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PCM master reset = BAD MPG!!
- Thread starter rehberg79
- Start date
Mudderoy
NAXJA Forum User
- Location
- Katy, Texas
I bet you damaged an oxygen sensor.
igotanxj
NAXJA Forum User
- Location
- Citrus heights
what is "master reset"?
Blaine B.
NAXJA Forum User
- Location
- Northwest Indiana
How did you clear? I hear the best way is to disconnect both leads from the battery and touch them together. And then leave them both disconnected from the battery and go and turn the key to "start" for a few seconds. Then reattach battery cables, start it up and let it idle for awhile.
Mudderoy
NAXJA Forum User
- Location
- Katy, Texas
No I thought you may have damaged the O2 sensor when you changed the cat. You might want to put the old O2 sensor back on and see if the gas mileage returns.
Blaine B.
NAXJA Forum User
- Location
- Northwest Indiana
The post cat O2 sensor doesn't affect fuel mileage, only checks the efficiency of the cat.
Only the o2 sensor on the downpipe regulates fuel mixture.
Only the o2 sensor on the downpipe regulates fuel mixture.
I had to replace the lower O2 because the old one was not coming out, so theres not swapping them.
The reset will erase the "Adaptive Memory" stored in the PCM and allow new memory to be developed.
Heres the link for the how to and to what it does: HERE or HERE
Another link with the same procedure says that "Once your engine has gone through 50 warm-up cycles in at least a 500-mile distance the PCM adaptive memory is set. It WILL NOT Change unless you flash it out and start all over again.." Im pretty sure I dont have 50 starts on it yet and I dont have 500 mi.
I hope thats what Im waiting for.
Mat
The reset will erase the "Adaptive Memory" stored in the PCM and allow new memory to be developed.
Heres the link for the how to and to what it does: HERE or HERE
Another link with the same procedure says that "Once your engine has gone through 50 warm-up cycles in at least a 500-mile distance the PCM adaptive memory is set. It WILL NOT Change unless you flash it out and start all over again.." Im pretty sure I dont have 50 starts on it yet and I dont have 500 mi.
I hope thats what Im waiting for.
Mat
Last edited:
Mudderoy
NAXJA Forum User
- Location
- Katy, Texas
Good to know, thanks!
Mudderoy
NAXJA Forum User
- Location
- Katy, Texas
Well I don't know then. I've reset mine several times and it never effected gas mileage, at least not noticeably. I'd like to know what it was if you figure it out though.
- Location
- MilkyWay Galaxy
What year is it?
96 and up has a relearn procedure you need to follow right after the reset.
lawsoncl
NAXJA Forum User
- Location
- North Idaho
So what on earth does turning the headlight on/off in the procedure do? It's not like the engine computer knows when they get turned on/off.
lawsoncl
NAXJA Forum User
- Location
- North Idaho
Since the gas gauge isn't terribly accurate, I would wait until you refill then divide miles/gallons. Besides 125 miles on 1/4 tank sounds pretty good to me. What kind of mpg do you normally get?
- Location
- MilkyWay Galaxy
I don't know for sure but these computer & sensor networks are getting pretty darn smart. It affects alternator load, battery system voltage and possibly the back voltage on the ground wires. Perhaps the computer has an algorithm that senses those voltage changes and uses them in number crunching and making corrections.
It was @ 125 mi on 3/4 of a tank. I'm normaly around 180 mi on 3/4.
- Location
- MilkyWay Galaxy
No. Should be in the 99 FSM.