoms, but the onset of symptoms also coincided with removal of the intake runner flaps. I’m wondering if the intake runner flaps played a role in “hiding” the symptoms by reducing intake air flow at idle and cold start. I’ve also been wondering how long I had before a complete failure. I wish I had known what I know now about fuel trim diagnosis before I started having symptoms. The fix would have been a lot quicker and cheaper.

I think fuel injector maintenance should be integrated into the maintenance schedule on these cars. In a forced induction configuration I think it would be wise to frequently monitor fuel trims to detect a lean condition caused by partially clogged injectors as soon as possible.

As far as improving the injectors, I don’t think there’s anything to be done. The injector fouling is just a symptom of them being exposed to the combustion chamber.

I think there is a forum member testing a metal version of the oil separator of their own design, but he hasn’t posted any results on that yet.

Going to read this later and will add my finding once I get my injectors back from being cleaned and flow tested.

I’m starting to think you’re right. This is becoming more than just a couple outlier cars, this is now a thing. Great work/research and thank you again for posting up your findings.

Wonder if there’s anyone in the GTA who does this. Shipping my injectors to America for a week is not an option.

Start here maybe?

The Canadian guys are actually 2x farther away from me than the American ones lol

Koolade9 thanks for posting that! I’m going to email that company now, there is also a local diesel shop to me called BDdiesel have a friend working there, I know they do rebuilds as I was going to use them, but I’ll double check if they have an asnu machine.

BD Diesel also has a asnu machine, they will be getting my injectors as my shipping cost will be driving about 2 blocks to their shop lol!

Ozcar, make sure they have 8x of the nylon bushing that fit towards the bottom tip of the injector. My guy said they are the same for most GDI injectors. He had to order them from somewhere in Kansas since he only had 6 in stock which extended the service time a few days.

Here is a place in the GTA for you guys


Do you happen to know if FWP! changed his injectors when he was troubleshooting his pinging issue after the JHM tune? I know he did a lot of stuff, not sure if it included the injectors.


Doubt it. He instead called flying fat fuck and badneighboirhoodalwaysgettinhomeinvadedrs4 for advice on how to proceed. Their advice? Skewer jhm online.

Thanks! I emailed them


Haha yeah I love how that guy has just laid into JHM for giving him bad tune/parts. The same parts that their many hundreds of customers run without problems.

Anyway, I think a lean condition could definitely cause the pinging he was talking about. All I saw him mention was that he changed a bunch of parts per the recommendation of various people. I wonder how much actual technical analysis was performed on the cause of the problem.

That’s a negative.

There were some basic maintenance items that needed to be addressed regardless. Beyond that, we narrowed it down to a TB that was acting significantly different than mine (I had him swap mine in to prove it out). When I looked at my logs vs. his, knock voltage (across all cylinders) was nearly 10x higher than mine in similar ambient conditions. My thought is the TB is sending the ECUs incorrect throttle position feedback, but I couldn’t find a procedure on how to test the TB…

However, it wouldn’t surprise me if there was a looming injector issue exasperating the problem…