CEL & P0326 - what's going on??
 

Hope one of the engine gurus can help with this one. Car has been driving fine recently. Doesn't sound or feel like it is knocking. I use 93 octane fuel, usually shell. Have a 15% pulley, colder plugs, CAI, otherwise stock engine. Did valve stem seals and re-ringed it last summer.

I have been getting the CEL every night cruising on the highway on the way home from work (8 miles on the highway). Reading the codes, it is always P0326. The only weird thing in the freeze frame data is it is reporting engine load as 99% two of the three times, but RPM's are around 3000 and speed was around 65 mph. And I was cruising at fairly steady speed. Engine was fully warmed up. I cleared the codes each time, and it would come back the next afternoon (not the morning drive - which is cooler).

Any thoughts? - maybe just a bad knock sensor, but why the 99% engine load reading? Anyone know what data goes into that calculation?

Thanks,

David

Here are the freeze frame readings from the last three times:

P0326
Closed Loop
Calculated Load 99%
Coolant 189 F
Short Term Fuel Trim -9.36 %
Long Term Fuel Trim 3.12 %
Intake Absolute Pressure 27.1 in Hg
RPM 3328
Speed 64 MPH


P0326
Closed Loop
Calculated Load 63%
Coolant 192 F
Short Term Fuel Trim 7.02 %
Long Term Fuel Trim 0.78 %
Intake Absolute Pressure 20.1 in Hg
RPM 2953
Speed 58 MPH


P0326
Closed Loop
Calculated Load 99%
Coolant 194 F
Short Term Fuel Trim -7.02 %
Long Term Fuel Trim 2.34 %
Intake Absolute Pressure 27.1 in Hg
RPM 3295
Speed 63 MPH

Just found this slide about OBDII that shows engine load calculation is related to air flow and intake vacuum. Anyone think this is a failing intake pressure sensor? or intake air leak?

According to OBD Codes here - Potential causes of a P0326 code include:

• Knock sensor connector is damaged
• Knock sensor circuit is open or shorted to ground
• Knock sensor circuit is shorted to voltage
• Knock sensor has failed
• Moisture in knock sensor connectors
• Incorrect fuel octane PCM has failed

Not sure about the load question, but it really could just be the sensor so maybe start there? Here is the sensor if needed. I believe it's a pretty labor intensive DIY. Maybe someone else will have some more input as well. Here is a thread on NAM about the knock sensor, and what other threads I am seeing is the sensor typically is their issue. Good luck!

I removed the intercooler and tmap sensor - found both to be oily. Cleaned the tmap with compressed air, cleaned the intercooler with acetone and so far my codes have gone away. That 99% load was a clue the tmap wasn't reading correct vacuum/pressure, but funny it didn't give its own code.

Still going strong with no new codes. I suggest anyone with a P0326 make sure to read the freeze frame data and pay attention to bogus high engine load (tmap) values. Glad I got the idea to investigate the math behind the engine load value to point me in this direction.