~~~> Please Help NOx Problem

Silence820

I really need some advice.

I have a 2005 chevy tracker. It came from the factory with a 2.0 suzuki engine. It has failed emission 3 times for NOx.

6 months ago, had the top of motor rebuilt. Coolant is good, fan is running, car does not over heat.

1 time fail, changed the Cat Converter. I don’t remember the data for NOx

2 time fail, changed the EGR Valve. NOx 1000+

(when I picked the car up the check engine light was on for the 1st time, then the mechanic cleared the code that caused the light. He said it was because of the change of the EGR valve.)

3 time fail, don’t know what else to do. NOx 800+

If you what to pm me --- [email protected]

Any advice you can give will be appreciated.

thecardoc3

Did you confirm that you had EGR gas flow when you replaced the valve? It's common to find the passages plugged up inside the intake manifold with carbon deposits.

Exactly what catalytic convertor did you install? You didn't specify where you are at so I don't know if California emissions is part of the picture or not.

Do you have the full print out of the tailpipe gasses? If so please post all of it, I'll need to do a lambda calculation to see if this is in fuel control or not.

Silence820

With New CAT Converter
Idle Engine under load
HC ppm 7 7
CO% 0.02 0.01
CO2% 15.2 15.1
CO + CO2% 15.22 15.11
O2% 0.0 0.0
NOx ppm 422 1021
Lambda 1.00 1.00

With New CAT and EGR
Idle Engine under load
HC ppm 3 1
CO% 0.03 0.01
CO2% 15.1 15.1
CO + CO2% 15.13 15.11
O2% 0.0 0.0
NOx ppm 829 365
Lambda 1.00 1.00

Mr_Shiftright

How many miles on this engine?

thecardoc3

You didn't specifiy, but is this a manual transmission?

First here is a Lambda calculator which basically agrees with the analyzer's calculation. http://www.smogstats.com/lambda_cat.aspx

What I can see is that it is lean, at least leaner than it should be. The catalyst is working at an efficency of 92.28%
In order to reduce NOx, the catalyst needs CO. The richer the A/F ratio is, the more CO that is produced.
You only have .01% which means you are running out of CO and therefore the catalyst can't do anything more than it already is with the NOx.

Now the problem is, this failure might be just be a transient where the ASM 2515(?) test simply tests the car at the wrong time. If the system would get to run at a different speed it likely richens up to a lambda of .990 which is only a tenth of a percent richer but that both reduces how much NOx is generated in the engine and it improves the efficiency of the catalyst to clean it up. Reports show the engines running clean in second gear at 24mph but to make the test happy it has to be shifted to 3rd and that's when the NOx spikes.

To see if I am right have the test run in manual mode and see what is being produced. If you have failing results, then your concentration should be on EGR flow and we are back to making sure that there are no carbon deposits restricting flow and from there look at injector flow rates. If it is clean at other speeds and simply spikes when you go to third gear for 25mph then you need to head off to the referee station.

Silence820

Thank you very much for the information you have provided.

To answer a question, it is a standard transmission with 92,000 miles

I was told that the problem could be a bad MAF sensor. So, I tested it by unplugging the sensor while the car was running and it idled a little better and it did not stall.

Based off of that I ordered a sensor, it will be here on the 12th. Do you think a bad MAF could cause the car to run lean?

thecardoc3

Silence820 said:

Thank you very much for the information you have provided.

To answer a question, it is a standard transmission with 92,000 miles

That means it follows the pattern that I uncovered. The automatics don't have this issue.

Silence820 said:

I was told that the problem could be a bad MAF sensor. So, I tested it by unplugging the sensor while the car was running and it idled a little better and it did not stall.

That is not an accurate test.

Silence820 said:

Based off of that I ordered a sensor, it will be here on the 12th. Do you think a bad MAF could cause the car to run lean?

Can a MAF sensor make the car run lean? Yes it can. But is that what is happening here? No it's not.
If you had a MAF sensor issue you would have a bigger problem than NOx emissions with the engine control system close to lambda (stoichiometric). What kind of corrections do you see in combined short and long term fuel trim at idle, 2500rpm no load, and 1800-2000 rpm driving?

Did you get someone to run a manual test on this and see what happens at other speeds?

Silence820

@thecardoc3
no i have not. could you explain to me exactly what i need to do?

Silence820

@thecardoc3
i made a typo error with an earlier post, it is not a standard transmission, it is an automatic.