Oh joy, P0401 is back... (and how 80's fail emissions)

[subzali]

I’ve been driving around with a vacuum gauge on the top of the EGR for a couple days. It seems max EGR is during cruising at light loads, like slightly down hill. I’ve seen down to 9 inches vacuum in that scenario. If you let off the throttle just a touch more to fully close the throttle, EGR VSV cuts it off and vacuum goes to 0. EGR VSV also doesn’t allow EGR when accelerating. 0 vacuum until you’ve reached cruising speed and start letting off the throttle. That’s when EGR pumps a little bit, as little as an inch or two and then maxing out per above. So if you’re on the gas and then off the gas back and forth you won’t see EGR.

Interesting as I would have thought EGR would engage during acceleration when the engine is making heat, thus in my mind high NOx. But the fueling system must manage it to be rich enough during acceleration to not have high NOx. It aligns with the graph; don’t see NOx spikes until after a period of acceleration when the throttle is let up.

 

[DaveInDenver]

@subzali you might this interesting.

 

[subzali]

@subzali you might this interesting.

Thanks Dave! Curious where that is from. I’ve been looking for a more thorough system description document.

And as I suspected EGR should be high at high engine load but that is not what I’m seeing from the vacuum gauge test I’ve been running.

I have some more tests to run, as something still seems off to me related to the vacuum signals from ports E and R.

 

[DaveInDenver]

Thanks Dave! Curious where that is from. I’ve been looking for a more thorough system description document.

I'm not 100% sure where it came from. I came across it at some point and squirreled it away. I've got more from that same training document, which I attached.

 

[subzali]

More findings:
1. VSV is functioning as it should. Tested it by applying 12V to its connector, hearing the solenoid click, and trying to pull vacuum on its hose.
2. It takes about 3" of vacuum to begin to actuate the EGR. EGR valve works great.
3. Port E is upstream of the throttle butterfly but pulls pretty good vacuum when its port is exposed from the throttle opening.
4. Port R is also upstream of the throttle butterfly but it does not pull good vacuum at all. Maybe a couple of inches. Tried removing and cleaning the throttle body, squirted carb cleaner through the passages, passages are clear, pulled vacuum on the hose, holds vacuum, so all should be as good as it can be. According to Dave's document it should be close to manifold vacuum when uncovered but it does not.

5. I also still cannot get this step to function as the FSM says. I don't know what else to try. It behaves the same way with either my old or new modulator, and with the exhaust hose on the modulator connected and disconnected. Really low, almost no, vacuum and no engine stumbling.


And here Dave's document expounds on what this test is trying to demonstrate:



I'm down to:
1. Replace air filter
2. Replace cat(s)
3. Replace O2 sensors.

 

[subzali]

New development. Have had some stumbling while sitting at stoplights and tonight threw a P0130 and P0133. I’ve been messing with the O2 sensor connector but it’s connected so it should be good? I wonder if I should go ahead and replace the O2 sensors though too just to be sure?

 

[subzali]

Let's get this thread back on track with passing inspection reports.
Before:

After 2 new cats like you all said. My last resort was going to be O2 sensors, which I may still do just because I don't know when they were last done and I never really figured out why my old cats went bad after only 13,000 miles. Now temp goes from about 400 to about 550 through the first cat.

 

[Lastresort576]

Hey congrats!! That’s awesome to hear.

 

[DaveInDenver]

After 2 new cats like you all said. My last resort was going to be O2 sensors, which I may still do just because I don't know when they were last done and I never really figured out why my old cats went bad after only 13,000 miles. Now temp goes from about 400 to about 550 through the first cat.

It does seem logical that if the O2 sensors are drifting but not failed, thus working but with error, that you could have been asking the converters to do more work they were happy doing.

The ECU doesn't know if a sensor is giving it an error per se, it knows when it's giving no data at all (like P0135 and P0136 in OBD-2) or if the data is so bad that it can't get into closed loop (e.g. CEL comes on). If the O2 is returning a value that seems to make sense, dithering around 500mV you can't know for sure it's not contaminated and that is calibrated 14.7 AFR. It's just *not* stuck high or low.

O2 sensors are at least cheaper than new converters, so seems like it can't hurt to answer an unknown.

 

[subzali]

It does seem logical that if the O2 sensors are drifting but not failed, thus working but with error, that you could have been asking the converters to do more work they were happy doing.

The ECU doesn't know if a sensor is giving it an error per se, it knows when it's giving no data at all (like P0135 and P0136 in OBD-2) or if the data is so bad that it can't get into closed loop (e.g. CEL comes on). If the O2 is returning a value that seems to make sense, dithering around 500mV you can't know for sure it's not contaminated and that is calibrated 14.7 AFR. It's just *not* stuck high or low.

O2 sensors are at least cheaper than new converters, so seems like it can't hurt to answer an unknown.

With my wide band now working again for the past few days, I have been watching as I've done some limited driving. AFRs are around 14.8-15.0 when cruising; maybe slightly above 15.0 at idle. So I'm not sure the O2 sensors are really a problem, but if I do some graphing of the O2 sensor voltages before/after replacement, it would be maybe an interesting data point for this thread.

 

[jps8460]

With my wide band now working again for the past few days, I have been watching as I've done some limited driving. AFRs are around 14.8-15.0 when cruising; maybe slightly above 15.0 at idle. So I'm not sure the O2 sensors are really a problem, but if I do some graphing of the O2 sensor voltages before/after replacement, it would be maybe an interesting data point for this thread.

Totally agree!!

 

[subzali]

More graphs for before (failing emissions)/after (passing emissions) comparison:

MPH vs. TPS before:

MPH vs. TPS after: I find it interesting that during my WOT 0-60 run my TPS only got to 73%. Am I leaving something on the table?

MPH vs. Fuel Trim before:

MPH vs. Fuel Trim after: The FSM says that the combined STFT and LTFT should be <30%, so everything looks good.

O2 sensor readings before:

O2 sensor readings after. A few notes:
-From 5:44 to 5:56 I got a 12 second 0-60 run in (going by the vehicle speed sensor)
-I'm a little concerned that the sensor 2 voltages (orange) are spiking high, given that both cats are brand new. Seems that having two efficiently working cats should cause that second O2 voltage to remain low. I get it on the 0-60 run but on the other normal accelerations the fuel management is at stoich and the cats should be taking care of the rest.