ridiqls

1 of those plots are from the 15-min drive, I think the other one was a start up after cleaning the EGR. I'll turn up the frames/sec if its an option in scan9495

ridiqls

Injuneer, I have a question about long term fuel trims. If you're running lean say in my case, the PCM will account for this and bump up the LT fuel trim in bank 1 is around 7-10%.

So once the computer makes this correction, the combustion chamber should not be running lean at all correct? Since it is compensated for.

There is a lean condition but due to the computer correcting for it, the end result is not a lean combustion correct?

Am I wrong in assuming that the NOX levels cannot be from a lean condition given that the PCM will take care of any lean condition with the LTFT?

The tail pipe sniffer is reading a perfect AFR of 14.7


I read your scanner guide and it says the engine cannot run rich (or lean) because the computer will compensate for this condition. Unless it's a false reading from the O2 sensor in which it would correct something that is not there.

But in case, the tail pipe sniffer is showing perfect O2, CO, CO2, HC levels and healthy levels of AFR. I would assume if NOX levels were high due to a lean condition creating higher combustion temps, then those numbers particularly AFR would be totally off?



If this is the case, then chasing down this lean condition wouldn't fix the NOX problems would it because it's already accounted for by the computer?

Injuneer

ridiqls

EDIT: Going to update once I figure something out. But EGR system only came on once during the smog test


Another potential issue:
I got a new cat and it still made no difference in NOX. I thought maybe I was given a 2-way cat (doesn't filter nox) or maybe it was defective so using my Infrared temp gun, I started to monitor the temps. And so did the smog tech. And what I found is that is this:

The temps on the exhaust pipe pre-cat (closer to the engine side) run about 475 Degrees F. That seems excessively hot. All the youtube videos and other resources on diagnosing a bad cat shows that this temp should be around 250-350?

The temps on the exhaust pipe post-cat are around 475 degrees F.

The smog tech suggested that potentially my cat is defective, given that if the cat was working it would be much hotter POST CAT.

I went home after a really long drive to heat everything up and used my temp guns once more.

My y-pipe goes from the stock 2.25" diameter to a 3" pipe. Then it connects to a 2.5" inlet Catalytic Converter, goes out a 2.5" outlet Catalytic converter, then a 3" catback exhaust.

Apparently the previous owner had some weird step up before it connects to the cat and now this area is essentially causing some sort of turbulence (not sure the right terminology) before it goes through the cat because the heat at this 3" pipe is 475 degrees. When it enters the 2.5" inlet, it drops to about 350.

I'm either going to replace this cat with the Magnflow which is a 3" inlet/oulet OR have the muffler shop make the piping all the same diameter or at least not cause a restriction going into the cat as it seems to be heating up pre-cat a lot.

My entire cabin was roasting and I can feel heat in my floor boards and trans tunnel after that 1 hour long.


I ran the heat on full and am going to check my coolant levels just in case it's not full too.



So, that about covers what I discovered. Address the exhaust/cat piping and see what I can do about the EGR. Maybe if the cat system is optimized the EGR doesn't matter.




Lastly, I put 1/2 bottle of Redline fuel cleaner and filled up on 91 octane and towards the end of my data log I noticed LTFT between bank 1 and bank 2 get a little closer but I could be mistaken. i dont know how long it takes for the PCM to make adjustments like that.

ridiqls

I'll sum up the EGR smog problem. It's actually a very stupid problem.

The CA smog test requires you to drive to 15mph and hold steady for a while. Then climb to 25mph and hold steady. The key here is to HOLD STEADY at these 2 speeds.

The PCM for the LT1 is programmed to come on ONLY when accelerating. I have a full hour long data log of this but basically you cannot engage the EGR solenoid at a standstill, it doesn't come on usually on deceleration... the EGR duty cycle primarily happens when you are accelerating around 1300-1900 RPM.

So they are inherently opposite of one another.

Of course my Nox levels aren't controlled because during the entire smog test, my EGR duty cycle came on only ONCE and it was a second or two.

Injuneer

ridiqls

Looking up the cat, it's the right EO number for the car. But the previous owner had a 3" pipe step down which is my guess as to why it might be causing some issues? I dont know about that. I have to go to another muffler shop. As for aftermarket cats, there's only 2 available here in CA for this car.. the walker with 2.5" inlet/outlet and the magnflow which is 3" inlet/outlet and slightly more expensive and slightly longer. I have to get an expert opinion on this.. not sure what's going on with the temps pre-cat.

So I understand correctly, the PCM should activate the EGR solenoid when at lower RPM, running for several seconds with no changes in RPM, MAP, or throttle position? And then once there is a change in MAP readings from the EGR valve opening, it understands to close it off?

This pattern is not what I'm seeing in my car actually. I am seeing the EGR duty cycle come on ONLY when the car is accelerating. I figured this is normal.


This is a small snippet of an 1 hour datalog of pretty good driving. The EGR as you can see in purple, is commanded by the PCM when there is RPMs between 1300-2000, RPM rising AND speed rising. The car must be accelerating. The EGR does not open when trying to emulate this with the car at a standstill, nor does the EGR Duty Cycle turn on when the RPM is steady such as in the smog test.


Here is the datalog during a smog emulation:

The EGR is commanded to open only ONCE by the PCM and that is when accelerating from the 15mph steadiness test to 25mph. Only during acceleration.


I'm not quick to say that this is CA emissions or Chevy error, it could be my PCM possibly a fault with a sensor but in the past couple days I thought I remembered reading that the EGR should come on when accelerating. Maybe I'm wrong.

I'm not sure what to think about this but in my limited knowledge, I'm not sure how the PCM would send a signal to the EGR solenoid when accelerating including taking into consideration RPM and Speed unless it was intentional? Anything you can shed light on here?

I'm using 91 octane but I'm unsure of the ethanol content.


The tricky part is, something is going on with my catalytic system the exhaust temperatures are too high pre-cat. I know the cat can affect nox big time. The EGR is messed up, also implicated in EGR. So not really sure which direction to go.

It's really hard to diagnose when you have to get on a dyno and do a full sniffer test just to see if the 1 or 2 changes you done made any difference.


EDIT: I went to the scan9495 thread and downloaded someone else's CSV file to check it against mine for EGR. Mine looks to be operating the same. The only difference is the EGR duty cycle does come on longer at steady RPM on high way speeds but at stop and go, it really just shows up upon acceleration.

Injuneer

I seriously doubt that the minor flow disturbance due to the 3"-->2.5" reduction is causing any problems. The structure of the cat ensures uniform flow distribution through the catalyst. What happens after the cat has little effect on flow distribution or system back-pressure. If the piping is 3" on either side of the cat, he should have used a 3" cat.

You lost me on this one. You measured 475-degF on the pre-cat 3" pipe, but after the reduction (pre-cat) to 2.5", the temperature dropped to 350-degF. Then you indicate "it seems to be heating up pre-cat a lot". If the temp is dropping, what is heating up? Or are you saying something (turbulence?) is elevating the exhaust pre-cat to 475-degF?

The exhaust had to be at least 600-degF at the O2 sensors, or they will not operate correctly. It is typically well above 600-degF. I'm not sure why you think your pre-cat temperature is too high. I have a thermocouple in the #7 cylinder header primary, and record exhaust temp as an indication of A/F ratio. 1,000+ deg F is not unreasonable under moderate load. Yes, that is a true exhaust gas temp and it's going to be lower temp on the surface of the exhaust piping, But 475-degF pre-cat doesn't seem too high.

Measuring the surface temp of the metal with an infra-red temp gun does not mean that is the temp of the exhaust gas. There is a temperature profile from the inner surface of the pipe to the outer surface. The thicker the metal, the larger the difference between the inner and outer surfaces. The infra-red method is also affected by the emissivity (affected by reflectivity, surface finish, material of construction). of the surface being measured.

You misunderstood my paragraph in post #55. The first sentence explained when EGR is used to control NOx. The rest of the paragraph explains how the PCM runs the diagnostic to detect if there is adequate flow of exhaust gas into the manifold. That is not how the EGR system normally works to control NOx. That is the mechanism used to determine if DTC 32 should set. EGR is activated to control NOx when the PCM determines the engine is operating at conditions that promote the formation of NOx.... and "lugging the engine" (attempting heavy acceleration) at low RPM is one of those conditions.

The PCM knows when you are trying to accelerate because it sees the throttle position increasing, and it sees MAP increase which indicates the engine is under load. There may be other things that trigger the use of EGR, but without access to GM's technology, the only one I know about is the one I have described.

ridiqls

Thank you for the clarification.


Regarding the exhaust, I am feeling a lot of heat in the floorboards which is why I thought it might be abnormal. Other cars tested no more than 300 deg F pre-cat so I was under the impression this was running hot. My cabin gets really toasty if I drive the car for a while

The y-pipe precat measured around 550 today. When it gets to the 3" pipe precat, it drops down to 420. It's quite interesting how the temperature changes drastically from the 3" pipe over to the 2.25" stock pipe. Post cat temps were same as the ypipe at around 550.

I think a picture would explain it better so I might get one later. But I tested for exhaust blockage and didn't find any.



Update: Car passed smog today. Nox was reduced to less than 600 at both speeds.

My front oil leak is getting worse so I will have to address that sooner than I thought but I'm glad that it passed and is registered.

Next up, fixing the passenger window which goes up about 1/2" every few mins (already bought a new window motor). Re-aligning and fixing the messed up windows. Fixing the front speakers. Re-installing all of my interior and then getting the AC fixed.

I thought my heat vents were not working but they are so it was an unexpected surprise.

DrewHMS97SS

ridiqls

The hot floorboards.. I'm not sure if it's normal though. It's not overly hot like I can't touch it but it is toasty like there is heat coming off of it. I owned a 350z that had the same problem.. right around the transmission tunnel and pedals after about an hour of hard driving would get toasty and make my feet sweat. But according to Injuneer, temps above 600 isn't abnormal.. mine tested at about 450-550 pre-cat so we'll see. Maybe it is just the way these cars are with the engine so far back behind.





Final Update on Smog:
Regarding emissions... here is my opinion on the matter. I don't want to get political but I'm only going off of facts and things I can back up with datalogging and paperwork.

I believe that a lot of older cars (OBD1 due to non-standardized nature of it) are going to fail emissions PERIOD (at least in CA) even if they are in original working condition because the manufacturer's emissions design could not foresee the current 2018 standards of emissions. Emissions has been ever changing and getting more strict, it's quite impossible for GM to have designed something that holds up to tail pipe outputs to today's standards especially in CA.

It's not a matter that is clear as PASS or FAIL.

Look at what the NOX maximum threshold was back in 1999 for this car:


1900 and 1700! This car would have passed with flying colors and levels of 1/2 of the maximum allowed limit back when the car was new and only a few years old.

Now the limit is 500-700. Emissions standards has not (and probably could not) take into consideration every single make and model's emissions systems, the way the EGR opens, when the computer tells it to open, etc. so there are cars on the road that INHERENTLY will never pass smog here, even in working condition equivalent to the factory. The emissions has to be BETTER.

Look at HC.. they are much stricter now with I believe the upper limit being 54? Catalytic converters have become worse, smaller, ****tier with aftermarket companies taking the place of OEM and yet the emissions standards are stricter.

I believe that when they set emissions laws, it's almost impossible to account for all the potential cars out there for the past 20-30 years.


Now it makes sense why CA has so many emissions related assistance:
- If your car does not pass smog, you can trade it in for $1500 assuming you can drive it on its own power to a certified dismantler.
- If you spent more than $x on emissions repairs, you can apply for a waiver or financial assistance for a certain amount to fix the problem.

They're trying to get polluting cars off the road. And old cars will just pollute more by today's standards.


Based on the data of when my EGR solenoid is commanded to come on by the COMPUTER, and comparing it with someone else's datalog. I'm currently of the opinion that a lot of OBD1 LT1s (cant say for sure if all) here will have a very hard time passing smog here. We don't see many of these cars around at all, they are usually beat to ****, sold as rollers, or the car fanatics buy them and deal with emissions in other ways that aren't standard. I see a lot of these cars being sold because they can't pass smog even though the sellers won't admit it and the previous owner of my car had mentioned that was one of the reasons why he sold it and why the owner before him sold it. They had to continually trace down "smog" technicians and it was a pain in the *** to do and quite expensive.

I can't say about other states but with the current nox limits, this car could have spent all day at the mechanics and they would not have been able to get it to pass. Talking with the smog technicians and them telling me start throwing parts at it such as a new solenoid, new MAF sensor(?), being told I need a new cat after I just bought a new one.. it was a result of people grasping at straws. Even I was double guessing myself until I took a datalog. The nox limits, I know are individual for cars... so I cannot say for sure with 100% certainty if ALL lt1 camaros will have this problem.

But I know limits are getting stricter.


The EGR system in my car is fine. It works. It works as intended by chevy. It just doesn't jive with the 15mph steady drive, 25mph steady drive test at the limits set today.

I got the car to pass and it wasn't due to me paying a "smog" guy. But I did have to change something out of necessity. I won't say more than this but those of you that already monitor this thread, if you PM me I can let you know.


What I'm talking about above only applies to OBD1. It's the nature of the beast, OBD1 was not standardized so a lot of older cars will not be able to keep up. It's not necessarily CA emissions laws fault. OBD2 is standardized and here, they pass you if there are no DTCs and you pass a quick visual. So OBD1 cars are going to be a pain to deal with in the future.






Anyway, other issues..
Went to pull a vaccum on the AC today. This is what I like to see:

Vacuum pump turned off. Holds vacuum for 30 mins +


Before I did the engine rebuild, the vacuum would disappear within 5-10 mins. I changed all the o-rings and replaced the accumulator, so it looks like it fixed whatever leak existed!

Time to fill up with Freon... getting AC fixed is going a lot smoother than I expected. I was expecting to have to pull parts and diagnose a leak. With the vents working, pretty damn good news.


Also fixed the loose window... i thought something was broken but nope.. just adjusted the little window furry things and now, now more shaking window.

DrewHMS97SS

Even ODB2 can be a pain in CA. My Dad had my 1997 RS for awhile, and got a random notice that his smog needed to be done at a state run facility. They failed it because it didn't have stock exhaust, even though it was still running 2 CATs. California has the right intention with cutting down on pollution, but a BS way of going about it. In retort to your statements about how many models and how much data, they have enough of that information to fail a car based on visual inspection, and some awfully detailed notes on stock parts. That said, they could also have NOX numbers from when the vehicles were new.

ridiqls

Yeah I really do not like the way they are going about handling the emissions here. I get it, if you look at pictures of Los Angeles back in the 70s the smog was insanely ridiculous. The amount of people here in the cities, its imperative to keep it down but some things can be handled better.

Regarding the visuals... I'm not entirely convinced they know a whole lot. The only thing they check on the visual for the older cars in my experience was the egr valve and that it exists, and the fuel cap. It doesn't say on the paperwork so I dont know if they check the # of cats. I think they are supposed to check the cat and if it's aftermarket, they should cross reference the EO # with the right cars. But I don't see a lot of smog techs doing that but I could be wrong.

I think the tricky one is the EGR control from the computer. There's really no way to do this and I wouldn't have known that the PCM doesn't even tell the EGR solenoid to open unless the car is accelerating (usually)... without a data log. I think the fact is, things were not standardized back then so GM's protocol for EGR operation is probably going to be a lot different than Toyota in this time period. Whereas OBDII, might be more similar to one another. But it's mostly educated guesses at this point, I can't say anything for certain.

ridiqls

Does anyone happen to know what this clip is for? Fell when I removed the passenger door panel. Can't see where it came from

DrewHMS97SS

It depends on the show, were you at a state run shop?