After going into boost car starts hesitating with throttle transitions.

[IDRIVEAG8GT]

2.5 bar OS,

Car runs great, but has a really weird issue. You can fire it up, drive it around, mess with throttle and it never misses a beat, but as soon as it builds two or three pounds of boost it all goes downhill.

What I mean by that is anytime after you get out of boost and go back to normal driving, the car starts to hesitate violently with quick throttle transitions.

When you blip the throttle after building boost, the engine just cuts out like it's dead for a split second, the RPM dips, then it comes back alive with a nasty backfire occasionally and accelerates as it should.

Is there anything that would cause something like this. I have tried changing DFCO settings, turning LTFT's on and off, forcing OL, Nothing seems to work. The issue is probably staring me right in the face but I can not for the life of me find it.

Like I said when you blip the throttle it acts just like fuel cut.

I don't have a good log of it doing right now, my tune is attached.

Note: If you turn off the car and restart it, everything goes back to working normally. Also tried a write entire to no avail.

Let me know!
-Robbie.

[ingsteve]

ETC issue?

[IDRIVEAG8GT]

Nope, throttle blade does exactly what it's supposed to no matter what.

[HoP]

Backfire is going to come because of the excessive amount of fuel on decel. Log with a wb your decel afr. Sounds to me like an over fueling situation upon decel.

[IDRIVEAG8GT]

~14.9 AFR on decel, 17:0 AFR during DFCO. It's whenever you pop the throttle that the O2's hit the floor (around 30MV)

For instance, cruising along in third gear at 20% pedal position, then quickly transition to 50% pedal position, the O2's hit the floor and it cuts out for a split second, then takes off as it should.

It happens wether you're decelerating or not.

[DSteck]

Tune the SD and it'll get exponentially better.

[IDRIVEAG8GT]

Tune the SD and it'll get exponentially better.

You wanna elaborate on that?

I've tried adding fuel, taking it away, to no avail.

Funny how I can drive the car and continually play with the throttle and it never misses a beat, but starts to miss and stumble after the MAP KpA exceeds about 115 you can then turn off the car, restart it, and all works perfectly again until it hits boost.

[IDRIVEAG8GT]

Considering my VE table has the STFT's around -3% all the time no matter which cell it's in, is that really where you can see a problem?

[10_SS]

IS there something happening with the baro sensor? My LT1 shared a baro sensor reading with the MAP sensor, and by default, running a 2bar sensor with all the tables scaled to work with it, it would run fine UNTIL I floored it and if I floored it under a certain RPM, then the fueling tables would all shift a bit.

In the end, I realized the Baro reading would update at key on to be 98kpa then take a new update at rpm's below 2500 and TPS above 90%, so since I had a supercharger installed, then when I floored it under 2500 RPM's, the Baro would sample the MAP which was now 115kpa and it would store that as the new baro setting, and adjust fueling accordingly.

So I was getting huge changes in WOT fueling depending when I entered WOT. Sometimes it would be pig rich, other times lean. For me it wasnt enough to notice it in normal cruise mode, but it was affecting fueling there too.

Is there anything that could be building up pressure, or the MAP or Baro sensors getting messed up after seeing boost?

[IDRIVEAG8GT]

IS there something happening with the baro sensor? My LT1 shared a baro sensor reading with the MAP sensor, and by default, running a 2bar sensor with all the tables scaled to work with it, it would run fine UNTIL I floored it and if I floored it under a certain RPM, then the fueling tables would all shift a bit.

In the end, I realized the Baro reading would update at key on to be 98kpa then take a new update at rpm's below 2500 and TPS above 90%, so since I had a supercharger installed, then when I floored it under 2500 RPM's, the Baro would sample the MAP which was now 115kpa and it would store that as the new baro setting, and adjust fueling accordingly.

So I was getting huge changes in WOT fueling depending when I entered WOT. Sometimes it would be pig rich, other times lean. For me it wasnt enough to notice it in normal cruise mode, but it was affecting fueling there too.

Is there anything that could be building up pressure, or the MAP or Baro sensors getting messed up after seeing boost?

Very Interesting point. However mine seems to update just fine. Since the typical key forward MAP kPa here is 89, this thing will do it only during rapid throttle transitions only after it hits boost, without turning off the car. If I roll on the the throttle after going into boost and coming back out it doesn't have an issue at all. WOT fueling is just right all the time, (11.5:1) AFR in BE mode. It's just the sudden fuel cut effect. I really need to get a decent log for you guys. This problem IS DRIVING ME NUTS!

[10_SS]

Gotchya. Well I don't know if it's related but I just got my whipple installed and I'm trying to figure out why there is a MAP update delay when mashing the throttle after say shifting from 1st to second (lifting and re-applying boost).

Along with the MAP slow responding, there seems to be a "AFR CMND" delay too. Combine these two together, and the AFR runs lean long enough to make harsh knock then corrects as PE mode finally enables.

It's a bit different than yours, maybe:
Once I shift (let off, then WOT very fast) and the MAP finally starts showing 150-180kpa of boost, the Commanded AFR still shows 14.68AFR for a data point or three. By this time the AFR is lean as heck, boost is built, and knock is though the roof.

All of this happens within 0.3seconds, but the MAF updates instantly, along with knock, 02's, and Throttle position (both pedal and plate). The MAP updates slow, but once it updates, then next in line is PE Mode which is followed by lower Commanded AFR values.

Is this anyhow related to your problem? I'm not sure if there is a "Stomp fuel" on these E38's or if the limited transient fuel settings play a part in any of this?

I found this topic, not sure how it relates.. but talks about the E38 being slow to respond to MAP readings. http://www.hptuners.com/forum/showth...ght=MAP+FIlter

You mention "whenever i pop the throttle, 02's hit the floor". Well, basically I see this too if I "pop the throttle fast enough" while shifting. In the mean time I wanted to slow down the rate of throttle increase from 100% to something, if that setting even works (it doesnt work with key on, engine off, datalogging, 100% is just as fast as 25%), and there is only a 1000-5000rpm window.

[Ben Charles]

WEIRD this came up, but I have a customer with a boost setup and he is telling me this is happening with him as well??

I have done several boost tunes and this is the first time I am seeing this.

[bluegoat06]

Idrive, try this
Engine/fuel/transient
lower the transient fuel qualification/ enable delay, from 30 to 15
and transient fuel mass gain impact factor/maximum mass, from 2048 to 1024

[IDRIVEAG8GT]

Idrive, try this
Engine/fuel/transient
lower the transient fuel qualification/ enable delay, from 30 to 15
and transient fuel mass gain impact factor/maximum mass, from 2048 to 1024

Will do but can you elaborate on what that does?