vr4play350

iTrader: (10)

just wondering if someone out there has a fix or sugestion why only in 5th gear on the h-way it will randomly misfire or seem like it drops a cyl. usually happens around 3k or so only in 5th and when it starts to studder i can let off and it goes away when i get back on . it seems like at a certian load point only that it does it. i just changed the plugs with 7es's id did the same thing before and after the plugs. possibly coil pack? wires? and it only throws p0300 (random misfire) not a perticular cyl. if anyone had this problem shoot me a pm or post. thanks! i hate my celhaha

oneonlywgs

iTrader: (2)

when I get that code, I swap out the plugs.

barneyb

The tuners have found where in the ECU the P0300 code can be shut off to never return. If you aren't into digging around inside the computer some Evo speed shop can do it for you.

barneyb

Since you are new to the list (1 post) I should add that the P0300 code is something that about everybody here has had to experience. Search and you will find plenty of reading. On the Evo 8 it is exactly as you describe and can take the fun out of driving. When it happened to me I always felt the car was about to break down and leave me on the side of the road.

Anyway, the random misfire emissions test is one of those government mandated things that probably serves a purpose on most cars but on the Evo 8 enough drive train vibration is fed back to the crank to set the code. Get it fixed the way I explained above. There's posts on this site concerning the fix too.

1d10t

iTrader: (19)

I think that there is a bulletin on the input shaft on 03-04 transmission and p0300.
However, most evo owners from any year suffer from the p0300.

vr4play350

iTrader: (10)

wow thanks for the info guys... ya you could say im a newbe for sure on this site

so its a vibration thing in 5th gear that set's it off... wow thats weird. i just dont get how it can kill spark / injector, or whatever its doin.

im looking into getting a tune/flash soon so hopefully i can get that code deleted

i just changed my plugs a day ago and it didn't make a lick of difference

thanks again !

Slo_crx1

iTrader: (9)

No, it's not a vibration that sets the code. The way it works is if the ecu sees a random misfire once, it sets p0300 as a pending code. Happens again, and it sets it as an active code, pops the SES light on, and usually gives that cylinder drop effect as well. The ecu gets feedback from the knock sensor, crank sensor, cam sensor, and I'm sure a few others that actually have an effect on whether or not the p0300 is triggered. So you could be getting it due to excessive knock, or simply from old plugs, or even from an old stretched out timing belt. If you still have the older 2003 rom ID 94170008, most of the p0300 issues can be resolved simply by updating the rom to 94170015. That's the factory mitsu patch to fix that particular issue, but if you have larger than stock cams most of the time the code will still come back. The best bet to getting rid of it for good is by disabling it through the ecu periphery bits, but there is another way as well that I've found works and will keep you obd inspection compliant (not that that's really an issue in most of PA). So far I use the latter way that I found without any p0300 codes for almost 2 years, but most choose to disable them.

barneyb

I'm reading in the 2003 Evo Service Manual under the section DTC P0300 RANDOM/MULTIPLE CYLINDER MISFIRE DETECTED.

It says, “If a misfire occurs while the engine is running, the engine speed changes for an instant. The ECU checks for such changes in engine speed.” The sensor it mentions is the crankshaft position sensor.

It lists some possible causes including the ignition system, the crankshaft position sensor itself, incorrect air/fuel mixture, low compression, skipping teeth on the timing belt, EGR failure and the failure of the ECU.

Since I had this problem since the car was new I suggest none of the above is usually responsible – although anything that causes misfire (or anything that fools the ECU into thinking there is misfire) could set the code. As the above poster mentioned there is a bulletin out concerning slop in the transmission and the P0300 code. Since my transmission is otherwise fine going this route seems like a bad investment to me.

There were also a couple of code updates for the ECU made available from Mistu. New code did not fix my car.

Anyway, enough for the rehash.

vr4play350

iTrader: (10)

ya im not exactly sure what rom i have as of now. i know there's new plugs in it. just put them in last weekend. i was planning on having a tune soon so hopefully i can get all this crap worked out soon cause its really annoying! its got stock cams/airbox with a k&n 9 turbo. 02 housing/downpipe. stock cat back(going away soon ) once i put an exhaust on it ill get it tuned and we'll see how things go.

thanks for everyone's suggestions. i appreciate it!

vr4play350

iTrader: (10)

update!

i decided since my partial throttle boost was quite agrivating with the POS forge bov that was in the car when i got it i took it out and replaced it with the stocker.

the car hasnt had a hickup since. it drives GREAT and now i can mid throttle it all day long on and off without it blowing all my boost off. (what a peice of junk)

i had it in for about 2 days with some moderate hw driving. and it hasnt broken up at all yet. i found it did it every time at 3500 rpm and 80 mph. consistantly.

so i cleared the codes last night that it threw and im gonna see what happens ill hope they dont come back .

thanks for the input ill keep you posted

evoterp

iTrader: (3)

how many miles do you have on the car? I'm hoping it was fixed because the higher mileage evo's have experienced this code and a tranny rebuild was necessary to get rid of it. there is a thread on here.

EatSleepBoost

iTrader: (9)

good to hear. yea bov's give you alot of problems if you have the wrong one. i run the ngk 8's for plugs and they clear up my p0300 and i just replace them every 2 or 3 months. also in 5th with the cold weather you could have boost creep. since your running more boost then you should be due to creep it may knock

vr4play350

iTrader: (10)

i think she has about 64 on the clock. and i just put 7's in maybe ill try the 8...

its been off for about 40 miles or so now after a code clear. it runs a million times better and hasnt studdered even once onthe h way yet. so ill cross my fingers thanks !

bigric09

iTrader: (37)

just have the P0300 disabled... its pretty easy

vr4play350

iTrader: (10)

well it came back on after about 75 miles...but its the egr...i think previous owner has some vaccum line issuse...;