P0300 Random Misfires
09-02-2015, 05:27 PM
#1
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P0300 Random Misfires
Figure I'd keep this post separate from the overheating one to make it less complicated.
I got a P0300 code a week or two back. I'm still struggling with diagnosing it.
Symptoms:
- Crank time is slow.
- Rough idle after start up.
- The first few seconds/minute of driving will have accelerating issues. The gas pedal just presses down and no accelerating, has to be tapped again etc. NOTE* This is a more recent issue. It wasn't happening when I first got the code.
So far I've replaced all the spark plugs. That appears to have solved the rough idle at start. I did this just last night, so again, need a few more days to know for sure.
The battery and alternator were checked and came back as a-ok.
Additional Notes*
- The previous owner was putting it 87 Octane when the manual calls for 91+. I switched to 91 after buying it and around that shift is when this issue kicked in. I've tried a couple of bottles of Lucas fuel injector cleaner, yet to no avail.
I purchased a fuel pump and will install that, hopefully by Friday.
Guessing that octane change is what induced the problem, so I'm thinking the fuel injectors would be the next step if not the fuel pump.
Thoughts?
I got a P0300 code a week or two back. I'm still struggling with diagnosing it.
Symptoms:
- Crank time is slow.
- Rough idle after start up.
- The first few seconds/minute of driving will have accelerating issues. The gas pedal just presses down and no accelerating, has to be tapped again etc. NOTE* This is a more recent issue. It wasn't happening when I first got the code.
So far I've replaced all the spark plugs. That appears to have solved the rough idle at start. I did this just last night, so again, need a few more days to know for sure.
The battery and alternator were checked and came back as a-ok.
Additional Notes*
- The previous owner was putting it 87 Octane when the manual calls for 91+. I switched to 91 after buying it and around that shift is when this issue kicked in. I've tried a couple of bottles of Lucas fuel injector cleaner, yet to no avail.
I purchased a fuel pump and will install that, hopefully by Friday.
Guessing that octane change is what induced the problem, so I'm thinking the fuel injectors would be the next step if not the fuel pump.
Thoughts?
09-03-2015, 08:14 PM
#2
Did you install the correct $8 each NGK spark plugs?
forget lucas- get 2 cans of Seafoam at wallyworld- cheapest there
1 can to just under half tank of gas, do that 2 times
87 octane left behind a lot of crud that seafoam will get. Lucas works used at max dose which is not how its labeled~
91 or 94 octane if you can get it. Tier 1 quality brands are preferred
don't get ahead of yourself with fuel pump and injector replacements.
Do the needed maintenance- guessing well over 100kmiles? time to remove the intake manifold from engine and place on workbench. Using 3 cans carb cleaner and a wire coat hanger you will poke decades of carbon/exhaust crud blocking the egr passage and port system. Makes car run poorly as you described
Needs to be done every 75kmiles!
Clean the IACV Idle Air Control Valve (rod with air slit that's clogged up) that's inside the Throttle Body- which comes off the car with the intake manifold
easy diy 2 hours at casual pace, does wonders!
Slow cranking with good batt test suggest bad ground wires. And crud on the battery terminals?
The main ground wire from battery has a problem with the wire coming loose
inside its connector to the frame- under battery box. CK that- loose is not good!
Start with cleaning all the grounds - 5 small braided wire ones from body or frame to engine parts, and the larger ones at battery and trans case. Ck each wire for resistance, they get old and fail!
forget lucas- get 2 cans of Seafoam at wallyworld- cheapest there
1 can to just under half tank of gas, do that 2 times
87 octane left behind a lot of crud that seafoam will get. Lucas works used at max dose which is not how its labeled~
91 or 94 octane if you can get it. Tier 1 quality brands are preferred
don't get ahead of yourself with fuel pump and injector replacements.
Do the needed maintenance- guessing well over 100kmiles? time to remove the intake manifold from engine and place on workbench. Using 3 cans carb cleaner and a wire coat hanger you will poke decades of carbon/exhaust crud blocking the egr passage and port system. Makes car run poorly as you described
Needs to be done every 75kmiles!
Clean the IACV Idle Air Control Valve (rod with air slit that's clogged up) that's inside the Throttle Body- which comes off the car with the intake manifold
easy diy 2 hours at casual pace, does wonders!
Slow cranking with good batt test suggest bad ground wires. And crud on the battery terminals?
The main ground wire from battery has a problem with the wire coming loose
inside its connector to the frame- under battery box. CK that- loose is not good!
Start with cleaning all the grounds - 5 small braided wire ones from body or frame to engine parts, and the larger ones at battery and trans case. Ck each wire for resistance, they get old and fail!
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