Where do open loop fuel trims come from?
08-01-2005 | 08:57 PM
#21
Hmmmmmmm...still trying to word this correctly. Fuel trims don't learn, or adjust themselves unless they have feedback from a closed loop source (in this case, it is your narrow band O2 sensors). But once this feedback is given, it is telling your engine how much more (or less) fuel your engine needs, and saves this information for the next time you are running your car. Then, when you are in open loop, it still knows how much more (or less) fuel your car was needing, and applies this until it gets more feedback from the narrow band O2 sensors once they are warmed up and functioning properly.
I've found that with my headers, since the O2 sensors are operating cooler, they see this as a rich condition. So when I'm tuning in open loop, I get my AFR spot on with the wideband O2 sensor. So when I put the car back in closed loop, it should read 14.62xxx, right? This isn't the case, since the feedback the PCM is getting is telling it that it is running rich (since the O2 sensors are running cooler). Therefore, it pulls fuel (about -4 on STFTs on average across the board). Shitty, but I guess that's the price to be paid when running headers...the feedback the PCM gets just isn't correct, but since it is only leaning the car out at cruise, it is actually okay for me since it saves a little fuel. I do have my PE set though to come in fairly early under heavy throttle, which puts it right where it needs to be since I've already told it exactly how much fuel it needs to add to get to my desired AFR by tuning in open loop @ WOT.
I've found that with my headers, since the O2 sensors are operating cooler, they see this as a rich condition. So when I'm tuning in open loop, I get my AFR spot on with the wideband O2 sensor. So when I put the car back in closed loop, it should read 14.62xxx, right? This isn't the case, since the feedback the PCM is getting is telling it that it is running rich (since the O2 sensors are running cooler). Therefore, it pulls fuel (about -4 on STFTs on average across the board). Shitty, but I guess that's the price to be paid when running headers...the feedback the PCM gets just isn't correct, but since it is only leaning the car out at cruise, it is actually okay for me since it saves a little fuel. I do have my PE set though to come in fairly early under heavy throttle, which puts it right where it needs to be since I've already told it exactly how much fuel it needs to add to get to my desired AFR by tuning in open loop @ WOT.
08-01-2005 | 09:19 PM
#22
I appreciate the response, but I still think you're missing this jist of this thread. In fact i'm beginning to think everybody is responding to the title and not reading my first post, or has looked carefully at post 8. Either that or nobody knows the answer.
08-01-2005 | 09:19 PM
#23
on my car when i start up the trims add more fuel when the o2s are cold, as the car and o2s heat the trims get closer to zero. so my assumption woudl be the car gets a false LEAN reading from cold o2s, just by what i have seen on my car from cold start, might be wrong but i dont really know lol.
what i dont get is this:
start the car in open loop FTC 20, trims were +11, car entered closed loop into FTC 19 and instantly the trims went to -1.6, that was closed loop which recieves feed back. so wouldnt one think next start up i would see these -1.6 from closed loop memory? the car should not remember anything in open loop at all, shouldnt being the key word here. all the numbers my car was using in open loop NEVER showed in closed loop. which has me puzzled??
what i dont get is this:
start the car in open loop FTC 20, trims were +11, car entered closed loop into FTC 19 and instantly the trims went to -1.6, that was closed loop which recieves feed back. so wouldnt one think next start up i would see these -1.6 from closed loop memory? the car should not remember anything in open loop at all, shouldnt being the key word here. all the numbers my car was using in open loop NEVER showed in closed loop. which has me puzzled??
08-01-2005 | 09:21 PM
#24
unless the car hit closed loop when i put the new o2s in the car, they were not warm but the car thought they were, and remembered THESE numbers that were screwy. either way cold start i see trims up to +7 at times, closed loop when the car gets hot and has been running they go to about -3 and stay there.
