I have an issue that I am trying to track down. When I drive on the highway past 70mph I get a flashing CEL. Below 70 I don't get any CEL. I dont feel any vibrations or heavy misfires when starting up. Just a tiny rpm jolt from time to time. I've replaced the spark plugs. Put sea foam and techron into the tank. I even replaced the o2 sensors and still. The only code I pulled was a generic P0300. What I did recently at the mechanic was a Crankshaft relearn procedure. So far nothing has came up yet. Here is the Data I have logged from my scanner.

Live Data 5/32 frame

Number of DTCs stored in this ECU 0

Fuel system 1 status --

Fuel System 2 status --

Calculated LOAD Value(%) 30.6

Short Term Fuel Trim -Bank 1(%) -3.9

Long Term Fuel Trim - Bank 1(%) -100.0

Short Term Fuel Trim -Bank 2(%) -1.6

Long Term Fuel Trim - Bank 2(%) 7.8

Intake Manifold Absolute Pressure(psi) 11.9

Engine RPM(rpm) 2654

Vehicle Speed Sensor(mph) 73

Ignition Timing Advance for #1 Cylinder(¡ã) 31.5

Intake Air Temperature(¡ãF) 82.4

Air Flow Rate from Mass Air Flow(lb/s) 0.19

Location of Oxygen Sensors B1S12--B2S12--

Oxygen Sensor Output Voltage Bank 1-Sensor 1(V) 0.640

Short Term Fuel Trim Bank 1-Sensor 1(%) -5.5

Oxygen Sensor Output Voltage Bank 1-Sensor 2(V) 0.000

Short Term Fuel Trim Bank 1-Sensor 2(%) -100.0

Oxygen Sensor Output Voltage Bank 2-Sensor 1(V) 0.000

Short Term Fuel Trim Bank 2-Sensor 1(%) -100.0

Oxygen Sensor Output Voltage Bank 2-Sensor 2(V) 0.665

Short Term Fuel Trim Bank 2-Sensor 2(%) -100.0

OBD requirements to which vehicle is designed OBDI

Power Take Off(PTO) Status OFF







Live Data 6/32 frame

Number of DTCs stored in this ECU 0

Fuel system 1 status --

Fuel System 2 status --

Calculated LOAD Value(%) 30.2

Short Term Fuel Trim -Bank 1(%) -3.9

Long Term Fuel Trim - Bank 1(%) 9.4

Short Term Fuel Trim -Bank 2(%) -2.4

Long Term Fuel Trim - Bank 2(%) 7.8

Intake Manifold Absolute Pressure(psi) 11.8

Engine RPM(rpm) 2653

Vehicle Speed Sensor(mph) 73

Ignition Timing Advance for #1 Cylinder(¡ã) 31.5

Intake Air Temperature(¡ãF) 82.4

Air Flow Rate from Mass Air Flow(lb/s) 0.19

Location of Oxygen Sensors B1S12--B2S12--

Oxygen Sensor Output Voltage Bank 1-Sensor 1(V) 0.755

Short Term Fuel Trim Bank 1-Sensor 1(%) -4.7

Oxygen Sensor Output Voltage Bank 1-Sensor 2(V) 0.570

Short Term Fuel Trim Bank 1-Sensor 2(%) 99.2

Oxygen Sensor Output Voltage Bank 2-Sensor 1(V) 0.640

Short Term Fuel Trim Bank 2-Sensor 1(%) -2.4

Oxygen Sensor Output Voltage Bank 2-Sensor 2(V) 0.655

Short Term Fuel Trim Bank 2-Sensor 2(%) 99.2

OBD requirements to which vehicle is designed OBDI

Power Take Off(PTO) Status OFF

 

Are you using AC O2 sensors? Auto part store brands are not to be trusted.
Bank 1 sensor 1 and bank 2 sensor 1 are the primary fuel regulating sensors and should pretty much match each other's highs and lows at idle. O2 sensors have to be checked while driving steady or at idle not revving it up in neutral when doing live readings.
I chased a bad MAP sensor in my 5.3 that killed my MPG by 3 mpg. If it was not for my high-end scan tool that has 2 tests for it, I never would have found it as the MAP sensor was not setting any codes, yet it was erratic.

 

So far so good. Since they did the crankshaft relearn it does idle much quieter since this posting the random misfire has not come on. In other words, I did clean the maf sensors and intake. I’m at odds that I didn’t know about a CRP before. I should of did that first. But that is what the benefit of researching online is for lol.

 

That is a general misfire code. Does you scanner show you which cylinders are misfiring? Does it allow you to do a live "freeze frame". If it does then you should dig a bit deeper to see exactly where the problem is occurring. seems like a waste of money to just start swapping out things which "may" be causing the problem in the hope that it will fix it. Do you have a vacuum leak? Is your gas cap on tight? You replaced the plugs but didn't mention if the old plugs were fouled or if you just replaced them anyways. Might have been wasted money. Did you replace the wires too... i'm on a screen now that can not see that. I'm looking for a better OBD scanner without breaking the bank. Mine is pretty basic but it does allow me to identify the exact cylinders which are misfiring and watch them misfire live. Seafoam is a dated product and won't really make much difference on newer engines is my understanding... something about being for 2 cycles if I recall correctly.