100 BHP Down on Power

[phatfocus]

Today my dad (04' V8 RS6) and myself (84' Ur quattro) went to the rolling road. I was pleased as punch with a calculated reading of 205 bhp at the flywheel and 245lbft. (stock 200 and 210lb ft)

However, Dad's RS6 was approx 100bhp and lots of torque down on stock, and on top of that it has a MTM chipped ecu and gearbox so should be putting out closer to 500 flyswheel bhp.

The screen calculated 400 flyweel bhp, but the operator said that as it is an auto that is an exaggerated figure. So it is quite possible there is only 350-380 bhp from what I understand, the car doesnt feel very quick. There was 200bhp at the wheels.

The Mass air flow sensors were replaced when the MTM chip was fitted as it was down on power, that was approx 10 months ago.

The car is going back to the rolling road for a day for a check and probe over to see if they can find any faults. Not sure how sophisticated their fault code reading etc is though.

Can anyone help/share their experiences? are there any particularly suspect areas/mechanical failures to look for.

My 25 year old technology has triumped for now.....

[Z07]

A V8 RS6 made 200bhp @ wheels? Must be ill.

[RS6-4dr911]

check for rat's nests in the intakes:lovl: !! (it happened to me, calculated loss based on 0-60 times was around 80hp)

[grizz]

Get some new dv's and a n75 valve fitted .

[DetailersDomain]

wow I have the same problem.

we have already changed the purge valve, replaced temp sensor, checked DV's.

I'm going to have to change the dv's and maybe look at changing the n75 valve.

I have the Dahlback chip.

We reset the chip by pulling it out completely and let it sit unplugged for a few hours.
Then it works again full boost and the car kicking ass.

We get about 200-400 miles and the car stops boosting, it feels weaker than my old b6 S4.

Not sure what to do next if it doesn't work.

When we put the stock chip back in it works.

[grizz]

What fault code do you have ????

[RS6C5]

Could be a checksumm error when it logs this fault the ECU goes into limp and limits boost to 0.5bar

[DetailersDomain]

problem with my car is there is no fault code the boost just shuts off and goes into limp mode, that's the messed up thing.

[RS6C5]

That still doesnt mean that the file is 100%.

The tuner can turn off fault codes for certain things, such as if you want to run an external boost controller he can disable the N75 valve so you can remove it totally and it wont throw a code or affect performance.

If you say you put the standard program back in and it works 100% then my money is on the program.

[DetailersDomain]

I do agree with that but its an off the shelf Dalhback chip that the others have on this board and no one else seems to have the problem.

[RS6C5]

How was it loaded?

If it was flashed it may need to be re-done as the file can be corrupted during transfer. If it is a plug-in chip then they may be a dry joint on the EEPROM.

[DetailersDomain]

it was sodered on.

[RS6C5]

Have the soldering checked

[DetailersDomain]

would you think that the readiness testing is not completing.

[RS6C5]

Doesnt play a role with the issue's you are facing

[DetailersDomain]

but remember I'm taking the ecu out and resetting it each time and the car will boost and run strong then it goes into limp after 300-400 miles.

what about checksum?

or a bad ecu?

[RS6C5]

If the standard program runs fine in the same ecu the program is at fault.

The checksumm error could be causing it as I have seen this with my own eyes on an RS6 but it could also be other things such as EGT etc.

Do you have vag-com?

[CinciRS6]

Hey PYIU.....

what kind of wheels do you have on your RS6?


thanks

[HeadShot]

Can someone explain the N75 Valve, what it does and where it is located??
Is it a weak point?? If YES - replace with an aftermarket one?? Options..

i have the DVs covered.. have seen mention of the N75 valve before but never had it explained...

Here to learn... anyone want to enlighten me lol.

Thanks

[hahnmgh63]

The N75 is the valve that plays a large part in regulating the wastegate. An unenergized solenoid (0% duty cycle) permits full charge pressure on actuator diaphragm. So the turbocharger naturally regulates itself. As boost builds, the wastegate opens. The ECU can operate the N75 to vent some of this pressure so the wastegate either does not open, or opens less. For example if reading is 62.8% duty cycle it means over a 100 millisecond period (1/10 of a second) the charge pressure in the actuator line was filled for 37.2 milliseconds and vented for 62.8 milliseconds. An orifice in the charge pressure connection restricts the flow rate of charge air into the actuator system. If you are seeing a large difference between the two reading off block 115 (request high, actual low), and you see that duty cycle on the N75 is high (90-100% range), then you are probably leaking boost from a pressure hose (turbo outlet to intake manifold) or the diverter valve (DV). You should then check all clamps and hoses along the whole pressured tract as well as swap DVs.

So, when we look at, let's say, log 115 and see that actual boost is less than requested boost while ECU is yelling "somebody close that f%cking wastegate!" (N75 duty cycle close to 99%), we know there is a problem: either there is a boost leak, or the wastegate is not closing all the way (stuck).

[phatfocus]

Pleased to report that after months this car is finally sorted. It is now running approx 495bhp at the flyhweel and an amazing 783NM of torque (MTM Remap). The cause, a holed intercooler and a boost hose that would suck colapse under certain conditions.

At 88,000 recorded miles, lets just hope the gearbox holds together.

It's awesome, especially after having driven the new RS6 and been dissapionted (overweight, overpriced and not significantly quicker until 80mph plus)

I think these car's still take some beating.

[hahnmgh63]

Damn Angus, now your gonna make me pull my intercooler to fix and/or replace. This is gonna cost me time and money and I'm lazy. I'm sure I'll be happier afterwards though, as I know my right side intercooler has a leak although I don't know how large.