Procedure for turning off MAF and forcing open loop for SD?

[AllCammedUp]

Ross and I were discussing this the other day:

If you are happy to drive around with a flat AFR of say, 13:1 then try using bidirectional controls to command the AFR to 13:1 which effectively turns of all PCM fuel control. (You can use whatever AFR you like).

I don't think it is necessary to set the Open loop bidi control or the Fuel learn bidi control because you are forcing 13:1 ALL the time. The PCM will use the VE table to try and figure out the correct pulse width to achieve 13:1 and whatever error you see in the BEN PID will be the amount your VE table is "out".

As soon as you switch off the ignition, bidi conrols are terminated and it is "back to normal". But you'll still have your map for auto updating your VE.

I have not tried it, I do not know if that will work, but I thought I might throw it the thread for discussion.

Regards
Paul

Paul,

Good to know we have two options! I was considering this before I started the thread, but I've never heard anyone talk about it before, hence me starting the thread. I knew that you/Ross, Rick, Jesse, Steve B., John S., Brains, Delco, etc. al. have obviously done a good bit of this work, so I wanted to see how the 'people in the know' were going about it.

I like the bi-di control approach 'better' because I don't have to maintain an 'open-loop' version of a specific TUN. Anyone else tried it this way?

[GMPX]

I am actually going to venture out of the house tommorrow and plan on logging as discussed above. Hopefully I might have something to report back.

Cheers,
Ross

[Bruce Melton]

I am actually going to venture out of the house tommorrow and plan on logging as discussed above. Hopefully I might have something to report back.

Cheers,
Ross

I hope you make it back! :roll:

[SinisterSS]

With Bi-Di active, I've never been able to log data at the same time.

Obviously I'm not patting my head while rubbing my tummy in the right way... :?:

[Tydriver]

Ross and I were discussing this the other day:

If you are happy to drive around with a flat AFR of say, 13:1 then try using bidirectional controls to command the AFR to 13:1 which effectively turns of all PCM fuel control. (You can use whatever AFR you like).

I don't think it is necessary to set the Open loop bidi control or the Fuel learn bidi control because you are forcing 13:1 ALL the time. The PCM will use the VE table to try and figure out the correct pulse width to achieve 13:1 and whatever error you see in the BEN PID will be the amount your VE table is "out".

As soon as you switch off the ignition, bidi conrols are terminated and it is "back to normal". But you'll still have your map for auto updating your VE.

I have not tried it, I do not know if that will work, but I thought I might throw it the thread for discussion.

Regards
Paul

Weird, I thought I already responded here, I musta not hit SUBMIT before closing the page.. Anyhow..

I got a chance to do this in my '02 5.3L Silverado.. I didnt go to a 13:1 AFR tho.. I went to 15.7-16.0:1 just to see what it would do.. I suspect that there is some sort of protection feature active in the PCM tho.. The truck was seriously down on power when I was driving it.. Heck, it wouldnt even turn over the tires from a stop sign..

With that said, I did a couple of WOT blasts and I didnt notice any KNOCK, so I think it must also retard the timing a bit as well.. You can watch it drop off as the RPMs come up, I never saw over 19.5-20.0* of total advance under WOT(remember tho, I was watching the road primarily)... I did a couple of runs with where I re-enabled the stock PCM controls (shut off Bi-Di controls while I was going WOT) and there was a sizeable increase in the SOTP (Seat of the pants) dyno. The truck pulled harder and quicker to redline with it disabled during the run..

Just some additional food for thought, it must pull timing as well.. In any other event other than WOT, it was almost completely un-noticeable while driving however...

I may try this on my next road trip to see if it can be an INTERIM version of LEAN CRUISE while we await the COMMERCIAL version and overseas OS's so we can utilize it here in the US..

I saved a couple of logs if anyone is interested in them let me know.. I barely know what I am looking at since I am still NEW to this stuff !

[Blacky]

With Bi-Di active, I've never been able to log data at the same time.

Obviously I'm not patting my head while rubbing my tummy in the right way... :?:

If you start logging in 10fps mode then EFILive prevents you from opening the bidi window.
If you start logging in Dynamic mode then EFILive allows the bidi window to be opened.
If you have the bidi window open, then start logging in 10fps mode, EFILive drops logging speed to dynamic.

Regards
Paul

[Tordne]

I've just logged a couple of runs using the Bidirectional Controls to set the AFR to 13.0:1. It works really well, and if I understand correctly it shortcuts having to tune out all the other aspects/functions of the calibration which affect and/or interfere with the final commanded AFR.

Very happy with that solution, thanks Paul/Ross.

[daveb]

Sorry for the late response.

I do not understand why you would want to disable PE mode.

When tracking commmanded AFR and logging AFR from a WBO2 sensor (eg PLX300 - which is what I use) we can log the difference between the two and adjust the fuel maps accordingly. They are not really polluted because we are not aiming for stoich anymore and the commanded AFR value indicates by how much we are deviating from the base values.

Running too lean at WOT would be risky, particularly if the MAPs are wrong and you run lean. So I would have thought running WOT with the leaniest mixture (ie no PE enrichment) would be the LAST thing you would want to do. Better to start rich and work lean to get the optiminal power output.