2005 evo 8 currently bucking and afr reading lean and rich. When the car bucks/bogs the afr will dip and go to the lowest below 11 on aem gauge and then blip to rich all the way. This will happen completely random during constant throttle and the loss of power isnt as dramatic since the throttle is cruising constant speed. Blips happen super fast - like the car stutters. At wot the car has major bucking and loss of power blips along with afr dipping during blips below 11.
Tested for boost leaks with pressure system, couldnt find any. Dont visually see any broken/cracked hoses either. Replaced front o2 sensor because obd tool said o2 rich/lean and lean/rich on b1s1 but wasnt throwing a code. Cleaned MAF, throttle body, checked plugs - just replaced 3k miles ago but figured it wouldnt hurt to check. Looked new still. Disconnected battery and installed new o2 sensor and car ran well for 6 days and then same issues started up again. Disconnected the battery again. Issues still persist.
Car has COP system, turbo manifold, greddy exhaust, dump pipe. Walbro fuel pump. Tuned by english racing. Nothing crazy done to the car.
Car has ran perfectly with small things replaced (belt/harmonic balancer, etc maintenance) for the past 35k miles.
Im not sure what else to check. Open to suggestions. Should i test injectors? Just seems like its something electrical like a sensor rather than mechanical, but not 100% sure. Does anyone know of any reliable Evo shops around puyallup/auburn Washington?

 

Do you have the stock coils or spares for the COP? This sounds a bit like loss of spark to me. I had similar issues when my homemade COP harness had some issues and I found it by swapping back to the stock coils to verify it went away and then built a fresh harness.

 

I don't unfortunately. I think im around the 8th owner of the car and the cop system was already there at purchase. If it was a coil wouldnt it throw a code? Granted when my spark plugs went out last time it didnt throw a code for misfire. So maybe. Good thought though ill check into it.

 

Mine didn't throw a code either. It seems it has to be real bad for it to throw a code.

I would probably start there. You can hit a junkyard and get some coils for cheap to try and swap them out. There are also ways to check them with a multimeter but in my case it was a harness issue so that wouldn't help.
You could also try and check the harness with a meter while moving it around to see if it ever loses continuity.

Honestly, with the COP setups, I think having a known set of good stock coils is invaluable for troubleshooting. It really helps isolate if its an issue in there somewhere.

In theory, if it does it enough, one of the plugs will start to look a bit off because of the richness and you could use that to help sort through what coil is possibly bad too.

 

Have you logged for knock? not an expert here but I wonder if the low octane/high octane map switching is what you're experiencing

 

Oo thats a good call too. I didn't think about that.

 

Cruise throttle is below the load threshold for the ECU to care about knock.

If the car runs fine at WOT, I'd start with getting the injectors flow test, checked for drips, and cleaned.

 

He did say he has issues at WOT

 

I replaced plugs (although they had less then 2k miles on them) and checked coils. Coils are toyota. I've driven the car overall for 32k miles with no issues whatsoever and only preformed maintenance parts (air filter, belt, tensioner, walbro 255, etc). I have no idea how to read logs and what program to use to view it all. I recorded a couple of logs, but again I have no knowledge of actually reading it. I dont feel comfortable driving the car to english racing as the misfire or whatever is so random and sketchy lol. There is a shop sort of near me (pacific auto import) that I will probably see if they can figure it out. The car bucks at completely random, whether barely on throttle or wot. Car bucks at cruising, climbing hills completely intermittently. In the logs I recorded only one instance it blipped and i was driving slow.

 

Sounds like a fuel delivery issue. Could be something that you can fix by running a bottle of techron or seafoam through the fuel tank. That's a pretty easy thing to try so that you can cross it off the list. When was the fuel filter housing last replaced? You can check that. It's under the rear seat and it is very easy to pull and inspect. Unfortunately, the Evo doesn't have an inline filter, the fuel filter is integrated into an expensive plastic part that also houses the fuel pump. Next, if the fuel treatment didn't help or helped but not 100%, you can pull the injectors and inspect them for clogs and any kind of build-up. You can also clean them after removing them using a syringe and seafoam or chemtool b12.

For fuel additives, anything that uses Polyether amine (P.E.A.) should be very effective at cleaning clogged injectors, but who knows what the previous owners did. If there is build-up on the fuel rail side you will have to clean that out by taking it apart. You can tell if this is the case by removing the injectors and looking at the inlets, which will have mesh screens. If the mesh screens are not almost 100% clean you'll probably want to run fuel through the lines and into a container to get any debris out.

 

hey i had similiar problems and mine turned out to be my TPS, replaced with a buddys and i havent had issues