So I just bought a 98 A4 1.8t, I noticed that the engine knock during acceleration. I told the guy I bought it from that I would only purchase the vehicle if he would by for the repair, and he agreed. A local mechanic and others told me that the car is running lean. So here's my questions.

Is there something inparticular I should check before anything?
Is this common for older A4's?
I'm going to get a compression test done at a local mechanic, is there anything else I should have him check to make sure the engine's not going to blow on me?
Does any one in the San diego area know of any good audi mechanics in the area?

So this is the first Audi I've ever bought, and my knowledge of audi's (and any euro's for that matter) is pretty bad. any help from you fellow audi enthusiasts would be much appreciated. Obviously you guys know more than anybody else would.

Thanks
James

 

sorry about the typos (knocked, buy...and whatever else i missed)I was rushing to send this out before class started ;P

 

Is the car stock? How many miles are on the car? And the sound is only during acceleration? or can you hear it at idle to?

 

The car is bone stock, and I don't think the previous owners did any performance mods on the car eithier. Currently has 110,700 miles, but still runs great besides the knock. The knock only happens during acceleration or whenever the you press hard on the gas. At idle you can't hear it, even if you put it in neutral and rev, no knock. Mechanic suggested to me to try and fill up again and run 91octane (he's thinking that maybe the previous owner may have tried to save money and put in 87 instead). Any other suggestions?

 

Timing and fuel octane are the most common causes by far. Its possible your car has a chip in which case it really requires premium fuel. Im not sure how you could tell if its chipped or not... you could tell if you had a boost gauge I suppose. Maybe drive another A4 and see if yours is significantly faster.

 

anything other than 91 and you will hear that knok, Its called detonation (where the air/gas mixtrue ignites due to heat, compression, and fuel type without a spark, can be bad for the car, run 91 and see if that helps.

 

Hmm..we call it pre-detonation over the pond..[:-]

 

sorry, same thing, as far as I'm conserned. Same chemical and phisical things going on, just not as much damage.

 

I thought our engines had an inhibitor which prevented the "knocking" sound...it just automatically reduces performance when it detects lower octane fuel. Or maybe I'm full of BS...