Under part thottle boost, my AEM wideband will read around 15.5 for a second or two until it drops down to around 12.5. I'm a little worried about it starting out so lean under boost. AFR bounces around from 14.5-15.5 during cruising and around 10.5 at full throttle. Any ideas?
lean under part throttle boost?
- Thread starter jake8790
- Start date
I had the same issue and used the maft-pro to tune around it.
What I think is happening (at least in my case) is that since it's only part-throttle the TCCS doesn't really expect boost and tries to hold it at 14.7ish as usual. Since flow is increased by the more open exhaust you're turbo is spooling earlier than it would when completely stock and the TCCS can't keep up or doesn't realize that you're in boost at only half-throttle or so.
At least that's what was causing the part-throttle/part-boost leanness in my case...
What I think is happening (at least in my case) is that since it's only part-throttle the TCCS doesn't really expect boost and tries to hold it at 14.7ish as usual. Since flow is increased by the more open exhaust you're turbo is spooling earlier than it would when completely stock and the TCCS can't keep up or doesn't realize that you're in boost at only half-throttle or so.
At least that's what was causing the part-throttle/part-boost leanness in my case...
Poodles;1881897 said:
How can the EGR valve actuate with higher than atmospheric pressure to the modulator?
VSV is controlled by the ECU based off of water temp signal, throttle position, and reading from the AFM.
Agreed but how can the EGR diaphragm be pushed up to open the valve if there is higher than atmospheric pressure above the diaphragm?
It's not. The VSV can block the flow.
While I can't find enough info to confirm that's how it functions. The TSRM only shows how to test the system, not exactly how it operates under ECU control outside of referances in the TEWD as to what sensors are used by the ECU to determine what it should do with the VSV.
If it didn't take AFM and TPS into account, I could see it functioning as a dumb system based entirely off of temperature and the EGR vacuum port in the TB.
While I can't find enough info to confirm that's how it functions. The TSRM only shows how to test the system, not exactly how it operates under ECU control outside of referances in the TEWD as to what sensors are used by the ECU to determine what it should do with the VSV.
If it didn't take AFM and TPS into account, I could see it functioning as a dumb system based entirely off of temperature and the EGR vacuum port in the TB.
All I am saying is how can the valve be pulled up with vacuum if there is positive pressure before and after the throttle plate?
All the VSV can do is vent the line between the throttle body and the modulator to prevent EGR operation, at least that's how I thought it worked. Looking at the TSRM it looks like I am wrong though, what I am describing is more like the way the NA works.
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Just saying how it could work, not how it actually does work 
3P would have to do some digging in the ECU code to tell us what it's really doing.
3P would have to do some digging in the ECU code to tell us what it's really doing.
Walbo, probably not. 12V mod might, but it's doubtful as you're still on the stock ECU without tuning aids.
Crack me up...
OP: The leanness is normal or I should say stoich/closed loop is normal up to about 3 psi.
OP: The leanness is normal or I should say stoich/closed loop is normal up to about 3 psi.