Perplexing PLX !!**??

[Dirty Howie]

Started a new thread for those that have the PLX and are having issues with its AFR reading being too lean in closed loop at non-PE cruise conditions.

I spoke to PLX today. The guy is a tuner. I explained the problem of accurate open loop but lean closed loop readings.

He is confident it is a tuning issue and that I should adjust (richen) my VE tables. I explained to him that others have this same problem and that two other tuners (Doug and Russ) are sure its a PLX issue ..... that closed loop reading should be 14.7

Anybody have a PLX and checked OL vs CL readings and had them match ??


DH

[5_Liter_Eater]

Not trying to hijack your thread Howie but as you know through the other threads I seem to have the same sort of thing going on with my AEM WB. Maybe we can make this a "How accurate is your WB thread" but if you'd like to keep it PLX specific let me know and I'll whack this post.

In open loop my AEM reports very close to the commanded AFRs (14.7:1 and in PE 12.8:1). When I switch to closed loop the AFR averages ~15.6:1 and trims are negative by ~5% or more. Logging LTFT against mass airflow there is a definite correlation between airflow and accuracy of the wide band. Above 40 g/sec the trims are -3 to -1. Below 40 g/sec they are -5 to -8. It's pretty linear meaning that the AEM is less and less accurate as airflow goes down. Either that or the narrow bands are less and less accurate as airflow goes down. It's kind of hard to tell without another WB to verify one way or the other. Doug (EC Tune) had a similar issue with his PLX and when he replaced it with a Dynojet Wideband Commander on the same tune, the problem went away.

So we're looking for other people, regardless of their WB model, who do not see ~14.7:1 reported by their wide band while in closed loop.

[Dirty Howie]

Bill

Absolutely get into this thread!!!!!!

There are a couple of threads about this and I was hoping we could get to the bottom of this.

I'm kinda busy this weekend and have a track day on sunday. So next week I will do more logs in OL, maybe play with my VE and try your histogram (maybe you can post it to this thread)

Hopefully Russ and Doug will respond to what PLX told me.....


DH

[5_Liter_Eater]

Here is the histogram used to generate the above screenshot.

[Dirty Howie]

Here is the histogram used to generate the above screenshot.

Bill

Thanks,

I will try it out and post my results for comparison ......


DH

[S2H]

this happens on all modified cars.....
anything that changes how the heat of the exhaust is will change the accuracy of the narrowband o2's
in turn it causes the voltage to drift...usually so that the crossing voltages will be leaner than when the car was stock...

you can attempt to change the o2 switching voltages or use some of the adders/subtractors to get the narrowbands to follow suit for what our widebands do much more accurately

or my personal favorite...use the wideband as a narrowband and fix the crossing voltages and adders so that they match what your wideband uses on its narrowband output side.....and you then also need 2 widebands for this as well...

of course you could also just run in open loop....no big deal...do it all the time too

[Dirty Howie]

this happens on all modified cars.....
anything that changes how the heat of the exhaust is will change the accuracy of the narrowband o2's
in turn it causes the voltage to drift...usually so that the crossing voltages will be leaner than when the car was stock...

Scott

So you are saying that the WB IS reading correctly. That the 02 sensors in closed loop are causing switching at a leaner AFR due to headers, bigger engines etc.

This makes more sense to me intuitevely ....... but Russ and Doug are convinced otherwise And finally had me convinced it is the WB

Can you think of any emperical test that we can do to prove this one way or the other ????


DH

[S2H]

Scott

So you are saying that the WB IS reading correctly. That the 02 sensors in closed loop are causing switching at a leaner AFR due to headers, bigger engines etc.

This makes more sense to me intuitevely ....... but Russ and Doug are convinced otherwise And finally had me convinced it is the WB

Can you think of any emperical test that we can do to prove this one way or the other ????


DH

I'll say my wideband can be the proof...which I have done a completely stock vehicle and the narrowbands line up nicely with the wideband....
then I tuned a modded car and the narrowbands were following leaner than stoich...and then I tuned another stock vehicle and they were back in line again...so I know its not my wideband being wrong....
correcting the issue may be adder tables or it may be the switchpoints themselves...but either way the stock O2's dont like modded vehicles

[Dirty Howie]

I'll say my wideband can be the proof...which I have done a completely stock vehicle and the narrowbands line up nicely with the wideband....
then I tuned a modded car and the narrowbands were following leaner than stoich...and then I tuned another stock vehicle and they were back in line again...so I know its not my wideband being wrong....
correcting the issue may be adder tables or it may be the switchpoints themselves...but either way the stock O2's dont like modded vehicles

Scott

This seems very compelling to me !!!!!

Just to verify ..... you have also watched the AFR go from stoich in OL to lean in CL on the same car right ??

I don't think I'm ready to be adjusting 02 switching points.......
Would you be willing to make some changes to my tune for me to test???

Also here is a log from today....50 miles of frwy cruising with some WOT to 120mph. You can see in histo#6 that my AFR is around 15.1-15.2 and at WOT it is pretty inline with my commanded which is 12.68 - 12.92 depending on IAT.

[S2H]

at this time I cant do it...but I might be able to when I get home from this current week of on the road work....

I'll gladly make an attempt..I might have to send you a scanner config and a few histograms to set up... as well as a few changes for you to make in the tune.

and yes..tuned a stock car in open loop and watched narrowbands switch around 14.7
then tuned a modded car and watched the closed loop switch at leaner than 14.7 when I know it was 14.7 in open loop

[Dirty Howie]

at this time I cant do it...but I might be able to when I get home from this current week of on the road work....

I'll gladly make an attempt..I might have to send you a scanner config and a few histograms to set up... as well as a few changes for you to make in the tune.

and yes..tuned a stock car in open loop and watched narrowbands switch around 14.7
then tuned a modded car and watched the closed loop switch at leaner than 14.7 when I know it was 14.7 in open loop

Okay Scott have a good road trip. I am very interested in testing this out so will glady run some logs with recommeded config/histo setup when you return.

Thanks !!!!!!!!!


DH

[S2H]

I need a log in open loop and closed loop
with the following things in the Main table
LTFT Disabled in closed loop so that only STFT's are active(still remember toi reset fuel trrims)
LTFT and STFT diabled in open loop and fuel trims reset

RPM
MPH
MAP
MAF HZ
MAF Airflow
Dynamic Airflow
Dynamic Cylinder Air
STFT both banks
O2 voltage both banks sensor 1
AFR Commanded
Wideband Sensor(preferrably in a way that you still have both Stock O2 sensors fully functional)
ECT
IAT
TPS
Fuel Trim Cell
Ignition Timing Advance
Timing Retard

nothing else

before you star logging...make the #'s in your Closed Loop vs Airflow Mode tables read
0,2,4,6,8,10,12,14,16,16,16,16,16,16.............

then post the logs...I'll take a look when I get a chance

[5_Liter_Eater]

I had the same opinion as Scott. I had always been under the impression that all the mods to the car made the narrow bands skewed. All the hub bub lately got me thinking otherwise but I'm still not convinced one way or the other. Still looking for a definitive way to tell which sensor is off without having to buy another WB.

[flea]

Experiencing the same issues described in the post. Everything dialed in nicely in open loop ........... go back to CL and running lean (~15.1 - 15.5 AFR). I do have a PLX but without more information it's difficult to blame the WB. PLX voltage output appears to be OK in CL (~2.35).

Mods on this particular Goat are CAI and LT headers. From Scott's description I'm leaning toward the O2 switchpoints as the most likely suspect. Has anyone actually recalibrated O2 switchpoints on an E40 LS2? I'll give it a go and share the results if someone can supply the proper way to go about this.

BTW: before the bolt on mods this was not an issue. CL and OL AFR lined correlated quite nicely.

[5_Liter_Eater]

I'm working in a histogram that will determine the optimal switchpoints for each airflow mode. Having trouble with the necessary plot filtering. May require a beta patch.

[S2H]

Experiencing the same issues described in the post. Everything dialed in nicely in open loop ........... go back to CL and running lean (~15.1 - 15.5 AFR). I do have a PLX but without more information it's difficult to blame the WB. PLX voltage output appears to be OK in CL (~2.35).

Mods on this particular Goat are CAI and LT headers. From Scott's description I'm leaning toward the O2 switchpoints as the most likely suspect. Has anyone actually recalibrated O2 switchpoints on an E40 LS2? I'll give it a go and share the results if someone can supply the proper way to go about this.

BTW: before the bolt on mods this was not an issue. CL and OL AFR lined correlated quite nicely.

log all of the stuff I listed above and I'll plug data thru my histo's and spreadsheets and give you a good Idea on a starting point

[flea]

Thanks Scott, I'll forward the data over the next day or so.

One more odd thing I forgot to mention.

MAP has always been around 40-41 KPa at idle [550 rpm] (before and after the mods). When I re-enable CL all of the sudden I'm logging 45-46. I scratch my head a few times and go back to OL ....... MAP is right back to 40-41. What am I missing here?

[Dirty Howie]

BTW: before the bolt on mods this was not an issue. CL and OL AFR lined correlated quite nicely.

This seems to verify exactly what Scott is saying !!!!!


DH

[Dirty Howie]

Scott please confirm these Editor tables and the config before I start.

Not sure I understand this....."before you star logging...make the #'s in your Closed Loop vs Airflow Mode tables read
0,2,4,6,8,10,12,14,16,16,16,16,16,16............." Mine were different but I changed them as requested. Will I be changing this back???



DH

[S2H]

there are multiple patents and scientific proof of heat causing drifting on o2 sensors....
its well documented....
I wish I could find a graph but tonight my google skills seem to be eluding me..

so by the nature of heat causing sensor drift it should make perfect sense to anybody that changing the heat range of your exhaust by modding will cause sensor drift...
the most common example of this is headers..especially coated headers...
the design of the coating is especially made to keep the heat insode the tubes which creates a super heated surface on teh inside which allows for faster scavenging of exhaust...alowing for a fuller exhaust charge and thus allowing for a better cleaner intake charge as well with less exhaust gasses left in the combustion chamber.
the hotter gasses hit the O2 sensor and skew the readings as the o2 sensor reacts differently when its used in a different heat range than its designed range...
this is also the reason why there are so many anrrowband o2 versions and why if you go to buy a replacement it has to be the right one....its not just about the connector and the length...its also about the heat range