I've noticed lately that there's a lot of confusion as to how the ecotec ecu operates.
I've read some intelligent posts changing my mind or setting me straight on some things, and others that will argue against things I
know as facts based solely on speculation.
To satisfy my ego, and at the same time, do the community a service, I've had the idea to start a series of topics on my investigations of the ecotec ecu, in hopes of putting these myths to bed with PROOF.
lets establish the basics:
the ecotec ecu is an alpha-n fueling setup, whereas it bases its calculations primarily on RPM and TPS inputs. MAP is NOT taken into consideration when calculating fueling. The MAP is used primarily for spark tables, and for zero-throttle conditions (such as idle, and coast-down fueling). The only other feature the MAP is used for is for a multiplier which effects injector pulsewidth. This tab will be investigated in a future MYTH.
There was a lot of problems getting proper fueling to the ecotecs in the past that were boosted (without the reflash) and not many knew why. This was because of what I realize now to be 2 problems:
The first problem was nobody knew it was an alpha-n efi system. This was only realized after HPT gave us our first glimpses into the programming tables. So everyone kept trying to modify the MAP signal, and would do nothing to the fueling but would mess up the ignition advance.. causing even more confusion.
The second problem was nobody knew about the PE delay number on the power enrichment tab. There's been a lot of theorizing how this particular feature works, even people claiming that the number was 'ignored' on cars and only used on trucks.
Well tonight I figured it out with log data for PROOF.
my test vehicle is my daily driver.. .a 2004 ecotec cavalier 5 speed.
the engine is STOCK except for an rksport intake I salvaged from the skwirl.
MYTH: J-body ecu does not utilize PE Delay feature
I decided to test this theory.
I used my 2004's narrowband voltage output as a 'power enrichment' detector. When the vehicle goes into power enrichment, the O2 sensor stops switching, and stays at a fixed value because the car is no longer trimming for stoich, and instead shoots for a pre-programmed AFR for maximum power (in the case of the jbody, 13:1 AFR is the target). The further operation of this function is irrelevant to the point of this post, so we'll move on for now.
The ecu on my 04 is untouched, so I did a basic test. PE delay on a stock ecotec ecu is set to 6200rpm.
I let the car warm up to operating temperature, and simply took it out on the road and mashed the throttle.
take note of O2 mV and commanded AFR when TPS = 100%
notice how the O2 is still switching. Strange. Also, take note that commanded AFR remains at 14.6:1
This time, I decided to take it all the way up past the delay RPM, and continue the pull into the next gear.
What happens is pretty interesting.. again, take note of the
O2 mV and
commanded AFR:
another go.. same as above:
as you can see.. once the delay rpm is surpassed, the O2 STOPS switching and then enters PE mode.
This changes my theory on the system because I always assumed it would only be in PE mode for the last 300rpm (until the rev limiter), then enter back into closed loop until 6200rpm is reached again.
But apparently, the way the system works is that when the TPS threshold is met, and the PE Delay RPM is met, PE is engaged.
there must be some other variables such as TPS drop thresholds, or something to tell the ecu to go back to closed loop, because as I changed gears the ecu carries PE with it (even tho the TPS and PE Delay settings are lost). There is clearly other settings we do not see here.
To be certain of what I was seeing, I set the PE Delay to 0RPM, flashed the ecu and ran the same tests:
mashing the pedal in a single gear:
taking it through a few gears:
single gear again:
as you can see, with the PE Delay essentially disabled (set to 0 RPM) the O2 mV stops switching, and commanded AFR drops to the calculated PE value the
instant the TPS threshold is met.
MYTH BUSTED. The Jbody ECU does, in fact, utilize PE Delay RPM
I have several other tests I will be starting threads about. Hopefully the mods will allow separate topics for separate issues, that way it can be searched individually, and be easily found in the future.
