Hi EvoM,

This is my first post here. I'm from Australia and have recently purchased my first Evo (Aus spec Evo 9). It's a mostly stock car with the only mods being a Plazmaman intercooler and piping kit, 3" turbo-back exhaust, Walbro 255 Fuel Pump, 14psi Turbosmart wastegate actuator, Grimmspeed 3-port BCS and a 21psi flash tune on the stock ECU.

My car currently has an issue where under very specific circumstances, the engine will stutter or misfire for a moment. The scenario that causes it is when you use turbo boost to accelerate in the higher gears (mainly 5th/6th) and then back off the throttle to cruise. When the boost drops back to zero the engine will momentarily misfire once or twice before resuming normal operation. This typically happens within less than a second. You can feel these little bucks/jerks through the car when it happens too.

Here are some interesting points to note about this issue:
- It mostly occurs in higher gears at low RPM, around 2000-3000RPM. It's harder to reproduce at 4000RPM+ and in lower gears.
- It doesn't occur when you shut the throttle entirely, only when backing off to very low throttle % to maintain speed after loading the engine and building some boost pressure. Can also be mitigated by backing off the throttle slowly enough.
- I can't seem to get it to happen early in a drive, it seems to start happening as the engine bay gets heat soaked.
- The engine also starts to sound like it has little tiny gaps/misses every couple seconds at idle when heat soaked, but the idle speed is perfectly steady and the car drives normally otherwise. I've been told not to worry about it but wanted to mention it just in case it's related.

It's worth noting that I had the car retuned recently to eliminate the common "rev-hang" or "throttle-hang" issue associated with earlier tunes, however something like this was present before the tune as well, though seemed to be a bit different with the rev-hang present. I have spoken to my tuner about it, I believe he was saying that it's a phenomenon called "MAF air reversion" and that even stock Evos have this issue under the same circumstances. He said a speed density tune or a complete aftermarket ECU are the only ways to eliminate it. The car drives very nicely otherwise, but I have never personally driven any other Evos, so I wanted to ask those of you on this forum if you've ever experienced something like this with your MAF-driven Evos? What do you think about it?

Thank you in advance for any advice/insight

 

Forgot to mention, here is some of the work I've already carried out:

- Fuel filter and pump replaced
- Injectors cleaned and flow tested
- Rebuilt throttle body with new shaft seals
- All boost leaks fixed
- New OEM 8/9 MR BOV (metal type)
- TPS calibrated to spec
- ISC motor swapped
- Ignition coils swapped for new M&W coil on plug kit (Denso Yaris Coilpacks)

 

Could be the load and the tune. That is a LOT of load so maybe too much/not enough gas in the tune. Get a tuner and take him for a ride.

 

Your tuner is talking out of his rear end, you dont need to have SD or any after market ecu to solve this

 

Thanks for the reply! Any idea what causes this to happen? which part of the ROM I should be looking at?

 

Also, an update on the situation:

^^ This turned out to be a problem with one of my injectors, maybe a slight leak after having them cleaned. I replaced them and now the idle normal again. However the engine is still having the same momentary cutouts/misfires, mostly in 6th gear.

I've refitted my wideband gauge so I can monitor the AFR when it happens, and I've noticed it consistently spikes very rich for the duration of each misfire/cutout. The gauge shows a graph of the last 5 seconds or so which is handy for reading this. If it misfires twice I can see two spikes on the graph. However I'm not sure if the rich spikes are the cause or a symptom of the engine cutting out momentarily like this.

 

you need to log to see whats causing it

But if you post your map here , i can check if there is anything obviously wrong in it.

you car is almost stock, it shouldn't definitely not do this.

 

I did take some datalogs a few weeks back and had a good look through them. I couldn't find anything particularly alarming, but I'm definitely not an expert when it comes to reading this data. I did notice that it looks like the closed loop/open loop crossover point is at about 30% throttle (evoscan reading) and that's probably around where it misfires when backing off from accelerating in top gear. I could post the datalogs but I'm not sure exactly where the misfires are happening in the logs because there's nothing to indicate it. I can't log my wideband because it's a PLX which I don't think is supporting by evoscan yet. If I could log it, that would tell me where the misfires are.

I have attached the tune, however. If you'd be happy to take a look at it I'd be extremely grateful! It's on Tephra v7 88580714 (AUDM Evo 9). Let me know what you think.

 

your injector scaling seems off for stock injectors running stock fuel pressure
Mivec map has been set a bit on the rough side, might cause some overlap causing to much pressure
load offset is quite high at 200
open load tps is too low ( would make it switch a lot between open & closed)
also not seeing all correct changes done for throttle hang

start by setting your 2 openload throttle tables to

 

Thanks! Looks like the stock open loop throttle table. I'll give it a shot. What about the open loop load tables, should I leave the value they set?

Oh, it's worth noting their tune did in fact fix the rev hang. I'm not sure what they missed, but it definitely does not rev hang anymore. If I remember correctly, what my tuner told me is that the AUDM ROM this version of Tephra v7 is based on (88580014) is a later revision that doesn't have the rev hang issue, and it's the first AUDM ROM which was in there before that does have it (88580013). I don't know how accurate that is but it's what I was told.

 

for rev hang you can disable certain functions regarding fueling etc in higher ranges, which is still at default value's in this rom, but the only thing that counts is that the rev hang is not an issue currently.

the load ones look ok. you could set them to 110 ish if you want to stay in closed loop longer to keep it it there until you actually start building pressure

also your boostcut delay is set to 100ms... thats 0.1 secs... set it to 1000

 

Okay gotcha. Thanks Kk0ng, much appreciated. I'll make a copy of the tune with the stock open loop throttle table and see if that improves it.

I'll also put this here as it's related to this tune. I've been noticing some strange closed loop behavior since getting this tune as well. Today I took a video to save having to write too long of an explanation, but basically anytime I decelerate and the AFR goes full lean (as it's supposed to) my AFR then goes quite rich once I either stop and idle or go back into closed loop cruising. You'll see in the video after it shows LEAN on decel, I then stop and idle and it slowly dips below 12 AFR, holds for about 15 seconds, then slowly and gradually starts to come back up until it reaches the target 14.5.
This behavior is easily repeatable, and seems to occur on return to closed loop operation after a lean deceleration, regardless of whether I'm moving or idling. However it doesn't seem to have any noticeable effect on the cars idle, driving or sound. Any clue what part of the tune this might relate to? I don't recall this being present on the car's old tune.

 

start with changing the open loop values that i posted in my previous post

 

Alright I had a chance to give this a try today. I changed the Open Loop Throttle tables to match the values in your previous post and flashed it to the ECU. In testing I can't tell if anything has changed, it still goes very rich and cuts out/misfires when backing off from boost/load in 5th/6th. It still idles very rich for 15 seconds or so after lean deceleration. I took a datalog during the test drive on this ROM but I can't really find anything useful in it. I've attached it anyway, in case someone else can.

One thing I noticed is that when trying to replicate the miss in the lower gears, the AFR doesn't go as rich when backing off the throttle as it does in the higher gears. It seems to go richer the higher the gear, with 6th obviously being the richest in this scenario. This makes me wonder if over-fuelling in this scenario is what's causing the engine to momentarily cut/sputter/misfire. Could the injector scaling have something to do with this?

 

Edited the OP because I realised I forgot to mention the car also has a Walbro 255 fuel pump... That might be important info here..