2G Random Misfire P0300

PrimerPLus · May 23, 2016

I am trying to diagnose a P0300 Random Misfire CEL.

Here is what I have done so far to try and solve / figure out the problem.
Had my FIC 1150s tested. All were checked by FIC and passed. No issues.
Replaced power transistor, coil pack, plug wires NGK, plugs (BPR7ES gapped .025" due to being told I was getting blowout at high rpm when at .028"), Cam Position Sensor, and Alternator to a Galant 90amp.

Not sure what else to check. I am pretty sure my o2 sensor is good as it cycles when watching a log in ECMLink.

I found a website that talks about EGR and that it can cause rough idle and random misfires if not working properly.
http://www.aa1car.com/library/egr.htm

I also have CELs for P0443 but I just disabled with ECMLink.

I am thinking about just doing a complete Emissions Delete if it is the EGR valve as I am pretty sure the evap system isn't working because I have this CEL that I still can't figure out the cause.

Any suggestions on what to check etc would be helpful.
I do have an EGR blockoff plate that I have not installed. Maybe I can install it and leave the EGR valve connected to the vacuum lines just for testing purposes to see if I get the code again?

I also can't help but wonder if the gap on my plugs are causing the misfire.
I see that others experience some sort of power loss or "limp mode" my car doesn't show any signs of that. I usually get the code when I am letting it warm up at idle or just get into the car and take off. If I clear it with ECMLink right then I won't see it again for a while maybe a day later.
It hasn't affected the driveability of the car but I know there is some reason for the CEL and would like to fix it.

usmcjay · May 23, 2016

This was a simple fix for me. My crank position sensor was going bad. Changed it out and no more code.

PrimerPLus · May 23, 2016

Okay I will look into it. Thank you for the suggestion.

Spades · May 24, 2016

PrimerPLus said:
I usually get the code when I am letting it warm up at idle or just get into the car and take off. If I clear it with Link right then I wont see it again for a while maybe a day later.
It hasn't affected the driveability of the car but I know there is some reason for the CEL and would like to fix it.

Man I have those exact same symptoms, always pops up every 2 days while warming it up. One time it lasted 3 days. I did the plugs and wires and made no difference.

I thought I had it when I did the ignition module but after 5 days it returned. Gonna look into the crank sensor next and then the ECU.

Like yours, my car shows no signs of misfire and drives perfectly fine. My code is mostly P0301 but once it was a P0300 code

PrimerPLus · May 25, 2016

Just tested the Crank Position Sensor. Seems that all the Voltages are within Spec.

Following this from thread http://www.dsmtuners.com/threads/crank-and-cam-angle-sensor-testing.98536/

"First you need a multimeter.

CAS is the rectangular plug and crank is the triangular plug.

Disconnect CAS connector.
Measure the voltage on harness side pin 3, the red wire, with the key turned to on voltage should be 12 v or more.
Then make sure you have continuity, 0 ohms, on harness side pin 1, the black wire, to ground.
Then measure the voltage on harness side pin 2, the blue and red wire, with key on should be 4.8-5.2V.
Reconnect CAS.
Measure voltage on pin 2, blue and red, while starting the engine it should be 0.4-3.0V. With the engine idling it should be 0.5-2.0 V. If you have 0V your CAS is dead since you should get some sort of volt reading.

It's the same for the crank except the cranking voltage will be 0.4 to 4.0 v and the sensor wire, pin 2, will be blue and white. Idling is 1.5 to 2.5 v.

props to luv2rallye he taught me how to do this test."

Using the Blue/white wire as my 2nd pin.

Idleing with multimeter in pin 2 (blue/white) and ground I get 2.0-2.1Volts

Car off but with Ignition ON
With probe in Pin 3 and other to ground (battery negative post) I get 11.88V
With probe in Pin 2 (blue/white) and other to ground (battery negative post) I get 5.0V
With probe in Pin 1 (Black wire) and other to ground (battery negative Post) I get continuity.

These all pass the book test.
Should I look elsewhere or change the sensor anyways?

Spades · May 27, 2016

On 2nd thought i will look at crank sensor LAST, it is the most difficult to replace. This weekend I will do the cam sensor testing, injector swap, coil, and lastly the crank sensor

And thanks for the test procedures

PrimerPLus · Oct 1, 2016

Update:
It has gone from Random misfire to Cylinder #2 Misfire.
Also takes much longer to come back when I clear the code.
Still doesn't affect the feel of the car, but I think it is causing false reading in ECMLink as lean.

The O2 sensor is cycling but the shielding has come off due to heat from exhaust manifold.
I found a boost leak at throttle body shaft seals. Replacing those as soon as new ones arrive. Don't know if it will change anything for the misfire.
I removed the EGR and blocked it off, left in the charcoal canister, and lines running to it (mine is behind driver headlight). Capped off all the throttle body ports and the check valve from valve cover to intake manifold. (I have a catch can setup).

Checked all the injector plugs and they are all reading at their correct values.
Spark plug resistor box values all check out, Coil pack values check out.

I leaning towards it not being anything mechanical, and most likely electrical. My problem is I do not have all the required tools or manuals to check all the wires to make sure they are at the correct values.

PrimerPLus · Oct 4, 2016

Would a Noid Light help me even if I tested the injector voltages of which all pass 12v.

laurence riggs · Dec 17, 2019

I have a. 1997 gst. it has a walbro 255 fuel pump, fic 950cc injectors, greedy cat back exhaust, greedy bov, 16g td05h turbo, fuel pressure regulator. my problem is the car when worms up check engine light comes on and pulls the code p0300. misfire on number 2 and 3 cylinder. I have replaced the plugs and adjusted the fuel pressure regulator, its now running better but its stuttering now at 4k and check engine light comes on. As soon as I drop the rpms it runs better.
I was thinking it might be the bigger injectors. the other guy put in. But now I'm thinking maybe the. coil. Also I can't get any heat to work with the heater. thinking it might be the heater control. valve but I'm not sure were the valve may be. I think it may be inside up bye the firewall but not sure. Any help would be grate.

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