2 problems with s4 - down on power and knock from clutch

[gareth215]

Hi, just got my S4 avant that I bought on ebay its a 1998 Avant with full service history and 84000 mils.

But it has two problems, it is meant to have had a remap circa 315bhp (dts i think) but feels like it might not even be making the standard 260BHP to me the car seems to drive perfect ly smoothly although a diagnostics check has shown a misfire on number 2 cylinder (which has not been fixed by new coil) I think there were also a couple of boost fault codes.

The car has within the last 300o miles had a cambelt and MAF.

Any ideas? so I can point my mechanic in the right direction.

The 2nd problem is that the when taking up drive on the clutch unless you are very smooth there will be a pronounced knock/clunk from the transmission, again any ideas - the previous owner said he had a new clutch and dual mass fly wheel fitted about 3k ago.

Thanks for any advice.

gareth

[quattronutter]

could have worn box or engine mounts or prop centre bearing causing the clonk,most likely have a boost leak causing the problems

[gareth215]

is the prop centre bearing a common problem? cant hear a boost leak, any common places where boost leaks occur? cheers

[quattronutter]

could have sprung a leak anywhere,you need to pressure test it,get it up in the air with the engine running and someone operating the clutch to locate the clonk if you cant find any play in mounts etc

[Trig]

cant hear a boost leak, any common places where boost leaks occur? cheers

Throttle body boot.
No you can't hear it unless you know what to listen for, or its a BIG leak

[Bluebrakes]

Personally I would just do a full check on everything if you can or take it to MRC for a £50 health check depending on where you live.

I would certainly check the Diverter Valves with a hand vacuum pump.
Check the system for pressure leaks on inlet. A bit of DIY involved here.

Despite the MAF sensor being new I would check it anyway. Ideally using vag-com to monitor it whilst engine is running and taking it up the road with a 2nd person. Just because it hasn't logged a fault code does not mean its not on its way out. If it was bought from audi it should be covered under warranty.

It should peak at around 0.8 of your horse power. So for example, around 214-220 peak maf on a standard s4. If the maf is kaput then you might get fault codes suggesting the engine is running lean on banks 1&2. Also you would get lack of power. You could temporarily disconnect it and take it up the road, see if there is any difference. Be careful though, when you disconnect the maf sensor you loose traction control and ABS (as the systems need a load signal from the engine). If it makes a difference (seems more powerful), suspect the maf sensor. Don't get tempted to leave it off until you buy a new one. The engine management predicts the MAF readings based on throttle position and therefore cannot make an accurate judgement so may run richer than it would do normally, and this could eventually damage you CAT.

014,015,016 - to check for missfires, it may reveal bad plugs/coils

block 020 should not be retarded by more than 5 degrees i think.

That should keep you going for the moment

[Bluebrakes]

As for the clunking, it could be down to a few reasons.

1. Too much backlash in differential.
2. Worn drive shaft joints CV etc.
3. Gearbox.

Does it clunk in neutral?

Does it only clunk in gear?

P.S I would be a bit worried if you are having to ask a forum for advice for your mechanic on issues such as this.