Random Multi-cylinder Misfire (dtc code p0300)

[Eclipse_Tuner]

I need some help here.

I recently rebuilt the heads on my Eclipse and upgraded the cams to a larger N/A lobe, along with stiffer valve springs. Also put in new valves, seals, etc.

It starts and is drivable, but I get a misfire around 2000 rpm or when I accelerate. Its a noticable misfire too…however its not intermitant.

I have replaced plugs, wires, cap, rotor, distributor, tps, crank sensor, knock sensor and all gaskets. Also did a vacuum leak test and had no issues there either.

Any suggestions would be greatly appreciated.

Topic

[Anonymous]

Larger cams, stiffer springs, has the ECU been updated to increas pusle width of the injectors and have you installed larger injectors.

The P0300 is like you said, random, so my first looks if it was me was the supply side of fuel or make sure the ignition wasn’t dropping out and also if the injectors are opening properly.

To bad you couldn’t see what specific cylinders where missing enough to kick a P0300 but not enough to kick a 0301/02/03/04

[moparkid25]

lilwillie wrote:

Quote:

Larger cams, stiffer springs, has the ECU been updated to increas pusle width of the injectors and have you installed larger injectors.

The P0300 is like you said, random, so my first looks if it was me was the supply side of fuel or make sure the ignition wasn’t dropping out and also if the injectors are opening properly.

To bad you couldn’t see what specific cylinders where missing enough to kick a P0300 but not enough to kick a 0301/02/03/04

I agree, sounds like a fuel delivery problem. The ECM will have to be tuned to run with the new cams if its not already, and you may need larger injectors or an adjustable fuel psi regulator.

[Eclipse_Tuner]

I have an adjustable fpr, and fuel delivery isnt an issue. But I will investigate the injecter pulse as well as the timing advance.

It doesnt feel like a fuel issue though based on how the car behaves during the misfire. If I breathe the throttle a bit and get back into it, the misfire will stop.

[moparkid25]

Eclipse_Tuner wrote:

Quote:

I have an adjustable fpr, and fuel delivery isnt an issue. But I will investigate the injecter pulse as well as the timing advance.

It doesnt feel like a fuel issue though based on how the car behaves during the misfire. If I breathe the throttle a bit and get back into it, the misfire will stop.

What kind of air filter do you run, K&N? Have you recently cleaned and re-oiled your filter?

GM has a bulletin about the oils from performance air filters getting thru the screen on the MAF sensor and causing drivability issues. I’ve seen this on other vehicles also, like mustangs, where the MAF is located between the air cleaner and throttle body.

[Eclipse_Tuner]

That thought crossed my mind right away, so the filter is new and clean, and the maf is clean and functioning correctly.

[Anonymous]

Eclipse_Tuner wrote:

Quote:

That thought crossed my mind right away, so the filter is new and clean, and the maf is clean and functioning correctly.

If you are sure of your fuel supply and pulse width I would again pull the plugs and inspect them with a magnifying glass to see if they are showing any signs that could lead to your issue.

If you have a different set of plugs, try them, it is possible the porcelian is cracked in one or two and under severe load you are getting spark jump.

What brand of plug are you using?

http://www.explorerforum.com/photopost/data/503/medium/reading_spark_plugs.jpg

[Eclipse_Tuner]

Ive gapped and checked them, but I will look again. But Ive swapped plugs and it didnt really make a difference.

The are Denso Irridiums.

[Author]

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