VE tuning means to tune for the right mixture for your engine.
The VEMS v3 has the fastest wideband circuit available, and the best integration with the engine management system (including confidence information, to detect disconnected or broken sensor and not apply EGO-correction).
With wideband oxygen it is fun and really fast. It's so fast in fact, that the VE-learning is rarely used by experienced tuners, but WBO2, lambda table and EGO-correction is used to help speed up the tuning process with added safety.
The allowed EGO-correction authority range depends on the tuner and the engine though.
- maintain a lambda table that you like. Don't cheat with the lambda table,enter the desired lambda to all loadsites. Forget all 1.0 table !! That is equivalent with an ECM that does not know about lambda (where injector pulsewidths - or proportional numbers - are entered, takes you back in time with 2 decades).
An introduction to the different ways to tune a 'True VE' engine management system.
Text is ignoring the propriatory systems like Haltech, Electromotive, Link, Prospark and their equals and only discuss true VE systems like Motec, Autronic, FAST, Accel, Zytec and an endless list of systems that did at least the VE / lambda table separation right - there is another requirement of proper WBO2 - ECM integration, which is digital interface with confidency information (which notifies the ECM about bad / missing WBO2 sensor or unreliable reading for any other reason). With the commonly used analog interface the ECM reads bad lambda in these cases, which is not a good thing to controll injection upon.
In the early days of true VE engine management there was only the open loop mode. That means that most experienced tuners still choose to use that procedure, this is mostly because it feels safe to do it the way you have always done it. There are other reasons too that we will come to later.
Since the introduction of the wide band lambda sensor in the early 90's there has been a few systems with closed loop tuning ablilities. Now 15 years later a few tuning methods that utilise the closed loop operation has matured. The one that we feel is the best use closed loop WOT during tuning and you basically tune by adjusting the VE table until you get minimum EGO correction.
The traditional way of tuning a system that is capable of running closed loop at full throttle is to allow it to add and subtract around 20% fuel depending on the input from the WBo2 sensor. This usually works well, there are however a phenomen that make a WBo2 sensor read a missfire as a lean condition. If the ECU is allowed to enrich based on that false lean reading the missfire condition usually get worse regardless of the original reason for the missfire. For someone that is is a bit unexperienced it's very hard to diagnose the problem correctly and for an experienced tuner it's easy to overlook it.
By setting up closed loop operation to allow around 20% enleanment but only 1-3% enrichment you eliminate 99% of all potential false readings. The inability to enrich the mixture doesn't protect you if you use a too lean start map but it's easier to make sure that the base map is rich enough then it is to detect false lambda readings.
Why closed loop tuning isn't always best:
The most important reason is when an experienced tuner that prefer tuning in open loop is tuning the car, he is likely to do the best job in the shortest time if he does it the way he is used too. No use argumenting with that.
The second most important condition where closed loop tuning may be unsuitable is in VERY fast cars where the EGO correction may be too slow to apply the correction in the right loadsite. In fast cars like this you often have to keep track of the actual lambda, target lambda and also check that the EGO correction is on track. This can usually be worked around by using a longer straight, more brake and higher speed. When that is not possible it's time to turn WBo2 correction off.
The third is when the car is acting up for some reason, for example leaky valve seals that soil the WBo2 on overrun or a turbo that does the same. When there are periodic missfires you are also forced to tune without EGO correction.
EGO correction
- EGO correction means fuel pulsewidth correction based on "Exhaust Gas Oxygen" measurements.
- Correction means to add or take-away fuel (pulsewidth)
- Authority range is the range from maximum take-away to maximum add percentage.
Let's say one wants to maintain an appr 20% authority for EGO correction. This is a decision of the tuner. This might be reasonable for production operation (street / racing). During tuning, often a bigger authority is used. Lower (than 20%) authority makes sense when the WBO2 sensor is to be removed (for whatever reason?) after tuning. Also, smaller (but non-zero!) authority range is usually used for extremely fast-revving engines.
The image shows a range of VE=162 .. 202 configured in 2 different ways:
- good: 200 based, -19% .. +1%
- bad : 174 based, -7% .. +16%
One might believe (before thinking about it) that setting ego_rich_limit higher than ego_lean_limit is the way to go. But there are very good reasons to use the "good" method which relies on ego_lean_limit rather than ego_rich_limit. Makes little difference when the authority range is small.
Notes:
- in parenthesis are the percentages in the higher resolution 1/256 units that are used internally and for EGO-correction display
- -19% = -49/256
- +1% = +3/256
- -7% = -18/256
- +16% = +41/256
- The VE value is scaled up (from appr. 100 to near 200) for better resolution: max VE value is 255 (200 and 174 in the example). The req_fuel must be scaled accordingly. The final pulsewidth (for speed-density) is req_fuel * (VE / 100) / lambda * (MAP / 100) * enrichments
Why is the "good" better than the "bad" ?
- The good method means you start from rich and approach the desired fuel quantity from above.
- The bad approach is to approach from below (danger of leaning out).
- remember that the actual ranges are exactly the same in the 2 case (162..202), just defined from a different starting point
- When the (calibrated) WBO2 sensor reads rich, you can be sure that it's rich(er than the desired lambda, configured in the lambda table).
- when the WBO2 sensor reads lean, it might be lean, or it might be tricked by a missfire. Missfire (no matter how much gasoline you put in!!!) reads lean because of "unburnt oxygen" gets to the exhaust.
Also, (for the case when WBO2 sensor fails), engines tolerate rich condition much better than lean condition.
This justifies adjusting higher (richer) than required VE values, and only allow a marginal ego_rich_limit, effectively stuff most of the ego-correction authority in the ego_lean_limit.
- It is not impossible to tune the engine with the "bad" method just takes more time and attention
- it is even possible to use a very narrow EGO correction range (0.8 .. 5%)
- With extremely fast-revving race-engines low EGO-correction authorithy range makes it impossible for the controller to "carry over correction values from one loadsite to the other". This is a concern when loadsites are tuned unevenly (eg.one loadsite for EGOC=0 and neighbor loadsite for EGOC=-8%. EGOC=+-0.4% (ego_lean_limit=ego_rich_limit=0.4%) is the minimum reasonable range.
- with a narrow EGO-correction authority range the "good" and "bad" are effectively the same: both ego_lean_limit and ego_rich_limit are very low, only used for indication to help the tuner, not effective correction
There were good reasons in the past (eg. WBO2 or proper EGO-correction not available) It's just harder, takes more time and involves more risk.
Developers
- consider dropping the ego_rich_limit variable (=0 wired in) and only allow leaning. It's easy to scale req_fuel up to compensate for this.
- allow ve-learning to learn for a certain ego-correction (=> eg. 10% above actual VE, that will result in egoc=-26=-10%)
See also
- GenBoard/Manual/Config/VeLearn
- GenBoard/Manual/VeLearn
- TuningSession/ClosedloopTuning A step by step tuning procedure for tuning with the WBo2 correction activated. You only look at how much the ECU correct the mixture and base your changes on that. Probably better for inexperienced tuners.
- TuningSession/OpenloopTuning A step by step tuning procedure for tuning without wbo2 correction. You look at the actual mixture and the target mixture and base your decisions from that. What most experienced tuners use.
Questions:
What WBO2 and EGO settings are capable to compensate running such rich??I mean my ECU cant handle even a 1.05 lambda at idle,it tryes to richen it up to the desired 1.0 lambda but it cant.
I also tried to run richer but than it cant lean the mixture out.Please tell me where to start tweak it!!