1992 m50 nv backfire and bad idle high altitude

[Lucas325]

He guys,
Hoping someone can shed their view on this.

Im actually intensely pissed off on this bmw garbage but here goes.

I've fuuullllyyy serviced this asshole's fuel system and intake and ignition.
Car runs great at normal levels, oonnnlyyy when i go in the alps at + 2km heights it starts to act like a scumbag.
Idle goes up and down, sometimes stalling and it it backfires except on wot.

New plugs and coils, 02, full injector rebuild, fuel pump, fpr the lot. Maf sensor exchanged even while on the alps.
I got a extra maf from a tested car.
Good quality fuel, you name it. Original airbox and oem airfilter...
This issue actually makes me wanna trash this piece of shit, i've put so much effort in it and still this happens.

[xxxxxxx]

Have you done a smoke test?

What are your engine temps?

[Lucas325]

Yes forgot to mention, did a smoke test also, some hoses that were even a bit questionable are replaced.
I had these issue last year and in that year have done alot of testing, some trackdays but not high altitude.
At the moment im in the swiss alps and just gotten this issue again.

Temps are all good, mishi radiator, cooling system 100% good and effective, at no point have i ran hot.
Speeding up the alp always goes with high pace high rpm,
But coolant temps are consistent and under control.
Still running with visco, off course a good visco clutch too.

[Eric93se]

You have to use the highest octane gas you can get when going high altitude.

[Eric93se]

Should probably run some fuel injector cleaner cause that will also help clean carbon off the valves and pistons and even the cat.

How did you go about rebuilding the injectors?

[Lucas325]

Should probably run some fuel injector cleaner cause that will also help clean carbon off the valves and pistons and even the cat.

How did you go about rebuilding the injectors?

Fuel cleaner aint gonna do anything.
Injectors were cleansed by professional company with a great reputation, connected with motorsport tested checked and all.
They said they werent even that badly fouled.
Off course new o rings etc, and it runs really strong and fantastic in normal circumstances.

Valves and pistons have minimum carbon buildup, headgasket was replaced 2.5 years ago, head was skimmed cleaned, checked etc.
Pistons still look great!

Its a m50nv, complete decat, o2 is before the cat anyway and makes no difference, this already has been done 5 years ago.

- - - Updated - - -

You have to use the highest octane gas you can get when going high altitude.

Was thinking about this too, but everything i researched says the opposite! https://www.google.com/url?sa=t&sour...db-Uds&ampcf=1

https://saemobilus.sae.org/content/872160/

The lowest available here is 95oct. But 98 is easy available, 100oct sometimes too.

[xxxxxxx]

Have you cleaned or replaced your ICV?

[Lucas325]

Have you cleaned or replaced your ICV?

Yes, functions good, not clogged.
Clean and opens smoothly.
Checked when replacing the hose to it.

[xxxxxxx]

To me popping/backfiring usually indicates running lean or timing is off. So either you're not getting enough fuel, or you've got a vacuum leak sucking in a bunch of air. Since you replaced all the fuel parts, and did a smoke test, I have no clue.

What color are your plugs when it starts running poorly?

Have you check the intake boot for cracks?

Fuel filter replaced?

[samy01]

You have to use the highest octane gas you can get when going high altitude.

nonsense

[Lucas325]

To me popping/backfiring usually indicates running lean or timing is off. So either you're not getting enough fuel, or you've got a vacuum leak sucking in a bunch of air. Since you replaced all the fuel parts, and did a smoke test, I have no clue.

What color are your plugs when it starts running poorly?

Have you check the intake boot for cracks?

Fuel filter replaced?

Yeah fuel filter off course also replaced.
There is no crack or bad hose anywhere.

Im suspecting it might be a ecu issue, i think its running rich.
I didnt pull the plugs at the peaks, not really the place to do so lol.
Somehow it isnt able to correct the mixture with the thin air.
Maybe too much fuel for the lean air, and it just doesnt correct it properly...

[samy01]

that would indicate bad MAF sensor

[Lucas325]

that would indicate bad MAF sensor

Yeah but i did switch that one out, no difference.
Did that right on the peak!

But why wouldnt that also cause an issue without the altitude?
On a trackday with 30c outside its also very hot, didnt have any issues then waiting in line to the paddock, idle was good then.
Im completely lost on this fuckin issue :/

[samy01]

How did you get a new maf sensor on the peak of a mountain? How do you know it is functioning?

[Lucas325]

How did you get a new maf sensor on the peak of a mountain? How do you know it is functioning?

I've got a bucket of backup parts with me when i travel that far.
Coil packs, fuel pump etc.
And another maf, however it is a used one.
I find it difficult tho to believe it it would be bad, that it would not give trouble in more situations.
With both mafs situation is identical.

I did test both, not a 100% secure test but by checking the voltage of the heatwire and having x airflow and then increasing airflow.
To see how much voltage is increasing.
Seemed identical.

[Lucas325]

How did you get a new maf sensor on the peak of a mountain? How do you know it is functioning?

<br>
<br>I've got a bucket of backup parts with me when i travel that far.<br>
Coil packs, fuel pump etc.<br>And another maf, however it is a used one.<br>I find it difficult tho to believe it it would be bad, that it would not give trouble in more situations.<br>With both mafs situation is identical.

[samy01]

so you're saying as soon as you get to lower altitudes all problems disapear?