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To your problem
What makes you think it is running rich?
If it starts and runs fine, I doubt it's actually rich
Have you watched the O2 sensor switch?
Do you know what it means to watch an O2 sensor "switch"
A failed O2 sensor heater will just take longer for it to go into closed loop
Yes, I mean watching them switch with the truck running at idle
They need to switch (above and below 1/2 volt)
You have one stuck on say .27 volts, that means it is "stuck" lean and the system probably "is:" lean
If yours is stuck on say .77 volts, that is stuck rich and the system probably is rich
Yes, the O2 voltage goes from zero volts to .99v
They switch above and below 1/2 volt, where 1/2 volt would be correct stoichiometric ratio of 14.7:1
They can't just stick it to .5volts because you keep hitting the gas, so they switch above and below 1/2 volts all the while trying to maintain 14.7:1
It's a bit complicated until you get it, you got it?
Added note, we used to see Broncos and others with o2 sensor voltage around 9 volts about to fry the processor
Those werre the ones that had the o2 sensor wiring running down with the starter battery cable that would corrode
Those ran like puke too, not sure whether rich or lean
Yours is not one of those, is it?
I have not traced the harness from the O2 sensor plug where it heads up in the engine bay. The wires down below were in good condition....a bit oily
from the rear main bath. Will have a more thorough look tomorrow when it dries up.
Should I use dialectic grease on the plug when I put the ECU back in? There was some white/tan grease on many of the pins on the connector. I cleaned
that crap off. Pins were all straight with no sign of any green boogars.
I couldn't find an O2 sensor for the photo, here is a photo of how to backprobe a TP sensor
You use a paper clip and ram it in where the wire goes into the connector
Put negative lead on a good ground (processor ground is a good one) and the red positive lead to the O2 sensor signal return wire
Keep in mind, they do not start switching until they reach around 600F
Here are the results of performing the O2 test after bringing up the truck to temp (thermostat opened at 190 deg F btw ....so that is good).
I had my wife in the truck performing throttle bursts from idle - 2500-3000.....
Wire was shoved into the black wire on the O2 sensor and an aligator clip onto that onto the red probe on the multimeter. Black probe wire
was grounded on a large bolt on the frame.
Meter was set to DC volts.
Measured at around 101 millivolts at idle. as she hit the throttle got up to around 270 millivolts.
should I not be seeing the oxygen readings higher than that?
the thermostat neck where the ECT connects hovers around 185 once the thermostat opens and coolant begins circulating.
I measured the temp of the bung on the exhaust cross pipe that the O2 sensor threads into and it's only getting to around 300 F.
I took the truck up the road for a few miles to get it good and warm ....returned and immediately tested it. I then checked each
exhaust manifold pipe from the head where they connect. They ranged in temp from around 300 - 450F. Some hotter, some cooler.
I sprayed soapy water on each manifold pipe where they connect to the heads to see if there was any leaks. The spray just sizzled off
from heat..nothing bubbling from gushing leaking exhaust gases that I could determine.
The voltage should momentarily hit numbers above 1/2 volt
then back to number less than 1/2 volt and then repeat
if you are backprobing with a DVOM you need to watch for a while
The voltage should momentarily hit numbers above 1/2 volt
then back to number less than 1/2 volt and then repeat
if you are backprobing with a DVOM you need to watch for a while
I'm going to pull the O2 again on Monday (rain tomorrow again)....and do some more testing on it. I'm going to confirm
the heater bit to make sure that it is not shorted.
I read up some more on the cause of the low readings on the O2....and one can be a vacuum leak or exhaust leak.
I probed the big vacuum lines already and didn't find anything jumping out. I have a propane cylinder I can use to see
if there are any leaks there. I would think if it was exhaust leaking, I would hear noise there but am not.
Right, and you can use the propane to momentarily richen the mixture and watch for the O2 sensor number to go over 1\/2 volt (rich)
gotcha...will do this test as weather permits. I don't have a usable space atm to do things so have to work around weather.
on the air box on the truck there is a valve with 2 nipples on it that has 2 lines going a check air induction valve used for I believe cold start heating of the exhaust where it
introduces air from the exhaust into the air box to heat things up. on the nipple that goes to the throttle body there was a round disc that the line connected from the air box
and on the other side of that disc was another nipple that the air box hose connected to. What is that round disc's function? I'm wondering if that valve on the air box is
leaking and introducing air into the throttle body when it shouldn't. I'm just throwing s*it against the wall here to see what sticks.
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