snurb

A couple of days ago, my 1999 A6 2.8 Quattro started throwing the following codes:

16684 - Random/Multiple Cylinder Misfire Detected
16687 - Cylinder 3 Misfire Detected
16795 - Secondary Air Injection System Incorrect Flow Detected

This came 36 miles after I got it out of the shop for new valves, gaskets, cam shaft timing chain tensioner (right side), water pump, timing belt, thermostat, tensioner, roller, plugs, etc. Yep, the timing belt teeth had stripped off - after 154,151 miles!

The mechanic who rebuilt the engine said he did not think the codes were indicating anything wrong with the belt or timing since the car seems to be running smoothly.

Are the three codes related? Could the air injection system be causing the misfiring or should I be suspecting something else entirely? Any help will be greatly appreciated.

jseklund

Could be related. I bet that when he pulled the valve covers, he loosened or removed the combi-valves. If they are not put back on tightly and with the gasket correctly, you can have a leak that can cause a misfire and SAI codes.

You can listen for a ticking noise (like an exhaust leak) behind the heads...get a tube and put one end of it in your ear and the other around where the valve tube attaches to the back of the heads...you may hear the ticking then.

The best way to tighten them is to get a ratchet that accepts screw driver bits (they sell them at auto parts stores) and a 5 mm hex screw driver bit. The wratchet looks like a small box wrench and the bit sits in the circle...you don't want it to be a ratchet with a socket because the clearance is an issue. Otherwise, you'll be there forever.

4Driver4

I'd probably start with a leakdown test to verify that the valve work was done correctly. How old is the coolant temp sensor?

jseklund

He doesn't mention having the head removed...so do you think the valves were really replaced? Or did he mean to say, valve cover gaskets? I kinda bet on him meaning VC gaskets. If I'm wrong...I still would check the SAI system first. I'd think it would be an easier place to start and we know he's got a problem with that from the code...just my .02

4Driver4

Good question. I tend to be very literal. Then again, he does say something about a rebuild, which generally goes way beyond a few valves. Could be either.

jseklund

4D4- I know you are very literal. That is why you catch more issues when people explain them than almost anyone else on here. You picked up on the "rebuild" part, which I knew you'd see....but I'm not sure what was actually done here....maybe the OP can clarify...

Also - the valve stem seals could have been replaced without removing the head, which I guess could create too much pressure in the VC area, which could cause an issue with the SAI - but it just seems like a lot to follow through for me, while a loose combi valve seems to be one item that could cause misfire and SAI failure...I don't know....

5v/cyl

Sounds like a vacuum leak in the SAI system. Probably a old line that cracked or one didn't get put back on correctly. The vac leak would cause the misfires and the SAI code since the system isn't working properly.

It is also possible the two are unrelated. Since he stripped the teeth on a timing belt with 150k+ miles (OMG), then valves where most likely bent. He didn't specify if the 'rebuild' included new valves so we don't know. Slightly bent valves would cause misfires and cylinder #3 could be worse than the others. Leak down test would reveal the truth.