by crypticlineage, March 19, 2007
dom: What is a wide band O2 monitor? Can you explain that a bit? Can I check anything with a multimeter?
By closed loop, do you mean when car has fully warmed up? If so, this happens in both closed and open loop. Acceleration beyond 65MPH would trigger the hesitation in both conditions.
A wideband O2 monitor is simply an oxygen sensor on exhaust before the cat, with a display to monitor engine's operating A/F ratio. Can your multimeter give you your primary O2 sensor reading?
I'm asking you if it hesitates only at part throttle, and not a full throttle (closed loop).
dom: Is it safe to get under the lifted car when the engine is running? If yes, I should be able to check output voltage on the front o2 sensor. On second thought, I might even be able to do that from the top. I will have to get some back-probes for my multimeter leads.
As for your question about full throttle or partial throttle, I dont know the answer to that, since my car has had P0420 for years now, which I think indicates open loop problem.
Bank 1 o2 sensor - changed 2 years ago
catalytic converter - changed 4 years ago
Bank 2 o2 sensor - changed 5 years ago
MAF sensor - changed last week
^^^ Backprobe the sensor at the connector end inside the car. Don't try it from underneath unless it is on a lift, even then, can be tough. Depends on what equipment you have available to backprobe the sensor - thin probes to check from the connector side, or vampire taps to pierce the insulation.
The P0420 just indicates that the rear O2 waveform looks too much like the upstream one, generally due to a bad cat. This would also apply if the signal was too or steady-state, like if the sensor was dead or dying. The downstream O2 sensor does factor into the long-term fuel trim of the car, but generally - almost all the O2 feedback information needed comes from the upstream sensor. Car would also default to a limp-home mode if the ECM detected something more insidious - like misfires or other engine sensor is faulty.
Fish: Where exactly does the O2 sensor cable enter the dash? Do I need to open the dash panel to get near ECU? Last week I wanted to test my new MAF sensor, but found that backprobing with multimeter leads was impossible on the connector. The blue rubber inserts between the cable and the connector are very tight. I wonder how to get the probes inside them. The vampire inserts you're talking about, are they literally piercing that rubber to get to the wire?
Correct, those taps use the same principle they used to use on the old coaxial cabling they used to use before switching to twisted pair cables for ethernet connectivity. Just pierces the exterior insulation to get at the conductor.
Probes will work on the connector - just have to use the special backprobe leads or might try using sewing needles + alligator clips. Probing at the ECM, I'd save as a last resort. If you accidentally short out something while trying to backprobe the ECM connector - you'll have a dead or dying ECM to deal with.
As for the where the cable runs to - I believe it runs across either across the floor toward the rocker panel, then up the kick panel area up and over to the dash. Or it might just run up the transaxle tunnel on the floor, then up into the dash.
