Wondering if anyone on here has dealt with a code reding "random missfire." I can't remember the code (3900... maybe) but just need to know a little about it. Quickly list a few major mods that may be the issue (once again never heard of this)

Upgraded cams
upgraded LICP
Upgraded Fuel Pump
3" Turbo back exhaust (catless, think this may be the issue...)
Apexi air intake (stock piping...)

all i can think of right now. If you think any of these would be the culprit or had this happen to you, how can I fix it, will bring her to a shop tomorrow and get it fog tested for Intake leaks but thats all i can think of..

Thanks for your help evo M!!!
Kirk

 

Tune the car too???

I'd say its related to the cams you just put in the car. P0300 is likely the code you got alot of times the code can be tuned out if it's cam related.

Things the cause P0300 Random Multi Cyl Misfires

-Ignition components (Plugs, wires, coils)
-Big Jumps in Timing map Load Cells
-Idle timing too high
-Drivetrain Harmonics causing the ECU to pick up noise and throw the code

If your car proves to be real finicky with the code after exhausting some simple stuff it can be disabled in the ROM

 

^^ thank you!

It starts happening when you are around 4000RPM's on the highway.. idle is set for 950 RPM standing still.

 

No Prob.

As for idle causing it. It's more in the timing vs. the rpm
Since your seeing it pop up at HW cruise the things you'll want to look at then is likely.

-Jumps between cells in your timing map.
-Timing tuning itself (a little too much advance in those cruise cells maybe)
-Drivetrain Harmonics
-Ignition components

I still say that if you didn't have the issue prior to the cams. You should be able to tune it out fairly easy

 

Last time you put plugs in your car? How many miles on the car?

Random misfire should be a plug not sparking or a fuel injector randomly cutting out. Usually timing won't cause a random misfire. If your timing was off you should have a constant misfire. Do you feel the miss?

 

The miss kinda feels like a bog... untill i back it off then re-apply gas it will organize itself, its not too noticable (noisy and chunky) my passenger didn't really notice it till i pointed it out but it is there. The car is an 03 with 41,000 miles. New Walbro 255 pump and the plugs were changed around not too long ago, will change them again to make sure. Just a litte confeused thats all.

 

You would have to see which cylinder is misfiring to help diagnose it.

 

Not always the case depends on the load cells the car is hitting while cruising. If you jumping huge gaps between X number of cells the code will trigger. Smoothing of the timing map will fix that

You can search this site going back to 03 for P0300 codes. People tried everything to fix it. 90% of the time plus ingnition components will do jack to fix it

In 04-05 mitsu realized there was an issue and release a reflash to combat the issue. Changing the ROM from 0008 to 0014 then to 0015.

Common issue what the OP is seeing. Many of us have seen the exact same in the past misfire triggers on HW, car breaks up (due to the code triggering, not a real missfire but a sort of limp mode if you will) off then on the gas and the car is fine but the code is still there.

100% the bog/break up you feel on the highway is the ECU's response to the code triggering and not the actual misfire. Off then on the gas the car is fine again. Seen it soooo many times

Like I said look at the easy thing first. If worse comes to worse disable the code in the rom

 

It's likely a P0300 Random Multiple Cylinder Misfire

P0301, P0302, P0303, and P0304 would point to an individual cylinder. This is a random misfire and cannot be tracked to a cyl by the P0300 code being thrown.

 

You can try upgrading your 03 rom to the 0015. If you have ECUFlash and a cable I can send you a blank one you'll just have to copy over all your maps. The Wiki also has the 03 0015 rom in it's database for download

 

im having the exact same problem. gsrboi80 please send me that rom if you can. ive searched my *** of for a solution to no avail. and ive changed ALL ignition components with no change. the only thing that helps is disconnecting the battery and reconnecting it. i beleive it is clearing the fuel trims. is there any other steps in switching roms besides copy and pasting the data to the new rom?

 

ninja edit: disconnecting the battery only helps for about 100-200 mi or so.

 

Sure man PM me your email address. I'll send it from work in the am since my stuff is on my laptop. Yup just copy all maps from your current 0008 to the 0015 and flash it in.

Done deal. Not garanteed to fix it but it has fixed some in the past.

The reason it shuts off from pulling the battery is that you reset the ecu and it takes X amount of drive cycles for the ecu to read a fault and throw the code again.

Check the things i mentioned above. Timing and such too

 

ok guys I've been having this problem and all I have is an intake

my evo's a daily driver about 300 miles a week and it's been recently that I've been getting this code like once every three weeks, maybe more, and when it happens you FEEL IT!! it feels like I have a cylinder down and even if I get completly off the gas and get back on it sometimes will still be acting up

so I changed the plugs yesterday and this morning it threw the code again but this time it was pretty much unnoticable

so is a tune all I need?? or could it be a differant issue???

 

I have this problem too, but it only acts up about once every two months.

The CEL comes on and the whole car bogs, i lift off and it's gone.

The random mis is so random. i have even changed plugs and wire. ohmed all of them out too.

I usually just clear the check engine light and drive for another two months.LOL