loss of power when warm

RonD · Mar 6, 2014

lng tr 2 would be from averaging Bnk 2 O2 1

It looks like Bnk 2 O2 1 is changing so lng tr 2 should change

I would disconnect and reconnect OBD II reader, maybe even reset computer, unhook Neg. battery cable for 5 minutes.

DFracing · Mar 6, 2014

i've done all that multiple times, if the truck was running fine, i'd say ya maybe it was the obd scanner but to see that there is something wrong with the fuel trim it doesn't really surprise me. there's a sensor not hooked up correctly or faulty

RonD · Mar 6, 2014

Lng tr = LTFT = Long Term Fuel Trim

This number is calculated by the computer there is no sensor involved except the O2 sensor that is telling computer the results of fuel trimming, the computer then averages how little or how much fuel is being used to trim the fuel mix to the 14:1 air/fuel ratio, and thats the LTFT number you see.
14:1 would show as .45 on O2 sensor

If bnk 2 O2 1 isn't changing then lng tr 2 wouldn't either, replace O2 or check wiring
the 0.080 is outside of normal parameters, .2 to .8 is normal range you like to see, 0.16 would be marginal but acceptable

Try testing scanner on a friends car

Caesar · Mar 7, 2014

Could be a dirty O2 sensor too. Like the MAF sensor, the O2 sensors get coated with contaminants from the engine over long periods of time. They can cause a faulty or slow reading for the ECU. The only problem is that if you are going to bother taking it out to inspect/clean you might as well almost just change it for a new one. Granted you can get an OEM at a good price.

I am actually now considering swapping my two upstream OS sensors in the near future. Because my truck originally had the OHV and not the SOHC there is a possibility that the O2 sensors are wrong. I had the same problem with the spark plugs, the previous owner (not the guy who swapped the engine) had changed them out and didn't realize that it was the SOHC engine and not the OHV. The truck will run fine, but it may not perform well and could get bad gas mileage. Just swapping the plugs and the thermostat housing and sensors has gotten me better overall gas mileage. Im gonna monitor the live data when I get a chance to see if anything is off.

Ron D, is there a thread/guide for monitoring the live data from the ECU and deciphering any issues or values that are off? I am just learning about this stuff myself and would love to understand the fuel trims and how they are calculated and adjusted.

DFracing · Mar 8, 2014

i unhooked the bank 1 forward 02 sensor and the truck would never go use long term fuel trim, but when i unhooked the bank 2 forward 02 sensor the truck kept using long term fuel trim and the scanner was showing that the sensor was still active, so i believe that i have a bad ground or a short but not sure where

Caesar · Mar 8, 2014

Nice man, it sounds like you are on the right track. I am not sure with O2 sensors, but typically when any sensor is unplugged the ECU reverts to preset values. It could also be going back into closed loop mode when you unplug one or both...

DFracing · Mar 9, 2014

well its weird because it goes into open loop when i unplug one but not the other.

RonD · Mar 9, 2014

It reads and looks like the O2 sensor "2" is some how wired into the display as sensor 1.

Just out of curiosity what readings do you get for
Bnk 1 O2 2

This is the O2 sensor located after the Cat Converter, if you have a dual exhaust then there will also be
Bnk 2 O2 2
So two downstream O2 sensors

Caesar:
Google: stft and ltft explained

DFracing · Mar 9, 2014

ill try and look later today, but i dont have dual ehaust, there is only 3 02 sensors.

RonD · Mar 9, 2014

The downstream O2 sensor doesn't change much, it is there just to compare to upstream sensors to make sure Cat is working to clean up exhaust.
If somehow the wires were reversed, sensor 1 and sensor 2, then unplugging the upstream sensor would have no effect since sensor 2 is what you are seeing.
This would be an odd one, not sure how it would even happen.

DFracing · Mar 10, 2014

see i thought the same thing, but the connectors are different for each 02 sensor, so that doesn't happen,and i cant imagine that the wires are crossed inside the wiring harness, there is no that would be able to happen. To be honest i am not sure what happened, im sure its something stupid simple like a bad ground.

loss of power when warm

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