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TOPIC: Fuel + ATF = possible O2 trouble code?

Fuel + ATF = possible O2 trouble code? 03 Jun 2013 23:21 #1

  • EJDP
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Ladies and gents, hello again!

My bottom line question is "Does running the engine with 1 quart of ATF in my 24 gallon fuel tank have a possible harmful effect on O2 sensors or other systems?" For some background information and more precise questions, see below:

I have installed the Gadgetman grooved throttle body on my 2000 MITSUBISHI MONTERO Endeavor 3.5 V6 FI - 24V & SOHC (California Emission/kinda mute point, now LOL), along with a MAPster between ECU and MAP. With the grooved TB and MAPster installed, I ran 9 gas tanks (24 gallons/tank,) slowly tweaking the MAP with good success (No codes). I later ran two additional tanks with 1 quart of ATF added per tank. The engine ran great (smoother, quieter) and no codes (I had to adjust the MAPster to account for the "modified gas"). On the third tank (with ATF), which was going to be my last tank with ATF, I got a P 0141 DTC that indicates a failed heater circuit on O2 sensor Bank 1, Sensor 2. My research shows that it is the right side post catalytic converter heater circuit failed.
I seems to be confirmed as in running my OBDII and when I start the engine, the DTC light comes on, the O2 sensor reading shows 0 V steady, indicating the system is in open loop and accordingly, the LTFT goes +7 and up (richer). When the engine warms-up and I drive, the O2 sensor V returns to closed loop, fluctuating with load and the STFT/LTFT returns to where I expect it to be. I then clear the code and continue driving with no further codes. The OBD shows "0 stored codes and 1 pending code" while the confidence test shows all of them pass but all the emission related tests fail."
Once cleared, it seems like the light and associated code come back on every other start.
I tried to zero out the MAPster to see whether that made a difference: none.
I since depleted my last ATF tank and have run a full tank on gasoline, only and no ATF additive ... The P 0141 DTC still shows.
What do you all think/know?

1 Is it a coincidence that the heater circuit failed on Bank 1 Sensor 2 in the middle of running ATF in the gas tank? (PS: I also have 1 quart of ATF in the crankcase oil).

2 is it due to the continuous adjustment of the MAPster "screwing with ECU/MAP/O2 Vref" ?

3 is it due to ATF fouling the O2 sensor? (Sensor still works, just the heater circuit function does not).
I have ordered a Mitsubishi OEM post-cat sensor for ... $356 ... Just about everyone tells me to stay away from OE parts from other manufacturers that apparently fit but go U/S after a short period or simply do not produce the same results as the original part replacement. The reason behind my question is that there appears to be a benefit to the ATF in gas but I would rather keep my $356 sensor working if by chance the two were related. I have read all kinds of "opinions" in the line of "fuel belongs in the tank and ATF in the transmission" or "if engineers and manufacturer saw a benefit, they would market it that way" while similar comments seem to carry a punch, they are just that in my humble opinion "a tag line" but not necessarily accurate. There are many things that are not recommended or even are frowned upon and that are beneficial and vice-versa. In any case, I would appreciate your enlightened opinion. Thanks much!

Eric Du Pont

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Fuel + ATF = possible O2 trouble code? 04 Jun 2013 07:48 #2

  • dan
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Think a minute, if you add more heavy hydrocarbons what have you done different that would crack them? Nothing as it takes alot more heat with a catalyst to crack heavy`s. As far as o2`s fouling yes its possible I find if you do one thing at a time alot of headaches can be eliminated.

Do the groove then after a good successful run then try something else,sometimes one thing will hurt another.

If you have a big block high comp engine plenty of heat then yes it would get better mpg you can run dsl in this and mpg will go up but!!!!!!!!!!!! cold starts and alot of idle will foul plugs.

Dan Merrick

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