99 A4 2.8 30v


-ok so my catalytic converters blew out and forced debree into my muffler, so i had the cats replaced, and had an after market muffler put in to replace to old one, they took out that box looking thing too.

but now when i drive it feels like its missfiring and i can hear what sounds like gunshots coming out of the tail pipe and it sounds like a rattle in the muffler, tho when i bang on the muffler i dont hear anything move around.

Also ive replaced the ignition coils, spark plugs, and spark plug wires as well as the maf but anytime i plug the maf in it shuts off as soon as i start driving and gives me random missfire codes coming from only one side of the engine!

PLEASE HELP ive taken it to 4 mechanics each says a different thing! before i shell out $500 for a fix i want to make sure it actually fixes the problem.

157,000 miles!

 

Does it happen as soon as the car is started our after its warned up? Were the cats replaced with factory cats and in the same location?

 

cats are in the same location and i bought them online i typed in 98 audi a4 s.8 catalytic converters and bought the first ones i saw. it does it as soon as i start driving in feels like its jumping and i can hear that knocking near the muffler, the only way to get it to stop it to press in the clutch a little bit with some gas.

 

Do you have a check engine light?

There are a couple things that can cause backfire..

Backfire can be caused by too much back pressure (ie a plugged cat)..

Backfire can be caused by incorrect valve timing (ie stretched timing belt)

Backfire can be caused by incorrect fuel mixture (ie sensor failure or fuel pump failure)

Backfire can be caused by a exhaust leak between the heads and the cats..

The first thing I would try is making sure your o2 sensor connections are good.

Try disconnecting your battery overnight and seeing if that resets your fuel trims. The old cat might have messed with your fuel trims and now that there is less pressure it is trying to compensate.

You can replace/clean your upstream (front) o2 sensors..

If the cat you installed was smaller or more constricting it might actually be the culprite..

Beyond that your looking at some much more involved fixes.. Try those few things and get back to me..

 

Do you have a check engine light?

There are a couple things that can cause backfire..

Backfire can be caused by too much back pressure (ie a plugged cat)..

Backfire can be caused by incorrect valve timing (ie stretched timing belt)

Backfire can be caused by incorrect fuel mixture (ie sensor failure or fuel pump failure)

Backfire can be caused by a exhaust leak between the heads and the cats..

The first thing I would try is making sure your o2 sensor connections are good.

Try disconnecting your battery overnight and seeing if that resets your fuel trims. The old cat might have messed with your fuel trims and now that there is less pressure it is trying to compensate.

You can replace/clean your upstream (front) o2 sensors..

If the cat you installed was smaller or more constricting it might actually be the culprite..

Beyond that your looking at some much more involved fixes.. Try those few things and get back to me..

 

im in the process of doing a timing belt change once i get the the rest of the tools...hopefully tomorrow, i have all the parts, so ill check on it then...would these suggestions also be the cause of my car not running with the maf plugged in?

im also taking off my intake manifold and cleaning the insides to see if that helps...is there anything special i should do when cleaning the system?

 

As far as getting the intake clean it takes some work.. Try not to get too crazy cleaning any sensors that are attached to the intake.. Rubber hoses also are generally not too fond of solvents.

It should start and run without the maf. So your trims might be way off.. Removing the battery overnight should reset any trims..

 

You say you're getting random misfire codes only from one bank of cylinders - is it all 3 cylinders on that bank? If it is, I'd suspect a bad or failing cam position sensor or that the timing may have jumped a tooth on that bank.

 

Could this also be a faulty ICM?

 

the cam position sensor is that thing you take off when changing the cam seals right?

and i was thinking the timing belt as well so im in the process of changing it.

and as for the icm pretty sure that my model has that connected to the coild pack, but i could be wrong.