O2 sensor heater circuit
Hotshot
Joined: Jul 2020
Posts: 10,609
Likes: 2,685
From: Near Salt Lake City
when it warms/dries up here I'll be doing that very test. My brother just dropped off an inspection mirror to check the pipes/valves out.
I had taken the vacuum line off the TAB valve to test to rule out the air from the pump being the source of air being introduced into the mix
causing the lean condition.
I had taken the vacuum line off the TAB valve to test to rule out the air from the pump being the source of air being introduced into the mix
causing the lean condition.
Cargo Master
Joined: Aug 2021
Posts: 2,268
Likes: 745
From: Maryland
It could if there are leaks at the crossover tube to the back of the heads, or the check valve or diverter valve. A leak in one of those would leave the exhaust open to outside air like any other exhaust leak.
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More Turbo
Joined: Feb 2022
Posts: 657
Likes: 106
From: New Dominion, PE
the cold air heater tube that goes from the air box intake to the exhaust on the drivers side...I wonder if that may be malfunctioning and letting air into the exhaust on that side all the time..... I tested the valve by sucking on the vacuum line that goes to it and it holds vacuum...thinking that was a valid test to prevent the air from going from
the exhaust thru to the air box to warm it up. if air is passing thru to the exhaust from the incoming channel to the air box would that cause a major injection of
air into the exhaust?
the exhaust thru to the air box to warm it up. if air is passing thru to the exhaust from the incoming channel to the air box would that cause a major injection of
air into the exhaust?
Cargo Master
Joined: Aug 2021
Posts: 2,268
Likes: 745
From: Maryland
the cold air heater tube that goes from the air box intake to the exhaust on the drivers side...I wonder if that may be malfunctioning and letting air into the exhaust on that side all the time..... I tested the valve by sucking on the vacuum line that goes to it and it holds vacuum...thinking that was a valid test to prevent the air from going from
the exhaust thru to the air box to warm it up. if air is passing thru to the exhaust from the incoming channel to the air box would that cause a major injection of
air into the exhaust?
the exhaust thru to the air box to warm it up. if air is passing thru to the exhaust from the incoming channel to the air box would that cause a major injection of
air into the exhaust?
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More Turbo
Joined: Feb 2022
Posts: 657
Likes: 106
From: New Dominion, PE
meaning the air incoming thru the air snorkel in the grill, when that valve is opened via vacuum, just allows the cold air to route thru to the exhaust manifold and warm up but NOT enter the exhaust output stream....correct?
Hotshot
Joined: Jul 2020
Posts: 10,609
Likes: 2,685
From: Near Salt Lake City
That's why there is a 1 way valve on top of that crossover pipe
They leak exhaust like woo wee when that pipe or the one way valve fails
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More Turbo
Joined: Feb 2022
Posts: 657
Likes: 106
From: New Dominion, PE
how is the exhaust manifold leaking where it is pushing exhaust out...how is air making its way in in that case?
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Cargo Master
Joined: Aug 2021
Posts: 2,268
Likes: 745
From: Maryland
Correct.
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More Turbo
Joined: Feb 2022
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Likes: 106
From: New Dominion, PE
I ran more tests this morning. Checked out the EGR valve (working), EVP sensorV (working) and EVP solenoid - NOT working.... more **** poor quality parts...grrrr....
anyway...I let the truck warm up this time for a longer period...took it out for a 4 KM run...brought it back to the garage and checked the O2 sensor...and lo and behold
it is now switching from .4V - .7V back and forth....so it *IS* working.
now...this doesn't explain the poor mileage....
going to confirm the timing that the guy in Ottawa who I had do the initial work on it.
I marked the current position on the distributor base and the housing so I can return to it.
took spout connector out, fired up truck. if I went any further counterclockwise, truck would not throttle up cleanly.
so I worked it clockwise around 1/8". my timing light was not bright enough to see the markings on the crank pulley.
it is throttling up nicely now. there was a slight delay/lag before when I hit the throttle.
will do a mileage test in a day or so and report the results....thx for all the help/insight...I appreciate it very much!
anyway...I let the truck warm up this time for a longer period...took it out for a 4 KM run...brought it back to the garage and checked the O2 sensor...and lo and behold
it is now switching from .4V - .7V back and forth....so it *IS* working.
now...this doesn't explain the poor mileage....
going to confirm the timing that the guy in Ottawa who I had do the initial work on it.
I marked the current position on the distributor base and the housing so I can return to it.
took spout connector out, fired up truck. if I went any further counterclockwise, truck would not throttle up cleanly.
so I worked it clockwise around 1/8". my timing light was not bright enough to see the markings on the crank pulley.
it is throttling up nicely now. there was a slight delay/lag before when I hit the throttle.
will do a mileage test in a day or so and report the results....thx for all the help/insight...I appreciate it very much!
Last edited by mackendw; May 5, 2026 at 01:30 PM.
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More Turbo
Joined: Feb 2022
Posts: 657
Likes: 106
From: New Dominion, PE
Just re-ran the codes:
KOEO: clear (11)
KOER: 77 ( I'm obviously not doing the brake depress, turn left/right and flooring it at the right time in the test).
all other codes are resolved.
I'm noticing the exhaust whitening out now.
I'm wondering if my pushing air into the exhaust testing for the manifold leak loosened something up.
anyhew...I'll be doing a mileage test shortly and will post the results.
KOEO: clear (11)
KOER: 77 ( I'm obviously not doing the brake depress, turn left/right and flooring it at the right time in the test).
all other codes are resolved.
I'm noticing the exhaust whitening out now.
I'm wondering if my pushing air into the exhaust testing for the manifold leak loosened something up.
anyhew...I'll be doing a mileage test shortly and will post the results.
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