From reading all the threads it seems the Fields can't control the LTFT, and AF ratios are compensated after only 20 min. And the Apexi unit has the same problem? So both these controllers are worthless with OBDII? I've used the Fields unit with workaround for almost 2 years with no problem. And I thought both units would feed and receive ECU info, so they would adjust for the signals the ECU was sending and receiving and maintain their programmed AF ratios. Can one of you geniuses say if these units are a waste of money, and if Hondata or similar standalone is the only solution?
Originally posted by PreludeSSwhite From reading all the threads it seems the Fields can't control the LTFT, and AF ratios are compensated after only 20 min. And the Apexi unit has the same problem? So both these controllers are worthless with OBDII? I've used the Fields unit with workaround for almost 2 years with no problem. And I thought both units would feed and receive ECU info, so they would adjust for the signals the ECU was sending and receiving and maintain their programmed AF ratios. Can one of you geniuses say if these units are a waste of money, and if Hondata or similar standalone is the only solution?
No, your interpretation is wrong. I can understand how a non-technical person might be very confused about this....
Both the Fields and the VAFC work just fine with OBD2. They just won't have much value tuning part throttle. Full throttle tuning is what they are good for, and that is what all tuners I am aware of use them for. I have never seen anybody on these forums tune for part throttle with these units, even though it is theoretically possible. No tuner I know of does it either. I do plan on it, although I will be using some advanced tuning ideas (for a VAFC at least), a street wideband, datalogging, and my relative knowledge of the P5M ECU to achieve it.
In general, the OBD2 workaround is not necessary. Nearly everyone who has it on right now doesn't need it. If you have done it already and nothing seems broken, by all means keep doing it. As a general rule, I am not reccomending it to anyone unless they are able to tune fuel management systems by themselves, especially on the street as well as the dyno.
You are an exception. Most people with the workaround end up spewing black crud across their bumper because the car is running rich most of the time. If you don't experience this, then you can feel free to ignore my advice.
As long as the VAFC/Fields is tuned after the car has been driven for awhile with the workaround off, then the settings will stick. If you have the workaround on, then it is possible that your optimal AFC tuning will be altered after the 20 mins the ECU spends re-adjusting itself during closed loop (workaround or not).
This is the best way I can explain it. I've tried every other way, and this is about all I can give you now....
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However, with the Field unit you have no control between a high map/low map setting. So if you tune your field from 0-8k RPMS, eventually your computer will detune the settings that you experience during everyday driving (probably no higher than 6k rpm at part throttle). With the VAFC, you can set your high map to not come on until 60-80% throttle, and then those settings will never be recognised since they won't be used when the car is making fuel adjustments. Clear as mud right? Correcct me if I'm wrong about the Field, because I have one installed and would like to tune it someday.
hondata or a standalone is the BEST solution, but I wouldn't call a fields or VAFC useless. OBD1 will experience the same issues if the VAFC/whatever is set up improperly.
Artifex's post has basically got it.
Basically, the ecu OBD2 OR OBD1 has two modes.
Mode one is called closed loop.
What closed loop does is take the fuel maps built into the ECU, fires the injectors accordingly, and takes a reading from the o2 sensor. The ECU wants to have the o2 sensor read a certian voltage. The way a regular car o2 sensor works is it isn't terribly sensitive. It basically reads lean or rich.
Ignore that purple line. The rest are a typical o2 sensor. Notice it's output approaches 1v for rich, and approches 0v for lean?
See that vertical line? That's stoichiometric- what the ECU is shooting for. The o2 will never really read stoich. It basically jumps above and below it.
What happens in closed loop is that the ecu reads rich, and cuts fuel. On the next cycle, it has injected less fuel, and now reads lean, so it adds more fuel again. It stores this information in the short term fuel trim (STFT). If you could watch it, it would change values very quickly.
Over time, it takes the essentially the average value of the STFT, and stores it as the long term fuel trim (LTFT.) The ecu uses the LTFT when it is in a situation where it cannot operate in closed loop.
The second mode the ECU can run in is Open Loop.
The reason the ECU has 'open loop' is there are certian conditions that the ecu either needs to run the engine richer or leaner than normal, or flat out has to ignore the o2 sensor.
For cold starts, where the car runs richer, and deceleration with the throttle closed, where the ECU turns off the injectors, the o2 sensor's output is useless. The o2 sensor, like I said before is more of an on/off switch, and isn't able to reliably tell you how rich or lean the car is running outside of stoich. Knowing how rich or lean the car is in those conditions is impossible, as the o2 sensor just can't do it.
The other time the car is in open loop is because the o2 sensor does not respond fast enough for the car to make the proper adjustments. You would see this at high rpm or WOT, or both. Since the o2 response would lag so far behind what was happening in the engine, the ECU has to rely on those fuel tables to figure out how much to inject.
However, the ECU has all this useful data on how rich or lean the car has been running on average stored in the LTFT.
Whenever the car is running closed loop, it applies the LTFT to the fuel maps across the board. This keeps acceptable performance and emissions. Since the stock fuel map is erring to the rich side, that is why people running the o2 workaround tend to have all that soot on their exhausts and bumpers- the car is running rich until it can adjust itself back to where it needs to be!
The important thing to keep a vafc/fields useful is to make sure any changes you make are within the realm that the car is running open loop.
If you lean things out 10% at 2500rpm and 50% throttle, the ECU will notice, and richen things up correspondingly because the o2 sensor isn't reading like it should. This throws off your LTFT, and can undo your tuning.
If all your tuning is in open loop, the car never cares about what the o2 sensor is reading, and does not 'tune' itself back to how it was programmed from the factory.
Keep your vafc tuning all above 80% throttle, and you should be ok.
Keep your fields adjustments above 6k rpm, and you should be ok too.
I agree, When my motor was still new after putting the cams in and pistons in it didnt idle at all. HJust stalled, but after about 25 miles of driving or so it started to idle better and better.
Jo basically your saying to run the car for a few days without using the workaround or whatever before you tune, and when you tune (w/ VAFC) if you tune both the high and low trottle maps only the high will stick. Do i got it all right? Im guessing that if the car can tune it within its parameters it will get the car (my) idling right eventually?
Originally posted by NXLude Jo basically your saying to run the car for a few days without using the workaround or whatever before you tune, and when you tune (w/ VAFC) if you tune both the high and low trottle maps only the high will stick. Do i got it all right?
Almost but not quite.
If LTFT is settled (driven the car a few days w/no workaround) and then you tune BOTH high and low throttle, BOTH tunings will be undone by the ECU. Why? Because the low throttle tuning will be noticed by the ECU when it runs in closed loop mode and the ECU will correct for it. But the ECUs correction will change the LTFT, which means that your full throttle tuning will no longer be correct either, even though the ECU didn't know about the full throttle tuning.
Once LTFT is settled, you want the ECU to remain happy with where things are, which means you make no changes to low throttle A/F and therefore the ECU makes no changes to LTFT.
so with all this discussion, it seems to me that people are beliving that with OBD-II work around off will run less rich than then would with the workaround enabled, but to me, it seems there are more soot and build up on the bumper with the workaround off, is this just me?
Originally posted by shortysm22 so with all this discussion, it seems to me that people are beliving that with OBD-II work around off will run less rich than then would with the workaround enabled, but to me, it seems there are more soot and build up on the bumper with the workaround off, is this just me?
Most people experience the opposite. The workaround prevents the ECU from correcting a fuel map which seems to be 10% rich by design. With the workaround enabled, the car usually runs 10% rich (up until it learns after 20 mins, each time the car is started). Running this rich will cause soot to come out the exhaust.
Please let me know if you have more soot with it on.
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Originally posted by NXLude Ahh......I see....I think that we need to figure some method of stopping that primary sensor from seeing any changes. So we can tune it all we want.
If the o2 sensor doesn't behave like a real o2 sensor, expect CELs and limp mode. You need to find a way to keep the ECU in open loop. I beleive hondata has this ability.
If LTFT is settled (driven the car a few days w/no workaround) and then you tune BOTH high and low throttle, BOTH tunings will be undone by the ECU. Why? Because the low throttle tuning will be noticed by the ECU when it runs in closed loop mode and the ECU will correct for it. But the ECUs correction will change the LTFT, which means that your full throttle tuning will no longer be correct either, even though the ECU didn't know about the full throttle tuning.
Once LTFT is settled, you want the ECU to remain happy with where things are, which means you make no changes to low throttle A/F and therefore the ECU makes no changes to LTFT.
This makes sense but I thought that was one of the main reasons for doing to workaround was your LTFT would be wiped clean every time you start your car.
If I understand correctly the main problem is how quickly the ECU makes changes to the LTFT?
So if you aren't using the workaround your LTFT map won't change at all, is this correct? Because if you tune on a map that is already there and that map changes won't your tuned map be messed up?
I am by no means an expert at this and these are simply questions that I have regarding this issue.
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If all of this is true, doesnt it mean that if you dynoed and set your vafc properly, then if something happened like a dead battery or something then all your maps would change witht he reset of the computer and your vafc settings would be worthless and you would pretty much have to redyno it to get it back in order?
Originally posted by NXLude If all of this is true, doesnt it mean that if you dynoed and set your vafc properly, then if something happened like a dead battery or something then all your maps would change witht he reset of the computer and your vafc settings would be worthless and you would pretty much have to redyno it to get it back in order?
After 20 minutes of driving the LTFT would recalibrate. So what you've proposed would only be true for the first 20 minutes.
This makes sense but I thought that was one of the main reasons for doing to workaround was your LTFT would be wiped clean every time you start your car.
If I understand correctly the main problem is how quickly the ECU makes changes to the LTFT?
So if you aren't using the workaround your LTFT map won't change at all, is this correct? Because if you tune on a map that is already there and that map changes won't your tuned map be messed up?
I am by no means an expert at this and these are simply questions that I have regarding this issue.
The ltft stays pretty constant unless there is a major weather change, or you change your car.
If you have a OBD2 scanner, you can watch it before and after a mod to see if it changes. You can figure out if the car is taking in more or less air based on if the LTFT goes up or down. That won't tell you if you're actually faster, but you will at least know if the change made any difference!
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