Cylinder airmass drops suddenly WOT in boost
#1
Cylinder airmass drops suddenly WOT in boost
2009 e38 ecu with an Ly6, low boost 5 psi, SD 80 lb injectors. At the most dangerous time, without any warning, the cyl airmass drops from 1.07 for example to 0.60 or way lower. The whole time, the throttle position stays wide open, commanded and actual afr doesn't change. Just the nasty reality of lots of spark advance as it's somehow being fooled into thinking it's at a much lower cylinder airmass. I thought I'd play it safer so I reduced the 0.60 cyl airmass timing in case it happened again, and the damn thing went to as low as 0.00 g/cyl which was around 40* timing while in boost.
At first I thought it was reduced power mode related but I have disabled p0068 tests and set the p101, 106 and 121 codes to a temperature I won't get up to ever.
Has anyone ever seen this before?
At first I thought it was reduced power mode related but I have disabled p0068 tests and set the p101, 106 and 121 codes to a temperature I won't get up to ever.
Has anyone ever seen this before?
#2
I don't really know if this could be it, but in Efilive a while ago they found a hidden bit of the pcm that GM coded for a "desoot" mode. Apparently can cause a lean spot all of a sudden. It seems most people chased this by just adding more fuel at that spot. Worth a shot.
#3
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Does your map sensor go low also when it happens?
#5
I don't really know if this could be it, but in Efilive a while ago they found a hidden bit of the pcm that GM coded for a "desoot" mode. Apparently can cause a lean spot all of a sudden. It seems most people chased this by just adding more fuel at that spot. Worth a shot.
In my case the air/fuel ratio remains where it should be
#6
A far out possibility was suggested to me but it may be the cause as my HP tuners support ticket didn't come up with any explanation. One person was saying they had a similar issue and it was related to the injector wires too close to the coil and related wires.
This only ever started happening since the 80 lb injector swap and the swap required spacers which put the connector/wiring closer the the coils. The owner mentioned today that he noticed an injector wire was partially wrapped around one of the coil wires, so this may be those rare crazy scenarios.
Can't wait to test it out now. To be super safe, I'll put all of the timing in the table to 10 degrees so if it references 0.00 g/cyl again for instance, no engine killing will occur 😁
This only ever started happening since the 80 lb injector swap and the swap required spacers which put the connector/wiring closer the the coils. The owner mentioned today that he noticed an injector wire was partially wrapped around one of the coil wires, so this may be those rare crazy scenarios.
Can't wait to test it out now. To be super safe, I'll put all of the timing in the table to 10 degrees so if it references 0.00 g/cyl again for instance, no engine killing will occur 😁
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#8
TECH Senior Member
That means the insulation is compromised. Get some new harnesses. Moving the coils is a band-aid.
#11
I would have never thought of this, someone on an hp tuner fbook group said that happened to them before and wiring too close was the issue.
#12
Unfortunately it did it once again today. I was suggested to try setting Maf fail high and low to 0 hz, dynamic disable to 8192 and re-enable to 8191.
The old values were maf fail high and low =1 hz and dynamic disable 8000, re-enable 7900.
Since making those changes, it hasn't happened again and I've gone WOT from a few different speeds without issue.
As somewhat of a safety, I lowered the timing in the low cyl airmass part of 3000 rpm + as I'll never be reving much over 2500 rpm when cruising/driving normal.
The only time 3000 + rpm is seen is in boost so at least it follows the rpm axis and if it drops to 0.18 g/cyl airmass at 3500 rpm, the spark value there is 15 degrees. I'm not sure what effect it will have on deceleration but I'll try it out. Sure beats a 10 degree to 50 degree timing jump at 10 psi. It makes sense that the injectors will also follow the low cyl airmass and make it go lean...but at least the lack of spark will be better than tons of spark and a temporary lean condition.
The old values were maf fail high and low =1 hz and dynamic disable 8000, re-enable 7900.
Since making those changes, it hasn't happened again and I've gone WOT from a few different speeds without issue.
As somewhat of a safety, I lowered the timing in the low cyl airmass part of 3000 rpm + as I'll never be reving much over 2500 rpm when cruising/driving normal.
The only time 3000 + rpm is seen is in boost so at least it follows the rpm axis and if it drops to 0.18 g/cyl airmass at 3500 rpm, the spark value there is 15 degrees. I'm not sure what effect it will have on deceleration but I'll try it out. Sure beats a 10 degree to 50 degree timing jump at 10 psi. It makes sense that the injectors will also follow the low cyl airmass and make it go lean...but at least the lack of spark will be better than tons of spark and a temporary lean condition.
#14
It's hard to tell in the log if the order of events are seen as the delay in channels but here is what changes in order (while WOT in boost):
-timing changes first from the 8 degrees it was at to 22 then 35 then 45 degrees, this is based on pressing play and pause on my video of the actual log played back so it's chopped up in increments
-then VE mg*k/kpa drops next from 2737 to 0 and cylinder airmass drops from 1.35 g/cyl to 0.71 as it plummets to 0.00
-air calc mode still says "hi speed" all this time, dynamic airflow still at 410 g/s
-ve airflow then drops from 54 lb/min to 0, dynamic airflow also drops to 0, air calc mode says "unknown"
-at this time the commanded afr and actual are still in the low 11s, then while still at full throttle, injector ms drops to 0.3 from 19 ms.
It all recovers again shortly after that back to normal.
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#15
TECH Senior Member
I actually wonder if the wiring issue would have caused the ECU to be compromised.