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Phantom knock or Real Knock?

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91TSI505

20+ Year Contributor
256
0
Jan 10, 2003
Albuquerque, New_Mexico
Ok, i just got my car a few days ago with a fresh rebuilt motor. I babied the car on the way home (10 miles) because i though that the was the most common used method when breaking in a new motor. I then read here that some people were having problems with there rings sealing right when they baby there new motor, then i was reading from a wiseman that he liked to drive his car a little hard after a rebuild so he would get good compression within 100 miles on the new motor (More boost but not to much RPM's). So i decide to take it out and put a little boost on it, i made a couple 2nd gear pulls @6psi and at a max of 4,500 rpm's. I went and looked at my log and had 43 counts of knock????!!!!! I am almost positive that its phantom knock beacause i dont see how i could have that much knock with the setup i have, here is my setup:

-.20 over block/Wiesco pistons/Stock 6 bolt rods/Clevite bearings
-ARP everyting/Cometic headgasket
-PTE SCM 50/28x12x3 FMIC
-The rest of my mods are listed

H-fuel trim: 95%
L-Fuel trim:110%
o2's: Bounce around from 0-80
Timing Advace under boost: 15 degree's

I know that the loud lifters will trigger off a knock sensor but mine don't seem that loud at all. I have an open 3" downpipe that is extremely loud but i dont see that triggering the knock sensor, could it possibly be a bad knock sensor? i know the A/F gauge is almost worthless but it reads about stoich under boost. Could my logger be reading it wrong? Also whats good timing advance under boost? Please help me figure this out, Thanks! :)
 
It's impossible to only run 6psi at WOT on these cars. Unless you got an external gate set up with the weakest spring imaginable. Best way to tell if the knock is real is to drain your gas tank, and throw in some race gas. If the knock is still there, it's phantom knock. Most likely, that's your culprit. OR, it's a mechanical noise setting off your knock sensor. Dirty lifters, bad bearing, anything.
 
Well i have an internal gate on the PTE set at whatever the spring setting is, i thought it was about seven. Could my loud exhaust be triggering off the knock sensor? Thanks for the info NOSLO2PT0 :thumb:

Edit: Would race gas be of on the new motor, just curious?
 
The exhaust itsself can't set it off, but I've heard people claim that if something like their exhuast is rattling it may cause the knock sensor to think there is knock. I doubt this, but search around. There is a lot of info on phantom knock. I'd do the race gas thing myself.
 
Ok new info:

I made a couple more pulls and the logger will still read 43 counts of knock at about 7-8 psi (Not a WOT pull) but my o2's are at .85v when under boost on every pull!!......isnt that about where it should be? Fuel trims are all at about 100%, I have wiseco 8.5:1 pistons also,Thanks!
 
91TSI505 said:
Ok new info:

I made a couple more pulls and the logger will still read 43 counts of knock at about 7-8 psi (Not a WOT pull) but my o2's are at .85v when under boost on every pull!!......isnt that about where it should be? Fuel trims are all at about 100%, I have wiseco 8.5:1 pistons also,Thanks!

What gas are you using??? O2's should be in the .9xV range when using pump gas. On race gas, you can dip into the .7xV range with very careful tuning.
 
NOSLO2PT0 said:
What gas are you using??? O2's should be in the .9xV range when using pump gas. On race gas, you can dip into the .7xV range with very careful tuning.

I'm using pump gas.
 
.85 is appropriate when running the stock 1G compression of 7.8:1. Now that you have the higher compression pistons, the O2 voltage needs to be higher. .92 to .94 is about the range you are shooting for.

You also need to verify the base timing is correct.
 
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