so i got my car tuned for 30psi on e85...0 knock.. me and the tuner did about 15 street pulls and got the tune down perfect.. 0 knock...
so i went to the track the same night and ran some good times, with no knock at all...
drove home and got on it a couple of times before getting home with no knock..so the next day (yesterday) it started producing knock right round 4k rpm all of a sudden.
i changed the map to my old map on 25psi and turned the boost down and stil same problem....so its not the tune...

what can be causing this all of a sudden

 

IF your using a MAF still and not a AEM or other stand alone i would check check you maf.. my car started having little knock/miss fires here and there at higher rpm..It was the start of my MAF honey comb getting messed up. until the the honey comb got wrecked and the car would barely idle.

 

Same tank of E85?

 

the maf doesnt have a honey comb...itook it off a whileago...

and this was on a dif. tank of gas...

 

You could have potentially gotten an old tankful if it was from a different station. If this is the case, burn it up or drain it out and try again

 

Filled up wit another tank of e85 n still same issues..

 

Well if your 100% its not your maf i would check plugs , coils ect.

 

i just changed the plugs a day before the tune...n mycar doesnt drive any different at cruising

 

Check for a leak off the exhaust manifold. I had a false knock issue and it turned out there was an exhaust leak off the head to exhaust manifold.

 

wow.. can it really be tha simple??? cuz it does have a exhaust leak at the mani