Input needed - Just installed TCU / ECU tunes
Thread Starter
MBWorld Fanatic!
Joined: Mar 2011
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From: Nashville, TN
SLK55 AMG - Renntech Supercharged
Input needed - Just installed TCU / ECU tunes
What are you guys seeing for LTFT's and MAP pressure?
Here's a screenshot of a pull this morning. I've got LTFT's of -15% and MAP is 33.4 (18.7 PSI). Keep in mind, I had approximately the same MAP reading at the track when I was trapping 120 MPH. Do most tuners increase the boost with the tune?
I'm just wondering if I've got a boost leak and maybe had one when I ran at the track based on the claimed 22PSI car is supposed to run stock. Shouldn't I be seeing a MAP of 22 + 14.7 = 36.7 in cooler weather? Also, what are the tunned guys seeing for fuel trims?
One last question, do our ECU's make exact open loop adjustments to the A/F in response to the LTFT's in closed loop? I know we don't run wideband O2's, so it's obvious the car is oblivious to the the actual A/F ratio in open loop. I'm just wondering if it makes an equivelent adjustment. So if I'm seeing -15%, I assume the fuel tables in open loop will be leaned out 15%.
Here's a screenshot of a pull this morning. I've got LTFT's of -15% and MAP is 33.4 (18.7 PSI). Keep in mind, I had approximately the same MAP reading at the track when I was trapping 120 MPH. Do most tuners increase the boost with the tune?
I'm just wondering if I've got a boost leak and maybe had one when I ran at the track based on the claimed 22PSI car is supposed to run stock. Shouldn't I be seeing a MAP of 22 + 14.7 = 36.7 in cooler weather? Also, what are the tunned guys seeing for fuel trims?
One last question, do our ECU's make exact open loop adjustments to the A/F in response to the LTFT's in closed loop? I know we don't run wideband O2's, so it's obvious the car is oblivious to the the actual A/F ratio in open loop. I'm just wondering if it makes an equivelent adjustment. So if I'm seeing -15%, I assume the fuel tables in open loop will be leaned out 15%.
Last edited by Grip Grip; May 30, 2014 at 08:59 PM.
MBWorld Fanatic!
Joined: Aug 2013
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From: Anchorage
05 CL65
What are you guys seeing for LTFT's and MAP pressure?
Here's a screenshot of a pull this morning. I've got LTFT's of -15% and MAP is 33.4 (18.7 PSI). Keep in mind, I had approximately the same MAP reading at the track when I was trapping 120 MPH. Do most tuners increase the boost with the tune?
I believe they do adjust boost up with the tune. My car only made about 18#'s on the stock tune, and I am seeing almost 22#'s on my ECU/TCU tune. As for fuel trims, at WOT you go into open loop which you probably already know. At that time your trims should not be modifying the fuel table. This is based on my experince tuning Fords, not Merceds though so I suppose it could be different, God knows everything else is, LOL. If your LTFT is a -15% the base fule table is fat. I have never logged mine since solving my low boost problem, so I guess I should do that again to see where I'm at.
I'm just wondering if I've got a boost leak and maybe had one when I ran at the track based on the claimed 22PSI car is supposed to run stock. Shouldn't I be seeing a MAP of 22 + 14.7 = 36.7 in cooler weather? Also, what are the tunned guys seeing for fuel trims?
Atmospheric pressure is going to be around 1000 on the MAP sensor, and boost is pressure will read higher than that, vacuum lower. Most boost gauges are going to read 0 at atmospheric pressure so your only going to see 21-22 at most, not the 22+ atmospheric.
One last question, do our ECU's make exact open loop adjustments to the A/F in response to the LTFT's in closed loop? I know we don't run wideband O2's, so it's obvious the car is oblivious to the the actual A/F ratio in open loop. I'm just wondering if it makes an equivelent adjustment. So if I'm seeing -15%, I assume the fuel tables in open loop will be leaned out 15%.
Again, in my experince tuning domestics, no, LTFT's does not change open loop base fuel tables, but....... I counld be wrong about these cars.
Here's a screenshot of a pull this morning. I've got LTFT's of -15% and MAP is 33.4 (18.7 PSI). Keep in mind, I had approximately the same MAP reading at the track when I was trapping 120 MPH. Do most tuners increase the boost with the tune?
I believe they do adjust boost up with the tune. My car only made about 18#'s on the stock tune, and I am seeing almost 22#'s on my ECU/TCU tune. As for fuel trims, at WOT you go into open loop which you probably already know. At that time your trims should not be modifying the fuel table. This is based on my experince tuning Fords, not Merceds though so I suppose it could be different, God knows everything else is, LOL. If your LTFT is a -15% the base fule table is fat. I have never logged mine since solving my low boost problem, so I guess I should do that again to see where I'm at.
I'm just wondering if I've got a boost leak and maybe had one when I ran at the track based on the claimed 22PSI car is supposed to run stock. Shouldn't I be seeing a MAP of 22 + 14.7 = 36.7 in cooler weather? Also, what are the tunned guys seeing for fuel trims?
Atmospheric pressure is going to be around 1000 on the MAP sensor, and boost is pressure will read higher than that, vacuum lower. Most boost gauges are going to read 0 at atmospheric pressure so your only going to see 21-22 at most, not the 22+ atmospheric.
One last question, do our ECU's make exact open loop adjustments to the A/F in response to the LTFT's in closed loop? I know we don't run wideband O2's, so it's obvious the car is oblivious to the the actual A/F ratio in open loop. I'm just wondering if it makes an equivelent adjustment. So if I'm seeing -15%, I assume the fuel tables in open loop will be leaned out 15%.
Again, in my experince tuning domestics, no, LTFT's does not change open loop base fuel tables, but....... I counld be wrong about these cars.
Thread Starter
MBWorld Fanatic!
Joined: Mar 2011
Posts: 1,008
Likes: 8
From: Nashville, TN
SLK55 AMG - Renntech Supercharged
Thanks Doc. On the Crossfire, which is IMHO just a smaller version of the CL65, the ECU would modify the open loop fueling based on the closed loop fuel trims.
As for boost, I'm seeing the same levels as stock, so I'll take that up with my tuner. Can you please hook up your datalogger and let me know what your LTFT's are? I'd like to know what other tunned 65's are seeing.
I'm really going against instinct, as I should have already installed my external boost sensor and my wideband, but I wasn't expecting to modify the car so quickly.
Last edited by Grip Grip; May 31, 2014 at 11:47 PM.
