My A6 is running on three cyclinders, I have performed a few standard checks and replaced the HT leads (coils/whatever) and the spark plugs, but the problem still persists and seems to have got worse (Now the engine warning light is continually on). I have checked that the plugs are sparking and have noticed that the plug nearest to the radiator has either an intermittent spark or a seemingly weak spark compared to the other three. The spark plugs I removed looked to be in good order, apart from the plug nearest the radiator which had a darker and seemingly wet appearance. I put this down to the misfire as obviously it is not burning off the fuel in the cylinder.


So at this point I refer to the VW passat manual which has the same engine, chassis etc as the A6 which lists these as possible causes:

Fuel filter choked - I have had fuel starvation on a few cars I have owner previously and noted that this current fault is different from the indications that this is what is happening.

Fuel pump faulty, or low pressure.

Fuel tank vent blocked, or pipes restricted.

Vacuum leak at the throttle body, inlet manifold or hoses - Now this kind of makes sense as initially the problem became proggresively worse as the car warmed up (or hot)

Faulty ignition coil - which may be causing the weakness in the spark

Cylinder compression - I bloody hope not!

Blocked injector.



All the wiring under the bonnet seems to be intact, no obvious signs of damage. Another quick look through the manual indicated that the HT leads receive an amplified charge from the 'Ignition Amplifier' (Do these break down???) Is there a way of metering the terminals to check for electrical output and if so what should the charge be???

Can any one help me Obi One Kanobi, as your my only hope!

[Sobs quietly]

 

The ignition modules have been known to fail but every one ive seen fail goes out on cylinder number 2, not 1. You can attempt to measure voltage output from the module, but would require a wiring diagram to pinpoint the correct wires. Unfortuantly i dont know what the proper voltage should be but if you compare it to the operating cylinders you should be able to get a ballpark on the correct figures.

 

If its a 2.8 the injectors have been known to go bad

Its the purple bluish ones that have this problem so if you have those it will also be something to look for

 

AudiTech04
I did suspect the injectors initially (They are blue) and have removed them for expection, visually there doesn't seem to be an issue but that doesn't mean they are not fecked! Is there a way of testing these, I am guessing not and that they will have to be replaced. Exxxxpensive test!!! (it's a 1.8T model)

dankhound
I have a wiring diagram and as you suggest they don't supply any form measurable ouput – I will undertake the rest of your testing suggestion.

Thanks for your help

 

dude,don't frik out now.listen what i hade.same engine same car cyl 4,5,6, were misfireing between 76-130 per driving cycle
cyl 123 3-10 missfires.everything in order,checked fuel pressure ign coils wires injectors and you name it.My problem was the folowing .the engine harness is attached to the fire wall by tie strabs and then goes to the engine components.the wiring was broken inside.i had to start cheking the wiring one by one,and after 4 hours i have found theone.from outside was looking ok,but the isolation where the wiring inside was broken had a little bup on it.so i cut it and surprise.all but one onley attached every other was broken.so basickly the computer does not recognise short to + or - because there was one attachte still,but when accelerate the m.f was missfiring like crazy.so i fix the wire and now is perfect.cusumer happye i am happy.take a look at it .may be it is the same problem.i had absolutley the same simptoms.good luck.
P.S. SORRY FOR MY SPEALING ,MY ENGLISH IS NOT SO GREAT.

 

I think at this point the best bet is to replace that ign module on the air cleaner

Shouldnt be that expensive

 

Ignition modules like200 bucks new. If everything with the module checks out ok your may want to see if the weak spart will follow the coil, by swapping the coil to a different cylinder.

 

98 a4 2,8 with ign.module????????absurd

 

[quote]ORIGINAL: Henlow1

AudiTech04
I did suspect the injectors initially (They are blue) and have removed them for expection, visually there doesn't seem to be an issue but that doesn't mean they are not fecked! Is there a way of testing these, I am guessing not and that they will have to be replaced. Exxxxpensive test!!! (it's a 1.8T model)

Read here he has a 1.8t

And my bad i wasnt aware how expensive they were, but really thats the only option left

 

ahhh now at least we know what car it is 98 a4 2,8 "this information is vital to a correct diagnosis" the age of the car makes a big difference as to what system you have in there, ill go for the MAF sensor if the misfire only happens when driving