P0300 Help needed
#1
03-07-2018, 09:52 PM
P0300 Help needed
Hey people, I have a 2002 Blazer Xtreme that has the dreaded p0300. I have gone through what seems to be just about everything, checked the cap and rotor, all looked well no play or wear. Went through the plugs and wires, again all looked good, plugs gapped correctly and wires good. Changed the MAP sensor and AIC valve, sensor had a tear on the rubber gasket and AIC was not closing all the way. The truck drives great, no hesitation or any sign of a misfire, does have a low mph, but is better now that the MAP sensor has been changed. Only sign of the misfire is the DTC itself and the ses light will blink when at 65 mph or above (don't drive it on the freeway at all right now, only when diagnosing it). Forgot to mention the previous owner changed the injectors out and I checked for leaks all around the intake. Haven't done a compression test yet, that's next, but don't expect much with how well she runs. Here is the freeze frame data that I pulled today.
Fuel sys 1 = CL
Fuel sys 2 = CL
Calc Load(%) = 19.61
ECT(*F) = 161
STFT B1 (%) = 0.78
LTFT B1 (%) = -0.78
STFT B2 (%) = -3.91
LTFT B2 (%) = -1.56
MAP (inHg) = 17.72
eng rpm = 1808
veh speed (mph) = 31
MAF (lb/min) = 4.47
TPS (%) = 20.39
Any ideas or insights are appreciated greatly. Thank you for taking your time on this.
Fuel sys 1 = CL
Fuel sys 2 = CL
Calc Load(%) = 19.61
ECT(*F) = 161
STFT B1 (%) = 0.78
LTFT B1 (%) = -0.78
STFT B2 (%) = -3.91
LTFT B2 (%) = -1.56
MAP (inHg) = 17.72
eng rpm = 1808
veh speed (mph) = 31
MAF (lb/min) = 4.47
TPS (%) = 20.39
Any ideas or insights are appreciated greatly. Thank you for taking your time on this.
#2
03-08-2018, 04:50 PM
Sorry, but freeze frame data has limited usefulness here
If no miss is felt, but a misfire code ...
1. Make sure cam sensor retard is 0 degrees +/- 2 degrees or look for worn distributor gear.
2. Make sure fuel pressure is good at point when P0300 is setting
3. Induce a misfire by pulling a plug wire and make sure the misfire counter for that cylinder increases rapidly - this functionally checks your misfire system (there is such a thing as false misfire codes).
4. If still nothing apparent do a CASE relearn.
1&2&3 you can do with Android phone, software, bluetooth OBD2 adapter, and a loaner fuel pressure gauge - about $30.
#4 will require more serious bidirectional software (about $300) or a dealer with a TECH2
#1 and #2 are common and may or may not cause a felt misfire.
Report and we can go from there. False misfire codes can be cause by lots of things - even things like extra engine bearing clearance, bad transmissions, things driven by the serpentine belt, things out of balance, etc. Need to figure out if it is a real misfire first.
If no miss is felt, but a misfire code ...
1. Make sure cam sensor retard is 0 degrees +/- 2 degrees or look for worn distributor gear.
2. Make sure fuel pressure is good at point when P0300 is setting
3. Induce a misfire by pulling a plug wire and make sure the misfire counter for that cylinder increases rapidly - this functionally checks your misfire system (there is such a thing as false misfire codes).
4. If still nothing apparent do a CASE relearn.
1&2&3 you can do with Android phone, software, bluetooth OBD2 adapter, and a loaner fuel pressure gauge - about $30.
#4 will require more serious bidirectional software (about $300) or a dealer with a TECH2
#1 and #2 are common and may or may not cause a felt misfire.
Report and we can go from there. False misfire codes can be cause by lots of things - even things like extra engine bearing clearance, bad transmissions, things driven by the serpentine belt, things out of balance, etc. Need to figure out if it is a real misfire first.
Last edited by LesMyer; 03-08-2018 at 04:58 PM.
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