Running Lean, Spark Advanced, Knocking

[mark111]

I have a '98 chevy, 4WD, 5.7, auto. I have been experiancing low power. I noticed the manifolds were cherry red last night. I am assuming it is running lean. I have spark knock and put a scanner on the vehicle. It shows no trouble codes, and showed the timing to be 23 degrees advanced. I also do not have a check engine light on. Really desparate here, can anyone help? I was told to disconnect the BRN/wht wire and time it with the scanner. I can not find this wire. Please help.

 

Thanks in advance, Mark.

[Genuinefine409]

Before you mess with anything, did this happen all of a sudden or after is was worked on or what? If you can trace the problem backwards its much easier than trying everything till you figure it out. if you are having spark knock that comes from too much timing advance and 23 degress should not cause spark knock. If it does knock it should retard the timing. I would think it would be a fuel problem, not timing.

[mark111]

Can a fuel problem cause detonation knock? I thought 23 degrees was way too much, causing the knock, and the system was not properly retarding the timing the way it should. (Knock sensor maybe?, but then there should be a code???). Anyway, this is a tow truck that I bought with problems. It didn't run very well when I bought it, and yes, someone had tinkered with it. I replaced two bad injectors and the intake manifold gaskets and it got better. I do know it is running lean because of the hot exhaust manifolds, and there is an aftermarket mass airflow sensor in it. Thinking maybe this is bad too. But shouldn't this stuff show up on a scanner? I know I'm in deep and need help from a GM Tech. Please help.

 

Thanks, Mark.

[Genuinefine409]

I used to drive my S10 race truck on the street when it had a mild 355 in it and I had timing locked out at 36 degrees and I used 93 octance gas with no problems. I would like to think its not a timing issue. I hade seen on two trucks, both of them 95 TBI 350's where the knock sensors were bad and never threw a code. They both had the spark knock problem bad. Are you sure the intake is sealed back up good? no vacuum leaks? My 96 5.7 was always around 20 degrees if I remember right. Thats at an idle too i think.does it throw any codes at all?

[mark111]

No, no codes at all. If no code, how can I check for proper operation of the knock sensor? Can I check output voltage maybe? I'm pretty sure it is running lean due to the very hot Ex. manifolds. I wasn't aware that a fuel problem would cause knock. Is there a way to check the mass airflow sensor when there are no codes?

 

Thanks, Mark.