S: Car bogs, chokes when driving (rich exhaust)


May 06

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S: Car bogs, sometimes chokes when driving, runs rich.  SAFC cannot seem to subtract enough fuel, CONZULT shows rich mixture always below 0.5v (RICH) for front o2 sensor (OBD1).

** IF YOU HAVE A TURBOED CAR, CHECK THIS POST ALSO REGARDING CAR BOGGING UNDER ACCELERATION.

Replacing front oxygen sensor seems to help temporarily but quickly after it starts causing issues again.  O2  sensor voltage never goes above 0.5v when throttled & released, o2 sensor value seems to stick and not update on conzult.

*** NOTE: ON OBD1 CARS, front oxygen sensor (usually single wire) tends to be responsible for helping ECU control AFR (Air-Fuel Ratios) and operation.  The rear o2 (lambda) pre-cat sensor is usually just used for on-board diagnostics and emissions testing, etc. but doesn’t affect the running of the motor. ***

C: Problem may be electrical: O2 sensor wire possible not having continuity near the firewall.  This is especially easy to spot if o2 sensor seems to stick in value on CONZULT instead of providing feedback.  With heat from exhaust and o2 sensor wiring loose, often the wire isolation can become grounded or connector loose – look for loose broken section from exhaust manifold / downpipe to along firewall

Solution:

Once you find a potentially problematic section – start the car – don’t burn yourself but move wire around and see if you can get reliable voltage feedback from the sensor.  If you find it, turn off motor, replace the bad section of wire along with heat wrap.  Test it.  Afterwards your o2 sensor voltage should fluctuate between 0 and 1 volts (at least past 0.7v) on warm car if you give heavy throttle and let off.

***
Recently I found that when unplugged, the ecu generates steady 0.30-0.31 volts internally on the ecu pin #46 (front o2 sensor) if unplugged / wire cut off near ecu (was testing wideband->narrowband simulation). While unplugged, this causes car to run super rich obviously.


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