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

[subzali]

For @jps8460 with love

Let me know what you think. Lol.

30 seconds of O2 voltages at idle.

Fuel trims for a few minutes coming home from the store. The flat spot in the middle is where my logger lost connection for a minute.

The full O2 sensor run on the way home. The shot above was that period of idling from :34 to 1:09.

TPS we already know is above spec at idle.

 

[subzali]

I am still confused why I can't get vacuum above the EGR valve, but am not throwing a code.

Would excessive exhaust pressure on the hose on the bottom of the EGR modulator cause a loss of vacuum at the top of the EGR valve?

 

[subzali]

Were you able to replace the EGR modulator before the test?

I bought a mityvac today. I’ve now tested both original modulators (green 96 and white 97) and they pass all the tests including holding a vacuum on the diaphragm. I don’t see any problems with either of the originals so didn’t really need to spend the $100 odd that I did for a new one. Oh well now I have a spare like @RayRay27. I think something else is preventing me from seeing vacuum on top of the EGR valve and I’m thinking @JohnnyP is right and it’s a plugged cat. My green 80 burns more oil than the white 80 though and has never had a problem yet with not passing emissions so it’s hard for me to believe that just some oil usage is causing a 2-year lifespan on these cats.

 

[jps8460]

I am still confused why I can't get vacuum above the EGR valve, but am not throwing a code.

Would excessive exhaust pressure on the hose on the bottom of the EGR modulator cause a loss of vacuum at the top of the EGR valve?

That looks like it’s probably a cat efficiency issue, but not enough to trigger a p0420. I would expect the downstream o2 voltages to look more stunted than that under light acceleration like that.. You can see at idle that the cat is working, but even there I’d expect it to look flatter.

Perhaps someone with known passing obd2 truck would be willing to hook up and show you what theirs looks like.

No idea on the EGR, but you should be able to run a test cycle, or 12v+ the pin in the harness to trigger the vsv. I would think that if you had an exhaust over pressure on the diaphragm it would be melty and weird, but not sure.

 

[MonPetiteShoe]

I would be willing to offer my NA OBD2 truck as a benchmark. You guys are doing nerd stuff. I'm in.

I can also confirm that exhaust over pressure makes the diaphragm melty and weird, then throws codes.

For a little context, my valve stem guide bushings were wallowed out and dumping a lot of oil into the combustion chamber. I was getting a lot of oil downstream into the cats/exhaust/EGR. I was burning a quart of oil every 500-800 miles depending on my driving style. At the time my truck had ~260k miles on it. I opted to get the head rebuilt. Gunn swapped the bushings and valve stem seals. Once the new head was installed, new exhaust/Cats, VSV it passed emissions. My last inspection was OCT 2023 at 288,017

HC: 0.0943 (1.000)
CO: 2.1020 (15.000)
CO2: 747.4944 (N/A)
NOx: 0.5528 (2.500)

I'm not saying it's the fix, but I do have a suspicion that the valve stem guide bushings start to walk out of tolerance around 220k-250k on the 1FZ. My evidence is purely rhetorical at this point. Take that with a grain of salt.

 

[J1000]

For @jps8460 with love

Let me know what you think. Lol.

30 seconds of O2 voltages at idle.

Fuel trims for a few minutes coming home from the store. The flat spot in the middle is where my logger lost connection for a minute.

The full O2 sensor run on the way home. The shot above was that period of idling from :34 to 1:09.

TPS we already know is above spec at idle.

Your upstream O2 sensor voltage is swinging widely from .1v to .8v, it should be much tighter around .5v. This means your air fuel ratio is swinging from lean to rich both in idle and cruise. .8v is approximately 13:1 and .1v is approximately 16:1. Rich will cause high HC and lean will cause high NOx. Misfires cause high CO and lean mixture can cause misfires. When cruising at steady state the O2 voltage should be bang on .5v, +/- .1v, approxmiately 14.7:1.

How are your fuel injectors? Have you had them cleaned? Also what is the condition of your fuel pressure regulator? I would expect there is something going on with fuel delivery. Inconsistent fuel delivery causes the ECU to make big changes to target .5v, but unable to hold it steady. You can tell from your emissions graphs the HC and NOx are spiking up and down which is consistent with the AFR swinging up and down.

I would also recommend disconnecting the wastegate when doing emissions testing so the turbo doesn't try to make boost, that will help keep things consistent as well.

 

[subzali]

Your O2 sensor voltage is swinging widely from .1v to .8v, it should be much tighter around .5v. This means your air fuel ratio is swinging from lean to rich both in idle and cruise. .8v is approximately 13:1 and .1v is approximately 16:1. Rich will cause high HC and lean will cause high NOx. Misfires cause high CO and lean mixture can cause misfires. When cruising at steady state the O2 voltage should be bang on .5v, +/- .1v, approxmiately 14.7:1.

How are your fuel injectors? Have you had them cleaned? Also what is the condition of your fuel pressure regulator? I would expect there is something going on with fuel delivery. Inconsistent fuel delivery causes the ECU to make big changes to target .5v, but unable to hold it steady. You can tell from your emissions graphs the HC and NOx are spiking up and down which is consistent with the AFR swinging up and down.

I would also recommend disconnecting the wastegate when doing emissions testing so the turbo doesn't try to make boost, that will help keep things consistent as well.

Are you talking about the upstream or downstream O2? The upstream is supposed to swing from 0.1V to 0.8V, correct?

 

[J1000]

Are you talking about the upstream or downstream O2? The upstream is supposed to swing from 0.1V to 0.8V, correct?

I'm talking upstream. It should oscillate around .5v, 14.7:1.

 

[jps8460]

I'm talking upstream. It should oscillate around .5v, 14.7:1.

That should be the average perhaps, but upstream should oscillate at approximately 1Hz from approximately .1-.9.

Downstream o2 will be much less active and depending on application and PID will hover tightly arounds a given value, typically.4ish on a healthy system under normal driving conditions with exception to hard acceleration and quick lifts on accelerator. It depends on a number of factors.

 

[subzali]

I adjusted my TPS to 8.2% at idle. I just loosened the two screws and turned it a little bit and watched the data stream on my OBD2 app. Prior to that I checked the TPS per the FSM and everything was within range, except I couldn't get the feeler gauges in as specified. But the result should be the same absolute % number I'm looking for here. Here's some new graphs.

MPH vs. TPS


MPH vs. Fuel Trim. STFT got down to -10% which is...concerning? Normal? I don't know.


O2 sensor readings for the run I did


Close-in on O2 voltages at the very tail end when I got back and idled in the driveway

 

[subzali]

A couple other thoughts. I’m sorry to clog up this thread but perhaps it’s all related?

In the past before I replaced the old cats I had high exhaust pressure and clogged cats to the point that the hose on the bottom of the modulator popped off. Which blew soot all over the bottom of the modulator and could then melt the modulator. But that is not what’s happening now.

On today’s drive where I charted those graphs above, I had a vacuum gauge hooked up to the top of the EGR valve and I finally did see some vacuum on the gauge. Only like 1-2 inches, so not much at all. I will have to test with the mityvac (finding out this thing is handy) and see if that’s enough to actuate the EGR valve.

I also found tonight that my catalyst monitor is not ready. So that’s something else.

 

[jps8460]

The STFT and LTFT moved as expected with a large tps adjustment. It will take a little bit of time for them to normalize. 3-4 drive cycles from cold to operating temp. The big swing could be causing a catalysts monitor to not be ready.

Or the monitor not ready could be due to cat inefficiencies. The b1s2 reading is still looking pretty bad. I’m still thinking that you have a cat or 2 that needs some love.

 

[60wag]

Is the cat mounting hardware in good enough shape to easily pull the cats to see if they are plugged up?

 

[subzali]

The STFT and LTFT moved as expected with a large tps adjustment. It will take a little bit of time for them to normalize. 3-4 drive cycles from cold to operating temp. The big swing could be causing a catalysts monitor to not be ready.

Or the monitor not ready could be due to cat inefficiencies. The b1s2 reading is still looking pretty bad. I’m still thinking that you have a cat or 2 that needs some love.

I figured the vehicle is trying to figure out what to do with the new TPS setting…

…and new cat is on the way. I’ll try one and see what happens, if not enough then I’ll do the second one. Head was redone 100,000 miles ago by Robbie, not sure if injectors were done at the same time. It sounds like oil consumption may need to be addressed if I expect to have long cat life. But that’s probably going to involve a bottom end rebuild as well as another head rebuild for valve stem seals, I’m betting.

I am set up with two catch cans, which I’m sure is helping, but maybe not enough.

I will still check the FPR after it warms up outside a little and I receive some parts I ordered.

 

[subzali]

Is the cat mounting hardware in good enough shape to easily pull the cats to see if they are plugged up?

It’s an all welded 3” mandrel bent system, so can’t get to it without cutting.

 

[jps8460]

I figured the vehicle is trying to figure out what to do with the new TPS setting…

…and new cat is on the way. I’ll try one and see what happens, if not enough then I’ll do the second one. Head was redone 100,000 miles ago by Robbie, not sure if injectors were done at the same time. It sounds like oil consumption may need to be addressed if I expect to have long cat life. But that’s probably going to involve a bottom end rebuild as well as another head rebuild for valve stem seals, I’m betting.

I am set up with two catch cans, which I’m sure is helping, but maybe not enough.

I will still check the FPR after it warms up outside a little and I receive some parts I ordered.

It’s tough to say what it will need. 1qt per 5000 miles is not enough to concern me and I wouldn’t be so quick to start tallying up major work. The bar just got moved for emissions on your truck as well.

Aftermarket cats are notoriously short lived when compared to OE cats. I’m sure that forced induction compounds that.

I’d poke at your EGR a bit more, you seem to have found something amiss. Who knows what that could be affecting.

Get that sorted out, probably do an exhaust pressure test (cheap, but not fun to do). Verify something isn’t plugged up. Again probably not plugged, usually you’d see something super strange going on with fuel trims (and boost, and power, and overheating) But worth a check.

Then take it for a couple nice drives, then take it for a long drive to the emissions place and try again haha.

Then replace a cat.

 

[Lastresort576]

How’s timing, worth taking a look at. Could hitting boost on the dyno be causing the ECU to adjust too much timing causing you to fail?

 

[subzali]

How’s timing, worth taking a look at. Could hitting boost on the dyno be causing the ECU to adjust too much timing causing you to fail?

I adjusted timing to be dead on. Have never had a problem with boost on the dyno in over 20 years so not inclined to think it’s a problem now. But anything is possible I suppose.

 

[Lastresort576]

I adjusted timing to be dead on. Have never had a problem with boost on the dyno in over 20 years so not inclined to think it’s a problem now. But anything is possible I suppose.

I only bring it up cuz it was one of the things I checked when I went through testing hell. Took 6x to pass.

 

[MonPetiteShoe]

Head was redone 100,000 miles ago by Robbie, not sure if injectors were done at the same time. It sounds like oil consumption may need to be addressed if I expect to have long cat life. But that’s probably going to involve a bottom end rebuild as well as another head rebuild for valve stem seals, I’m betting.

I am set up with two catch cans, which I’m sure is helping, but maybe not enough.

I will still check the FPR after it warms up outside a little and I receive some parts I ordered.

I can't remember the numbers you mentioned about oil consumption. If it was a quart every 5000 miles, I'd say that's well within the norm.

If Robbie rebuilt the head 100k ago, I am less inclined to recommend the valve guidebushing/seals.

I had assumed some issues with the bottom end as well. When we pulled the head, even after 260k miles, it looked pretty good. Cylinder crosshatching was all intact. There was no scoring, and piston rings were doing their thing. I was impressed at the lack of wear. Not all engines wear the same, but I don't believe it's your issue either. I also don't believe the addition of abnormal aspiration would have increased piston ring wear.
I think Jackson talked me off the edge for a bottom end rebuild. 1FZ blocks are stout.