Help, engine feels like it's misfiring

[imported_spuddie007]

Hi All

Haven't driven the car for a few days, took it for a spin today (it's an S3) and usually feels juddery for half a mile, then fine when it's cold.

Today, the car wouldn't pull away, although there was power if youi put your put down, but felt like there was no power in the mid-range at all.

Still feels juddery, afetr running the car on side roads for a few miles, but isn't feeling right? I'm no mechanic or expert, so just wanted to know if anyone had any ideas as to what it could be?

Cheers in advance for your help guys!

Spuddie

 

[ChriS3]

Coilpacks?

 

[imported_spuddie007]

That sounds dangerously, hideously expensive. Okay, what am I looking at in cost then? Hit me?

 

[god_thats_quick]

Coilpacks are about £28 each from audi for the part, it could also be your MAF (mass airflow meter) which is about £80 for the part, but it's quite unlikely this would have failed so suddenly without any hesitation before.

Does it feel like it's only running on 3 of the 4 cylinders - if it does it's probably coilpack related.

 

[ChriS3]

Not sure, York Audi replaced mine for free,said it was a warranty/recall thing - long after my warranty expired. Not expensive anyway.

 

[imported_spuddie007]

[ QUOTE ]
Coilpacks are about £28 each from audi for the part, it could also be your MAF (mass airflow meter) which is about £80 for the part, but it's quite unlikely this would have failed so suddenly without any hesitation before.

Does it feel like it's only running on 3 of the 4 cylinders - if it does it's probably coilpack related.

[/ QUOTE ]

Yep, definately feels like all the cylinders aren't firing, so to speak. Oh well, another expensive trip to Audi Stealer tommorrow (don't really feel comfortable doing that kind of stuff myself!)

 

[god_thats_quick]

[ QUOTE ]
[ QUOTE ]
Coilpacks are about £28 each from audi for the part, it could also be your MAF (mass airflow meter) which is about £80 for the part, but it's quite unlikely this would have failed so suddenly without any hesitation before.

Does it feel like it's only running on 3 of the 4 cylinders - if it does it's probably coilpack related.

[/ QUOTE ]

Yep, definately feels like all the cylinders aren't firing, so to speak. Oh well, another expensive trip to Audi Stealer tommorrow (don't really feel comfortable doing that kind of stuff myself!)

[/ QUOTE ]

It's a pain to identify which coil it is so I'd agree if you're not comfortable head down an Audi or VW dealer (and take it easy as there will be a lot of unburnt fuel being pumped into the failed cylinder) it's shouldn't be expensive if they do charge you and I'd expect them to do it within 30mins if not less.

 

[imported_spuddie007]

Okay, cheers for the advice guys, did a search here, and sounds like the coil packs for certain, massive hesitation at 4k revs, will take the car gently to the stealers in the morning! Cheers. . . . .

 

[imported_spuddie007]

Just at the stealers, MAF needs to be replaced. £130 all-in, not cheap, but at least I'll have the power back to it's old self!

 

[benk]

You should be able to get that as an exchange part for about 90 quid - they take the old one and keep it.

 

[god_thats_quick]

[ QUOTE ]
Just at the stealers, MAF needs to be replaced. £130 all-in, not cheap, but at least I'll have the power back to it's old self!

[/ QUOTE ]

That's not bad, I take it that's around £50 for 1/2 hour labour to fit the thing.

 

[madvw]

presumably its 90 for the maf and 40 for half an hours labour.

 

[benk]

Ok, forgot they would be fitting it for half the cost of the part...

 

[RichA3Turbo]

Can change a maf in under 30 seconds!

 

[imported_spuddie007]

Yep, £78.18 for the part then labour added, oh and they cleaned and vac'd the car too! Lucky me!

As you are quite knowledgeable god_thats_quick, what's the MAF do exactly? I've seen many posts relating to it, but as I said, not really mechanically minded unless it involves ripping apart a computer!

By the way, cheers for all your advice lads, much appreciated!

 

[god_thats_quick]

[ QUOTE ]
As you are quite knowledgeable god_thats_quick

[/ QUOTE ]

Only because my car has had every problem under the sun... /ubbthreads/images/graemlins/laugh_roll.gif

The MAF is the sensor that tells the ECU how much air is flowing into the engine.

 

[benk]

Doesn't it pass a current through a thin wire, and the airflow cools the hot wire, changing the resistance, and the ECU monitors that and increases fuel delivery (partly-)based on this information?

 

[imported_hookie]

To quote the official Bosch decription!

The hot-wire and hot-film air-mass meters are both thermal load sensors. They are installed between the air filter and the throttle valve, where they monitor the mass flow (kg/h) of the air being drawn into the engine, The two meters operate according to a common principle.
An electrically heated element is mounted in the intake-air stream, where it is cooled by the flow of incoming air. A control circuit modulates the flow of heating current to maintain the temperature differential between the heated wire(or film) and the intake air at a constant level.
The amount of heating current required to maintain the temperature thus provides an index for the mass air flow.
This concept automatically compensates for variations in air density, as this is one of the factors that determines the amount of warmth that the surrounding air absorbs from the heated element.

The heated element on the hot-wire air-mass meter is a platinum wire only 70µm in diameter. A temperature sensor is integrated within the hot-wire air-mass meter to provide compensation data for intake-air temperature. The main components in the control circuit are a bridge circuit and an amplifier. The hetaed wire and the intake-air temperature sensor both act as temperature-sensitive resistors within the bridge. The heating current generates a voltage signal, proportional to the mass air flow, at a precision resistor. This is the signal transmitted to the ECU.