Hello folks,

Is anybody here good at just looking at the smog numbers and figuring out what the problem is?
I have a stock 97 GSR with 154,xxx miles on it. New plugs 2 weeks ago. Just 2 days ago, I got a timing belt and valve adjust from the mechanic. (I assume the timing was set also.) Here are the numbers from 2 yrs ago, and today:



Basically the NOx went from zero to fail, and the HC got worse also.

My first worry is that the cat didn't get hot enough. The car was somewhat warmed up, but then was off for about 5 minutes while waiting in line. Is there a way to tell from these numbers? Or how can I tell if the cat is hot enough? I asked the smog technician if a cold cat was a problem, but he didn't really know. You would think that the smog test places would have figured out this problem by now.

Oh yeah, the car also burns about a qt of oil every 1-1.5k miles, but it has always done that, and never smokes. It also has dry soot on the rear bumper.

I tested the primary O2 sensor today and it seems to be ok as well. (Not sure)
https://honda-tech.com/forums/tech-misc-15/o2-sensor-testing-3094436/

 

Hi Beanbag,

I ran your numbers on the lambda calculator and you are in fuel control. 14.66 to 1 is great.

You say you tested your 02 sensor. Did you do it with a scope? It's the only real way to tell. I have had my 02 sensor stuck at .5v which on an average would be good.

Your cat is not using all the 02 which point's to the cat. Could be an exhaust leak but I don't think so. If your 02 sensor is not toggling fast enough (8-10 times a second)could also cause this.

All of the numbers are up at the 15mph test. There is only one thing that could cause this, the cat.

Car's that burn oil will make the cat less effective. The more oil, the more often you have to change out the cat. My rex has 242K on it.

The BAR has been b*tching about pre-warming up cats. This is causing alot more cars to fail. Also the BAR is grading us on what the car's do on the next smog check so we have to run the vehicles after idling for 3 minutes because that is the only way of getting an accurate test for the car's next time thru.

Just so you know...I change out both the cat and 02 every two years. $200 bucks isn't that bad for a pass every time.

If you have any questions give me a yell - thesmogman

 

When you changed your plugs how did the old ones look ? Were they white, black, or brown ?

 

Thanks for the info so far.
As pointed out in that other thread I linked, I did check the primary o2 with a scope, and it make one complete rich /lean cycle once every 3 seconds at idle, and 2-3 times per second at 2-3000 rpm. (i.e. 4-6 flips per second) Does that sound about right?

I recently heard that it is often the secondary o2 (after the cat) that tends to go out. Any thoughts on that? I didn't check it yet.

What is the difference between the 15 and 25 mph tests that helps in your diagnosis of the cat?

If the fuel control is so great, how come there is dry black soot on the rear bumper? If it was from the burning oil, wouldn't it be oily soot instead?

I also read about the 3 minute idle requirement to warm up the cat. Would it help for me to drive the car hard before the test, or does the cat cool down and heat up too fast for that to matter?

Finally, if you hypothetically were a Gold Shield station, what would you be doing as a diagnosis?

Thanks for the useful info.

 

2-5 times per sec at 2000 rpms is the standard. However that is only frequency. Can the O2 reach full rich (over 800mv) and full lean (below 175mv)? It must also have a rise time(transition from rich to lean or viceversa, not a full cycle) of no more than 100ms(miliseconds)
It does not affect fuel control on this model year Honda
Light off temp for the cat is around 600F. But optimal operating temp is 1000F to 1200F dergrees. At 25mph the load is greater and the cat will be hotter, allowing it to work better.
Your A/F ratio is much worse at WOT, or during "spirited" driving...
Really depends on how soon the test is done once you arrive.

Put up some generic OBD scanner data at idle, cruise, and WOT and I can get a better picture of your cars health. But right now, on the surface ,it looks like the cat is bad. Probably killed by your oil consumption issue.

 

Here's a picture of my plugs currently (about 2 weeks old). You can see that two look awesome and two look black.



It is a dry black soot. How can I tell if it is oil burning or excess fuel? Another weird thing is that in the mornings, the piston tops for these two cylinders look wet. When I dab this moisture and spread it on aluminum foil, it doesn't stink like gas, yet it also dries up and evaporates after a few hours. Almost like water...

Here is an O2 trace at idle.



The horizontal time scale is 8s total, so it's about 25ms per pixel. Does this count as a fast enough transition?

I don't have a real time obd scanner, sorry.

 

I hope that's not coolant. How does your car run ? You should do a compression test.

 

The morning wetness you speak of is consistent with a blown head gasket. Pressure test the cooling system(a pressure tester can be rented or borrowed at most autoparts stores,if you dont own one) and allow the pressure to bleed down 2 or 3 times. Then check the offending cylinders. (Another sign of a leaking HG is a vehicle that misfires in the morning or after sitting for several hours. The mis would likely only occur when the car is cold and would then clear up for the rest of the day...) BTW a leaking HG will kill a cat very quickly, as well as the O2's...

 

Car runs fine, no mis-starts even after a few days vacation, no smoke at startup.
Compression is 210-230 across the cylinders.
No coolant loss (or less than 2 cups in 2-3 years)
Coolant loss into a cylinder would have cleaned up the combustion chamber, right? These chambers still have a coating of black on the piston tops.

 

Hey bean,

I would swap your injectors and see if the soot on the plugs follows. Might have two crappy injectors. Replace your seals on the injectors too.

You can try and soak the tip's of the injectors in carb cleaner or seafoam for a hour or two.

BTW, it looks like two are lean and two are rich and on down the line the O2 sensor does not know what to do . "can not compute"

 

oh, good idea

 

I got the cat changed out and the car passes smog now.

I was also told by the mechanic that changed the cat that the o2 was on its way out too, so time to change that as well.

But if two injectors were rich and two were lean, would it still be possible to get a good AF ratio according the smog numbers?

 

Prob oil getting I to those cylinders. I doubt its a leaking I hector. If it is you'll noticed a bad idle and how often do u get two Injectors that's leaking. Really uncommon.