2.7 MRC advice

[Jason Burchell]

hi all,
I recently bought a b5 s4 with rs6 turbos and rs4 maf.
I have just been to mrc and had the timing belt done. I also went with a low boost problem.
When I bought the car it was really fast. Damn angry power but also difficult to drive at very low speed in 1st or 2nd.
I scanned it with vagcom and cleared the codes. It came up with coolant temp sensor and both the lambda sensors.
Once I hade done this and reset the learned values it lost most of the power.
Struggling to make high boost. Where it used to be really angry and boost was almost instant.
Anyway. I had an issue with soldering in the EGT's that fixed them.
The car then didn't run rich and reported no faults for days. Still low boost.
I went to mrc for the timing belt, Doug also fitted the coolant temp sensor and a new N75, he said I had the old type and it was most likely the reason for the loss of boost.
Once he was done and road tested it he told me I was making 20psi. He checked the last time it was mapped and the car was pulling less timing and was making more in the region of 25.5psi
When I bought it it was making 25.5 and a simple fault code clearing lost all the go goes.
I'm thinking that replacing the standard DV's and getting a boost leak test will get me on the right path.
Still I don't exactly know what to do. Are there actually and good DV's and what ones or should I stick with the Oem Bosch ones.
Does anyone have any other suggestions and advice how to fault find a car that reports no faults but clearly isn't right.

 

[aragorn]

What did doug suggest? Surely they should have boost leak tested it when it was there, given it was down on power etc?

OEM DV's are fine.

 

[Jason Burchell]

It does have a leak on the offside turbo inlet.
I'm not sure what to do to fix this. They didn't have the bits there, I wasn't walking home.
I need to somehow work out what bits fit between the upgrades. I have RS6 turbos and RS4 maf.
After that I don't know.
I have a local garage with a smoke leak tester going to check it on Wednesday.
I think I also need to get the exhaust looked at a bit. Sounds like it's blowing from the flexi joint.

 

[desertstorm]

Seems to me MRC have pointed you in the direction of where the boost leak is so why are you now looking at changing the Dump Valves.
Fix the Boost leak and go from there.

 

[Jason Burchell]

I will be fixing the boost leak. I do also think the DV's might be tired. I know they work but that doesn't prove that they hold the boost.
Once the leak is fixed.....

 

[aragorn]

bear in mind theres no boost present at the turbo intake.

Often they might leak when pressure tested but dont actually cause any issues when driving normally, as they're never under pressure.

They have O-Rings which seal onto the intake pipe, i guess the orings are just tired.

DV's are cheap so might as well stick some new ones in.

 

[Jason Burchell]

That is what I'm thinking.
It seems odd that the car was incredibly quick, I clear the faults and reset the learned values so I can see what faults come back. From then on far less power.
No faults found and I check daily.
The only thing that is definitely different is the n75 as it was replaced with "the new type" at MRC.
I don't know what else to do.
The cars power has gone from OMFG that's damn fast to quite quick but not astonishing. I hope that my description there kinda explains how much of a difference.
On the cars gauge it had a measured peak of 24.5psi. It used to get there almost instantly and it had a lag time so short that it wasn't an issue. Now it's much slower to raise the boost, only hits 22.5 on the same gauge eventually instead of almost instantly and the lag is much bigger on gear changes.
When MRC logged it it was pulling more timing and making less boost than when it was mapped before. They have copies of logs and the map from when they mapped it.

 

[aragorn]

Well a leak means the turbos will take longer to produce boost, as a % of the air its pumping is escaping.

The bit i dont get, is the people most qualified to say whats going on are MRC. They mapped it originally, and they had it in their possession with the current fault present, and they know pretty much all there is to know about these engines. So why didnt they diagnose it?

The difference between 22 and 24psi might be nothing to worry about, the ECU adjusts the pressure based on various factors, its very cold just now, which will generally mean less boost is seen. The question is why the car is now slower, despite making largely the same boost pressure.

Is it running the same fuel?

MAF could be dying?

Again though, all just guesswork.

 

[Jason Burchell]

MRC had a long day doing the cam belt.
Told me of a leak on OS turbo inlet but didn't have parts to repair it in stock.