What does this O2 sensor data mean?
Thread Starter
Teching In
Joined: May 2024
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What does this O2 sensor data mean? I'm pulling my hair out trying to figure out why I have random misfires and pinging/KR on the highway at throttle inputs above 1/4. The truck will idle all day long and not register any misfires. However if you raise the RPM to 1000, it will misfire all over but most specifically in 1, 4, and 7.
Here is some completed diagnostic efforts:
I smoke-tested the motor and found a leaky PCV fitting on the aftermarket valve cover. I also found the cover did not have an orifice. I replaced the cover with a Granetelli item and installed both a check valve and an improved racing restrictor. This fixed the issue and motor reliable holds 4 psi of smoke without an leaks.
I also smoke-tested the brake booster and found it had failed. I replaced it with a new OEM part and it passes.
I replaced the MAP sensor (reading taken at hot idle @ 4600', drops to 7.5psi in gear at hot idle), cleaned the MAF, installed new plugs and wires, and cleaned the grounds on both sides of the motor that ground the PCM/coils.
Compression on all cylinders is 170-175psi on my gauge
I had all of the injectors professionally cleaned and flow rates documented. I installed them with my fattest injectors in cylinders 7 and 8.
Here is a data set now, taken at idle:
THe
The
Here is some completed diagnostic efforts:
I smoke-tested the motor and found a leaky PCV fitting on the aftermarket valve cover. I also found the cover did not have an orifice. I replaced the cover with a Granetelli item and installed both a check valve and an improved racing restrictor. This fixed the issue and motor reliable holds 4 psi of smoke without an leaks.
I also smoke-tested the brake booster and found it had failed. I replaced it with a new OEM part and it passes.
I replaced the MAP sensor (reading taken at hot idle @ 4600', drops to 7.5psi in gear at hot idle), cleaned the MAF, installed new plugs and wires, and cleaned the grounds on both sides of the motor that ground the PCM/coils.
Compression on all cylinders is 170-175psi on my gauge
I had all of the injectors professionally cleaned and flow rates documented. I installed them with my fattest injectors in cylinders 7 and 8.
Here is a data set now, taken at idle:
THe
The
Last edited by FastGas; Oct 3, 2025 at 12:07 PM.
Thread Starter
Teching In
Joined: May 2024
Posts: 27
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I obviously notice the fat fuel trim on bank 1 and don't understand why. I replaced both banks #1 O2 sensors thinking I had a bad one but here is the voltage data for both sets at idle:
Bank 1:
Bank 2:
Bank 1:
Bank 2:
Last edited by FastGas; Oct 3, 2025 at 12:08 PM.
Thread Starter
Teching In
Joined: May 2024
Posts: 27
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I'm not sure if I am chasing 2 separate issues or if my bank 2 cat is bad which is causing bank 1 to run lean? I can't find any vacuum leaks or fuel restrictions. I am running an aftermarket coil harness from Holley and could try swapping back to the OEM coil harness but I don't think that will yield anything. I have gone one by one, unplugging the coils, noting a change in idle, and then the fuel injectors, noting a change in idle.
Thread Starter
Teching In
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Thank you so much for the feedback! This is a supercharged vehicle and that log was taken on a hot day with lots of heat soak. I have since made efforts to improve my heat exchanger efficiency (increased total fluid capacity by 3 gallons, re routed all lines well away from anything hot, and switched to liquid chill coolant) and went through my ignition system (new spec'd whipple TR7 plugs, tried OEM coils/wires and harness and aftermarket accel coils and 10mm wires) without any improvement. I also performed a crank relearn (at least I think it was successful). The truck continues to pull that 15.5 inhg at idle in gear @ 4600' and misfire randomly on all cylinders with no load at 1000rpm. I will post another log from the Efi Live shortly.
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Verdad Gallardo Thread Starter
Teching In
Joined: May 2024
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at one point this setup had injectors 4 and 6 backwards and I am wondering if that is the cause of my issues. I am curious if I had sent a log with this error to black bear and it was read as bank 2 running lean and bank 1 running rich due to free fuel floating around the intake? I verified and corrected this issue and now possibly have bank 1 running lean due to the elimination of extra fuel and bank 2 running rich due to appropriate injector timing?
TECH Apprentice
Joined: Oct 2018
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From: Glendale, AZ
The one bank is consistently several points higher than the other. An exhaust leak esp upstream from the o2 sensor can throw off the readings, have you checked that?
Timing will get pulled if the knock sensor is registering knock.
Timing will get pulled if the knock sensor is registering knock.
Thread Starter
Teching In
Joined: May 2024
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This vehicle has AR LTs with high-flow cats. I will have this this assessed later this week by some pros. I've been chasing my tail, fruitlessly and expensively for too long. I suspect I have either a gross timing issue (due to a CPS, VVT component, crank relearn required, worn timing set (how @ 62k??), etc) or a tune that doesn't properly account for VVT at all (this would be a very curious development since Black Bear produced the current tune and they're allegedly very familiar with this platform).
I can certainly check my mani bolts but I haven't seen any related symptoms like clicking/ticking when cold.
I can certainly check my mani bolts but I haven't seen any related symptoms like clicking/ticking when cold.
Thread Starter
Teching In
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To follow up. I decided to just go ahead and replace the MAF on this with an OEM part since it was inexpensive. My LTFTs both dropped from +17 to +6 at cruise and I'm not seeing any KR unless I lug in top gear going up hills. I seem to be on the right path. Again, this is without throwing any codes or weird behavior aside from the occasional misfire at hot idle. I'm now wondering if I need yet another crank relearn procedure, these injectors are just junk, and if my ported throttle body isn't closing 100% at idle....
Before:
af
Before:
af
Thread Starter
Teching In
Joined: May 2024
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I wanted to follow up one more time.
I have purchased a FAST 102mm TB to rule out the GPE ported LS3 throttle body I have been running (I was told these can behave strangely even when ported correctly). I am still waiting for an ICT adapter arrive to finish installing it but will also look into boring the Whipple the next time I remove the rotors housing for....injectors?
I am now curious if these issues aren't the result of a damaged timing chain tensioner/slack timing chain and VVT. When I changed the oil this past weekend I discovered a chunk of orange plastic stuck to my magnetic drain plug. At the time, I wish I had passed a camera into the sump in search of the metal spring that's know to fall out when the tensioner fails. Would this be a cause of just enough timing issues to produce these issues while at the same time not enough to trip a check engine light? As you all know, barring my finding something significant in the sump with an endoscope, investigating the timing system is a very big job.
I know I am close as I continue to see data like this while under low engine loading/cruise conditions:
I have purchased a FAST 102mm TB to rule out the GPE ported LS3 throttle body I have been running (I was told these can behave strangely even when ported correctly). I am still waiting for an ICT adapter arrive to finish installing it but will also look into boring the Whipple the next time I remove the rotors housing for....injectors?
I am now curious if these issues aren't the result of a damaged timing chain tensioner/slack timing chain and VVT. When I changed the oil this past weekend I discovered a chunk of orange plastic stuck to my magnetic drain plug. At the time, I wish I had passed a camera into the sump in search of the metal spring that's know to fall out when the tensioner fails. Would this be a cause of just enough timing issues to produce these issues while at the same time not enough to trip a check engine light? As you all know, barring my finding something significant in the sump with an endoscope, investigating the timing system is a very big job.
I know I am close as I continue to see data like this while under low engine loading/cruise conditions:
Last edited by FastGas; Dec 17, 2025 at 12:10 AM.