Do fuel trims really affect open loop fueling?
I can't speak for the IX, but on my 8 I agree with Eric's observations. I have spent hours playing with scaling and latencies to adjust trims, and the end result was that improperly set latency or scaling changed the trims to bring back closed loop to stoich . Open Loop AFR was not affected except if scaling was too low or too high, making afr global rich or lean
In your example, what if the injector scaling was changed from 636 to 630 (I know 630 is not possible, but say it was). With that small of a change, the question is whether or not the resulting change in the closed loop fuel trims would compensate for the injector size change and bring the open loop AFR back to the value at 636?
I do know, for a fact, that if you change the injector scaling and do not change the fuel map, your open loop fueling while be skewed.
I see this a bunch on the dyno with 9's being a perfect example since the trims revert to zero every time you flash them. (8's do not).
I do pulls right after flashing so the trims are still zero. If I change injector scaling to a smaller number, without changing the fuel map between the flashes, the next pull will be richer, if I add injector scaling it will be leaner. Zero fuel trims each time.
I've also observed fuel trims changing from +/- 5 and doing a pull with no other changes and the open loop AFR is exactly the same. I would have to look up some logs but I think I have even seen no changes with over +/- 7 fuel trims.
One thing that I have noticed that might put a wrench in the whole fuel trims don't matter at open loop idea is that if you disconnect the front 02 sensor, Open Loop fueling will be around 1 full AFR point leaner. I have seen it happen about 4 times on the dyno when somebody forgot to plug back in the front 02 sensor after installing cams. Not sure if this has to do with trims or that the 02 sensor has something to do with open loop fueling that we don't know about yet.
Last edited by razorlab; May 3, 2008 at 06:05 PM.
I have spent hours playing with scaling and latencies to adjust trims, and the end result was that improperly set latency or scaling changed the trims to bring back closed loop to stoich . Open Loop AFR was not affected except if scaling was too low or too high, making afr global rich or lean
I do know, for a fact, that if you change the injector scaling and do not change the fuel map, your open loop fueling while be skewed.
I see this a bunch on the dyno with 9's being a perfect example since the trims revert to zero every time you flash them. (8's do not).
I do pulls right after flashing so the trims are still zero. If I change injector scaling to a smaller number, without changing the fuel map between the flashes, the next pull will be richer, if I add injector scaling it will be leaner. Zero fuel trims each time.
I've also observed fuel trims changing from +/- 5 and doing a pull with no other changes and the open loop AFR is exactly the same. I would have to look up some logs but I think I have even seen no changes with over +/- 7 fuel trims.
I see this a bunch on the dyno with 9's being a perfect example since the trims revert to zero every time you flash them. (8's do not).
I do pulls right after flashing so the trims are still zero. If I change injector scaling to a smaller number, without changing the fuel map between the flashes, the next pull will be richer, if I add injector scaling it will be leaner. Zero fuel trims each time.
I've also observed fuel trims changing from +/- 5 and doing a pull with no other changes and the open loop AFR is exactly the same. I would have to look up some logs but I think I have even seen no changes with over +/- 7 fuel trims.
Originally Posted by razorlab
One thing that I have noticed that might put a wrench in the whole fuel trims don't matter at open loop idea is that if you disconnect the front 02 sensor, Open Loop fueling will be around 1 full AFR point leaner. I have seen it happen about 4 times on the dyno when somebody forgot to plug back in the front 02 sensor after installing cams. Not sure if this has to do with trims or that the 02 sensor has something to do with open loop fueling that we don't know about yet.
So, most people seem to have data that fuel trims don't affect WOT fuelnig, yet a couple of people seem to think that they do or have some sort of data that shows it in some way.
I truly just don't think fuel trims affect WOT fueling for a couple of logical reasons:
If open loop fueling had some sort of fuel trims applied, which one is it? LTFT Lo, LTFT Mid, LTFT hi, or some sort of average or mix? The different LTFTs based on what I have seen from disassembly are for different airflow levels. LTFT Lo is for an airflow range that will be seen usually at idle, LTFT mid for cruise, and LTFT hi for a higher airflow cruise condition, which usually is never met. These LTFTs and STFT are based on the front O2 sensor reading to stay at a stoich ratio (closed-loop). The font O2 feedback isn't used in open loop fueling, so it makes logical sense that any type of trims wouldn't be either.
In terms of which trims to apply, it wouldn't be logical to use the LTFT Lo for an open loop correction. Heck, a .1 ms latency correction to 1000 cc injectors can change your LTFT Lo by 10%. That's only a .1ms change. That same .1ms change at WOT is negligible, but not at idle, where your IPW is around 1ms. So, that .1ms wouldn't change WOT fueling at all (about .5%), where it would change idle about 10%. That same .1ms change would change LTFT mid by about 5%. It all depends on what IPWs you are running at. It just doesn't affect WOT (in this case, less than 1%), unless the ECU is forcing that trim correction during open loop, but which one?
I don't really think we will get to the bottom of this until the routine is disassembled. But, if anyone has more data, keep it coming. It's definitely an interesting topic, but I can't think of any logical way to apply a closed loop fuel trim, (idle, cruise, or whatever) to an open loop situation where your IPWs are going to be 10-20 times the closed loop values.
Eric
Last edited by l2r99gst; May 3, 2008 at 07:41 PM.
I think this a safety feature that probably affects global fueling, so that closed loop and part throttle will not run too lean. Since the trims are dictated by the front O2 sensor, if it is unplugged, then the ECU can't compensate richer when needed, so I think Mitsu probably just put a safeguard when the front O2 isn't functioning or removed, it would be safer to go richer rather than leaner for the entire range of fuel delivery (global correction).
Also if the front 02 doesn't cycle, circuit is bad or not plugged in, idle and cruise are very very rich.
I have no doubt in my mind that on my car the fuel trims affected the AFR in open loop operation. Mixmastermat is right. I have no doubt that he is.
here is what I said in the thread that mixmaster linked to:
The sequence of events points DIRECTLY to fuel trims being the culprit. If this is happening to you, mrfred, then re-scale your injectors and re-do your AFR map. After I re-scaled my injectors, I had rock steady AFR no matter how many miles I drove. The trims were very close to zero all the time.
But since you have biggie injectors, then forget about the stockers and install and scale the biggie ones.
I am running 1000cc injectors as well. I have them scaled to +/-4% and I still get 21-22 mpg when I do not boost.
here is what I said in the thread that mixmaster linked to:
I think it is related to driving for a sustained period of time at steady speeds. Yesterday, I flashed the ECU with an AFR map. I did not drive the car much. I only drove it for one trip which was short and local.
This morning @ 9:45 AM I did a log on my way to work. The AFR was where it should be. The temp was around 23* C, humidity around 53% and baro @ 101 kpa.
My trip to work is about 25 miles one way. I park the car. I leave @ about 2:30 pm and about 20 miles later I do two logs. The AFR has turned rich in the 3000-6000 range @ WOT. Above 6000 it stayed the same as it was in the morning log.
For some reason driving the car for 35-40 minutes on the Freeway at steady speeds of 65-70 mph triggers this thing to happen. I do not know why and how, but that is the sequence of events.
This morning @ 9:45 AM I did a log on my way to work. The AFR was where it should be. The temp was around 23* C, humidity around 53% and baro @ 101 kpa.
My trip to work is about 25 miles one way. I park the car. I leave @ about 2:30 pm and about 20 miles later I do two logs. The AFR has turned rich in the 3000-6000 range @ WOT. Above 6000 it stayed the same as it was in the morning log.
For some reason driving the car for 35-40 minutes on the Freeway at steady speeds of 65-70 mph triggers this thing to happen. I do not know why and how, but that is the sequence of events.
But since you have biggie injectors, then forget about the stockers and install and scale the biggie ones.
I am running 1000cc injectors as well. I have them scaled to +/-4% and I still get 21-22 mpg when I do not boost.
Sorry, I read your quote wrong. I thought you were saying that WOT was richer by one point.
The reason that I ask about the RPM is because in my experience over the years, if your fuel trims change, negative or positive, it will affect your transitional AFRs. By transitional I mean the AFRs going from closed loop to open loop. You will usually see a dip or a bump in AFRs when transitioning that you usually didn't see. I'm wondering if this is what was happening in your case, since you said the AFRs above 6000 remained the same.
Let me explain what I mean and see if it makes any sense. Let's say your car is running fine and your LTFTs are around 0. Your ECU isn't adding or subtracting any fuel to maintain your 14.7:1, When you transition from closed loop to open loop you have a smooth transition from that 14.7:1 to whatever the open loop maps are calling for.
On the other hand, say that your LTFT mid drifted to +10%, due to weather, intake temps or something else that altered the LTFT. Now, during a cruise your ECU is adding 10% fuel to maintain this same 14.7:1 AFR. During that brief transition to open loop, your +10% trim is now NOT applied, so whatever was causing the trims to drift, isn't corrected anymore, and you lose that +10% correction. So, your AFR during open loop will get leaner. However, the biggest change will be right at the transition from close to open loop and diminish as the RPM rises, to almost no or no change at redline. This is because as the IPW increases, that +10% in fueling at cruise is negligible to the IPWs now being run.
Does that make any sense? I have seen that effect many, many times in the past, mostly on DSMs. That's why I always tell people that it is important to get your fuel trims as close to 0 as possible. Because, in my experience, they are NOT applied to open loop fueling, and if they are to far out of whack, it will mess with your transitional AFRs. To me, it sounds like your situation was similar to this, but I think you were seeing the opposite effect? Weren't you seeing positive LTFT mids and LTFT lows and your AFRs were going richer?
Also, on a side note, the reason I asked about coolant and/or intake temps is because the ECU has several tables/routines that deal with enrichment during these situations. If those conditions changed much during different pulls, then your AFR can be affected as well.
This is definitely interesting now and I am curious to know exactly what is happening now and whether or not VIII and IXs act differently. I guess I will have to find some time to do some logs myself until someone can disassemble these routines.
mixmastermatt - Have you ever asked Bez about this? I would have imagined that he would have disassembled these fueling routines already with the work that he has done with the speed density patch.
Eric
Last edited by l2r99gst; May 4, 2008 at 07:15 AM.
The ONLY fuel trims I ever concern my self with are the STFT and LTFT that can be viewed with an OBDII scanner. I have seen several times on the dyno the difference in AFR with trims maxed and then zero'ed.
Here's a good read, which I have personally seen this effect on many makes and models of cars I have dyno tuned:
Here's a good read, which I have personally seen this effect on many makes and models of cars I have dyno tuned:
When you are cruising and idling (the emissions cycle) the DME uses your oxygen sensors ( O2 sensors) to determine what AFR the engine is running at. The O2 sensors sense how much O2 is in the exhaust and send a voltage signal to the DME to give the mixture. Different manufacturers of O2 sensors send different voltage signals to the DMEs they are used with. However the DMEs logic behind the O2 sensor data is the same.
The DME will adjust the mixture so that the engine runs at 14.7:1 AFR under emissions cycle. Actually, what it does is 'dither' the mixture which is swing it rich to lean and back centered around 14.7:1 AFR. It does this as it is better for the catalytic converter. When the DME is using the O2 sensors feedback it is considered to be in 'closed loop' mode.
As the DME makes its adjustments to the mixture, called the short term fuel trim(STFT), it keeps an average of what adjustments it has made over time. That average is applied against something called the long term fuel trim (LTFT) and is the 'adaptation' that is always talked about. During closed loop operation BOTH the STFT and the LTFT have an effect on mixture.
For example say your have a car that its emission cycle mixture is roughly 5% rich. We clear the adaptation (LTFT= 0.0%) and take the car for a drive. What happens?
Once the car has warmed up and gone closed loop the DME will detect, using the O2 sensors, that the mixture is 5% rich. The STFT will equal -5%. That is the DME is reducing the fueling to the car by 5%. This results in the mixture being 14.7:1. At first the LTFT=0.0%. Over time the LTFT will slowly move negative.
As that occurs the STFT will move to be less negative because the LTFT is now also removing some of the extra fuel. So the correction needed by the STFT will be less.
After driving for awhile you could see the following:
LTFT= -1% STFT= -4%
then a little later
LTFT= -3% STFT= -2%
then a little later
LTFT= -5% STFT= 0%
If the conditions stay the same the car has 'finished' adapting. Because the STFT is now 0% adjustments to the LTFT will stop until STFT moves away from 0%.
In reality the STFT tends to move all over the place if you watch it while regularly driving which is why the DME slowly adjusts the LTFT based on what the STFT tends to be centered around.
The adaptation is important to understand because the long term trim is applied against your wide open throttle (WOT) fuel maps even though the DME does not use the O2 sensors at WOT. It is running 'open loop' (no O2 sensor feedback) when it is in the power cycle. During the power cycle the DMEs maps are programmed to intentionally run the engine somewhat richer in pursuit of more power. Aftermarket 'chips' tend to run WOT richer yet to try to extract maximum power.
If you mod your engine to run richer all the time, say by just putting in larger fuel injectors, then during the emissions cycle the DME is going to know it is running rich based on the O2 sensors feedback. It will adapt out the extra fuel, at first with the STFT then later more and more with the LTFT to get the mixture back to 14.7:1 to reduce emissions. Now when you go WOT the DME will stop using O2 sensors feedback but it will still remove however much fuel the LTFT tells it to. The net effect is that your mod to richen the mixture won't work after you have driven the car a little while. In fact it could lean you out depending upon how much fuel the LTFT removes.
This will work in reverse to. If you lean out your mixture during emissions cycle the DME will ADD fuel as needed to get back to a 14.7:1 AFR and this will be seen in the LTFT. It does this because running lean increases emissions which the DME doesn't want to do. Now when you go WOT the LTFT will add fuel.
If you make your emissions cycle mixture 'perfect' at AFR 14.7:1 then adaptation will NOT occur and it will have no effect at all on your WOT mixture.
The DME will adjust the mixture so that the engine runs at 14.7:1 AFR under emissions cycle. Actually, what it does is 'dither' the mixture which is swing it rich to lean and back centered around 14.7:1 AFR. It does this as it is better for the catalytic converter. When the DME is using the O2 sensors feedback it is considered to be in 'closed loop' mode.
As the DME makes its adjustments to the mixture, called the short term fuel trim(STFT), it keeps an average of what adjustments it has made over time. That average is applied against something called the long term fuel trim (LTFT) and is the 'adaptation' that is always talked about. During closed loop operation BOTH the STFT and the LTFT have an effect on mixture.
For example say your have a car that its emission cycle mixture is roughly 5% rich. We clear the adaptation (LTFT= 0.0%) and take the car for a drive. What happens?
Once the car has warmed up and gone closed loop the DME will detect, using the O2 sensors, that the mixture is 5% rich. The STFT will equal -5%. That is the DME is reducing the fueling to the car by 5%. This results in the mixture being 14.7:1. At first the LTFT=0.0%. Over time the LTFT will slowly move negative.
As that occurs the STFT will move to be less negative because the LTFT is now also removing some of the extra fuel. So the correction needed by the STFT will be less.
After driving for awhile you could see the following:
LTFT= -1% STFT= -4%
then a little later
LTFT= -3% STFT= -2%
then a little later
LTFT= -5% STFT= 0%
If the conditions stay the same the car has 'finished' adapting. Because the STFT is now 0% adjustments to the LTFT will stop until STFT moves away from 0%.
In reality the STFT tends to move all over the place if you watch it while regularly driving which is why the DME slowly adjusts the LTFT based on what the STFT tends to be centered around.
The adaptation is important to understand because the long term trim is applied against your wide open throttle (WOT) fuel maps even though the DME does not use the O2 sensors at WOT. It is running 'open loop' (no O2 sensor feedback) when it is in the power cycle. During the power cycle the DMEs maps are programmed to intentionally run the engine somewhat richer in pursuit of more power. Aftermarket 'chips' tend to run WOT richer yet to try to extract maximum power.
If you mod your engine to run richer all the time, say by just putting in larger fuel injectors, then during the emissions cycle the DME is going to know it is running rich based on the O2 sensors feedback. It will adapt out the extra fuel, at first with the STFT then later more and more with the LTFT to get the mixture back to 14.7:1 to reduce emissions. Now when you go WOT the DME will stop using O2 sensors feedback but it will still remove however much fuel the LTFT tells it to. The net effect is that your mod to richen the mixture won't work after you have driven the car a little while. In fact it could lean you out depending upon how much fuel the LTFT removes.
This will work in reverse to. If you lean out your mixture during emissions cycle the DME will ADD fuel as needed to get back to a 14.7:1 AFR and this will be seen in the LTFT. It does this because running lean increases emissions which the DME doesn't want to do. Now when you go WOT the LTFT will add fuel.
If you make your emissions cycle mixture 'perfect' at AFR 14.7:1 then adaptation will NOT occur and it will have no effect at all on your WOT mixture.
I'll email him and see if he has seen trims involved in the final fueling calcs.
mix'n'match
interesting, one would conclude from your post that running open loop has a failsafe for declining injectors.
Unless, running in open loop without ever being in closed loop the trims have not "engaged". In other words, does the ecu need to have some time in closed loop for the fuel adjustments to be formulated? Or are those formulations being made in the background even in open loop?
interesting, one would conclude from your post that running open loop has a failsafe for declining injectors.
Unless, running in open loop without ever being in closed loop the trims have not "engaged". In other words, does the ecu need to have some time in closed loop for the fuel adjustments to be formulated? Or are those formulations being made in the background even in open loop?
Open loop effects closed Loop operation but not the other way around. The fuel maps are nothing more than a IPW table. Each cell is a specific IPW setting in mS. The fuel maps are scaled from 0 load to max load as well so just looking at the raw byte values won't help you understand how its calculated either (until we can crack the scaling). In open loop, the only thing that changes the IPW value in the fuel maps are compensation tables for things like baro, coolant temp, air temp,etc. These are also the "target" IPW's for closed loop operation. The +/-12.5% has to deviate from a "set in stone" setting and this open loop IPW setting is just that. In theory, to edit your "LTFT low" percentages, you can simply edit the fuel maps open loop cells at idle, rather than edit the MAF scalings like many do.
Closed loop operation needs open loop data, open loop data doesn't need any feedback from closed loop since its data is non adjustable (except thru the compensation tables).
Closed loop operation needs open loop data, open loop data doesn't need any feedback from closed loop since its data is non adjustable (except thru the compensation tables).
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From: UK
I do not believe that fuel trim affects open loop on the evo ix based on what I have observed - no effect on ipw or wbo2 when trims are zero or maxxed to 12.5% - you would certainly notice 1.5 afr!
Lean spool, water temp, air temp and baro are I think producing spurious effects that are being interpreted as due to fuel trim.
I will have a look at the asm later if I get time.
Lean spool, water temp, air temp and baro are I think producing spurious effects that are being interpreted as due to fuel trim.
I will have a look at the asm later if I get time.
The ONLY fuel trims I ever concern my self with are the STFT and LTFT that can be viewed with an OBDII scanner. I have seen several times on the dyno the difference in AFR with trims maxed and then zero'ed.
Here's a good read, which I have personally seen this effect on many makes and models of cars I have dyno tuned:
Here's a good read, which I have personally seen this effect on many makes and models of cars I have dyno tuned:
In the quote you posted, they mentioned the LTFT being applied to open loop. Which LTFT? As I metnioned previously, there has to be some sort of logic or formula to determine what trim to apply to a WOT situation, since IPWs are drasitcally different. Something that can affect an idle trim by 10% can affect the WOT fueling by .5% (1/2 percent), so it wouldn't make much sense to apply the same correction at WOT that is being applied to idle.
This is just one of the many reasons why I don't think trims are applied during open loop. The trims are calculated during drastically different conditions, and there are different LTFTs within the ECU solely because of this fact (Lo, Mid, High). Idle has it's own LTFT because the IPW will be roughly half that at cruise. So, cruise needs it's own LTFT. So, what is applied to WOT then? At WOT the IPW can be 20 times that at idle.
Also, this goes back to what mrfred said....if one of these trims were applied to WOT, then you should be able to change your injectors and never change your open loop fuel maps, since the trims will take care of WOT fueling. We all know that is NOT the case. That's where I'm getting at, and why I don't think our trims are applied to WOT.
Eric
Last edited by l2r99gst; May 4, 2008 at 08:12 AM.
That is interesting, and seems a bit 'bass ackward'.
The Ford EEC fuel vs. load table cells are scaled with a lambda value. The EEC applies clsoed-loop LTFT history to a lookup table, and uses that as a factor with respect to the measured MAF signal and rpm to generate the necessary IPW to reach the specified lamba target. It's too bad Mitsubishi didn't go that route.
The Ford EEC fuel vs. load table cells are scaled with a lambda value. The EEC applies clsoed-loop LTFT history to a lookup table, and uses that as a factor with respect to the measured MAF signal and rpm to generate the necessary IPW to reach the specified lamba target. It's too bad Mitsubishi didn't go that route.
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. These are also the "target" IPW's for closed loop operation. The +/-12.5% has to deviate from a "set in stone" setting and this open loop IPW setting is just that. In theory, to edit your "LTFT low" percentages, you can simply edit the fuel maps open loop cells at idle, rather than edit the MAF scalings like many do.
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The dsm and evo both work on models of vortex pulsations per cas with compensations to produce a load which is then converted to pulse width through desired afr and other comps. The physics of airflow and fuel flow are modelled rather than a lookup of ipw like a speed density aftermarket ecu.
Last edited by jcsbanks; May 4, 2008 at 08:22 AM.