STFT deviation issue. Help!

zmon1300

Corporal
Nov 3, 2016
181
114
0
Chicagoland
Ride
'10 335xi
Hey guys,

I recently been having issues with the car bucking up top when doing WOT pulls. I have pure stg2 turbos. BMP pi. Full e85 car. Index 12 injectors that are about a year old. I noticed a few months ago my VC has a hairline Crack in it. I switched from mmp pi to BMP pi because of this issue and that didn't fix it.


Attached is my log: https://datazap.me/u/zmon1300/log-1554249370?log=1&data=3-23


Here's the situation.
I don't get any misfire codes. No o2 sensor codes. No injector codes. No hard starts. Plugs are about a year old. Ngk 97506 gapped at .020 with PR coils.

I used ProTools to log my injector voltage and duty cycle and that all checks out.


My STFT 1 goes whack while STFT 2 seems to stay on track. I'm pulling my hair out trying to chase this problem.

Was wondering if you guys can point me in the right direction to get this fixed?

My tuner says my Index 12s are bad. I've never seen a case Where's that's happen in such a short period of time. I do full up e85 all the time. Even in the winter.

Looking in this section I noticed another thread in which an individual suggested a cracked VC could cause this issue. Anyone have experience with this? Any other tips or experience with this STFT deviation. I was thinking of doing the follow diagnosis in this order


Compression and leakdown test
Replace VC
Replace bank 1 injectors.

Any help would be appreciated. I miss 600awhp
 

doublespaces

Administrator
Oct 18, 2016
9,249
4,259
0
AZ
Ride
2009 E93 335i
Is it at idle and also during a pull?

Do you get a stumble when you startup?

How long does your car sit without being driven?
 

shushikiary

Sergeant
Jun 4, 2018
255
133
0
Ride
335xi
I've seen short spikes in AFR like that happen from multiple things:

-bad injectors
-slight miss fire (usually coil or plug related, aka bad/weak coil or spark plug gap is not small enough)
-exhaust leak (pre O2 sensor)
-intake seal leak

So I'd be looking for all of those things. Obviously due to cost injectors would be last.

REMEMBER that you cant just swap injectors without re-compressing the seal on the tip, or else the seal might not do its job and you'll buy a new head as combustion gases can leak past the injector and damage the head.
 

zmon1300

Corporal
Nov 3, 2016
181
114
0
Chicagoland
Ride
'10 335xi
Is it at idle and also during a pull?

Do you get a stumble when you startup?

How long does your car sit without being driven?


Happens during a pull. I'll get a log of it at idle today. No stumbling when starting up the car. Car is driven everyday. It may sit for a few days or a week when I go out of town but nothing crazy.
 

zmon1300

Corporal
Nov 3, 2016
181
114
0
Chicagoland
Ride
'10 335xi
I've seen short spikes in AFR like that happen from multiple things:

-bad injectors
-slight miss fire (usually coil or plug related, aka bad/weak coil or spark plug gap is not small enough)
-exhaust leak (pre O2 sensor)
-intake seal leak

So I'd be looking for all of those things. Obviously due to cost injectors would be last.

REMEMBER that you cant just swap injectors without re-compressing the seal on the tip, or else the seal might not do its job and you'll buy a new head as combustion gases can leak past the injector and damage the head.


So maybe I should do a smoke test to see if any gaskets are leaking?
 

shushikiary

Sergeant
Jun 4, 2018
255
133
0
Ride
335xi
A smoke test is a good idea, both intake and exhaust. Replace any seal that needs it.

Personally I'd dump the coil packs and go straight for an upgraded ignition system, like the precision raceworks one, but if you don't want to drop 400 bucks, then I'd replace all 3 bank 1 coils, pull all the plugs and check their gaps and correct if needed.

After all the above, if the problem persists, then I'd replace all bank 1 injectors.

That's how I'd tackle it.
 
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zmon1300

Corporal
Nov 3, 2016
181
114
0
Chicagoland
Ride
'10 335xi
Might want to check your PI injectors, I have heard some bad things about certain brand's injectors.

I have the new BMP pi. They come with Bosch 750cc injectors flow matched with certificate. Unless I'm mistaken..

A smoke test is a good idea, both intake and exhaust. Replace any seal that needs it.

Personally I'd dump the coil packs and go straight for an upgraded ignition system, like the precision raceworks one, but if you don't want to drop 400 bucks, then I'd replace all 3 bank 1 coils, pull all the plugs and check their gaps and correct if needed.

After all the above, if the problem persists, then I'd replace all bank 1 injectors.

That's how I'd tackle it.

I have the PR coils on the car. Had them on for about 1.5 years now....
 

zmon1300

Corporal
Nov 3, 2016
181
114
0
Chicagoland
Ride
'10 335xi
I took a look at the log again and noticed my rail pressure is 2600-3100 throughout the entire WOT pull....Is there a such thing as too much rail pressure causing that STFT issue?
 

shushikiary

Sergeant
Jun 4, 2018
255
133
0
Ride
335xi
If you have a leaky injector you'll have more issues at high pressure sometimes, but usually it will make your AFR too low not too high (and thus your fuel trims would be negative not positive).
 

zmon1300

Corporal
Nov 3, 2016
181
114
0
Chicagoland
Ride
'10 335xi
Found 2 cracks in my valve cover. Replaced the valve cover and did spark plugs and wires and the issue is now resolved. I blame the VC because my old wires and plugs were not super worn out or anything. Very weird.