Boost and the auto S4

Started by attilathehun, July 13, 2011, 03:31:27 PM

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attilathehun

When I bought my car it had some codes that I just lived with through lack of time and inclination. The MAF showed static on my VAGCOM error code reader doohickey and the N75 valve had a open/short circuit code. The car wouldn't idle worth crap unless you unplugged the ISV. Obviously I had very liitle performance :-[. So---I installed a MBC and set it up 2.1 bar MAX on the gauge and all was fine >:D.

SO the car was running without the MAF and just using default ECU settings as per TPS, heavy as all hell on juice. This week I got some time on my hands so I decided to investgate. Turns out the the loom has some broken wires due to a PO or POS mechanics efforts. The N75 wire was broke off as well as 2 of the wires to the MAF. The one that actually sends the signal as well as the one that heats the MAF filament for one second post shutoff.

Repaired the wires by splicing in some new wires and Viola as the frogs would say. I now have a perfect idle from cold start up, N75 works and my MAF works. NO MORE CODES. -all gone after clearing and no return after a quick burn on the highway.


HOWEVER, the most boost I see on my lcd dash gauge is 1.8 BAR, now I know my manual used to go to 2.1BAR in overboost when I floored it. My question is, is the auto limited to 1.8 BAR?

RS ZWEI

1.8 Bar is 26 PSI and 2.1 is 30.
Your car shouldnt be running anywhere near that amount of boost.
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2005 Mini Cooper S
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00quattro00

Its 1.8 bar absolute so its actualy boosting .8 bar
Land Rover Discovery 300tdi
Land Rover 110 4bd1t

attilathehun

#3
 ;D Thanx Basil - that absolute thing catches a lot of people. So back to the question, does the auto also go to 2.1 ABSOLUTE boost? I suspect I may have a dodgy BPV or the N75 has been inoperative for so long its not opening fully or or or ....

attilathehun

 ??? I may be misreading this, but apparently the auto transmission has its own ucu that can cut back the boost if it detects too much torque. Anybody have an auto and can tell me what boost they pull please?

RS4

You need to run some diagnostics and look at the torque limiters on the transmission on the ecu files.
Easy to modify if you want more power/boost etc.
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00quattro00

Quote from: RS4 on July 14, 2011, 09:11:07 PM
You need to run some diagnostics and look at the torque limiters on the transmission on the ecu files.
Easy to modify if you want more power/boost etc.

Are you able to easily modify the AAN 5cyl ecu and tcu files?
Land Rover Discovery 300tdi
Land Rover 110 4bd1t

user2154

#7
The most I get on my auto is 1.8bar, normally, except I know I have seen 1.9 at least twice, 2.0 maybe once I am sure when it was raining and quite cold one day.

I have replaced a lot of items since I have owned the car hoping to fix my "limited to 1.8bar" problem (but now I am pretty sure 1.8 is the norm for autos), but mostly because of my own boredom and wanting something to do... and I like buying stuff online... lol..

So before you go and waste your money, here are some of the things I have replaced over the last couple of years. None of this made any noticeable difference to anything, except that the O2 sensor did seem to make a slight difference to fuel economy, for a short while at least.

N75 (I now have a spare)
PCV breather valves (this needed doing)
cleaned PCV pipes & intercooler of oil sludge (lowers octane of fuel)
cleaned TB and ISV of varnish (with carb cleaner)
new O2 sensor (this was probably due)
new forge diverter valve (my OEM was blown, didn't notice a difference so I assume a working DV matters more on a manual driven by a boy racer than an auto driven by me)
fuel pump (apparently they need doing well before I did mine @ 260,000km, no difference)

The N75 plug for the harness is the same as the plug on your brake reservoir, one you need, one you don't. Or you can order the plugs, I'll see if I can find the link... no I can't sorry.. somewhere on forums.quattroworld.com/s4s6

attilathehun

Thanks for that, its kinda what I suspected. I have reinstalled the Manual Boost Controller and my auto boosts 2.1 again -wheee. The MBC actually seems to work a lot better than the N75 as it seems to boost much earlier (subjectively) than what the WGCV allows it to.

I suspect my fuel pump may be on the way out, as it just randomly dies when the fuel tank drops below quarter,   :-\ --unless the fuel gauge is just wildly inaccurate.

user2154

Quote from: attilathehun on July 23, 2011, 08:11:09 PM

I suspect my fuel pump may be on the way out, as it just randomly dies when the fuel tank drops below quarter,   :-\ --unless the fuel gauge is just wildly inaccurate.

It's possible that if it has been replaced before then the arm with the float on it is getting hung up on the internal fuel line or on the fuel pump power wires... and not going below 1/4 or whatever.

It's easy to check, there is a hatch under the carpet on the hump in the boot, or you could wait for it to run out and then fill it up with 80 litres.. if you have a spare $180.00 that is :)

http://www.audiworld.com/model/s4/94/94-s4.shtml