WARNING: DUMB QUESTION ALERT
The best kind!
If an oxygen sensor senses oxygen (its off to a good start, eh?)
Nope. Actually, oxygen sensors sense the LACK of oxygen. They read
0.9V when there’s no oxygen in the exhaust, 0.1V when there is oxygen
in the exhaust.
and the sensors output varies from 0.1 Volt (lots) to 0.9 Volt (none)
Ah, so you knew it sensed lack of oxygen already!
then what reading is the ECU going for? (Attempting to adjust to
The ECU is constantly looking for the OTHER reading. If it’s reading
0.9, it’s trying to get to 0.1. If it’s reading 0.1, it’s trying to
get to 0.9. Hence, it’s trying to surf the break point between the
Seems to me that if the car were perfect, there wouldn’t be any excess
oxygen (it would have been all used in combustion)…
Yeah, but you could get there by just pouring gobs of fuel to it –
which would be bad for many reasons. You want to burn all that
oxygen by providing JUST ENOUGH fuel to do the job. So, when the
sensor says you have enough fuel in there, the ECU starts cutting it
back until there ISN’T enough in there – then it starts adding
again. It’s a neurotic little control system.
I was expecting a midrange value of 0.5 Volts so the very high 0.87
Volt reading I get at hot or cold idle has me spooked. Should I be?
1992 XJS- 4.0L
Means it’s running rich. I have no idea what it should be running,
PS. This occurred to me on the way to work this morning.
One of the secrets of asking dumb questions is to ask fast, before too
much thought can occur.
– Kirbert | Palm’s Postulate:
| If anything is to be accomplished,
| some rules must be broken.
| – Kirby Palm, 1979From: Rick Drozdowski email@example.com