The wires to the EGR throttle butterfly motor are intercepted so that the butterfly motor can be powered, isolated from the ecm supply, for 15 seconds after the ignition is switched off although aborted if the ignition is switched back on. A double pole relay ensures no feed-back to the ecm. The wires can be readily intercepted near the throttle housing on the 2.7/3.0 but not so readily on the 4.4 so mine were intercepted at the ecm plug. Ignition and permanent 12V power via a fuse plus earth are also required.
The EGR butterfly is normally used to deprive the engine of fresh air to increase recirculated exhaust gases though the engine to decrease oxygen content. One of the European car manufacturers, which IIRC is Audi, added the closing of their EGR throttle butterfly on their diesel V8 on engine shut-down to rid the engine of compression roughness in the final second or 2, a smoothness that I immediately noticed on my 4.4 TDV8.
It appears from DTCs (fault codes) for the 3.6 TDV8 that the 3.6 TDV8 ecm will do the same trick if it detects uncontrolled engine operation but no equivalent DTCs exist for the 2.7, 3.0 or 4.4 engines which have all suffered self-destruction from runaway.
MY12 RRV 4.4 TDV8 AB, +LLAMS, +e-diff, +ACC stop/go. Produce LLAMS for LR/RR, Jeep GC/Dodge Ram
VK2HFG and APRS W1 digi
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