Hi I have a 1997 A4 with the 1.8t non quattro. couple months ago was driving and the car started to run rough then was followed by a backfire and then started the knocking. It sounds like its coming from the top end and back by number 4. Anyone have any idea what it could be. also about 3 weeks prior the catalytic converter was plugged and had it hollowed out. Just replaced the timing belt and camshaft chain tensioner no luck still knocks.

 

check compression, use decarb, put high octane fuel in it

 

Ok so i checked the compression dry and wet.

1 2 3 4
dry 80 80 95 65
wet 90 100 100 90

That tells me that my number four piston rings are bad right? I wouldn't think that the piston rings would make that much noise if any at all. What do you all think?

 

piston rings is a possibility, now you need to do a cylender leak down test. loss of compression can be due to valves, piston rings, blown head gasket, cracked head ect.

did anything go wrong with the timing belt change? its very easy to chip a valve doing it. and it would take some time for it to show affects from a bent valve to burn and give you these problems.

after reading you post again im pretty sure its a burnt valve. when ever a valve gets chiped. it creates a hot spot where you have pre ignition. so do that clt on number 4 and find out which valve. then its all repair wook after that.

good luck

 

Not sure what the leak down test is. But the valves looked perfect there is no piston to valve contact marks. Could this be something I can't see. By doing the wet compression test that shows its the rings not a head or valves. But then again the noise sounded like its top end So I am lost. The timing did confuse me though i put a new belt on and counted teeth when i put it on and it turns out the old one was off one tooth. So I corrected it and now it runs like its off.

 

Also i have the head off and turned the crank and there is a solid line of oil. would that be from a cracked ring.

 

a leak down test is similar to compression test. you put your cylinder at tdc compression and put compressed air in it through the spark plug and listin for an air leak to find out where your loss of compression is.

you are right about the dry and wet test.

chiped or bent valves arnt nessisarly visual.

well having your timing off is a very good reason to be knocking, if you mechanically out of time there is only so much the ecu can do as far as retarding for knock. if it runs good now and theres no knock then you should be good for a while befor you consider overhaul.

not sure what you mean by solid ring of oil. ontop of the piston? yes that would be from bad rings

 

The oil line on the piston wall i was referring to was a line of of oil the runs vertical on the cylinder wall as if there is a crack in the rings.

And the timing issue. It was off by a notch accoding to the timing marks but it ran fine. So I corrected it and it made the car run rough. so could the timing marks be off? or what is the deal there.

 

sounds about right with the oil.

but also there is a gap in every ring to allow for heat expantion. it might be nothing. unless this is only happening on #4

the marks dont generally get moved. the only one that could would be the cam sprocket one. but there is no reason to do it.

timing is tricky, with lining up the marks sometimes you think you have it right and its really off. i must have taken my tentioner and belt on and off 25 times befor i was sure it was right. the first time i did my timing belt.

also when you change the timing mechanically. it takes a few runs for the addaptive statagy to figure everything out so it will run crapy weather your changing it wrong or right. just so much as you change it

you dont really need to count teeth. you just need to make sure when the belt is compleatly on that both the crank and cam timing marks are aligned.

i wish i could see your car maybe try pivate messageing one of the site moderators or long time members like auditech79, crazyhawk, or cincytt to look at your tread and see what they say

 

Yea the oil thing is only happeneing in 4. I appreciate all the help you have givin me hopefully i will be having a running car here soon. This engine has been removed before so i am gonna have to do some digging I just bought it but one of the allen head bolts that caonnect the engine and drive line were loose and the head was stripped so I'm wondering if this isn't the first time this engine has had issues. Thanks Again for your help.