Misfire at high revs

mac79

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Hi guys,

It's been a long time coming, after a long while researching all my needs via your experienced and valuable posts, but I've come across something I need some advice on. I've had my S3 8L for around 18 months and am gently, progressively working on getting it up to scratch. I like to keep as close to OEM as possible, making enhancements where the benefits are obvious but without being noticeable. It's a Denim Blue 210 facelift with silver alcantara/black leather interior.

I've recently had a bunch of things sorted in relation to handling and balance... namely a new N/S rear trailing arm, rear shocks and bushes... with the aim of getting the car pointing straight and true at last. It's always had a habit of wanting to wander/push left at fast road/motorway speeds. I knew the alignment was out both ends after a couple of inspections at various places. Major toe out on front sorted by Micheldever Tyres, also identifying the rears to be massively toed in - well past recommended limits. The trailing arm has sorted that now. Soon to have all new tyres to replace those that have been scrubbed by the rubbish geometry... at the same time as a full four wheel setup. In the mean time it needs some re-alignment and care with paintwork...

Since the work was done the car's had an unexpected misfire around 5000 rpm. The OBDII diagnostics shows intermittent misfire error codes (not always visible) but it always seems to drive just fine otherwise. It's had a Stage 1 ECU remap (239bhp/255lb/ft) since I've had it but no other mods that I know of. All appears to be OE otherwise.

Also fitted Osram Xenarc Nightbreaker D2S bulbs, new headlight levelling sensors and had new clutch and other bits and bobs sorted.

Just wondering if anyone's experienced high RPM misfires and could point me in the right direction with some suggestions... and introducing myself and the S3 at the same time.

Thanks,

Tom

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Hi badger,

Thanks for the suggestions. I'll be checking the coil packs and other usual things, as recommended... just wondered if anyone could suggest a reason why a misfire would suddenly appear at high revs when at all other points it's smooth and tractable.

Jobs for my next day off... :)

T
 
what fuel are you using Tesco momentum 99 / shell nitro 98 / BP Ultimate 97 or basic 95?

some people have commented on a non standard plug gap for mapped cars too.
 
Hi Stuart,

I always use a 97 RON fuel; usually BP Ultimate, Esso Synergy or Shell Nitro, depending on where I am. It had a starting issue a couple of months ago which diagnostics highlighted a crank sensor fault, so that was replaced and since then no starting issues; just this momentary misfire at 5000rpm. A fault code did show up in diagnostics at first highlighting a misfire but the last couple of times I've checked no codes are seen and the car drives just fine otherwise. I know a service is almost due and I've been doing a lot of miles up and down the country recently, so I'm not surprised if there's something needing sorted with the plugs, coil packs, etc. I was just surprised how specific the misfire is at 5000rpm! :)
 

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