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Thanks. That's what the mechanic did too (archive)
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Posted by Kevin on July 10, 2001 at 08:54:36:

In Reply to: Re: Vytas - do you drop the exhaust... posted by vytas on July 09, 2001 at 10:00:04:


Kevin,
I usually lower the exaust system some 10" to get a decent access. Put front on the ramps, support exhaust in the middle with the jack, undo two rubber rings at the intermediate muffler, unscrew 12 copper screws at the headers, 4 screws at the transmission support, disconnect O2 plugs, pull and lower the whole assembly with the jack. I've done that maybe 10 times, takes about 1 h. Just my $0.02
Vytas


pipes/cats when you replace your sensors. The last mechanic I saw perform the operation dropped the pipes from the end of the headers... seems to me that with the right tools you should be able to do the operation without that added trouble...
curious.


Kevin


Wayne,

I really appreciate your latest post. From waht I recall it all now makes sense: The car was running lean until I sealed intake manifolds. Soon after that O2 sensor codes flashed. They could become damaged and slowed down. Now they are slow and unable to correct the mixture in real time. The other day I've checked O2 sensor on my other car (Audi) and it was way faster. In conclusion I am ordering new sensors today. It really helps to have expert advice.
Thanks,
Vytas

Vytas, I meant to get back to you on this sooner but life has not been too cooperative.

I have read more on the Bosch O2 sensor operation and have confirmation on what I had suspected. You recall in your earlier posts (see link), that one of the sensors operated 0.2-0.8V (rather slow) and one 0.4-0.6V (very slow). From what I have read in the Bosch material about the dynamic response of the sensor, well let me simply quote "An oxygen sensor exposed to excessively high temperatures for an extended period of time may start to react more slowly to changes in the air-fuel mixture. This leads to extended phase durations (periodicity) in the two-state control pattern." It shows some examples of phase durations with normal being in the 3 second range and two 'aged' sensors with phase durations of 8 and 11 seconds. This bears a strong resemblance to your situation.

Assuming this is correct, the sensor has been operating at too high of a temperature for some time...too lean, yet you indicate a high fuel consumption. You also indicated having replaced them twice already. Maybe the failed sensor is just one of the symptoms rather than the cause. Just thinking here but,
a) the bad sensor bank may have an air leak,
b) maybe the heat from the CAT running too rich toasts the sensor.

'88 750iL

...O2 sensors were replaced twice with no effect. O2 heating circuits OK as tested between fuse28 and ground (2.8 Ohm with both connected, 4.2 with one). O2 voltage
0.2-0.8V (rather slow)on one and 0.4-0.6 (v.slow) on the other...





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