PE Threshold Unpredictable & Inconsistent
PE Threshold Unpredictable & Inconsistent I am trying to diagnose a lean condition on the launch of my drag car (which sometimes results in KR). In the Tune, PE Enable is set to MAP 15 kPa, PE Delay 0 RPM and 0s Delay, 64% TPS.
I have logged Commanded AFR and discovered that PE on consecutive runs comes in anywhere between TPS 45-98% and MAP 68-88 kPa. I understand that the TPS threshold may actually be related to % Throttle area, but I can't find any consistent relationship between the Tune and Log.
Should I try setting the TPS to a very low value (like 5-10%) and use MAP as the trigger?
I have logged Commanded AFR and discovered that PE on consecutive runs comes in anywhere between TPS 45-98% and MAP 68-88 kPa. I understand that the TPS threshold may actually be related to % Throttle area, but I can't find any consistent relationship between the Tune and Log.
Should I try setting the TPS to a very low value (like 5-10%) and use MAP as the trigger?
Last edited by MikeSp; Aug 10, 2017 at 07:00 PM.
It might look like PE is delayed more than it should be, but the conditions for PE must be met before enrichment is commanded. So naturally these higher TPS and MAP values will be available on the CAN before the updated EQ ratio is. It's possible it is simply going lean on the airflow transition before PE has a chance to come in and cover up for an issue with transient fueling. If it's knocking, now you know why burst knock retard is a thing 
If transient fuel is indeed the issue, OLFA or VE wouldn't be the place to put fixes. Really depends on what ***** you have available in whatever software you're using. I've found transient fueling calibratables in HP Tuners in certain vehicles to be pretty limited, often with the older P01 and P59 controllers.
I dont see why you couldnt bandaid a problem with PE by using the VE map, but it might take longer.
PE has a little setting for ramp in rate- make sure it is high, around 2 or 3 I think.
I would also try to make the MAP and TPS setting more... accurate. In other words, wherever the VE map transitions from part throttle or high vacuum into higher pressure regions (maybe 3-8" of Hg) the VE map might be around 14:1 but PE should bring it down further. If you are entering PE at 5" Of Hg then you might be around 67KPA, and set the TPS early like 22% or 25% (for my LS engine that is where I get 67KPA). It should kind of match. Like, you dont want to be at 25%TPS with 88KPA and have the PE mode set for 66% TPS, that doesnt make any sense. The PE needs to come on when you deviate from lean-ish cruise type of VE map regions, before you go into the rich region but after you leave the 15's area.
cliffs;
try 25% TPS and 50KPA with a ramp in rate of 2.0 or 2.5
that should get you into PE pretty fast, adjust from there. If you dont "See" PE on the wideband you need to increase the PE table.
You could also work from reverse- disable PE and tune the base VE map up until power regions on the map (usually from full vacuum until around 5" Hg) Then enable PE and watch it drop the last couple of AF units.
PE has a little setting for ramp in rate- make sure it is high, around 2 or 3 I think.
I would also try to make the MAP and TPS setting more... accurate. In other words, wherever the VE map transitions from part throttle or high vacuum into higher pressure regions (maybe 3-8" of Hg) the VE map might be around 14:1 but PE should bring it down further. If you are entering PE at 5" Of Hg then you might be around 67KPA, and set the TPS early like 22% or 25% (for my LS engine that is where I get 67KPA). It should kind of match. Like, you dont want to be at 25%TPS with 88KPA and have the PE mode set for 66% TPS, that doesnt make any sense. The PE needs to come on when you deviate from lean-ish cruise type of VE map regions, before you go into the rich region but after you leave the 15's area.
cliffs;
try 25% TPS and 50KPA with a ramp in rate of 2.0 or 2.5
that should get you into PE pretty fast, adjust from there. If you dont "See" PE on the wideband you need to increase the PE table.
You could also work from reverse- disable PE and tune the base VE map up until power regions on the map (usually from full vacuum until around 5" Hg) Then enable PE and watch it drop the last couple of AF units.
At 25% TPS I am at 70kPa, so that is very similar. I don't actually see a Ramp-in-Rate on my PE screen (or thru Navigator, for that matter).
I will be at the track tomorrow and will try lowering the TPS to around 25%. I did a mini-VE calibration tonight and that seems to be off at least 15% in the ~3000-4,000 RPM region, which is where the engine is coming up onto the converter (and where the KR sometimes appears). So I will try to do a better VE calibration as well.
Thanks for the suggestions!
I will be at the track tomorrow and will try lowering the TPS to around 25%. I did a mini-VE calibration tonight and that seems to be off at least 15% in the ~3000-4,000 RPM region, which is where the engine is coming up onto the converter (and where the KR sometimes appears). So I will try to do a better VE calibration as well.
Thanks for the suggestions!
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PE Threshold This past weekend, I lowered the TPS threshold for PE to 25%, which helped quite a bit, but the engine goes rich (12.1 AFR) right at 100% TPS, then recovers. You can see this rich spike at time 10.149 on the attached log.
So, at the higher TPS threshold (65%), the PE seems to come in too late, but at the lower TPS setting (25%), it goes momentarily rich. I'm concerned that this is slowing the car reaction time and 60'.
Rich_At_WOT.hpl
So, at the higher TPS threshold (65%), the PE seems to come in too late, but at the lower TPS setting (25%), it goes momentarily rich. I'm concerned that this is slowing the car reaction time and 60'.
Rich_At_WOT.hpl
The idea wasn't to try 25%. It was to try lower numbers, starting maybe around 25%. You also have to try, 30%, 35%, 20%, 40%, 50%, 65%, make some educated guesses based on what the engine does so you can minimize the number of attempts. For example based on what you said, I would try next around 33% perhaps. You want the enrichment to come in where the VE map fails to fully fuel the rich WOT air fuel ratio. If the map zings quickly to a rich spot in the VE table where a normal PE setting wouldn't include any extra fuel, it would naturally start out rich to begin with if the table were factory, but once you modify a single constant this no longer may apply. Watch the map box move as you press down on the throttle so you can find the spot on the VE table where the PE enrichment is coming into effect, then modify one or the other to get the a/f where you need it. Alternatively you can use tps delta settings and many other fuel settings in the computer to fine tune these areas, you could even use the primary BARO table for global injector constants to target this one specific spot across the board.
I am not sure how much you have tuned cars yet, so I wanted to make sure I was clear. The rate of change of the throttle is the delta tps. Most computers have a way to compensate for quick rate of change of throttle somehow by recognizing the delta tps and adding or subtracting fuel- the MAP can also be used in the same way (delta MAP). You should be aware that if you moving the throttle quickly, you will get different results than if you moved it slowly.
Fine tuning the percentage at which the PE is enabled has nothing to do with the delta TPS, it doesn't care how fast the TPS got to 25%, it just waits for exactly 25% or less to enable.
When you stab the throttle, it can become difficult to distinguish which enrichment is due to delta tps, delta map, the VE table, or the PE enrichment, and often these are blended. Try not to get hung up with making the tune perfect by only adjusting one of them- such as the PE enrichment. Instead, think of all of them at once, watch the map box move and try to imagine or determine when each enrichment is active, and correlate that with what you see on the wideband gauge.
Fine tuning the percentage at which the PE is enabled has nothing to do with the delta TPS, it doesn't care how fast the TPS got to 25%, it just waits for exactly 25% or less to enable.
When you stab the throttle, it can become difficult to distinguish which enrichment is due to delta tps, delta map, the VE table, or the PE enrichment, and often these are blended. Try not to get hung up with making the tune perfect by only adjusting one of them- such as the PE enrichment. Instead, think of all of them at once, watch the map box move and try to imagine or determine when each enrichment is active, and correlate that with what you see on the wideband gauge.