7A Misfire / hesitation

[Martin62]

Yet another issue with my 20v Quattro coupe !

It has developed what i can only describe as a misfire when warm.

On idle the engine is perfectly smooth and when stationary seems to rev fine, however when warm and under anything other than gentle acceleration it starts to misfire at around 2000rpm.

You can get it to accelerate by putting your foot down but it doesn't feel happy at all, very sluggish.

Back down to idle or low throttle settings all OK again.

I've tried 2 sets of plugs, one Bosch one NGK with no effect.

I thought when I put the NGKs in it was fixed but then after taking it upto 4000 rpm symptoms were back again

Has anyone experienced anything similar or have any idea what the issue could be ?

Cheers

Martin

[RichLV]

Check the distributor cap and rotor. Also, if possible, swap another set of spark plug wires. Could be the ignition coil as well. Had similar symptoms when ignition coil was on it's last legs.

[simon20vq]

Spray dizzy, leads and coil with wd40 and see if it improves things momentarily. I have some spares if you need anything drop me a pm.

[John.]

....... anything other than gentle acceleration it starts to misfire at around 2000rpm.

If it's that bad then maybe blipping the throttle whilst watching the leads in pitch darkness you may see where the spark is escaping to!?
If the insulation is gone anywhere on the leads then the spark will use the dirt on the leads to go to earth, cleaning the leads, coil tower and dist cap will likely help.
......assuming it's an HT misfire you're dealing with?

[steve briance]

I've seen sparks coming out of my leads before. It is worth doing - with the damp we are having at the moment - failed insulation anywhere will be well and truly shown up. When was the distributor cap changed? They are surprisingly durable but good job because of how tricky they are to get to.

Its interesting that it only does it on load though... suggests there may be some merit in checking the knock sensors as they only come into play when accelerating. Not sure they always throw up a code but its worth checking for fault codes if you haven't already.

have you run a different grade of fuel through recently?

[Error404]

Check codes first. Knock sensors will show a code sometimes - not always.
7A knock sensor fault manifests as a very flat and lifeless engine but still very smooth.

[Martin62]

Thanks for all of your responses and suggestions.

I checked for tracking from leads etc in the dark last night and nothing.

Today I will try pulling the codes to see if there is any indication of a knock sensor fault.

I will also take the dizzy cap off and check for condition as suggested as I have no idea when they were last changed. The car had been stood for a couple of years before I bought it so it may not be in the best of condition.

The fault occurs when using both standard and super unleaded with no noticeable difference.

Thanks for the offer of the spares Simon, I'll get back to you after my investigations today.

Cheers,

Martin

[jimmcf]

http://www.audifans.net/ftopict-33855-.html

Have a read of this might cure your problem

[Martin62]

Right,

I pulled the codes this morning and found this:

2144 - Knock Sensor 2, cylinder 4, just as Error404 suggested !

20v.org gives symptoms as:

- High fuel consumption
- Impact-like power loss (like misfire)

Exactly what I have although I haven't driven it far enough to notice to consumption issue.

I am about to check the wiring and then re-torque the sensor now.

If that doesn't sort it then I will have to replace it.

The part number I have is: 054905377B which has a built in attachment bolt.

Does anyone have one by any chance ?

Thanks,

Martin

[Error404]

I'd replace both while you are in there, they are a pain in the *** to get to.
Unfortunately those early sensors are not as common as the later ones. Knock sensor is essentially just a microphone though I wouldn't be surprised if they are interchangeable although I have never tried.

I did have a handful of these early 7A sensors but I have a feeling I gave them away. I will take a look in a bit, if I still have them you are welcome to them FOC

[Martin62]

Error404,

That would be great if you still have them.

Am on my way to Germany later today and there is a parts place there which I use, MC Auto Teile, they don't have any unfortunately so i'm guessing they are pretty obscure as they tend to have most things.

Cheers,

Martin

[yodasfro]

Yes you can use the newer style sensors http://www.motorgeek.com/viewtopic.p...ensors#p578206

[Mikes2]

And do they work ?

Can the Hitachi ecu read and use the signal produced by the Siemens knock sensor.

Why did Audi introduce a different knock sensor for Bosch Motronic ecus when the Hitachi knock sensors were already available.

[Error404]

Martin I checked and unfortunately I don't have any spares, I must have donated them as I thought.

Sorry
Alex

[yodasfro]

Yes they work.