Rough running

[Hib Halverson]

Originally Posted by Billy Mild

I replaced the fuel pumps last night and the car overall runs better. Smoother idle, feels like more power up top. The stumble still remains.

Conditions when it happens, decel from 3000+ RPM slow down to around the 2000-2200 RPM range and give it just a little throttle 10-20%. It will stumble. I noticed while on decel the left side INT drops drastically from 120-125 range to 64, while the right side stays around 120-125ish maybe 113. I notice the lower INT on the left side the worse the stumble is. If I got WOT the stumble stops right away, but I think that has to do with it is enriching the mixture immediately and ignores the sensors. This stumble happens with power key ON or OFF

So on the scanner I'm not sure what side of the engine is the left vs. right side. Could this be an exhaust leak, O2 sensor issue, or something else?

Just guessing, here...

If the bank 1 integrator is going down to 64, that means the system is taking a whole lot of fuel out. If the stumble is worse, the lower the bank 1 integrator gets--that makes sense.

I'm going to guess that the stumble is being caused by a suddenly way lean AFR (64 integrator) and that the system, while in closed loop, cannot change states (from a pulse width typical of a 64 integrator to a pulse width wide enough to provide proper fueling) fast enough to prevent a lean sag during a modest throttle opening.

You don't get the stumble when you go straight to WOT because the engine goes instantly to open loop with both integrators at 128.

Let me know what you think.

[Billy Mild]

Originally Posted by XfireZ51

You have headers and exhaust. In decel, you have high vacuum and basically with the increased breathing the exhaust provides, it could be necessary to richen up the AE pumpshot at lower TPS% changes.
Again, Billy it would be helpful to see what the % TPS change is at the time of the stumble, plus are the secondaries kicking in or is this happening w just the primaries.

I will run a datalog and try to limit it down to when the stumble is occuring a little before and a litttle after.

The thing is the stumble goes away if I just go WOT. I have noticed that sometimes it is not during secondary operation. once the secondaries come on it may stumble at the low 25-30% throttle opening The sound the engine makes is terrible as well. I will try and get a video of that too.

[Billy Mild]

Originally Posted by Hib Halverson

Just guessing, here...

If the bank 1 integrator is going down to 64, that means the system is taking a whole lot of fuel out. If the stumble is worse, the lower the bank 1 integrator gets--that makes sense.

I'm going to guess that the stumble is being caused by a suddenly way lean AFR (64 integrator) and that the system, while in closed loop, cannot change states (from a pulse width typical of a 64 integrator to a pulse width wide enough to provide proper fueling) fast enough to prevent a lean sag during a modest throttle opening.

You don't get the stumble when you go straight to WOT because the engine goes instantly to open loop with both integrators at 128.

Let me know what you think.

This sounds accurate. I don't know what would be causing the lean condition. Could it really be as simple as O2 sensors?

[Billy Mild]

Video to follow. Here is one Datalog that shows the stumble. Anytime the INT hit 64 on the left side the car would pop/backfire through the exhaust and if I go lightly on the throttle it will stumble. If I would give the car more throttle then the secondaries would kick in and smooth out the mixture.

I was able to get the secondaries to stay open while on the highway and i slowed down to 2000 RPM while maintaining partial open throttle. There was absolutely NO STUMBLE when the secondaries were open at 2000 RPM.

Does that sound like a tune issue or something else?

https://youtu.be/Tntnk9KFTQg

https://1drv.ms/u/s!AmLeM5vTSQEtuBsaMsSzfVVO565i

Datalog file to follow the video.

[tpepmeie]

I haven't looked at your data logs. When the int goes low, do the fuel pulse widths go to zero? That would be expected when decel fuel cutoff is active. Given your description it sounds like conditions where dfco would be active. It's easy to disable in the calibration to check if that makes a difference.


Sent from my iPhone using ZR-1 Net Registry

[XfireZ51]

Todd,

I think Billy originally stated that this was a Haibeck calibration w DFCO disabled. If this were my motor, I would try either increasing fuel(3-4%) in the
Port Throttle Closed VE table for the cells in the vicinity of the rpm/kPa where the stumble occurs, and/or increasing the AE pumpshot at the 0-5% of the
AE v TPS% change table. Again, probably starting w 3-4% increase. I'd need to take a look at the bin just to determine how it varies from stock.

[Billy Mild]

Originally Posted by tpepmeie

I haven't looked at your data logs. When the int goes low, do the fuel pulse widths go to zero? That would be expected when decel fuel cutoff is active. Given your description it sounds like conditions where dfco would be active. It's easy to disable in the calibration to check if that makes a difference.


Sent from my iPhone using ZR-1 Net Registry

Haibeck was supposed to enable the "anti-backfire" mode for my tune. My only issue is that the LEFT side is the one that goes very low on the INT side. The right side INT goes down to only 110 or so.

Originally Posted by XfireZ51

Todd,

I think Billy originally stated that this was a Haibeck calibration w DFCO disabled. If this were my motor, I would try either increasing fuel(3-4%) in the
Port Throttle Closed VE table for the cells in the vicinity of the rpm/kPa where the stumble occurs, and/or increasing the AE pumpshot at the 0-5% of the
AE v TPS% change table. Again, probably starting w 3-4% increase. I'd need to take a look at the bin just to determine how it varies from stock.

On my old 944 Turbo there was a switch on the ECU to do just this without changing the tune at all. Is that possible on the ZR-1?

[XfireZ51]

Originally Posted by Billy Mild

Haibeck was supposed to enable the "anti-backfire" mode for my tune. My only issue is that the LEFT side is the one that goes very low on the INT side. The right side INT goes down to only 110 or so.



On my old 944 Turbo there was a switch on the ECU to do just this without changing the tune at all. Is that possible on the ZR-1?

Ah, no such switch. You probably had something like a "bin switcher" on the Porsche to fatten up the fuel. The disparity between left and right banks is not unusual especially in high vacuum situations. It could also indicate a vacuum leak of some sort. On decel, fresh air could be getting sucked past the O2 sensor. Check to make sure there isn't an exhaust leak somewhere on the left side. Perhaps near the collector.
How recent are the O2s?

[tpepmeie]

Good point about the exhaust leak and/or O2 problem Dom. I very much doubt it's calibration related.


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[Billy Mild]

My o2's were replaced when I put the headers on late last year. The o2 sensors were "Standard Motor Products" brand from RockAuto. I did use a O2 extension harness on the passenger side header. I have the o2 extension harness wrapped in wire loom and DEI high temp reflective tape to help prevent it from melting.

So I should be looking at a leak possibly on the passenger side of the exhaust or maybe the O2 on the left side is lose maybe? I will try and jack up the car and see if there are exhaust leaks.