Alright, I've got a daily driven 02 Z28 LS1 with all of the SLP external bolt on components (maf, lid, tb, bellow...etc.), stock Y pipes, no cats, glasspack muffler, 28.8 injectors, dyno tuned, and 115K on the motor. About six months ago I started throwing a code for knock sensors but had no noticeable change in performance or unusual noises. I pulled the intake and changed the knock sensors along with several engine management connectors and sensors. I also installed the 28.8# injectors and magnaflow cats, slapped it back together and continued to haul ***. The car was never re-programmed after the repairs and fuel injectors. Well about two months ago I started developing a tap that follows the rpm (sounds like an exhaust leak or lifter), but only on the highway or interstate. Running around town and hitting all the stoplights it will never tap, the only thing that seems to cause it is a sustained rate of speed over 50 and for a couple of miles. It will start real subtle and quickly grow to something that everyone around me can hear easily in their cars within seconds. Once I get off the highway the tapping goes away. Since this thing has started there has only been one time that I got on the highway and it never tapped over the course of 20 miles or so. I have on occasion (rarely) suffered a power loss when the symptom comes around, it's a slight loss, feels like 7 cyl vs. 8 and the tone varies a little. Doesn't really have the metallic sound to it, really sounds like exhaust leak or lifter...Anyways, last week the car was throwing codes for knock sensors and catalytic converter. I fabricated some straight tubes, eliminated the cats, and changed the spark plugs, and it tapped on the highway today after about 2 miles of 70mph and quickly quit as soon as I got off the exit. Oil pressure is good, temp is good, I run her hard but never exceed 5500 rpm, and rarely flirt with 4000, it's an A4, I've always used royal purple 10W-30 oil, and a K&N oil filter that I change religiously inside of 3 to 4K miles. I can think of one time I slipped and hit about 6200 rpm but the tapping didn't start until months later...I know it sounds like a lifter but it is very intermittent so I don't think that's the case, has anyone experience this....PLEASE HELP, I'M GOING INSANE!

 

C'mon, has this one really stumped the LS1tech community, can I really be the only one that this has happened to?

 

I had a similar tapping sound....thought it was a lifter at first...come to find out it was the fram oil filter i was using. I think it was starving the car of oil...hasnt dont it since. But yes it would start after 15-20 minutes or so of driving usually on the hwy. Your oil setup seems to be fine though...Thats the only experience I could give you concerning that...Id say check your lifters and your exhaust for leaks..though the 2 really sound nothing alike.

 

Does it only happen in 6th gear?

..WeathermanShawn..

 

Oops..I just say you were an A4.

Sometimes you can get a rattling that only occurs in one gear, but that is mainly a M6 anomaly. Or you can get a 'harmonic' rattling of your catback or catalytic converters that only happen at a certain speed. Same phenomena that occurs when a wheel is out of balance.

The bottom line is to get a knowledgeable friend or mechanic to ride along. If it not engine related, then you can start going through the list of all the other parts that can rattle at certain speeds.

You are probably going to have to do a little more self-diagnosing..we are probably just guessing on this end.

Good luck..

..WeathermanShawn..

 

MonmouthCtyLS7 - You nailed it, I forgot that the last time I changed the oil AutoZone was out of K&N Oil Filters. I had time to knock it out that night so I substituted a Fram Double Guard instead of my usual K&N...I changed the oil and replaced that pos with a K&N and sucessfully completed 150 miles of highway cruising this weekend with no tapping! Man what a relief, I was thinking everything from lifters to a spun main! The car sounds pretty mean with no cats too! That can't stay that way for too long though, we have to pass safety inspection in the next few months. But thanks again, and I'll warn everyone I encounted to stay away from those oil robbing inferior filters...

 

Hmm interesting, im having the same issue.. Looks like im gonna pull the car in and change the oil and filter..

 

i had a similiar issue. tapping would start after driving car for about 20 minutes. I changed oil to castrol 10-40 conventional and a k&n oil filter and seemed to go away for the most part. every now and then it comes back but it's alot better than before.