I have been getting engine misfire at 3.5k to 4k rpm. It happened during 5th gear highway speed. Obviuosly it trigger the CEL. I changed the spark plug and it was gone a while few k's miles then came back. I have TBE and custome Dynoflash.
Any input?

 

Is that your only mods? are all bolts tight on the coils? Year of car,did you get i new? Need more meat to chew on.

 

I bought it new with 10miles on odo and currently 21k. It's an 03. The coil is tight.
Yes, that's the only mod. no cat though.
It has been to the dealer 1.5year before for P0300 fix which is before Dynoflash

 

Are you using the stock plugs? what boost are you running? what does the "misfire" sound/feel like? you don't have the magnacore wires do you?

 

No magnacore. I am running BR8EIX (due to many open track event). I have same misfire problem too when running stock plug.
Usually happen at around 80-85mph and you can feel the engine loss power and some vibration from engine then CEL will come on.

 

I would say try the NGKBPR7ES plugs. I use the BPR8ES's. (due to my HP) 7's for less HP/mods I have heard. What is the gaps on them?

 

I just bought mine at the dealer, I had same exact problem, only at above 3500 rpm in 5th gear with pedal down, dealer changed the plugs = fine since.

 

hi im a newbie. just got an o3 evo n having the same problem. i have try almost everything ,changing out new spark plug, wire. when i get on the freeway it came back on right away. then i change the coil. with no luck to. i clean my afm it work for awhile about 150 mile later it came back on again. if anyone find the problem please help. its driving me crazy. love my first evo tho. thanx.

 

Only use the OEM plug wires or Ralliart wires. Then, get NGK BPR7ES and gap them to .026.

 

thats what i use ngk . they're not pregab?? change magnacore but change it back to stock.

 

does the dealer have a definite P0300 fix yet?

 

I have the same issue...in 5th gear cruising the CEL pops on and the engine sounds and feels like it just dropped a cylinder.

I use BPR7ES and have them gapped around .026. Replaced them often and tried different gap combos...still happens.

 

Take the time to read through all the P0300 code threads here at EvoM.

The only thing that ever worked for me was a rebuilt trans. I learned to live with it (for 3 years, no less) with a CReader until such time I wanted the trans work done anyway.

Good luck!

 

Uhm, thanks but I have read up on it and it's not my transmission causing the code to trip.

 

I too am once again throwing the dreaded P0300 code, even after flashing back to the latest 05 Evo Mitsu firmware available. I see that the ECU+ folks have released a supposed P0300 fix, though I have to say, my car has been through about every conceivable fix for this including the Mitsu recommended reflashes, a piggback, multiple new plugs and new gapping settings, and even a full tranny rebuild and later transfer case rebuild, and it has come back. The only thing I haven't tried is new injectors, which has been suggested.

I suspect that there is absolutely a massive defect with the manner in which the drivelines of early 2003 Evo's at highway speeds and RPMs produce certain frequencies of sound that are so close to the knock sensor's "trigger sound" that it triggers constant false positive knock detection when there is actually no knock (misfire).

I also suspect that Mitsubishi knows this, and rather than recall every 2003 Evo and gut the engines to replace faulty knock sensors or rework the drivetrains, they chalk it up to bad firmware and deny, deny, deny.

That's my theory anyway.

I have some hope that the ECU+ boys have figured out a workaround for this *mechanical* defect by manipulating the ECU with a certain new flash, but time will tell.

In the meantime, sorry the OP is having trouble. Welcome to the club of the long line of 2003 Evo P0300 sufferers.

Cheers,
Adam