OK. I started digging into the 62 today to fix a rough engine condition - rough idle and feels like there's a miss when it goes into closed loop...but it's oddly sporadic. No check engine light until I realized the bulb was blown (sigh). When I replaced the bulb, code 21 popped up - O2 sensor.
I followed the diagnostic tree in the FSM. Front sensor had .03v, back had 2.2 at the diagnostic plug.
Here's where it gets strange - I crawled under the truck to locate the O2 sensors to test resistance and it looks like the PO rerouted the front bank into the rear bank? And I could only find one O2 sensor!
You can see the original down pipe was cut and an elbow added.
The elbow merges into the rear down pipe.
Single O2 Sensor (with good resistance) on the rear pipe before the cat.
Did my 88 come with one or two O2 sensors?
And if the front O2 sensor is missing would that trigger and code 21?
Where would the front sensor ecm-side plug be located?
I followed the diagnostic tree in the FSM. Front sensor had .03v, back had 2.2 at the diagnostic plug.
Here's where it gets strange - I crawled under the truck to locate the O2 sensors to test resistance and it looks like the PO rerouted the front bank into the rear bank? And I could only find one O2 sensor!
You can see the original down pipe was cut and an elbow added.
The elbow merges into the rear down pipe.
Single O2 Sensor (with good resistance) on the rear pipe before the cat.
Did my 88 come with one or two O2 sensors?
And if the front O2 sensor is missing would that trigger and code 21?
Where would the front sensor ecm-side plug be located?
. The OEM exhaust tied together after the cat's this may be the reason for the codes. You can try removing the sensors and give them a good cleaning with some carb cleaner that might clear it up, but go easy those bolts are easily broken when they get crusty and that'll open up to a whole other project. Depending on your local regulations I'd de-smog the 3FE.
