Your engine may be producing excessive “blow by” which is gunking up the pcv valves. Check that before you spend another dollar on this car.
2 Likes
@ok4450 Thanks for your patience and catching it.
It is foolish to ignore VVTI!
I recently did the valve adjustment. I was also working on my car since my last post.
I ran it on freeway at 4k rpm (D3) and my downstream O2 was giving around 0.7v steady at cruising - will post photo later. This and temp difference of at least 198 making me to rule out CAT. So will be replacing the upstream O2 sensor soon.
There is no sign of oil burning - no smell, done 4k and did not top it up.
Is there anything I should look for?
4k rpm screenshot:
2k rpm to idle screenshot:
Is there any reason I should not eliminate the CAT? Thanks for any tips. I mentioned that I measured a temp diff of up to 198 degrees. So cat is working.
See the red graph line for the O2 sensor after the cat?
It should look like this.
The cat is bad.
Tester
1 Like
@Tester - thanks
https://www.gmforum.com/buick-172/downstream-o2-sensor-voltage-311039/
The scales might be misleading. If I change the scale on mine, the ripples might disappear - I am not sure yet.
Update:
If I squash my y-axis to that of yours, the ripples in mine will disappear!
The Bad one voltage goes from 0.45v to 0.9v - high fluctuation. Not ripples. Mine only has ripples - otherwise its steady.
@Tester - According to this, I do not think mine is bad:
https://www.smog-tech-training.com/Diagnoseabadcatalyst.html
Because the rear O2 is not switching from 0.2 to 0.8. It stays steady at 0.7v. I know for sure sensors are sensors - they will always have ripple.
The link says:
> There should be a 70% difference from the front 02 and the rear O2. If the front O2 sensor switches 100 times “which is more accurate.” the rear should O2 sensor should change less than 70% less.
Ripples are gone!
Does it meet the criteria of There should be a 70% difference from the front 02 and the rear O2. If the front O2 sensor switches 100 times “which is more accurate.” the rear should O2 sensor should change less than 70% less.
Source https://www.smog-tech-training.com/Diagnoseabadcatalyst.html
I think that you should do some tests to the oils to see if you have gasoline in it
Thank you - could u pls tell me what defects cause this?
Stop messing around with all the peripherals and do a compression test to see if this engine is worth all this angst.
2 Likes
Running rich.
Running rich can also be caused by low compression. As mentioned by oldtimer_11, you need to determine if this engine needs the Ole Yeller treatment…
Considering a new PCV goes to garbage in a week, I suspect Ole Yeller may be going for a walk…
3 Likes
A worn out engine. You’ve been told this a few times, but you are still looking for cheap, easy fixes. There are none.
3 Likes
am I the only one missing the compression readings?
Take it off and shake it. If it rattles, it is OK. If it doesn’t, pour some gasoline through it to clean out the oil and install it.
High compression will elevate the combustion temperature resulting in high oxides of nitrogen, however I don’t think that is the cause of the problem and a compression test is just going to delay the real repair.
PCV full of gunk, oil thin and smells like gasoline, engine has a misfire.
Why would you not do a compression test before spending any money on parts ?
2 Likes
We’ve asked that of the OP numerous times and he won’t answer.
3 Likes
Look at the exhaust gas report, there is no misfire, no indication of low compression.
There is nothing wrong with the PCV valve, the OP is over-examining it.
2 Likes