Random knock, possibly bad sensor?

[phase17]

I have a 1991 TSi AWD. Only mods are hacked aircan and BCS restrictor removed, which somehow has me at 15psi, reading from an accurate boost gauge. No lifter tick.

Well my main question is about knock and timing advance. Currently at idle of 750rmp my timing jumps between 8-10* there is 0 knock. These reading are from a datalogger with mmcd. When cruising timing is in the 30s and there is still 0 knock, my o2 readings jump all over which I've heard is healthy. My concern is that at WOT, sometimes the knock reading will jump to 43, and sometimes it's at 0. It seems completely random and pulls my timing into single digits. I've tried retarding the timing multiple times. No change. I've advanced it for shits, no change. Do I need to ground the ECU when adjusting timing? I've heard that I do and I've heard that I don't from all sorts of people. I've tried grounding it, still no change. I put in NGK BPR7ES plugs, that didn't help either. Is this a sign of a bad knock sensor? . I feel like an idiot because nothing I do seems to help. I'm very new to this and very confused.

 

[pooker]

When using a timing light you have to ground timing. Have you checked to make sure your cas is functioning properly? I used to have that problem it was 180 degrees in the wrong direction there is two positions it can be in.

 

[DallasN2O]

So if the CAS is backwards it will cause symptoms like he is describing? My car is doing the same exact thing and I suspect the CAS as well. Although some people say you can put it in backwards and it has no affect on the way the car runs at all. That doesn't make sense though or they wouldn't have marked the darn thing on which way its supposed to go in. Let me know if turning it around fixed your knock problem.

 

[BUCK]

BTW it makes me think about HOW we set these things at base Timing - the oblique ANGLE that we are at when look at the Timing marks is very poor - you can't get a "straight on" look/angle at the Timing marks like ANY other vehicle I ever owned & I've owned a lot of them - Lay one finger in front of the other & change the angle from head on - then stretch your arms - the "oblique" really changes things - IMO when you are squatting down & peeking thru the belts & "see" 5 BTDC you are really about 7 BTDC - when you see 2.5 BTDC - it's actually about 5 IMO. - I try to be in the same position/angle whenever I set mine halfway between 5 & 0 BTDC & IMO that is 5 in the real world & "seeing" 0 would be 2.5 BTDC real world IMO... I'm pulling 22 - 25 at WOT (Tuning guide reccommends NO LESS than 15 at WOT) & see as much as 46 degrees advance on Pocketlogger in some throttle positions - 0 knock on 92 or 93 Octane in Winter (which of course means I could bump up Timing OR Boost) - seeing 13 PSI on Stock gauge - but it runs great & I don't want to fry this old Turbo quite yet

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1g Idle & Timing Adjustment STRAIGHT FROM DSM MANUAL...

- Reset ECU 15 Minutes to clear all the crap out.

- With car off
- Ground that pin on the Diagnostic Connector
- Fully warm car up, No accessories on.
- Run at 2500 rpm more than 5 seconds
- Let idle for 2 minutes
- Adjust BISS 700-750 rpm
- Cut car off
-Disconnect Jumper at Diag Conn

- With Car OFF
- Connect Timing Jumper
- Fully warm up car - No accessories
- Check CURB IDLE is at 750 + or - 100 rpm (may take a little while to settle down being you just reset BISS)
- Set Timing at 5BTDC (which means you'd see 4 IMO due to bad angle)
- Cut Car OFF
- Disconnect Timing Jumper
- Cut car ON
- Check Basic Engine Timing 8BTDC (kinda jumps from 7-9 usually).

- AFTER setting Base Timing correctly per the above you could then "bump up" Base Idle a little (50 - 100 rpm) to help with the Fan cut-on - The ECU can pull more than you can retard! - Some of us have BOTH Fans cutting on simultaneously so that is loading your Alt more than a stock setup - Typically you can retard one when setting base Idle & it idles smoother as long as Idle is close to spec - Setting it where you see 4 will make it more resistant to losing RPM when fans cut on.

- Now get to work & report back...