Oxygen sensor and/or ECU causing issues?

[wepeel]

This first started when I noticed some bucking while driving a few days ago. Then the van (1983.5 water cooled 1.9L) began having trouble starting. It would crank, but not fully start. Everything seemed to be ok with my rudimentary visual check of the engine. After some reading here I unplugged and plugged the ECU, which has gotten the van to start the last couple times. After one of these fixes, the temperature and gas gauge stopped working. My gas mileage has also dipped by about 4-5 mpg, further leading me to believe this may be an oxygen sensor issue.

I don’t have a record of the van’s last oxygen sensor replacement, but I’ve had the van for a year with ~25k miles and the PO kept pretty good maintenance records so I’m guessing it’s due. I’m planning on replacing it once I’m back home in a couple days. I’m also due for a fuel filter replacement which I’ll have taken care of then too. What could explain the gauge failure?

[tencentlife]

Gauge failures may be due to wanky connection at the 14-pin instrument cluster connector, very common, but since both went out it's also probably the voltage regulator chip that feeds them regulated 10V has failed. There's simple tests for that in Bentley.

You haven't given enough info to make any guesses about your mileage or the oxygen sensor.
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[wepeel]

I’m hoping it’s just a wonky connection, as it happened right after I plugged t. ECU back in. But I’ve unplugged and plugged it back in a couple times to no avail. Maybe just some more wiggling is necessary? I’ve got a Bentley and will check out the voltage regulator chip as you mentioned.

The van’s about to roll over to 207k miles. I’ve put about 25k on it in the past year.

[tencentlife]

I wanted to add that the O2 sensor has nothing to do with the engine starting or not, it isn't monitored at all until the coolant reached operating temp.

Automotive ECU's are very robust, but aged electronics can develop cold joints and sometimes hairline cracks in PCB's that can be affected by physical stresses like strain on the connector. The easiest way to test that is to try a different one.

Make sure the ignition switch is off any time you disconnect or reconnect the ECU.
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Please don't PM here, I will not reply.

Experience is death to doctrine.

[wepeel]

Thanks for the heads up - I’ve been doing that so far.

I thought I had read that some symptoms of possibly oxygen sensor failure were stuttering, starting issues, and decreased gas mileage?

[DanHoug]

you likely have multiple issues going on.. a gauge power issue, starting issue, drivability issues. so. you need a systematic approach for resolution.

- start with cleaning engine grounds. this is a baseline that MUST be met before any other troubleshooting is done. this alone COULD resolve your starting issues as well as drivability. consider crimping on new ring terminals on each ground as many times the wire is corroded in the crimp of terminal. buy the best quality ones you can, say from NAPA, and make sure the copper wire has the blackness removed from the strands before crimping a new connector on.

there are MANY grounds on these buggers and you must hit them all. battery negative post and short cable in the battery box, transmission to body strap, braided cable on drivers side of engine, ground stud with multiple wires under coil, ground stud on engine by distributor. consider ADDING an additional ground cable, 2 ga minimum, to a bolt holding the starter on.

do this and report back. from knowing your grounds are good, further troubleshooting can be done, if needed at all.
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'87 Westy & '89 Westy both 2.1 4spd

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[wepeel]

For what it’s worth, the oxygen sensor light came on today.

[blackglasspirate]

The O2 light is just a reminder based on mileage. It doesn't have anything to do with the health of the sensor itself. There's a little box under the front that the speedo cable attaches to and it just counts the miles. You can reset it by pressing the little button with a pen or something.

As said previously, the O2 has nothing to do with starting the engine and the ECU doesn't start using the signal from it until a few minutes after running. However, if you want to be sure, you can just unplug it. The ECU will run in a default (rich) setting and you can remove that from the equation.
Just don't forget to plug it back in eventually or you may foul up plugs and such by running rich, not to mention bad mileage.
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