One would think. So yeah pretty far fetched.
O2 sensors are in spec for resistance per the FSM.
Oh joy, P0401 is back... (and how 80's fail emissions)
- Thread starter nakman
- Start date
O2 sensors are in spec for resistance per the FSM.
So I’ve been researching and thinking…and remembered when I pulled the cap off the modulator that I found a couple spots of carbon on the filter material. Would this mean that possibly the diaphragm is compromised and the modulator no longer working? With the cap off air blows pretty freely from port Q to the filter area but I’m not sure how I would be able to determine that it’s still doing that with the engine at 2500 rpm like the FSM says to do. Way too much noise at 2500 rpm.
EDIT: there is a diaphragm in the bottom of the modulator that isolates the exhaust gas from the filter. So the presence of soot on the filter I think might indicate a failed diaphragm.
EDIT: there is a diaphragm in the bottom of the modulator that isolates the exhaust gas from the filter. So the presence of soot on the filter I think might indicate a failed diaphragm.
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JohnnyP
Rising Sun Member
@subzali If you had a massive leak you would have codes and running problems. I’m going to go with your cats are clogged. I think in another post you’ve said that you’ve been burning oil, 1 qt/ 5000 miles, that’ll do it. Not building boost because it can’t exhale and let the turbine wind up the compressor. We’ve had this on a few of our own turbo installs. We disconnect our downpipe from the rest of the exhaust and find the lost boost every time.
If you don’t have any codes and all emissions monitors are in the “ready” state then borrow someone’s 35” tires and go test at a station that can’t run 35’s. They’ll pass you on the diagnostic plug in showing everything ready.
Doesn’t fix the issue but gets you time to figure it out before the next round.
If you don’t have any codes and all emissions monitors are in the “ready” state then borrow someone’s 35” tires and go test at a station that can’t run 35’s. They’ll pass you on the diagnostic plug in showing everything ready.
Doesn’t fix the issue but gets you time to figure it out before the next round.
I have read that 1qt/1000 miles is acceptable, so 1 qt/5000 miles seemed ok in my mind. I'll look into that some more.
JohnnyP
Rising Sun Member
1 qt/ 1000 miles is definitely not a healthy motor and would be in need of a rebuild. If you're sticking to 5000 mile oil change intervals that's replacing 62.5% of your oil before the oil change and even 1 qt per 5000 is 12.5% consumption which also isn't great. 1FZ in good shape should have zero consumption. 100K on a rebuilt 1FZ in my 80 and there is no visual change in level on the dipstick between 6-8K mile intervals. Healthy 80's don't burn oil and once a cat is compromised by oil it wont take long for it to not work properly. @MonPetiteShoe just recently did his valve stem seals at 260K and now doesn't burn a drop between changes and he passed emissions no problem.
The best way to check O2 sensors is with a scan tool that can graph o2 voltage vs time. There are a bazillion videos explaining this, so I won’t bother here. Essentially you’re looking at peak voltages, and responsiveness.So with my recent emissions failure I checked some things out today. The EGR modulator is not behaving per the FSM. But if it has failed wouldn’t that throw a P0401?
View attachment 140249
Step 6 here.
Also step 2 here
1. Replaced spark plugs, cap and rotor.
2. Adjusted timing. It was slightly retarded, maybe 2.5 deg instead of 3. I almost left it but wanted that notch dead on the 3.
3. Checked the EGR modulator per above. Still head scratching that one. Might buy a new one just to try and have on hand.
4. Washed the air filter. I think I’m done with the washable air filter. I think it’s cool and all but I think I will just buy new regular ones when needed.
5. Checked the EGR valve. Works like a champ.
6. Checked the temperatures of the cats. Outlet is about 150 degrees higher than the inlet, so that seems good.
7. Put some Lucas fuel injector cleaner in and ran up 285 to Bailey and back.
8. Checked spark plugs wire resistance. Well within spec.
I dunno
After checking them….
O2 sensor wiring can have a huge effect on O2 sensor, get some de-ox it and hose out the connections by the sensors (do this if you are replacing as well).
80’s rarely hit the parameters necessary to get the EGR working during the test, and it has a bit to do with how the person drives the truck on the dyno.
Lastly, cat efficiency can be sort of calculated by comparing upstream lambda to downstream lambda on your scan tool. Again there are a bazillion videos on the internet. But essentially you are looking for a significant decrease in voltage from upstream to downstream.
I don’t have much experience with forced induction on 80’s and emissions, but looking at the usual suspects is probably a good idea, TPS adjustment, MAF voltages (perhaps a cleaning if it looks wierd) I don’t know what fuel trims look like on an 80 with a turbo, but normally I’d look at STFT and LTFT numbers to gauge if something is wierd.
If everything checks out I usually default to a cat or 2.
You can test back pressure pretty easy using one of these, if I was still over there I’d let you bum my test rig. Usually anything above 3psi at average driving rpm indicates an issue in an NA truck. The best way to do this is to put one for and aft of the cats and look at delta P it should be negligible in a perfect world, and if they both read hi, it can indicate a clog further downstream.
And, double check this is the right one.
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I was going to add that sharing the graph of the failures can help. The graphs aren’t incredibly helpful unless there is a really out of normal graph. If the mean numbers are being driven up by giant spikes, it can be helpful to diagnose different things.
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I just re-loaded my test reports to my two previous posts, with graphs. Thanks Jackson!
I did notice that the high NOx spikes seemed to follow a period of acceleration. That's about all I could get out of the graphs and not sure exactly what that would mean?
There is no real smoking gun in my opinion, but some things maybe worth investigating further.
Sec 0092 is either idle in gear or coming off idle to accelerate. So thus is not necessarily a solid diagnostic indicator but…. A TPS of 14% at idle is high, this should be in the 8% range. A mis-adjustment is possible especially since STFT is neg 3%. So I'd double check that it’s set properly.
Generally when you see NOx, CO, and CH all spiking “abnormally” together It can be a sign of weak cat efficiency. If you look at your b1s2 sensor voltage matching your s1 voltage it could also indicate a cat efficiency issue. However, you’d really want to graph both of them side by side. The fact that it’s actually fluctuating is a good sign both for the sensor and the cat.
If all you had to go off of was that result and no other diagnostic equipment, I’d double check TPS, put premium in it, maybe pull some timing (this may cause your HC to go up boo hiss), drive it to the furthest away station from you and retest in hopes that the cats are a bit hotter and more efficient.
After that I’d replace a cat and see if it got better haha.
@jps8460 , is this what I need to check? Its not in % so not sure how to convert to your languageThere is no real smoking gun in my opinion, but some things maybe worth investigating further.
Sec 0092 is either idle in gear or coming off idle to accelerate. So thus is not necessarily a solid diagnostic indicator but…. A TPS of 14% at idle is high, this should be in the 8% range. A mis-adjustment is possible especially since STFT is neg 3%. So I'd double check that it’s set properly.
Generally when you see NOx, CO, and CH all spiking “abnormally” together It can be a sign of weak cat efficiency. If you look at your b1s2 sensor voltage matching your s1 voltage it could also indicate a cat efficiency issue. However, you’d really want to graph both of them side by side. The fact that it’s actually fluctuating is a good sign both for the sensor and the cat.
If all you had to go off of was that result and no other diagnostic equipment, I’d double check TPS, put premium in it, maybe pull some timing (this may cause your HC to go up boo hiss), drive it to the furthest away station from you and retest in hopes that the cats are a bit hotter and more efficient.
After that I’d replace a cat and see if it got better haha.
Yea, you’d need a scan tool to see %. But if you use that method it will net you the same results.
Edit: Actually setting it is a different section, but it should be close to that. That is checking to see if the sensor is bad
Yep it’s the same. EG-158 in mine
Well I hooked up a different vac/pressure test gauge and my turbo is making boost just fine. Around 5-6 psi like it should. So I think it’s just my in cab boost gauge that’s malfunctioning.
I did find that the vacuum hose to my fuel pressure regulator had a small hole in it. As much as I wish that were a contributor I don’t think it is because that is where my in cab gauge is hooked up and I’m seeing 18 in Hg vacuum consistently at idle. And it didn’t change when I pushed the hose on a little further to get the hole over the pipe part so it wouldn’t leak.
at idle, throttle position is 12.2%. FSM says 7-11%. I will adjust as soon as I can.There is no real smoking gun in my opinion, but some things maybe worth investigating further.
Sec 0092 is either idle in gear or coming off idle to accelerate. So thus is not necessarily a solid diagnostic indicator but…. A TPS of 14% at idle is high, this should be in the 8% range. A mis-adjustment is possible especially since STFT is neg 3%. So I'd double check that it’s set properly.
Generally when you see NOx, CO, and CH all spiking “abnormally” together It can be a sign of weak cat efficiency. If you look at your b1s2 sensor voltage matching your s1 voltage it could also indicate a cat efficiency issue. However, you’d really want to graph both of them side by side. The fact that it’s actually fluctuating is a good sign both for the sensor and the cat.
If all you had to go off of was that result and no other diagnostic equipment, I’d double check TPS, put premium in it, maybe pull some timing (this may cause your HC to go up boo hiss), drive it to the furthest away station from you and retest in hopes that the cats are a bit hotter and more efficient.
After that I’d replace a cat and see if it got better haha.
STFT goes from -0.8% to -2.3% in cycles. Not sure how that is or is not impacting.
O2 bank 1 sensor 1 fluctuates between .04 and .75V. So seems ok?
Are you able to graph the o2 voltages? This voltages are a good indication, but it’s helpful to see them oscillate. At idle B1S1 should be oscillating at around .5-1Hz
Yeah it is oscillating at about that frequency. I will see if I can get a graph of it tomorrow.
Cool. O2 sensors are probably doing their job then.
After you adjust the tps sensor, take it for a spin up to op temp and see if your STFT gets less negative on average.