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P0300 Code Help

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crayzayness

Probationary Member
5
0
Jul 21, 2012
Madison, Wisconsin
I have a 1997 Eclipse GS 420a N/T with 171,200 miles on it that is throwing a P0300 code. I checked out the other posts with this code and none of them have the issue I'm experiencing.
Mods on the car are:
cold air intake
a/c delete
p/s delete
charcoal canister delete
stock exhaust with 5" can on the end

So my car has been throwing the P0300 code since i bought it. Originally when i code tested it, it showed P0301-P0304 as well. In effort to fix it i changed out the spark plugs and tested the wires and coil pack, all of which passed. I got Bosch +4 Platinum plugs. After that the P0301-P0304 codes disappeared but the P0300 remained. Also i replaced the front O2 sensor.
Shortly after i snapped the timing belt and bent the valves. I got a junkyard head with valves and took it to a machine shop to have it resurfaced and checked to make sure it was good to put on my car. The head passed with flying colors and was put on my car with a new timing belt and water pump. After that I noticed a gain in power and fuel economy. Compression testing resulted in 210psi in 3/4 of the cylinders with one cylinder at 185psi. All within spec.
Since then I still have P0300 code, and when I cruise around 3500rpm my CEL flashes at me. When this occurs I have no loss in power, no stuttering or shaking, and no other signs of a misfire. I've monitored the exhaust and have noticed no glowing or rotten egg smell from the Cat. No problems with exhaust pressure either.
I have also recently replaced the Crankshaft Position Sensor and that resulted in the light flashing more often.
The only problems I've noticed with the car are a rough idle (that seems to be effected by changes in the electrical load on the car. Also i just replaced the alternator)
So, I have a P0300 code with no discernible misfire or power loss, and no exhaust issue. Has anyone ever experienced a similar issue or have any suggestions as to what to look into next?
 
first off get rid of those +4 plugs they are no good with our engines they burn to hot. you need to get some ngk's 6 or 7's they sell them at checkers. you might need a new ecu if you can get one from the junk yard for 30 bucks i would try that out. with my misfire issue i had to replace the rear o2 sensor and buy a new coil pack. the coil pack i had was still good but it would not work right when it got hot. you can buy a coil pack and just see if it changes anything and if it doesnt you can take it back.
 
and when you say you tested the coil pack how did you do so? you have to check the ohms on the coil not just if it has power to it unless you did that. for the ruff idle i would clean out your iac sensor and see if that helps. are you running an egr too? that could cause a ruff idle also.
 
first off get rid of those +4 plugs they are no good

Agreed terrible plug, all of the bosch platinum's.
Disconnect/block off the EGR valve too, drive it & see if it goes away.
Cam timing also has to be dead on.

Sometimes these can be hard for a DIY to fix in some cases.
Why because it flashes the SES, but has no discernible drive ability problems.
Quite possible the ECU is misinterpreting a misfire.
Pretty sure my scan tool has a crank position relearn on these...
 
As everyone else stated, scrap those Bosch plugs. They are terrible. I had the PO300 on my old car using those. Swapped back to NGK's and the problem went away.
 
Thanks for the tips guys. I'm gonna try new spark plugs right away. I am running the stock EGR so i might try a delete on that for the rough idle. As for the IAC i'm almost positive that needs to be replaced. Also I did Ohm test the coil pack and that came out good. But i'll check it again to make sure. Again thanks for the tips guys and i'll get back to you soon about whether or not the spark plugs helped.
 
Even though this thread is totally dead, I figured i'd post my results to the problem! After much more looking and consulting a few others, we found that the plug wires are bad and are arcing inside the boot! New plug wires and I should be good to go.
 
hope this helps- eclipse manual

ENGINE <NON-TURBO> - Control System
&#65532;&#65532;
Diagnostic trouble code No.
Diagnostic items
Scan tool (MUT-II)
General scan tool
&#65532;

PO141 Downstream H02S heater failure <M/T>
&#65532;&#65532;
PO300 Multiple cylinder misfire* <M/T>
&#65532;
PO301 Cylinder #l misfire* <M/T>
&#65532;&#65532;
PO302 Cylinder #2 misfire* <M/T>

&#65532;&#65532;&#65532;&#65532;PO303 Cylinder #3 misfire* <M/T>
&#65532;&#65532;
PO304 Cylinder #4 misfire* <M/T>
 
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