*Moved here:https://www.thirdgen.org/forums/tech...l#post5889185*

TPI is the wrong forum. Sorry if this isnt allowed*

 

*moved to general thread*

 

You've been quite through. Are you sure the misfire/shake is when the spark advances higher? I've seen that anytime I've had an engine misfire so it may or may not be the problem. The backfire leads me to think either you have a cylinder loading up, a lean condition despite the datalog, or mixed up ign wires. Since you checked the firing order maybe start looking at a fuel problem. Have you checked fuel pressure?

 

Would a lean condition cause a backfire from the exhaust? I thought that was a rich condition symptom. I have not checked fuel pressure as I dont have a guage right now, unfortunately. Might be time to buy one.

I am not positive that the spark advance is causing the issue, more that the missfire happens around the same time as the logger seeing 24*. Im not 100% which is the cause or effect.

 

You're talking about a backfire out the exhaust, correct? It can be caused by either rich or lean conditions. Unburned gas getting into the exhaust that then gets hot enough from the exhaust itself that it burns/explodes. At least that is how I understand it. Judging by occasional pop you're talking about leads me to think lean. Could very well be just one cylinder going lean or not firing right causing it to load up. Again, I have seen this exact problem when the plug wires were mixed up just right. Not that I doubt your ability to check the wires, just want to point out it is possible problem.

 

Only time my car backfired, it was the fuel pressure regulator, the vac line runs back to the plenum. With the reg blown fuel was poring in and being sucked into cyl 8 mostly. Pull the vac line and see if fuel comes out. Could be tricking the ecm into running the rest of the cylenders lean.