wrc4ever

Hey,

I hope here I can get an answer for my problem. Since more, than 3 years I have an S4 B5 Avant (in yellow, what else which seems to be much more faster than my ex-S8 Tiptronic.
The car is tuned (runs on Rothe prog.) with the exhaust and metallic cats, and the Y-pipe of the RS4 and a total opened 3 inch inox system. In the last time I often feel, that engine doesn't react on giving gas so agressively as former, and sometime s its pretty weak, better said, in the upper rpm-range (up to 3500 cca) the boost will be faded. A friend of mine has a very smart Bosch-unit, which indicated lean mixture, that is the reason of the decreased boost. Yesterday I accelerated in 3rd gear from 50 kph (30 mph) and at cca 3500 rpm I heard a typical silly firing noise from the engine, I mean the mixture became lean (it was like a chain hitting something), and the boost was limited by the electronic. I got a red traffic light, so was standing there approx a minute (maybe less). 1st gear, 2500 rpm, then 2nd gear, I gave gas, the car began to pull like a beast (as it should).
In the first days of this failure I thought that maybe the manifold air sensor mokes me, but it was replaced last year (with the turbos). Then the sometimes silly coolant temperatures on the gauge (it seems to be colder again especially in the town, however according to Climatronic its 90 degrees Cels - its the Channel 51). BUT: somehow I feel there's anything in the fuel tank, I will replace the fuel filter, and maybe that filter basket of the fuel pump, it seems me that the pump fills up that plastic basket (for example at standing while red light), but later cannot supply the neccesary amount of fuel (at boost).
Does someone has any ideas?

Thanks a lot

Kind regards from Hungary

S4ME

most common cause is the throttle body boot, splits at the clamp at the throttle body sometimes hard to see it. but it will split. happen to me at vir a couple of weeks ago. lost low end power. had faults for over boost. got to looking and found the boot split at the clamp. had a extra one with me. changed it out in about 30min. fixed

wrc4ever

Hmm.. do You mean that Y-pipe made of rubber? I have replaced that some months ago for a Samco one, it was really damaged near the clamp. I have somehow a feeling, there is not enough volume of fuel in the system, however I installed an SX Performance fuel pressure regulator, and bought an acetylene gauge D in a welding shop, so I measured the system pressure, and I have enough psi/ bars. But maybe the fuel pump is not on the top anymore, and that should be the cause of a lean mixture and reduced boost. When the engine is cold, it runs really OK, but it becomes warmer, and also weaker. I will also replace the fuel filter, it can be also dirty. Next step (if its still weak) is the change of the fuel pump, or at least to check the delivery amount of that (I think there`s a description in VAG Com with a bin, how to measure the fuel amount in 14 seconds).

The car runs on modified ECU, I also thought maybe the Lamba-data are not OKay, and I have to read them, or buy a VEMS Lambda-sensor including an LCD for the data (and for optional exhaust gas temperature data).
Do YOu maybe know, how much Ohms is the impedance of the serial EGT sensors? If there is something not OKay, it can cause also lean mixture symptoms, or?

Thanks a lot in advance

Kind regards from Hungary

30vTurboQuattro

Are you running stock diverter valves? If you do the diaphrams are ripped and you need new ones. Look into Bosch 710n's.

cavalera

I have a similar problem, the ecu request 22psi (1,5bar) and the car makes 15psi (1 bar) I don't know if it is a fueling problem because I have Walbro 255lph fuel pump, and when I remve the hose from n75 to wastegates the turbos makes 22psi (1,5bar).
Did you try that?

wrc4ever

well, I use the stock DVs, maybe that should be the problem.
The joke is, that since we have colder weather, the car doesnt seem to be weak, however in the last 2-3 weeks I drove the car only to work and back to home, so I didnt really´flat out. I think that 710n`s are a must-have even when my stock DVs - this time at all - are OK.

wrc4ever

Nope, I dondt try to remove the vacuum hose from the n75 magnetic valve. When the ECU got the new eprom, the n75 was replaced, because it was wrong. But I dont think it had to go wrong within a good year. But I´ll try. Another failure code was the too hot exhaust gas, the failure was deleted, and some months after it was failure with temporary incredible signals / values from the EGTs. They were replaced 2007, so I dont know, if it should be a problem source too. The best would be to remove them, but the danger of a melt piston becomes very-very high.