MrGlass

Sorry in advance for the long post. My mods are light, just 5/16" plenum spacer and Popcharger.

I've had this problem for a while now, and it's starting to get worse. During WOT, I get the Check Engine light flashing at me. I don't notice any change in power, exhaust note, etc, just the light. I bought a cheap Bluetooth OBD adapter, and it told me the P0300 code. I was also able to look at the O2 sensors, which all dropped (.1 or .2 Volts), indicating lean condition (too much oxygen in exhaust).

I bought Cipher data logging, thinking I would be able to instantly diagnose my problem, but the available data doesn't seem to point me in a clear direction, maybe someone here has better understanding or a good insight. I have bought a few parts, hoping they will arrive by Saturday so I can eliminate some possibilities.

The service manual suggests checking the following for P0300. I've also ordered a new crankshaft position sensor, in case it is broken and causing a false DTC.

1. Check for intake air leak and PCV hose: I've checked and rechecked for intake air leaks. The car idles fine, so I don't think there's any intake leaks. I have a PCV valve on order, so I will replace that.

2. Check for exhaust system clogging: I have visually inspected the exhaust system, there are no visible dents, etc. I haven't been able to visually inspect the inside of the cats, but it seems like they should be fine because the oxygen sensors downstream of the cats work as expected...

3. Perform power balance test: I have used Cipher to shut down individual cylinders, and every cylinder causes rough idle. I don't think this is an issue.

4. Check injector: I have used a fuel system cleaner with no results. Injectors function (clicking sound) just fine. Maybe they need to be cleaned?

5. Check ignition spark: I have visually inspected all coil packs, nothing seems wrong.

6. Check spark plugs: I have checked and rechecked the spark plugs, and replaced them with Denso Iridiums. Never noticed anything wrong with any spark plugs and they all look normal.

7. Check compression pressure: I have not purchased a compression test kit, so I haven't checked this yet...

8. Check fuel pressure: I do not have a fuel pressure guage kit, but it wouldn't do me much good anyway; my symptoms only appear at speed while driving. I think fuel pressure could definitely be a problem, whether it's the pump, filter, or pressure regulator. If the fuel pressure is low, then the engine isn't getting enough fuel at WOT, but could still function normally at idle and partial throttle. I don't think Cipher can tell me fuel pressure. I have ordered a new fuel pump assembly, hopefully the problem can be confirmed and the solution identified before I try replacing the fuel pump just to see if it works.

9. Detect malfunctioning part: This section of the service manual just tries to identify whether fuel problems are caused by the pump, regulator, fuel lines, or filter. Not really sure why this matters, as the pump, regulator and filter are all part of one unit...

10. Check ignition timing: Not sure how I could go about this, because I have no problems at idle, but the service manual has target timing at idle only. My problem is at 3k+ rpm.

11. Check heated oxygen sensor 1: Sensors show normal voltage ranges and readings. Visual inspection shows no damage.

12. Check mass air flow sensor: I have used MAF cleaner with no effect. MAF readings from Bluetooth OBD and Cipher seem normal to me, maybe someone sees something different from the Cipher logs? I have not tried switching MAF with another Z owner yet.

aln

You've done some troubleshooting there, after you cleaned the MAF or any of the other tests did you reset the ECU and do below:

Accelerator Pedal Release Position Learning

Operation Procedure
1. Make sure that the accelerator pedal is fully released.
2. Turn ignition switch ON and wait at least 2 seconds.
3. Turn ignition switch OFF wait at least 10 seconds.
4. Turn ignition switch ON and wait at least 2 seconds.
5. Turn ignition switch OFF wait at least 10 seconds.


Throttle Valve Closed Position Learning

Operation Procedures
1. Make sure that accelerator pedal is fully released.
2. Turn ignition switch is ON.
3. Turn ignition switch is OFF wait at least 10 seconds.
Make sure that the throttle valve moves during above 10 seconds by confirming the operating sound.


Idle Air Volume Learning (Throttle Position Learning)
It is better to count the time accurately with a clock.

Operation Procedures
1. Perform Accelerator Pedal Released Position Learning.
2. Perform Throttle Valve Closed Position Learning.
3. Start engine and warm it up to normal operating temperature.
4. Turn ignition switch OFF and wait at least 10 seconds.
5. Conform that accelerator pedal is fully released, turn ignition switch ON and wait 3 seconds.
6. Repeat the following (steps 7a, 7b) procedures quickly five times within 5 seconds.
7a. Fully depress the accelerator pedal (HARD)
7b. Fully release the accelerator pedal.
8. Wait 7 seconds, fully depress the accelerator pedal and keep it for approx. 20 seconds until the Check Engine Light (CEL) stops blinking and turned ON.
9. Fully release the accelerator pedal within 3 seconds after the CEL is ON.
10. Start engine and let it idle.
11. Wait 20 seconds.
12. Rev up the engine two or three times and make sure the idle speed and ignition timing are within the specifications.

Dont think it'll fix your problem. I got the engine light when I had a bad tune sometimes while under WOT.

MrGlass

I have done all of the "Technosquare" reset procedures on several occasions, including after MAF cleaning, spark plug change, etc. No change.