misfire?

[approved]

been running the car on a mixture of 95/98 when i can get it, anyway, two days ago put a tank of tesco momentum in it, and it appears to have developed what i can only describe as a misfire...

intermittent from aobut 4k, 5.5k boost isnt there and after that its still 'retarded' slightly...it happens about once ever 7 accelerations into that range if that makes sense...

had the car booked in today but they were 'too busy' when i got there, so i took it for a good 'clearout'..after which i could smell burning...though that may be the brakes...

what say you lot?

bad tank of fuel maybe?

[aidanjaye]

been running the car on a mixture of 95/98 when i can get it, anyway, two days ago put a tank of tesco momentum in it, and it appears to have developed what i can only describe as a misfire...

intermittent from aobut 4k, 5.5k boost isnt there and after that its still 'retarded' slightly...it happens about once ever 7 accelerations into that range if that makes sense...

had the car booked in today but they were 'too busy' when i got there, so i took it for a good 'clearout'..after which i could smell burning...though that may be the brakes...

what say you lot?



bad tank of fuel maybe?

Could be fuel, could be a coil pack breaking down (with the cold damp weather). Fill up with some 98 and see what happens. If its a coil pack, dignostics will flag up which cylinder.

[approved]

would i get a warning light on the dash? and would coilpacks be covered under warranty?

[adsgreen]

Misfire detection is based on detecting a crank shaft acceleration when the ECU expects it in conjunction with a coil pack firing.
However it does have some wide margin on it so it doesn't go off constantly.
Usually they work with a system of "x number of sub optimal misfires in a y second timeframe". There's a second set of more severe parameters to activate the limp home/flashing warning light where unburnt fuel will damage or set light to the cats.

In short, If you're not getting enough misfires of sufficient magnitude for a long enough period of time then no light will come on.

The best thing to do is to put the engine under load - accelerate from 30 mph in 3rd/4th with the accelerator flat down. that should give it enough to trip the light.

[approved]

so even though there is no light the faults will be stored and show up when its plugged in monday morning?

the first service bod i spoke to tried to say it was probably the fuel, being supermarket fuel ( tesco momentum!), and then the second said a light would definately come on if there was a misfire.....

[aidanjaye]

so even though there is no light the faults will be stored and show up when its plugged in monday morning?

the first service bod i spoke to tried to say it was probably the fuel, being supermarket fuel ( tesco momentum!), and then the second said a light would definately come on if there was a misfire.....

Sevice bods can be a bit hit or miss....

Missfire should log even if its not showing up a warning light.
Highly unlikely that coilpack would be under warranty although I'd try your luck.

[Terry1948]

It is possible that it is vacuum related. the manifold flaps may be opening and closing due to loss of vacuum this would cause a misfire also your flap would not be opening so you wolud lose your kick at about 5.5k.

[approved]

no fault found.

no fault codes or anything...

wierd, so had to pay the hour investigation, they did the mot though as well, so wasnt a wasted journey..

does say on the work sheet that they removed debris from the plenum chamber...

whats that then?

[adsgreen]

Elsa refers to the area under the battery charge posts as the plenum cover.
I'd read that as 'leaves under the bonnet'

[ChrisCSL]

Jonathon. I seem to have the same problem you describe. A slight slow down of acceleration at about 4200 rpm with no 5.5k boost. I've noticed this at high gear, high motorway speeds. When I tried to replicate in 2nd or 3rd gear it seemed ok and pulled like a train and I got my 5.5k boost. Back on the motorway again and the problem appears. Not sure if it's intermittent or if it's only a problem in high gears (5th & 6th). I was guessing airbox flap but I'd like to hear any more suggestions from anyone?

[approved]

i took it for a drive today and i can make it happen pretty much on cue.

so have spoken to audi and want to get the tech in the car to show him.

if he cant fix it i'm getting rid.

i <beep> hate cars that dont work properly, and even more so, hate people who are supposed to know how to fix them not knowing what they are on about. More so i simply dont have the time to mess about with stuff like this.

a bad do all round.

[PetrolDave]

and even more so, hate people who are supposed to know how to fix them not knowing what they are on about.

You'll have to get used to that... cars are now so complex that the training given to most dealer "technicians" doesn't teach them half what they need to know to diagnose let alone fix many problems.

If it's not in the directed fault finding guide, because the software egghead who wrote that didn't think of it, then you're stuffed with most dealers of most makes.

[Terry1948]

I had a problem with a loss of 5.5k kick and on accelerating it would appear to hesitate fuel starvation or missfire. No faults were logged but did a power function test and the flap stayed shut. Double checked the exhaust vaccum pipes and resealed. new flap and solenoid and the smooth power was back plus the kick at 5.5k. I think Mac at colchester had a simlar problem.

[ChrisCSL]

I had a problem with a loss of 5.5k kick and on accelerating it would appear to hesitate fuel starvation or missfire. No faults were logged but did a power function test and the flap stayed shut. Double checked the exhaust vaccum pipes and resealed. new flap and solenoid and the smooth power was back plus the kick at 5.5k. I think Mac at colchester had a simlar problem.

Cool. I wouldn't have called it a misfire. More like a flat spot. I'm sure it's breathing related like your problem.

[approved]

absolutely what it is.

am going to discuss with the tech as to what the problem is and we can go from there.