Open/closed loop sensor issues
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Teching In
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Open/closed loop sensor issues Ignoring all previous posts in regards to my continuing saga of getting my T/A to run, I’ve noticed something that has me seriously stumped.
Running a log while cold start idling (OL), all my sensors are reading good, to include my front O2s (700-800mV range). As soon as it warms up and goes CL, my O2s start reading REALLY low (40-80ish mV), and my crank and cam sensors start flickering readings (dropping from normal readings to zero and back) and super rough idle. When I rev the car, the tach dies and ecu throws p0336 code, but scanner is still showing my idle rpms (meaning ecu is still outputting rpm reading through OBDII port). When I erase DTC, tach starts working again, then will die shortly after, rinse and repeat.
My O2s are brand new Densos, and I’ve scoped both cam and crank sensors at the ecu connector and am getting good waveforms from both at idle and revving, even when tach is dead with DTC.
AIR, EGR and rear O2s are deleted, LT headers and I’ve tried 2 engine harnesses/2 different ECUs/4 different tunes. Has anyone ever run across an issue like this before? Many thanks for any/all help.
Running a log while cold start idling (OL), all my sensors are reading good, to include my front O2s (700-800mV range). As soon as it warms up and goes CL, my O2s start reading REALLY low (40-80ish mV), and my crank and cam sensors start flickering readings (dropping from normal readings to zero and back) and super rough idle. When I rev the car, the tach dies and ecu throws p0336 code, but scanner is still showing my idle rpms (meaning ecu is still outputting rpm reading through OBDII port). When I erase DTC, tach starts working again, then will die shortly after, rinse and repeat.
My O2s are brand new Densos, and I’ve scoped both cam and crank sensors at the ecu connector and am getting good waveforms from both at idle and revving, even when tach is dead with DTC.
AIR, EGR and rear O2s are deleted, LT headers and I’ve tried 2 engine harnesses/2 different ECUs/4 different tunes. Has anyone ever run across an issue like this before? Many thanks for any/all help.
Last edited by Thatguy8898; Oct 10, 2019 at 10:21 PM.
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From: Norn Iron
7-800mV would suggest quite rich.
In closed loop, if all is working well then the readings should be switching either side of stioch pretty fast. This will be easy to see on a scope trace or logging at say 50Hz or above.
I would doubt it can be in closed loop with a static reading of 40-80mV, and this would be extremely lean.
Get some proper mixture readings from a gas analyser...and you also do not indicate if this is one bank or both.
In closed loop, if all is working well then the readings should be switching either side of stioch pretty fast. This will be easy to see on a scope trace or logging at say 50Hz or above.
I would doubt it can be in closed loop with a static reading of 40-80mV, and this would be extremely lean.
Get some proper mixture readings from a gas analyser...and you also do not indicate if this is one bank or both.
Thread Starter
Teching In
Joined: Nov 2016
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It’s on both banks, but it did show closed loop while the sensors were reading that low. Wouldn’t surprise me if it’s just another level of problems in this car. I was doing some more troubleshooting today, and it was still doing the same thing with both O2 sensors unplugged keeping it open loop. Seems it’s not an open or closed loop issue, but something that acts up only when the engine is warm.
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From: Norn Iron
So it is lean if both are reporting the same, ideally you'd confirm this with a gas analyser...find out why its lean.
If CL is active, you'd then expect the trims to be trying to add fuel...so are they ?
Has it ever run correctly ? When did it last run correctly ? Has it ever been tuned correctly ?
If CL is active, you'd then expect the trims to be trying to add fuel...so are they ?
Has it ever run correctly ? When did it last run correctly ? Has it ever been tuned correctly ?
