First and foremost, I know there are a plethora of threads regarding Misfire codes troubling other evo owners. I have read through all of those and I'm not sure deleting the code is the best course of action given my situation.

My car started throwing these two codes about 5 months ago. The car is a stock turbo running on 93 ~25lbs and e85 ~28lbs. When I first got the code it was during the summer on e85.

It would first only throw a p0303 and I had recently (~2 months ago) installed a Spoolinup COP. I figured a coil had gone bad, contacted Matt and he sent me some replacements. After swapping coils the code came back so the next though was maybe a faulty wiring harness. Matt once again was more than willing to help and sent me a replacement harness and 4 coils. The code(s) came back and thats where I stand today.

What gets me is that the car seems to run fine and the only time the code is thrown is when I'm in traffic or very light throttle situations <3000 rpms. During this time the car doesnt seem any more jerky or as if it isnt firing on all cylinders.

I switched back to 93 a couple of weeks ago and the same exact thing happens so I know it is not related to my tune.

The plugs and gap should be fine. When I 1st got the code I swapped plugs, originally running NGK coppers 7 heat range and switched to NGK Iriduims 8 heat range gaped at .025. I dont think going to a cooler plug changed anything as the code 1st started with the 7's

I dont think I have an ignition issue as I have swapped the COP to a new one and the issue is still apparent. I can throw back on the stock coils and see if that makes a difference, but I need to meet up with a friend to do so since I got rid of mine. Honestly though I'm skeptical that its the coils.

The only other that I can think of is the injectors. They are Precision 1000cc, and were checked and perfect last summer. I havent taken them out yet but I may do so if that could be my issue.

What else should I look at?

I know most people delete these codes altogether, however given that I never used to throw these codes I dont want to get rid of them if I actually have an issue.

Sorry for the long read, but if you made it through that and have any insight, it would be much appreciated! Thanks!!!

 

In this situation I would not disable the code. It sounds like an issue.

Have you tried swapping the injector on the miss firing cylinder to a different cylinder and see what happens?

 

Thanks for the response. What specifically do you mean by "in this situation" as in what is triggering you to think that there is something truly acting up?

I have yet to pull the injectors to inspect them. I know its a simple process I just havent had any free time recently and wasnt sure if it was even plausible that an injector is crapping out on me. What's strange is that the code is either a p0303 or p0300 and that's it. One would think that my issue lies in the 3rd cylinder. The past 3 times its thrown the p0300 but its usually either or. I'm not sure how the ecu triggers the code especially on a cylinder by cylinder basis though, so that might be interesting and beneficial to know.

 

The ECU monitors variations in the motion of the crank by way of the crank sensor. If the logic in the ECU can pin the problem to one cylinder it sets a code for that cylinder. Otherwise, it sets the more general 300 code.

 

That's interesting thanks for the information. So if it can correlate the misfire to cylinder 3 sometimes but other times it just throws the general 300 code can we assume that the issue actually does lie in cylinder 3 but sometimes the ecu cannot pinpoint it to that cylinder thus it throws the general code?

How would you go about tracking down the culprit? Had anyone had issues in the past with damaged wiring or something of that sort?

Is my best bet to pull the injectors and swap the one in cylinder 3 to a different cylinder or is there something else you would check first?

 

The reason I mentioned "this situation" is because I normally recommend disabling the P0300 code. When it is coupled with a specific cylinder miss fire like the p0303, then it is generally more than simply a phantom issue.

Swapping out the coil and coil packs is one test (which you have done) and the other is to change around the injectors to test and see if the miss fire follows. If the miss fire moves from cylinder three to the new cylinder that the injector was placed, then the injector is at fault.

If it follows the injector, look for bad injector seals or have it cleaned and flowed.

Also some people have had issues with E85 clogging injectors clogging with brown goo. It can happen kinda fast, might be worth a second look.

 

OK, thank you If I get a chance this weekend, I will pull the injectors and take a look.

Im not doubting you, but more curious, how would a bad injector seal cause a misfire? I did a boost leak test about a month ago and nothing was coming from my injector seals. When I installed the injectors I actually bought brand new FIC seals as I heard they were better. Is there a specific seal that I should carefully inspect?

Obviously if I pull out the injectors and they are gunked up that's a pretty tell tale sign of my issue. Have people had good luck self cleaning the injectors or am I going to have to send them to FIC? I dealt with FIC last summer and their customer support was absolutely fantastic I would just prefer to clean them myself if possible so I wont have to have my car out of commission for a week or two.

 

At the load and RPM where the code triggers what does the timing look like. May be very similar between the E85 and 93 tunes if its low load. (Compare the 2 timing maps)

If the timing is too advance there or transitions in that area of the mapping are not smooth you'll potentially get a P030X code for sure.

As an example, I have seen this in cars trying to up idle timing for cams advance it out to far and it'll trigger P030X codes

 

Unfortunately I do not have any logs when the CEL is thrown.

I would be quite shocked if the issue were due to the tune(s) on the car. The 93 tune is essentially the same as its been for the past couple of years, and it never had issue before. The e85 tune was finished summer of 2011 and I didnt start throwing codes until June of this year.

If the tune was at fault wouldn't this have been an issue a while back?

I appreciate that you chimed in as its always great to hear feedback from people who have experienced this issue. Given my situation however I am quite skeptical that the tune is to blame.

 

have you done a compression test?

 

That is one possibility and others here have addressed various things to check for if cylinder 3 is misfiring. The other possibility is that the p0303 code is a fluke and that the p0300 code is only indicating what most owners encounter, due to wear the engine is encountering feedback from the drive train.

I'd suggest you continue checking for conditions that might cause a misfire in cylinder 3 but if that doesn't pan out then you may have to accept the second scenario.

 

Nope, why do you ask?

 

Thanks!

I will take a peek at the injectors specifically cylinder 3 and see it I can spot anything out of the ordinary. If its obvious I will send the injectors in to be tested and cleaned if possible. If I dont see anything, I will swap that one with another one and see if the code changed cylinders.

Here's the breakdown:

Coils- should be fine unless my car doesnt like the Spoolinup COP for whatever reason
Spark Plugs- Fine
Injectors- TBD
Tune- No reason (in my mind) that its the culprit
Wiring- Looks fine

What else can I target?

 

If injector #3 is misbehaving, cylinder #3 could be getting trashed and would show low compression.

 

Oh makes sense, thanks for the information. That's definitely not something I want to happen. Unfortunately my wideband isnt the fancy 4 cylinder setup but the normal one that takes an average of all 4 and doesnt show anything out of the ordinary.

I dont have a compression tester unfortunately but I'm sure I could get a hold of one. Hopefully I'll find some time this weekend to pull the injectors and see if I discover anything. If an injector is bad then a compression test might be in order to make sure I havent caused damage.

Mrfred-now you have me paranoid I hope its not too late