I have been battling a code 31 and 41 on the "off test OBD1" procedure and that indicates the O2 sensor is always low. I tied a volt meter to the output oi the sensor and I read after warmup bertween 0.7 to 0.9 VDC and it stays at that voltage until I decelerate, at which point it drops to 0.03 to 0.4 VDC. It nevers "sweeps" between low and high voltages (for that I mean below and above 0.5VDC which theoretically would be the stoichiometric optimal value).

Not being an expert on Ford injection systems, does the computer sweep the sensor with a voltage to read its value, just like the Bosch systems L-jetronic, Motronic and others do?

If I had a healty running engine, what should I read on the O2 sensor tap I made? a steady voltage or a sweeping voltage?

Thanks for any input!

P.S.: Oh yeah, car drives like heck, stumbles, jiggers and it is not the fuel pressure as I have a calibrated gauge on the rail and it is spot on.

Namarena

 

I'd also post this question in the appropriate engine forum for the CID and model year you're working with. Because its in a van body doesn't mean these symptoms are specific to that installation.


HTH

 

You said these codes where from the KOEO "off test OBD1".
The KOEO is just an electrical test and not a running performance test.
The CM codes might tell you a lot more if you have not disconnected the battery.

KOEO Service Code 31 indicates that the EGR Valve Position (EVP) sensor signal is less than the Self-Test minimum value of 0.2 volts. Maybe bad (an open) wiring or EVP sensor.

The 41 code is not a KOEO code and you can only get from the CM or KOER self tests.
If it was from the CM list it and I will guess it was it says you are running lean.

You might try checking the fuel pressure as an bad fuel pump or plugged fuel filter can cause this also along with the running problem. You fuel pressure may be normal while the van is not moving but low under load. You need to check it with a gauge while on a hill under WOT.

 

the sensor is capable of reading from 0 to 1v. stoich is right around 0.8v. if its working properly while driving, its readings should be bouncing up and down too fast for your poor voltmeter to keep up. if you have test equipment able to read fast enough, it should be jumping up and down pretty fast around 0.8v. a steady reading like you're getting means that either your test equipment is too slow to give you live data, or your sensor isn't working well. it should sweep up and down fairly fast, but primarily around 0.8v