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  #1  
Old 06-15-2015, 08:22 PM
1997 E320
 
Join Date: Dec 2011
Location: NY
Posts: 82
Limp mode

How do I trigger limp mode on my 97 e320?
I installed the AEM water meth injection kit and it has a fail safe wire outputting a "1.7A Low Side output. Grounded when error condition exists."
When there is a failure for any reason I want that output to prevent further acceleration and stop boost pressure from supercharger.
The Aem FIC has a dual map configuration when grounded, but it takes about 3 seconds to automatically switch maps which I think is way too long.
Any other ideas?

Rock
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  #2  
Old 06-16-2015, 09:00 AM
whipplem104's Avatar
Registered User
 
Join Date: Oct 2008
Location: seattle
Posts: 1,166
I am guessing you want to trip a factory limp mode. You could do a few different things but they are all going to trip a check engine light. The best scenario would be to ground all the coil wires. So Take all three ground sides on the coils and tap into them and commonly ground the wires when you want. This will act just like a rev limiter. You could also short out the tps sensor. You are going to have to reset by stopping and turning the car off and starting again. So I do not recommend these as it could be unsafe.
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Old 06-16-2015, 11:52 AM
1997 E320
 
Join Date: Dec 2011
Location: NY
Posts: 82
Thank you Whipple,
I grew out of reckless driving and putting myself and others in danger. I just want to save my engine in the event the system fails at the dyno or an early morning drive on a long stretch
I did the supercharger route because I have never owned a fast car, to be different and I want some bragging rights here in the east coast having a supercharged w210...lol.
I never leave home without my obd2 scanner.
Once I still have power steering and brakes I'll be fine.
Would the limp mode trigger right away? I think I'll look into the tps route. How do I short out the tps, connect the fail safe wire to the ground, power or signal?
Thank you for your help.
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Old 06-16-2015, 12:15 PM
whipplem104's Avatar
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Join Date: Oct 2008
Location: seattle
Posts: 1,166
You would want to ground the signal voltage. This will cause an error and should do it. I do not know how fast it will work. Like I said if you want it to be instant just ground the coils. This is a better solution to be honest.
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  #5  
Old 06-16-2015, 05:53 PM
1997 E320
 
Join Date: Dec 2011
Location: NY
Posts: 82
I connected the fail safe signal (reading at 1.3v as the tank is empty and triggers the fail safe)to the TPS sensor signal wire at idle and the car started to rev to 2500 rpms by itself. If I stepped on the brakes nothing happened. When I step on the accelerator it stays at the highest rpms that I went too. It resets after I restart the car no engine codes. So that did not work.

Please help me to understand grounding the ignition coil ground wires. So if they all receive a ground signal at the same time this tells the Ecu that something is wrong and goes into limp mode? Just to clarify, at normal operation they pulse their ground signals independently? Is this how it works?
Thanks

Last edited by topdeez; 06-16-2015 at 08:36 PM.
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