jabol75

Hi there,

I have an Audi A6 from 1998. Recently MIL went off; a friend of mine used his palm pilot to determine that two cylinders (one and four) misfired. Can you tell me why is this so? How much does it cost to fix it? Your suggestions are really greatly appreciated. Thank you.

April

I suggest you connect the car to more sophisticated diagnostic tool, that may be able to tell you more. In the meantime:

How many miles?
Does the car have new plugs?
Are the plugs in tight?
Are the coilpacks in tight?
Are the connections to the coilpacks good?

jabol75

1) 84K miles
2) ?
3) ?
4) ?
5) ?

I am a newbie

fusilier

Could be one of the 3 coil packs as well, but I'd start with wires and plugs if it hasn't been done in a while.

Suds

Engine firing order is 1-4-3-6-2-5.
Coil-1 fires cylinders (1,6)
Coil-2 fires cylinders (4,2)
Coil-3 fires cylinders (3,5)

So whether the plugs, the wires or the coils failed, it is a double-failure -- odd...

The most common cause of failure on these engines is the wires, then coils, then plugs.

First try resetting the CEL and see if it comes back down -- i.e. it is not a temporary misfire.
(Note: if the CEL is FLASHING instead of steadily lit, driving the car can cause damage to the catalytic converter due to excess unburnt fuel.)

If it comes back on: If you have access to an identical vehicle, try swapping all 6 wires and seeing which (if any) cylinders misfire -- if still cylinders 1 and 4, you know it is not the wires -- must be either plugs or coils. (Be careful removing wires from either the coil end or the spark plug end, they can be frozen tight with age and it is possible to break the connector(s), causing much anguish and forcing you to buy new wires anyway. You can get special pliers at PepBoys or other parts stores specially to pull wires with the proper leverage.

If the problem goes away with the borrowed wires, then the wire(s) are bad -- makes sense to replace all 6 at the same time. ECStuning.com sells them a little bit cheaper than even the Internet dealers.

If you suspect plugs or coils, swap plugs from the faulty cylinder(s) with others from your engine and see if the misfire moves with the swap. If so, its the plugs, else it is the coils or worse.

Either way, if you have no mechanical aptitude, experience or tools (torque wrench etc.) proceed with caution and entirely at your own risk.

Edd W

fit a new set of plugs anyway as this is cheap and will do no harm.

If the fault for both cylinders appeared at the same time then it could be the control unit that switches the coils.

There is one point that I belive is noteworthy - the engine runs on a 'wasted spark' process. This means that the none firing cylinder that shares a coil with the one that is being fired, still fires. There are three coils each firing two cylinders so the fault is unlikely to be the coil pack because Suds has listed which coils belong to which cylinder and your two are not part of a 'pair'.

My guess is that you have had some cold damp weather and the leads are beginning to break down. Try starting the engine when it is fully cold, in the dark with the bonnet up and look and listen. You could see or hear the sparks tracking out, then try spraying WD40 over them and see if that cures it temporarily.

Suds

All good advice...