UrS4 Boost drop off at 5,000 revs :-(

Posted: Thu Mar 04, 2010 11:36 pm

This has been a long standing issue for my S4 which is now starting to annoy me slightly.

Boot the car over 5,000 revs in every gear with the exception of 2nd gear, and the boost drops off, then it hesitates and splutters a bit before boosting again at approx 7,000 revs.

I thought it might have been a coil issue, so replaced these today with set of OEM off a 56k S2, but the problem is still there (have to say though the car runs much smoother with the new coils)

Also, on an runway Wink

the car struggles to get over 120mph, again as it wont boost properly in 6th gear.......this is when the M3s start to pull away Evil or Very Mad

and bloody honda civics type r this week Evil or Very Mad

The camshaft sensor has been replaced, the plugs are fine, there doesnt seem to be any leaks in the breathing department so all thats left to check are the sensors (Beerbelly has kindly pointed these out to me before so will need to try new parts)

Is there anything else which Im missing and may be obvious to others? I dont think its an issue with the Turbo as it works fine in second gear. Goes like stonk from 1,000 to 7,500 revs in second no problem.

The reason its starting to annoy me mainly is that its difficult to ovetake in third gear as it takes to long for the boost to kick back in in 4th. I have to change gear before 5,000 revs to keep boost up, but in doing so I'm not getting the full benefit of that power when I drive.

Any ideas welcomed, its spoiling what is otherwise a top notch retro ride lol

Posted: Fri Mar 05, 2010 9:06 am

all that talk of 5000rpm reminds me of knock sensors on the 7A but it was the reverse, no power until you hit 5000rpm them WHAM off we go! dirty injectors?

Does vagCOM bring anything up?

If anything i have the reverse problem, on the top end it pulls like a proverbial choochoo its the lower end its not pulling strong. Bewildered a mazda 6 MPS on Wednesday,

Have you got a live boost gauge so you can see what its actually doing. I find the digital and the live give very different answers from time to time.

Posted: Fri Mar 05, 2010 9:24 am

As Istoo says it could well be the knock sensors, 2 on the AAN (these don't show up as a fault on VagCom)

I used to hit a 'dead spot' in most gears when giving it the beans, major splutter, down on power.

Check the insulation on all the coil packs, mine was a bit shot in places and 'arcing' across

Might be worth checking the thin plastic tube from the ECU for damage

Posted: Fri Mar 05, 2010 9:29 am

have you tried threatening it, I find that works sometimes...

Posted: Sat Mar 06, 2010 12:25 am

[quote="istoo"]have you tried threatening it, I find that works sometimes...[/quote]

pmsl!!

yes i have but not with new ownership - for once lol

will try all yea recommend, last vagcom showed cam shaft sensor problem so that was changed. Will replace both knock sensors for good measure next week, plus will check the ecu tube.

The coils came with wiring etc - insulation was spot on, they all looked new.

Car does go much better with the new coils I have to say, pulls nice Cool

till 5,000 Confused

Posted: Sat Mar 06, 2010 5:51 pm

Have you thought of fuel pressure? Put a gauge on it? Also how long since the fuel filter has been changed? Are the plugs the correct type?

If its any consolation, i have the reverse problem with my S6, hesitation on boost untill 5000 then pulls well, saloon pulls perfect, tried swaping ecu's and its the same. From the sound of it i may try knock sensors too.