Pre detonation knock.

[08grey]

Anyone understand the ins and outs of pre detonation.

My symptoms seem to be only when it's above 75 degrees outside and not octane related.

I get a decently loud cackle that I can only hear when it's bounced off a close by wall of highway barrier. It's loudest on take off and does not happen when in neutral. Only when In gear.

---------- Post added at 08:15 PM ---------- Previous post was at 07:45 PM ----------

Would a ecm blAck bear tune advance or retard timing?

 

[Wake]

You sure you're experiencing detonation? Maybe an exhaust leak instead?

If you had detonation the PCM either stock or aftermarket would retard the timing and you'd see some horrible fuel economy compared to what you're used to. Have you seen a noticeable drop in mpg?

 

[08grey]

Definite detonation or knock. I have always had horrible fuel economy. I average on the dic 10.2 mpg right now.

---------- Post added at 09:04 AM ---------- Previous post was at 09:02 AM ----------

In the summer I thought it was due to an exhaust manifold leak. I found a sheared off bolt but have since fixed that. It also got cold around the same time and the sound went away. It seems it has to be over 75 ish degrees for me to hear it.

 

[Wake]

Hmmm, no codes I take it?

Thinking you might need a scanner with some logging capability to see what the engine is doing under different conditions.

 

[08grey]

Gonna send black bear a data log since I'm running their tune. Just waiting for some warmer temps.

 

[OHSIXX]

Justin will definitely be able to tell you if something is wrong. Do always get gas from same place or do you switch it up? What type of tune are you running? FWIW-I get 16ish in the city and around 20 on the highway with their 93 tune.

 

[08grey]

I run 93 only and have been using bp fuel. I have a 91+ tune justin made for me and I get poor combined gas never really higher than 10 mpg. On a straight highway run I can get up to 17ish.

---------- Post added at 09:32 AM ---------- Previous post was at 09:29 AM ----------

My powertrain is Oem except for
Magnecore wires
Iridium ix ngk plugs
K&n intake
Helix tb spacer
A catch can
12909 magna flow.

 

[OHSIXX]

Interesting....the best MPG I get is when I use non-ethanol gas-but I can only find that up north. I'm basically stock except for GMPP CAI and Corsa exhaust. What motor do you have?

 

[08grey]

6.2.

 

[CHOO CHOO]

Maybe you have a bad spark plug? When I was on the dyno yesterday they told me I had a little pre detonation and said Justin needed to look at the tune. But after talking to another guy helping with the dyno, he said he does a lot of gm trucks and sees this every now and then. I told him of Justin and blackbear and he knew them instantly and doubted it was the tune. I told him I had e3 spark plugs and he said that was my problem. So maybe you just have a bad plug or a wire is bad?