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I installed AEM wideband and boost gauge. New test pipe, Downpipe, and upper intercooler piping. ETs intake. I have not been tuned but I am staying out of boost as my tuner has given me the okay on it. Anyways I was driving on the free way last night, AFRS seem to be 14.7 give or take it jumping around a bit obviously. Well anyways after about 20 minutes, it jumps up to around 17ish and fluctuates around there until I get off the free way, turn my car off, and back on. Then it goes back to 14.7ish. The same exact thing happened to me today on the free way. Turned my car off and back on, it goes back to 14.7. It’s almost like it bumps up 3 points just perfectly like it’s reading around 17.7 instead. I know AEM recommends that you have separate power for the gauges as it could throw off readings, but why does it read perfectly for a few minutes and randomly goes to 17.7? Is it because I’m truly running lean or is it just some kink I need to figure out? I don’t understand it. Please give me an idea! Thanks
 

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I installed AEM wideband and boost gauge. New test pipe, Downpipe, and upper intercooler piping. ETs intake. I have not been tuned but I am staying out of boost as my tuner has given me the okay on it. Anyways I was driving on the free way last night, AFRS seem to be 14.7 give or take it jumping around a bit obviously. Well anyways after about 20 minutes, it jumps up to around 17ish and fluctuates around there until I get off the free way, turn my car off, and back on. Then it goes back to 14.7ish. The same exact thing happened to me today on the free way. Turned my car off and back on, it goes back to 14.7. It’s almost like it bumps up 3 points just perfectly like it’s reading around 17.7 instead. I know AEM recommends that you have separate power for the gauges as it could throw off readings, but why does it read perfectly for a few minutes and randomly goes to 17.7? Is it because I’m truly running lean or is it just some kink I need to figure out? I don’t understand it. Please give me an idea! Thanks
I should also note my car is holding vacuum very tightly and I did a small pull to make sure it was all tight on the boost end. I don’t see how a leak could contribute to this unless it was exhaust. But even then the downpipe is not leaking. Is there any possibility the open dump downpipe could affect this? Thanks in advance by the way.
 

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i dont know if you ever figured out the issue, but it sounds like its going through fuel trim learning. you freed up alot of restriction, so thats going to mess with your long term fuel trims. the ecu targets 14.7. it looks at the actual afr and either adds or removes fuel using the short term trims to hit the target 14.7. it constantly updates the long term trims during idle cruise and wot. it does that by using the average of the stft values during a cycle that lasts like 13min or something in that range, then it changes the LTFT based on that average. it then uses that ltft as a base for hitting that target afr, until another cycle finishes and it changes again. when you change how much air you move in and out of an engine, you change how much fuel it takes at any given driving situation to hit its afr target.

being untuned, its got the ecu going crazy trying to hit that target. so its adding or pulling more fuel than normal. Typically a tuned car will only need small changes to trims because temperature, air density and humidity play a role in trims, just not a drastic one. i suspect thats why your seeing wild afr numbers. cutting it off starts over and for awhile its not aggressively trying to trim fuel. then after a bit of time, it starts again, and u see the swings. LTFT ideally, should be +/-5%.

btw, high fuel trim values are and wild afrs are most noticeable during idle and part throttle cruising. timing, any mod u do to change how air flows through the engine and how the engine delivers fuel, effects the afr and must be addressed by ecu tuning. all the ecu knows is all of a sudden the old trims dont work to hit the target afr, so its gonna do all it can to fix it.
 

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Discussion Starter #4
t
i dont know if you ever figured out the issue, but it sounds like its going through fuel trim learning. you freed up alot of restriction, so thats going to mess with your long term fuel trims. the ecu targets 14.7. it looks at the actual afr and either adds or removes fuel using the short term trims to hit the target 14.7. it constantly updates the long term trims during idle cruise and wot. it does that by using the average of the stft values during a cycle that lasts like 13min or something in that range, then it changes the LTFT based on that average. it then uses that ltft as a base for hitting that target afr, until another cycle finishes and it changes again. when you change how much air you move in and out of an engine, you change how much fuel it takes at any given driving situation to hit its afr target.

being untuned, its got the ecu going crazy trying to hit that target. so its adding or pulling more fuel than normal. Typically a tuned car will only need small changes to trims because temperature, air density and humidity play a role in trims, just not a drastic one. i suspect thats why your seeing wild afr numbers. cutting it off starts over and for awhile its not aggressively trying to trim fuel. then after a bit of time, it starts again, and u see the swings. LTFT ideally, should be +/-5%.

btw, high fuel trim values are and wild afrs are most noticeable during idle and part throttle cruising. timing, any mod u do to change how air flows through the engine and how the engine delivers fuel, effects the afr and must be addressed by ecu tuning. all the ecu knows is all of a sudden the old trims dont work to hit the target afr, so its gonna do all it can to fix it.
that all makes sense. thanks!
 
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