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Engine misfire problems

domesticpower

Track Addict
190
135
NS
I have been having a recurring misfire problem over the last few weeks. I have codes for random misfires and cylinders 5, 6 and 7 (P0300, P0305, P0306 and P0307). Cleared them and they keep coming back. The problem happens with the street key and Trackey. It's hard to pinpoint but it seems to happen if the engine is at relatively low rpm (~4,000 rpm) and I go full throttle.

There's data available for the random misfire (P0300) so I pulled it and the car is running lean which is very worrying. Long term trims are -8.5 and -6.2 for banks 1 and 2. At the time of the misfire, short trims were -2.3 and -0.7 for banks 1 and 2 so overall fuel trims were -10.8 and -6.9 for banks 1 and 2. The fact that bank 1 is so much leaner yet the misfires are in bank 2 is odd. Coolant temp was 194. Sometimes the CEL flashes and it goes in limp mode. Otherwise, the engine light is on solid and power seems normal.

I took it to the dealer and they said there's a TSB for EGT sensor seal cracking and leaking, throwing off the readings. I thought that made sense - maybe the leak is causing a slightly cooler exhaust reading, causing the engine to think it's running rich and pull fuel. They replaced the seal with a new, bigger unit according to the TSB and I thought it was fixed but it came back. I'm going to go back to the dealer but anyone has any ideas? I did a little research and saw that it is sometimes caused by vibrations and a crankshaft sensor relearn fixes the problem. Any other possibilities? Thoughts? I have more information I can pull from the code if it'd help.

Car is a '12 Boss 302 and the engine is completely stock aside from a catch can.
 
Read through this thread if you haven't already. https://trackmustangsonline.com/index.php?topic=2598.0 The P0300 can often be corrected with the TSB that adds an O-ring to the sensor to reduce vibration and then doing the neutral profile relearn at the dealer.

Your cylinder specific misfires could be bad coils. I just changed 4 or 5 of mine when having similar issues and it solved the problem. The dealer should be able to hook up their laptop and run the diagnostics to see that when you take it in to them again.

You can also get P0300 random misfires from hitting the rev limiter on track.
 
Black Boss said:
+1

Got a P300 at the track this weekend, and I Have the Comp pulse ring, TSB fix and the PRS harness....
I'm continuing to get them as well on track, but I think it could be from occasionally hitting the rev limiter. I read on SVT about an issue with buildup on the magnetic crank sensor from the dust coming off aftermarket steel clutches like the Exedy. We tried cleaning mine off when I had one go bad earlier this year, but still needed a new crank sensor. I wonder if that is possibly responsible for causing them? I tried to find the link on SVTPerformance.com but their site is currently offline. If you do pull the sensor to clean it off you have to do the relearn. The thread was from Sean at AED Performance.
 
You shouldn't need the relearn if you pull the sensor. I pulled my sensor for the new harness and to clean it and dropped the Trans -- no issues.

The re-learn is needed if you move the crank without power e.g when torquing flywheel or friction plate bolts...

I'm pretty sure my P300 was hitting the rev limiter also -- it only happened in one session -- I'm sure a re-learn or Harness issue the code would have repeated for multiple sessions
 

domesticpower

Track Addict
190
135
NS
cloud9, thanks for the link. It sounds like I'm having the exact same problem that zzyzx is having, judging by some of his data. I hope the answer is in the thread. I have an appointment at the dealer on Monday and will update after. If anyone has any suggestions, please post so that I can go in armed with answers if need be.
 

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