Whats the purpose of PE
Thread Starter
Joined: May 2005
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From: Valdosta, georgia
Whats the purpose of PE I know what PE does but why not just use the VE table to command the afr you want? IF there an advantage to say commanding 15.1 for lean cruise and idle then use your PE to richen? I want to tune for 15.1 at cruise, and idle to get better economy then use 12.5 for part throttle and 12.3 for full throttle.
There is no way to "Command" afr in the VE table. You can make the car read a certain afr using the VE table however the commanded afr is generally from the open loop EQ table(OLFA) that is based on ECT and MAP. PE is needed to command richer afr's under higher load situations. It can be done by using OLFA to enrich fueling at higher loads but PE is easier to manipulate commanded afr vs RPM and keep it from coming in until a certain TPS is reached.
Many different way's to skin a cat, in the end make your actual AFR = Commanded AFR
Many different way's to skin a cat, in the end make your actual AFR = Commanded AFR
Thread Starter
Joined: May 2005
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From: Valdosta, georgia
Thats kind of what I mean just maybe worded it wrong. If you change the values in the VE table it in-turn will change your a/f ratio correct? Thats what i meant. But I get what you mean i'll use the PE to allow it to richen when I want it too.
TECH Regular
Joined: Sep 2007
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From: Kansas City, MO
The VE table should be used to get an acurate model of the engine's volumetric effeciency. If this is correct then any of your adders (like pe) will be on target. If the VE table is off, when adders come into play, everything will be off.
Thread Starter
Joined: May 2005
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From: Valdosta, georgia
Ok so say I tune my VE to accurate levels then I go into tune my PE to richen it up during throttled pulls. Now would it be possible for the OLFA to mess up what I just tuned? Can I disable say OLFA and tune the PE with regards to throttle position, then turn OLFA back on, disable PE and tune the OLFA with regards to MAP? Hope that makes sense.
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Thread Starter
Joined: May 2005
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From: Valdosta, georgia
It's just confusing me it's been awhile since i've tuned but I tuned on HPT and had a pretty damn good tune in my trans am and I thought it was so simple but this efilive is just boggling my mind, can't get my head around it right now. Seems alot of other tables play onto other ones.
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If you want 15:1 in closed loop cruise, try setting your O2
switchpoint voltages in the appropriate airflow mode cells
to 250mV or so and see what the wideband says.
PE is the way you get into open loop fueling based on TPS,
MAP. Then it offers an enrichment (which may or may not
win the argument) based on RPM. Your EQ table, which is
now also in play, offers another based on MAP. Fat kid
wins. So you have those two (or maybe more like 1-1/2)
degrees of freedom to set up a high-load fuel map. Kinda
crappy but it's what you have to work with. Some OSes
offer additional *****. But it sure would be nice to have
a desired EQ vs MAP vs RPM response surface instead
of one-dimensional vectors more or less.
switchpoint voltages in the appropriate airflow mode cells
to 250mV or so and see what the wideband says.
PE is the way you get into open loop fueling based on TPS,
MAP. Then it offers an enrichment (which may or may not
win the argument) based on RPM. Your EQ table, which is
now also in play, offers another based on MAP. Fat kid
wins. So you have those two (or maybe more like 1-1/2)
degrees of freedom to set up a high-load fuel map. Kinda
crappy but it's what you have to work with. Some OSes
offer additional *****. But it sure would be nice to have
a desired EQ vs MAP vs RPM response surface instead
of one-dimensional vectors more or less.
TECH Senior Member
Joined: Apr 2002
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From: So.Cal.
It's just confusing me it's been awhile since i've tuned but I tuned on HPT and had a pretty damn good tune in my trans am and I thought it was so simple but this efilive is just boggling my mind, can't get my head around it right now. Seems alot of other tables play onto other ones.
It's not as complicated as it seems, there are various tables that modify commanded EQ and the PCM will use the highest one when it's condition's are met. In the OLFA table set everything on the 176*F column and warmer to 1.0. This will command stoich in open loop once the engine is warm. This way PE will be the only thing commanding the richer EQ at high load. Also remember to disable Cat Overtemp, sometimes it'll throw you a loop and activate causing 1.2x EQ.
I also agree with jimmyblue that a map based multiplier or a 3d graph to slowly ramp richer mixtures in instead of running stoich and instantly hitting PE of 13.0 afr or in a boosted app's case 11.50 or richer instantly. (BE is too slow to rely on)
I also agree with jimmyblue that a map based multiplier or a 3d graph to slowly ramp richer mixtures in instead of running stoich and instantly hitting PE of 13.0 afr or in a boosted app's case 11.50 or richer instantly. (BE is too slow to rely on)
.. btw, that was funny Cal! Thread Starter
Joined: May 2005
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From: Valdosta, georgia
Well in a nutshell thats what I said, that PE is used to richen up the mixture when your parameters are met. I knew that I was just wondering why you can't adjust your VE table to make a richer mixture instead of using your PE table, thats all I was wondering.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
You could adjust the VE table to give you richer at WOT (VE table has MAP on one axis)...
the PCM's model is to calculate airmass from the VE table, and then divide this by the commanded AFR (from the richer of the active AFR tables) to obtain fuelmass, and then use the IFR to calculate pulsewidth to spray this fuelmass...
so yes you could maybe trick the PCM into calculating a larger airmass and end up with the same fuelmass (by virtue of having a leaner commanded OLFA/PE)... (and some people take it further by adjusting the IFR table...)...
but (for example) this makes dialing in AFR at the track (for best ET/TS) much more difficult... getting the airmass correct allows you to very simply achieve the commanded AFR (what-you-specify-is-what-you-obtain), this will make your tuning life simpler (and the PCM is designed to help you do this).
the PCM's model is to calculate airmass from the VE table, and then divide this by the commanded AFR (from the richer of the active AFR tables) to obtain fuelmass, and then use the IFR to calculate pulsewidth to spray this fuelmass...
so yes you could maybe trick the PCM into calculating a larger airmass and end up with the same fuelmass (by virtue of having a leaner commanded OLFA/PE)... (and some people take it further by adjusting the IFR table...)...
but (for example) this makes dialing in AFR at the track (for best ET/TS) much more difficult... getting the airmass correct allows you to very simply achieve the commanded AFR (what-you-specify-is-what-you-obtain), this will make your tuning life simpler (and the PCM is designed to help you do this).
Last edited by joecar; Dec 20, 2010 at 06:40 AM.
Thread Starter
Joined: May 2005
Posts: 550
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From: Valdosta, georgia
I'm gonna get my VE table adjusted and use my PE table to richen it up, was just wondering if you could do that to get better knowledge of the inner working.
All you want out of VE and other such "calculation"
tables, is realism.
"Intent" belongs in PE, EQ vs ECT vs MAP (aka OLFA)
and adder type tables.
Lying to get a desired result, is a bad idea in the end.
tables, is realism.
"Intent" belongs in PE, EQ vs ECT vs MAP (aka OLFA)
and adder type tables.
Lying to get a desired result, is a bad idea in the end.