OVER BOOST LIMP MODE
09-26-2017 | 02:32 PM
#1
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2005 e55 AMG
OVER BOOST LIMP MODE
So what happens when you boost past the MAP sensor and the ECU goes into limp mode. Had a cold night few days ago and engine shot to 19.1 afr. It may have hit 17lbs but was not watching. Normally 15 lbs is average.
It was very strange and has never done it again but temps are much warmer right now.
It was very strange and has never done it again but temps are much warmer right now.
Last edited by SICAMG; 09-26-2017 at 08:47 PM.
09-27-2017 | 10:31 PM
#5
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From: Long Island New York
2003 SL55,2020 GTC ,2017 GTS sold ,2002 G500 Sold,2003 SL500 Sold,
Code is usually P2007-8 if MAP sensor problem, usually car runs like it has a miss until you cycle key,from what I recall .
Last edited by cnterline; 09-27-2017 at 10:34 PM.
09-28-2017 | 04:00 AM
#6
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2005 E55
From what I have read, it sounds like the ECU throws the car into limp mode at about 17psi even though we have a 1.5 bar sensor.
I'm amusing the car fell on it's face and you saw the 19afr? You might be right, hit just right conditions to creep you over 17psi and cut fuel.
A map clamp is hooked up in series with the MAP sensor output, and limits the voltage the MAP sensor can feed to the ECU, in effect limiting the total boost the ECU can actually see to a value that you can usually adjust with a rheostat on the clamp.
You are effectively just putting a cap on the pressure the ECU can see, even though actual pressure may go above it.
If you are just barley teetering the point of fuel cut, if you haven't already I would grab a set of long tube headers which should give you a nice power bump and drop that pressure a pound or two haha
I'm amusing the car fell on it's face and you saw the 19afr? You might be right, hit just right conditions to creep you over 17psi and cut fuel.
A map clamp is hooked up in series with the MAP sensor output, and limits the voltage the MAP sensor can feed to the ECU, in effect limiting the total boost the ECU can actually see to a value that you can usually adjust with a rheostat on the clamp.
You are effectively just putting a cap on the pressure the ECU can see, even though actual pressure may go above it.
If you are just barley teetering the point of fuel cut, if you haven't already I would grab a set of long tube headers which should give you a nice power bump and drop that pressure a pound or two haha
09-28-2017 | 10:09 AM
#7
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2005 e55 AMG
You know I said it didn't throw a code but only that there was no MIL light on. I will look in DAS tonight and see if something is there.
It has only done this twice...one time I must have lifted off the throttle just a tad and it ran lean in the summer but this time it did it twice back to back. The first time under heavy boost in 48 degree weather with ice in the tank and than back to back after that lean again but did not cycle key after the first time. also did not notice boost...was not looking at that just the AFR. I have since installed a fail safe that shuts the compressor off after 12.1 AFR so don't have to worry about popping the engine now.
It has only done this twice...one time I must have lifted off the throttle just a tad and it ran lean in the summer but this time it did it twice back to back. The first time under heavy boost in 48 degree weather with ice in the tank and than back to back after that lean again but did not cycle key after the first time. also did not notice boost...was not looking at that just the AFR. I have since installed a fail safe that shuts the compressor off after 12.1 AFR so don't have to worry about popping the engine now.
