Hesitant motor this evening...

[mac4RS]

I'm on holiday this week in Somerset and had the opportunity to have an hour on an Airfield which has a good driving circuit round it.

This is the first time time that I had driven down a runway...

Approx 1.1 mile long, very smooth, dry conditions & no wind, I wondered how fast I could go...

Had a trial run up & down before starting a quick run. Everthing was alright until about 130'ish, and then it was hesitant between that & 135, and was hard work to reach much more in speed.

Had a few more runs & the same thing happened, reaching about 140. Gave my daughter a drive round the airfield (had to - that was the deal for driving there) with a few runs down the runway again.

Temperture now up to about 118, but still slighty lumpy around 140. The last run we just hit 150...

Any ideas guys?

I will say that a couple of weeks ago on a certain road in Europe hit 165 with no problems...

Mac

[PetrolDave]

Bad fuel?
What was the temperature when you hit 165 a couple of weeks ago?

[Andyuk911]

The only way you are going to find out what it is, is to go to a dealer or plug in VAGcom. Can't see it being fuel as the ECU would pull back the timing to cope. Most likely a coil pack. Do you not have a problem say in 2nd gear going from 10mph to the limiter ?

If you want to do high speed runs, use good fuel, check oil and clean the air filter. Obviously in addition to any safety checks looking for nails in tyres etc

[mac4RS]

I don't think it is the fuel; always use super. Wasn't sure what the temperature was the other week, but probably slightly less than the other night. No problems in 2nd gear either. I'm also quite careful when it comes to safety checks etc Andy, including tyre pressures.

My problem seems to be like George1976's on the thread 'Hesitant @ high RPM'.

Certainly wasn't right tho'. Will take it to my local dealer next week. Hope this is not another widespread problem like the DRC...

[silverRS4]

..Can't see it being fuel as the ECU would pull back the timing to cope.

Thats correct. However, if the timing retardation gets excessive (pulling out 8-10 degrees under load, rather than 0-4) there are many things that are effected. The "power surge" at 5500 rpm, as well as the smooth power delivery from the RS4 engine when its running properly, is associated with many things working together. This includes the intake flaps, which open at 3500 rpm, the airbox power flap which opens at 5000 rpm, cam timing, and intake/exhaust tune effects - the latter being inherent to the engine. I have yet to pinpoint the exact cause/affect, but when timing retardation gets excessive, the power surge disapears and the high rpm power (6500-8000) is noticably decreased. If the ECU was taking out 10 degrees of timing, that alone would have a significant impact on power. As power output decreases, the relative "load" recognized by the ECU is actually lower even though you have the throttle at 100%. Many of the great characteristics of the RS4 engine are "load" dependant (i.e., below a certain load threshold, they simply do not happen). Bottom line, when lots of timing is taken out, the character of the engine changes dramatically. Why is the ECU taking the timing out? Well it could be the fuel or any carbon buildup in the combustion chamber. Or I could be completely wrong. Hooking up to VAG-COM would certainly help.

Most likely a coil pack.

Possible, but usually even intermittent coil problems will cause a CEL/MIL. An outright bad coil will cause one for sure.

[Marcus-RS4]

is there any additives that you would recommend to clear any carbon build-up? Pref something that I dont have to dissasemble the engine to use

[silverRS4]

Again, this is my opinion, but I think carbon build-up in the RS4 engine is responsible for a large number of problems. Reduced air flow into the heads, impeded fuel spray, damaged injectors, retarded timing, damaged coils, etc. I have 10k miles on my car and I've had my intake valves cleaned twice. Since I posted the results of my intake manifold work, I get private inquiries from abroad and the first thing they say after they manage to remove their intake is "geez, I can't believe the amount of gunk on my valves!". This is both on UK and US B7 RS4's. In fact, I do not know of one instance where a manifold was removed and there was no significant buildup found on the valves. The jury is still out on just why the 4.2FSI volatizes so much oil but at the very least the oil formula used should be a synthetic intended for direct injected (pump duse) engines. And before anyone asks, the engine is already equipped with a sophisticated "catch can". Its a multi-stage venturi system that separates the oil vapor out of the crankcase ventilation air.

After my second valve cleaning, and when I started using a high quality fuel additive from here in the US, the engine is running consistently better. I'm sure something is available in the UK (anybody have suggestions?). Good cold starts, no strange power losses, a very consistent power delivery. Data logging shows consistent mass air flow, good power, and little, if any, timing retardation. BTW, almost all strange "hesitations" or power losses that feel like a big head wind just hit the car are timing related.

But if any RS4 engine has the typical intake valve buildup, it would have to be cleaned first (by removing the intake). Its a job for the dealer or a very good mechanic. Any fuel additive is more of a "maintenance" tool used to keep the buildup from occuring. Possibly at a very high concentration it could have some impact...

Does your car have any history of codes at all?

[Oli]

Forte addidives are one of the best on the market over here, and I would strongly recommend them over any other make

[Andyuk911]

My car makes excellent power. I can't speak for the US, but in the UK I feel we have better petrol.

My car has never shown any of these problems as describe.

I put this down to the use of fuel .. I have mainly used Shell, some Tesco 99 and BP Ultimate(note Charlie of Surrey RR said to me that cars on BP Ultimate have been know to make less power .. possibly down to a lack of sales and thus 'old' petrol. SO ALWAYS use a busy petrol station.)

Here are some pictures that say a thousand words and explain the benefit of using high quality petrol ... they have more cleaning additives..


The first picture shows the probes into the manifold






Here we see the side that is running on BP Ultimate












Here is the side that is running STANDARD BP petrol







This picture shows the TWO tanks in the boot.





I hope this goes to explaining how looking after your car with good quality petrol will be rewarded.

Oh ... I don't work for BP ... in fact nobody!

[Marcus-RS4]

Oh ... I don't work for BP ... in fact nobody!

Still not Andy?

[silverRS4]

What engine is that exactly? Since I can see what look to be the fuel rails, it must not be FSI? There is no doubt that high quality fuel with additives can keep valves clean. That type of diagnostic imaging would be very interesting on a 4.2FSI. Thank for posting them.

[PetrolDave]

What engine is that exactly? Since I can see what look to be the fuel rails, it must not be FSI? There is no doubt that high quality fuel with additives can keep valves clean. That type of diagnostic imaging would be very interesting on a 4.2FSI. Thank for posting them.

It's certainly not a S4 or RS4 - wrong engine bay layout - look at the moulding that the monitor screen is standing on...

[Andyuk911]

I cheated, LOL, it is non FSI

[chris.s]

If this is the same car as I saw at the Autosport International show at the NEC earlier this year (and it looks the same) it's an A8 with the 4.2 V8

[almeister09]

Take a look under the air filter housing.There is a vacuum valve under there which is prone to splitting on the bottom edge.
You can access this part via the o/s/f wing liner. Replace this valve and you will all be surprised of the running difference. Especially at high RPM and speed. The valve "split" opens due the high amount of vaccuum being generated .