Problem with P0300 code can't figure out what's wrong
 

Hey i've been trying to fix this p0300 code (random multiple misfire) on my 2003 evo Viii that has 82k miles. (everything is stock) it randomly decides to turn on and off when it pleases. I've replaced the spark plugs and wires, i have not touched the coil packs and i'm planning on changing the crankshaft position sensor unless anyone has any better ideas..


Also, my car is hitting a fuel cut, or some kind of stutter between 65-75 just cruising on the highway... it's highly frustrating, i have to let off the gas and step on it to get going again just for it all to repeat itself. i was told it could be the stock plastic bov... i have no idea if that's right!

Please help! thanks!

this:

https://www.evolutionm.net/forums/ev...tsb-found.html

it sucks, the easiest thing to do is to turn off the test. Search the ECUFlash forum for info on how to do that.

That misfire is do to the lack of low compression, low fuel, spark or mechanical problem. We now know that you have random misfire so you have to look at it this way, If you had a misfire on one cylinder then you can suspect that it could be wire/coil, spark or injector. But since it says multiple it could be that your fuel pump is not sending the right amount of fuel to injectors, dirty/clogged fuel filter, or spark that cuts off due to crank sensor.
Hope this helps. I never heard of crank sensor issues yet on evos...so you might want to look into your fuel pressure. Fuel Pressure Regulator also tends to leak on other vehicles. Check it by disconectig the fuel regulator vaccum and if it has fuel on the tip then it is leaking.

Alright thanks! i will scratch the idea of the crank shaft position sensor then. I guess my next step is to order some coil packs and a walbro fuel pump then.

do you have an idea about the fuel cut though just cruising?
i'll also give the fuel pressure regulator a shot too today.

it's really frustrating because my buddy had the exact same problem with the fuel cut cruising and he doesn't really remember what he did besides change out the stock plastic bov for a better one..

This is a very common problem with an easy fix if you have a tactrix cable.

Search for disable p0300 test. There is a thread on here that talks about the code and how to disable it. I used to get the code and enter limp mode in the highway during gentle cruise every 30 seconds or so. I would see my after spike the car would rumble and have no power. A p0300 code would be thrown.

After disabling it, I have not thrown the code again. Nor has my car gone into limp mode. It has been years.

Awesome!!!! that is exactly what is happening to my car! i will have to invest in a tactrix cable i keep hearing tons of good things about it. (i hope it works with mac..)

Thanks a lot man that was great advice! i just hope it works... because i'm sure you know how frustrating that can be when you're just trying to cruise down the highway and you cant.

I am having this issue as well now. It started on the highway...I was cruising along and just got an immediate power loss, but once I let off the gas i was able to push it up again.

In my case though this happened after about two weeks of having slow starts. Im not sure if that makes a difference at all. Does constantly having slow starts wear on the spark plugs at all? If so, i may just need to change those. Havent actually looked to see if they are fouled or not.

I did check the EGR and everything is fine there

It is likely the P0300 Multiple Misfire gremlin as noted above.

I mounted Toyo RA-1s and shortly thereafter got the code and fuel cut with 18:1 AFRs, only on the highway at about 7000 rpm in 5th. I replaced the wires and plugs since the car had over 60,000 miles on it. No help.

It returned so bad on the way to VIR I thought I wasn't going to get there. Once at the track, I drove over 4 hours in 2 days at speed without and issue, then it returned on the way home.

Search for the xml to remove checking for the code, fire up ECUFlash, and turn the ability to check for the code off. I did it 15,000 miles ago and no issues since.

know anything about if having a long start for a period of time fouls the spark plugs?

Non starting issues should not affect the spark plugs in any way that will cause the misfire code only on the highway as I described. If you are having issues with the P0300 code and it only occurs at certain speeds and steady throttle, but not under boost or idle, I'd say you have this same problem, which is apparently caused by driveline harmonics. If you're having starting issues, multiple misfires under acceleration or at idle, and fouled plugs, it is probably another issue. Most of the driveability problems the P0300 code causes is due to fuel cut. This should not affect the plugs, nor should weak spark or inadequate fuel at startup.

thanks man. good info

:helpme::helpme::helpme::helpme::helpme::helpme::h elpme:hi i am having the same p0300 problem....every time i get on the freeway and every now and then it pops up... i was getting my car smogged and it popped up at last min....almost pass{thumbdwn}{thumbdwn}{thumbdwn}...my question is if i get this code erased from a ecuflash is it going to effect my somg when i go get a retest thank you for your help:confused:

My car has passed for years in NC with the P0300 code testing disabled. I don't think that there is any way for the machine to test if the software works or not, just if it throws the code.

OK thanks I'm gonna have to try that then.....I'm in CA and they just started this new STAR smog.... I don't know much about it.....I just need to pass this smog