MIL Eliminators?

Steve491 · Apr 11, 2009

Question for you ECM experts out there. The way I understand it that MIL eliminators are installed on the downstream O2 sensors in order to "fool" the ECM into thinking the catalytic convertors are working correctly when in fact they have been removed. Here's my question. Do MIL eliminators completely replace the O2 sensor's signal or just modify the signal? In other words do you still have to have a functioning O2 sensor to complete the loop?
My car has been running great with the MIL eliminators for a long time but now the check engine light is on with a p0136 code, O2 bank 1 sensor 2. Hopefully it is just the O2 sensor and not something major with the ECM or wiring.

Also, I installed high flow cats in the X-pipe so is it even necessary to have the MIL eliminators?

Thanks, Steve

RedDaemon · Apr 11, 2009

Steve491 said:
Also, I installed high flow cats in the X-pipe so is it even necessary to have the MIL eliminators?

Thanks, Steve

if the x pipe has bungs to fit the 02 sensors, MILs are not needed when cats are present. use the 02 sensors

if there are no bungs, you would need them either way. to fit the 02 sensors or the MILs. hopefully you have them

trinity_gt · Apr 11, 2009

Steve491 said:
Question for you ECM experts out there. The way I understand it that MIL eliminators are installed on the downstream O2 sensors in order to "fool" the ECM into thinking the catalytic convertors are working correctly when in fact they have been removed. Here's my question. Do MIL eliminators completely replace the O2 sensor's signal or just modify the signal? In other words do you still have to have a functioning O2 sensor to complete the loop?

They just modify the signal. An eliminator is really nothing more than a low-pass filter. It's an RC (resistor-capacitor) filter in the signal line that heavily filters and thus smooths out the signal from the O2 sensor

My car has been running great with the MIL eliminators for a long time but now the check engine light is on with a p0136 code, O2 bank 1 sensor 2. Hopefully it is just the O2 sensor and not something major with the ECM or wiring.

It could be a faulty MIL eliminator causing this or the sensor itself has died. I'd suspect it before anything original to the car itself.

Also, I installed high flow cats in the X-pipe so is it even necessary to have the MIL eliminators?

It depends. High-flow cats don't generally do as good a job with HCs, NOx and CO as the more restrictive OE cats. As a result, a high-flow cat may result in the rear O2 sensor seeing more rich/lean transitions which the PCM might interpret as bad cats. If the cats are high quality pieces, you may not need the MIL-Es. If they put flow ahead of exhaust gas treatment, it's likely you will.

Try them without the MIL-Es first. If the efficiency code appears, you have your answer.

Steve491 · Apr 12, 2009

Thanks Guys, I replaced the O2 sensor, left off the MIL eliminators, cleared the code and so far so good. We'll see after a few drives if the light stays off. If it doesn't then throw them back on.

AdRock · Apr 13, 2009

If you do put the MIL's back on there's one thing that could have been causing the CEL on that sensor.

When I first put the MIL's on my car everything was cool. No light. Ended up getting intermittent CEL's from the rear O2's after a while. I pulled the connectors apart on both sides of the MIL's, cleaned them with some contact cleaner, and put some dielectric grease in there. There was some moisture that got into the connector. The grease seals moisture out and I've never had another problem.

Just some food for thought if anyone else has a CEL with the MIL's installed.

Greenscobie86 · Apr 14, 2009

^^^ Good tip.. I will try that with my car. I'm having the exact problem you described...

Steve491 · May 24, 2009

After doing more maintenance and a 2 week vacation in the Carribean the Cobra is back on the road in great shape. I changed the tx fluid, coolant, fuel filter (what a pain), steering rack, and the strut bearings (UPR CC plates). I wanted change out the muffler bearings and the winter air in the tires but there is just not enough time.
Seriously, back to the original post about the MIL eliminators. I was always under the impression that the rear O2 sensors had no input regarding fuel mixture/timing via the ECM. My Cobra runs so much cleaner and leaner since I got rid of the MILs....
-Steve-

AdRock · May 24, 2009

Steve491 said:
After doing more maintenance and a 2 week vacation in the Carribean the Cobra is back on the road in great shape. I changed the tx fluid, coolant, fuel filter (what a pain), steering rack, and the strut bearings (UPR CC plates). I wanted change out the muffler bearings and the winter air in the tires but there is just not enough time.
Seriously, back to the original post about the MIL eliminators. I was always under the impression that the rear O2 sensors had no input regarding fuel mixture/timing via the ECM. My Cobra runs so much cleaner and leaner since I got rid of the MILs....
-Steve-

It's true, the rear O2's have no bearing on how the ECM does anything as far as tuning. They are there simply to show the ECM whether the cats are working properly or not. That's it. I'd guess that the difference in how the car feels could possibly be attributed to you changing the fuel filter.

Steve491 · May 25, 2009

It's very possible that it was the fuel filter given how hard it is to change. It looked very old, maybe original. Hopefully I'll get yet another gain when I put my new plugs and wires on.

MIL Eliminators?

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