Sharktrainer

Been having a random tap after deceleration following spirited acceleration when coming to a stop. Goes away like in 5 seconds. Started about a month ago and usually when it’s hot outside. Night time when it’s cooler no issues. 99% sure it’s not mechanical in nature.

Oil level and pressure good 10/30 weight oil
91 Octane being the highest I can get here on Maui
plugs good
wires good
cap good
rotor resistance in spec

could the O2 sensor have gotten ‘lazy’?

Rogviler

Pretty sure they did not have a knock sensor on any of the non-turbo engines of that era. I do believe they were putting the vacuum-assist pumps on them though, which can be a common source of knocking or ticking. If you follow the brake booster line, at about the halfway point you'll see it T off down to a contraption mounted to the head. This can be removed permanently if you wish, as long as you make a plate to cover the hole. Somewhere I have a template I drew on the computer to make one...

Anyway, it'll be hard to find for sure if it only does it while driving. If you suspect the engine is knocking you can back off the timing to see if that stops it, but typically you only get knocking under acceleration and especially under load, like if you're going up a hill.

BTW knock sensors are easy to spot, they're basically a flat donut with a bolt going through them into the block or sometimes just a giant plug with a wire coming out of it. I've only ever seen them on the driver side.

-Rog

Sharktrainer

Thanks, I was thinking it didn’t, just wanted to rule it out.

Another question if you are still around, do these Audi engines have a high nickel content, like enough that I should be using a ZDPP additive in the oil?
I use it in my 70’s BMW’s and Mercedes because of said reasons.

Rogviler

I've not heard anything on that. Most of the additives or special fluids that excite people on these are for the engine oil to reduce lifter ticking and in the transmission/diffs to reduce whine.

-Rog

Sharktrainer

Thanks again.

Sharktrainer

So finally took the vacuum assist device off yesterday and sure enough the ping/knock went away and seems like a little bit of pep came back as well.