One More Time: PE VS OLFA Commanded AFR

[WeathermanShawn]

Well, Joecar you finally 'broke' my car....just kidding.

For now, I will just post the tune & Log. Joecar had me do an interesting test. I put Table B3618 to the same value as B3601 (stoich). For B3616, Normal PE Mode Enable all TPS values were put to 10%.

Table B3605 was purposely changed to a richer value of 13.0 AFR at normal engine operating temperature.

Results:

1. Car started normally using the Table B3605.
2. Car went into Closed-Loop at 34C (normal).
3. When PE mode was hit, car went into OL-Drive..commanding 14.629 AFR. At 10% TPS it stayed continuously in OL-Drive.
4. 5-10 minutes later it attempted to do its EVAP Purge (FTC cell 22). It was unable to do its EVAP purge (cell 22 is also WOT). Car immediately threw a DTC Code P0131 and P0137..and defaulted into the Table B3605.

Pulled car over, cleared codes..reloaded 'normal' tune. Everything worked out.

Joe, or anybody else who might be interested. PE Mode (in my OS) seems to always initiate OL-Drive. When in OL-Drive, the EVAP Purge is not active. Believe me it was not long before I smelled gas fumes and I went rich. No Trim, no EVAP..it did not like that 10% TPS enabler. To minimize pids, I did not log IPW or H02S11..but my O2 sensors pulled a DTC and I found an unique way to use the OLFA Table..

Joecar interesting experiment, but the U.S. EPA may have done something tricky with FTC cell 22 and EVAP. Thats my theory. Any thoughts?

[joecar]

Shawn,

Very interesting...

During OL-Drive mode, where TP > 10%, AFR is stoich and I see that FTC is 4 or 5 and the LTFT's are +0.8% and 0% respectively... this tells me it is trimming... BEN is 1.00.

The thing is, I can't tell if PE has enabled... or is that what OL-Drive mode is telling us...?

[joecar]

I was looking thru the descriptions for the STATE/TSTATE pids...

These pids may shed more light on what is going on:
STATE01 (evap command)
STATE04 (cotp mode)
STATE05 (fuel trim learn, fuel loop status)
TSTATE03 (pe mode active)

(that's what I said: "what is pe mode doing in a trans pid).

[WeathermanShawn]

Well Joe, here is the conundrum. For the first 5-10 minutes at normal ECT, Commanded AFR was indeed 14.63. However, when TPS >10 % (irregardless of PE AFR being stoich), it would go into OL-Drive. Perhaps OL-Drive is unique to 2002's, but it appears to go into OL-Drive when in PE Mode and/or EVAP purge.

If you look about 10 minutes into the log, because FUELSYS reads OL-Drive for 5+ minutes at a time (narrow-bands ignored?), whenever TPS ,< 10% EVAP was continuously on (OL-Drive). So, bottom line for 10-15 minutes OL-Drive completely ignored the o2 sensors. I could smell raw fuel (EVAP could not purge?), and about 15 minutes later it DTC'd and went into 'UNKNOWN" Fuel Status..And went to my overly rich OLFA Table...

So, here is my 'conclusion'. In the 12212156 OP, EVAP and PE initiates OL-Drive..PE can not default to Closed-Loop (see log) unless you make TPS 100%. Whenever it says OL-Drive..those narrowbands are being ignored..

I know it is bizarre, but I have heard of 1 or 2 others with 2002 Camaro's that have had similar experiences. Believe it or not FTC cell 22 WOT and EVAP is shared. So if you start out with +5% LTFTBEN EVAP, you will see +5% at WOT fueling (FTC cell 22..).

I probably did not explain it well..but the car ended up running 100% Open-Loop at 13.0 AFR. I re-flashed a tune and 'clean' it out, but never did I see PE Mode and CL???

[WeathermanShawn]

Just a follow-up and conclusion:

On my Vehicle's OP system while operating in closed-loop, PE Table B3618 dictates the Commanded AFR Fueling, irregardless of the AFR value commanded in the OLFA Table B3605.

Any initiation of PE Mode, including TPS % in Table B3616 puts the vehicle into a variation of an open-loop. Table B3618 can not be 'disabled' even when commanding an EQ of 1.00.

If for any reason someone wants to initiate PE Mode at very low or part-throttle conditions, be aware that the EVAP purge appears to be disabled while in PE Mode. This may lead to an excessive release of EVAP purge during off throttle and lead to a an overly rich AFR.

Obviously that can significantly limit your ability to properly tune your vehicle while in closed-loop.

If anyone in the future runs into similar problems, at least you will have information to compare to.

Thanks..

[Raven]

hello everyone,
I was wondering if it is ok or wise to disable the PE altogether? if I'm getting the AFR I'm commanding using B6347 without the PE.
I'm using COS5.

--
Regards

[WeathermanShawn]

I have not ran that particular custom OS, but it is probably just a matter of personal preference whether you disable PE or not.

I like my fueling to come on more by TPS %, but if I recall several of the Custom OS's allow that.

In my situation, there does not appear to a PE 'disabling' function, but if you don't need PE.. by all means do what you need to do. My thread was just to illustrate that sometimes there are unusual consequences that you are not always aware of.

Hope that helps..

[Raven]

in this COS5 you command RPM-MAP instead of ECT-MAP.
I use B3613 to disable the PE.
I'm going to enable the PE above 80 kPa and set it to match my WOT commanded AFR.

unless you fully understand how something works it can be hard to track back the consequences.

thanks

--
Regards

[joecar]

You can disable PE as long as you set the high load columns of B3647 suitably rich.

[WeathermanShawn]

You know I guess even in my OS you can 'disable' it by changing B3613 (MAP threshold) to a higher MAP. Not really the original point, but as Joecar says..just make sure you have the correct fuel commanded regardless of what Table is controlling.

Good luck..