Codes 25 and 26

[savvy]

'92 3FE with 180K miles is now throwing 25 and 26 codes for last 3 days.
(Air/Fuel Lean, A/F Rich)
I have new Densco O2 sensors to install but haven't yet.
(looks like PIA to replace, any hints, I can see one but cant see the other)
How does one test the other possibilities?

Cheers!!

 

[Pitch]

I had the same codes in sequence once. I cleared them by disconnecting the battery, and no issues again in over 2 years. I attributed it to a bad tank of gas. A year later I swapped O2 sensors (recommended remedy for Codes 25/26) as a matter of PM on my rig with similar mileage to yours. She has ran like a top then, and has continued to, with no codes in >2years.

Swapping sensors took me about 20' to do both (non-rusty southwestern US vehicle)

 

[savvy]

I clear the codes every trip......continue to throw.
Did you have to pull anything?
I have a bunch of different wrenches, but nothing fits to give me leverage to spin the visible sensor.
I can see the second sensor wire, but it goes up between cat and body and I can't feel where it terminates.
Cheers!

 

[zapata]

I Had those codes...... found my air intake boot had a crack or three... epoxied it and cured the code problem

 

[savvy]

I Had those codes...... found my air intake boot had a crack or three... epoxied it and cured the code problem

New boot last summer.

 

[Brentbba]

10mm wrench IIRC on the O2 sensor nuts. Inboard one on the side by side cats of '94 and previous is a little bit of a pain to get to, but doable. Shoot them with some PB Blaster or WD40 a day or two prior to removing them.

25/26 has always been O2 sensors on my '94...except the last time. Cleared the code by pulling the fuse after I'd ordered the sensors, and the damn code hasn't come back. That was a couple of months ago. I've got a set of trail spare O2 sensors now.

 

[FJ80 Money Pit]

On the 3FE error code 25 & 26 is due to a vacuum leak, block or a vacuum hose disconnected. This causes the EGR to remain open during idle and coasting when it should be closed and causes the fluctuating rpm under 1000 and error code 25 and 26, because with the EGR constantly opening and closing the fuel air mixture to fluctuate between rich and lean.

1) check the throttle body vacuum out lines on top, make sure theyre clear and clean with a needle in a pair of vise grips from the bottom and spray cleaner in the holes from the top.

2) check the two metal lines under the intake from the throttle body to the egr modulator with a vacuum guage. If blocked run two vacuum line from the throttle body to the egr modulator, one to P and the other to R with a split tee to the BVSV. These two metal lines always rust out on older trucks and causes blockage.

If you think its the O2 sensors then remove, unplug, clean with mass air flow sensor cleaner and reinstal with new nuts.