[Skyhigh]

MHD Stage 2+ RON 98, TU HPFP, RON 98 fuel + 3L of (cheap and not great quality, in this case) Bio-ethanol to a full tank to keep corrections out.

After about 5+ hours of driving in challenging winter conditions today, following happened, in that sequence:

- Got low fuel warning and continued driving on the motorway for another 20-30km. Still taking over other vehicles but not WOT. One could feel power is reduced as it is when the fuel is low.

- Was going downhill, throttle off. As soon as I gently touched the throttle again, both me and the passenger noticed a very weird, short kick/stuttering but the car accelerated ok after that. There was a second, milder one as I tried to reproduce it. But all normal otherwise, continued driving. Couldn't reproduce again.

- Stopped at the gas station, maneuvered around - all normal.

- As soon as I filled the tank and started the engine, I could instantly feel it idle very roughly, shaky... sounding nasty.... within a few seconds I got CEL on the dash! Turned it off, on again - the same.

- Pulled a bit to the side, turned it off and read the codes with MHD:


- Cleared the codes and for the sake of it, switched to Stage 2+ RON 95 (Multi-map)

- Started the engine again - initially the idle was still rough and shaky, but only within 2-3 seconds it started clearing up and getting back to normal. Shortly after that it was smooth again - MHD showed no errors in the DME...

- Drove the remaining 40 km back home, first gently, then at higher RPMs, then with a few hard pulls .... - all normal. Also switched back to Stage 2+ RON 98 on the go... all fine.

- Measured the oil level back home - normal. Started the engine a few times after some cooling off - all normal. No more errors in DME.

What's the likely conclusion here!???
Bad fuel (potentially the poor quality E, although it did not cause any trouble for the previous 600 km of the trip with the fuel mix? Also E and water sink to the bottom, not the top of the fuel!?)? Low fuel? A combination of the two?

It definitely felt as if the problem disappeared as soon as the fresh fuel started getting to the engine, within seconds. I doubt it was a coincidence!
At the same time, apart from those weird kicks after going back on the throttle (which may have suggested problems firing up cylinders again after going downhill, during which time the ignition is cut off), why was it not shaky before I shut the engine down at the gas station!? Also - I tanked from the very same gas station as I did the time before (2 days ago).... so same fuel quality should be expected, minus the Ethanol which I did not put now)

Anyone with a similar experience?

[Skyhigh]

P.s. I also have Start-up roar activated in MHD.... could that have contributed at the first start after filling up (still with the old fuel mixture in the fuel lines)...?

[nosam1g]

pulled air into the hpfp since ur low fuel , As for drawing what ever sludge or water you had in the depths of your tank, yes that could cause it.
if no more code , all is well ^^

[Skyhigh]

But how is that even possible!?
I must have had something like 6L (1,5 gallons) of fuel in the tank when it happened (it was not critically low, range was showing about 70km). Plus why would it manifest itself after engine shut down and restart and not before that!?

Have driven on low(er) fuel many times before, incl with the HPFP…. Have never had that happen 🧐

I sincerely hope you are right though… it was scary.

[eff32fl]

Originally Posted by Skyhigh

But how is that even possible!?
I must have had something like 6L (1,5 gallons) of fuel in the tank when it happened (it was not critically low, range was showing about 70km). Plus why would it manifest itself after engine shut down and restart and not before that!?

Have driven on low(er) fuel many times before, incl with the HPFP…. Have never had that happen 🧐

I sincerely hope you are right though… it was scary.

I personally refuel when I hit 1/4 tank. Helps with HPFP longevity and avoids picking up crap at the bottom of your gas tank.

[nosam1g]

sparks good ? coil packs ?

[Skyhigh]

Sparks are 2 years / 10 000 km old
Too early for coils. And generally - 2 cylinders at once suggests a common divider in my head… 🤔

[nosam1g]

did u have the right octane for the map ? maybe was to low for the map ?

[Skyhigh]

Must have been, with the E I add. And again - I went through 50L of that fuel mixture without issues (incl some sporty driving), just so that it would misfire on fuel reserve during/after rather relaxed commuting, right after cranking it at the gas station?? Plus it would not misfire with the same fuel, from the same gas station, without any E added afterwards?

Doesn’t make sense.

What I also remembered is that I filled the car beyond the point at which the pistol stops… I added another 2-3 L. Which I have done many times before too, without issues… although I know it is not recommendable.
Could it be something related to the EVAP… / Fuel tank breather valve…? 🤔

[nosam1g]

if no more code , then all is well .. only time will tell , then address it then . are u on flex fuel ?

[Skyhigh]

No flex fuel.
Drove to the supermarket today - all good, normal start, normal behaviour, no errors.
Hope all is well indeed.

[toxik]

fuel tank breather valve is a good preventative maintenance item, i did mine from just have a rough idle once after fueling up… it never came back but i switched out anyways and kept the oem one. i dont think the issue you experienced is the valve though, especially since you felt a stumble before you fueled up

[WrxToBeamerGuy]

Originally Posted by Skyhigh

What I also remembered is that I filled the car beyond the point at which the pistol stops… I added another 2-3 L. Which I have done many times before too, without issues… although I know it is not recommendable.
Could it be something related to the EVAP… / Fuel tank breather valve…? 🤔

Yes I would think that could cause a problem as you are potentially damaging the EVAP system by doing so. A damaged EVAP can cause rough idle. Our cars are already prone to having the solenoids in the fuel EVAP line break.

The misfire while driving was probably fuel quality / fuel level related. You had very low gas in the tank and continued to drive it spiritedly as well as changing elevations which moved the fuel in the tank to one side of the tank.

[Skyhigh]

Well… both “very low” and “spirited” are rather an overstatement…. I had at least half of the reserve fuel still available (good for 70km, according to the board computer), which makes around 6 litres of fuel… been much lower than that in the past… and driven way more sporty, with the limitations the car applies as a safety feature exactly for that sake.

I find it hard to believe the two occurrences within just 10 minutes and 5km are unrelated….

[WrxToBeamerGuy]

Originally Posted by Skyhigh

Well… both “very low” and “spirited” are rather an overstatement…. I had at least half of the reserve fuel still available (good for 70km, according to the board computer), which makes around 6 litres of fuel… been much lower than that in the past… and driven way more sporty, with the limitations the car applies as a safety feature exactly for that sake.

I find it hard to believe the two occurrences within just 10 minutes and 5km are unrelated….

Ah i interpreted that wrong then. Yeah the fuel vent valve has failed on my car and others cars causing rough idle. I'm not sure what happened in your case.

[Skyhigh]

I read several threads on the topic (fuel vent valve), but neither of them mention misfires and CELs related to misfires…? 🤔

[WrxToBeamerGuy]

Originally Posted by Skyhigh

I read several threads on the topic (fuel vent valve), but neither of them mention misfires and CELs related to misfires…? 🤔

Yeah i dont think thats your issue. Or if it is an issue you have its seperate from the misfires and CEL. Does it click really loudly when you idle? Thats how i knew mine failed. It sits right on top of the intake manifold.

I wonder if an injector briefly got stuck open?

[Skyhigh]

No loud clicking...

Forgive me if I am missing something, but if 1 injector got stuck open, why would 2 cylinders misfire...?

[WrxToBeamerGuy]

Originally Posted by Skyhigh

No loud clicking...

Forgive me if I am missing something, but if 1 injector got stuck open, why would 2 cylinders misfire...?

Youre not missing anything. I just keep replying in between meetings and not remembering the whole conversation.... What you said before makes the most sense to me, that multiple cylinders most likely rules out injectors, plugs, and coils. Possibly pcv but you didn't hear any loud screech or report white smoke. Also the issue cleared up once you refilled the tank.

I personally would then think it was fuel delivery or quality related. Before the injectors

[e30 4 life!]

You should likely pull some logs. I also had similar behavior, but no codes relating to a weak primary o2 sensor.

[Skyhigh]

Drove the car today a bit - no issues, no fault codes. Pulled 2 logs - I don't see anything out of the ordinary, but those of you who would be kind enough - please have a look and let me know if you notice anything? e30 4 life!

(2 logs on drop down): https://datazap.me/u/shiny/pure-ron-...=0&data=4-7-17

[nosam1g]

stg 2 hpfp ? e30 ? needs more e