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Electrical noob wants failsafe (coolant temp sensor question)


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Howdy all,


So I have an AEM failsafe guage outputting to several relays, and will hopefully have an hfs-3 doing the same.


I have an normally open relay on my boost control solenoid, and a normally closed on my test connectors. So i have wastegate boost and and IAM of 0 in failsafe situations with base timing but not much change in fueling oddly enough. (1k cc sidefeeds fwiw). Id like to run richer and with more retard during these times.


I use AccessTuner to tune so I was going to do NSFW's idea of tricking the coolant temp sensor to read maxed out and adjust the timing and fuel compensation tables accordingly with a 150C breakpoint. My tables are now modified but I was thinking, or perhaps overthinking, since I want a maxed sensor for this to trigger and my sesnor is a 0-5v do i need to regulate down to 5v or can i just do a switched 12volt and regularion is handled inline somewhere? This is where Im drowning a little and getting confused. Or do I need a transformer? I know people use resistors to go the other way.


Any help is greatly appreciated, or name calling, also appreciated.:spin:

Thanks in advance!


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  • 2 weeks later...

No need to screw with the fuel temp sensor. If you tie the HFS-3 and AEM Wideband Failsafe outputs to the test mode connector (like I think you did) you can do it all in software.


Open up your base timing and timing advance tables. Remove the additional retard you need from the base table, and add the exact same amount back to the max advance table.


Open up your failsafe fueling table. Richen it up to the level you want under failsafe.


As soon as the test mode connector is pulled to ground, the ECU will use these tables.

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