5.7L running too lean (very high NOx), won't pass state emissions

**uncabob** · 03-09-2017

Hi bigmac:
Just curious about your O2 sensor: Is it a heated sensor? Is it located in or near the manifold or collector? Do you have headers or cast iron manifold?
What size exhaust pipes and are they dual going into a Y or crossover? One cat or two?
Bob

ps Didn't look at your .xdl.

**bigmac** · 03-09-2017

O2 is single wire (non-heated). It is located in the rear of the passenger side ceramic header (just above the collector area). Driver side exhaust connector pipe runs under oil pan to a y-collector on passenger side. A single 3" diameter exhaust pipe runs from the y-connector to a new cat then to a muffler then over the rear Dana60 axle terminating under the bumper.

Lee

**uncabob** · 03-09-2017

May not be getting hot enough? If nothing else is obvious you may want to go to a heated sensor.

Bob

**bigmac** · 03-09-2017

Thanks Bob. I will look into converting to a heated O2 sensor.
Lee

**Fast355** · 03-09-2017

If the 02 sensor was cooling off the engine would run rich, not lean. I would check your base timing and make sure it is set for TDC or 0*BTDC. Also check the base fuel pressure the engine is running at. These engines like to be in the 12-13 psi range even with a stock engine. Maybe as much as 14 psi with a higher flowing intake/exhaust setup. Finally check your injectors to make sure that you have the 61 lb/hr injectors, not the 46s or 55s from a 4.3 or 350. I would also suggest that dropping the coolant temp will help prevent the formation of NOx emissions. A 180*F thermostat will drop the numbers some as well.

**bigmac** · 03-09-2017

Fast355, I will check the timing and fuel pressure. However, I have a question about the injectors. Since this is a throttle body with two injectors, how do I tell what size they are? If I remove them, will there be a number somewhere on them? I have attached two photos, one shows Rochester Products 155Z64 and the other a number 312. As you can see from the pictures, both are on the throttle body. I don't know if the injectors have separate part numbers.
Lee

**Fast355** · 03-09-2017

Originally Posted by bigmac

Fast355, I will check the timing and fuel pressure. However, I have a question about the injectors. Since this is a throttle body with two injectors, how do I tell what size they are? If I remove them, will there be a number somewhere on them? I have attached two photos, one shows Rochester Products 155Z64 and the other a number 312. As you can see from the pictures, both are on the throttle body. I don't know if the injectors have separate part numbers.
Lee

If they are GM injectors the factory part number will be eteched into the top of them. Should be able to read the numbers without removing them.

I know my old TBI in my 1983 G20 van passed with a fraction of the allowable limits. It was also not stock at the time. Had an edelbrock intake, 454 TBI unit, open center TBI spacer, 1.6:1 roller rockers, and doug thorley tri-Y headers feeding a large high flow 3" converter.

This was the last smog test it ever had to go through.

**lionelhutz** · 03-14-2017

I can't follow what you are doing with the piston stop by your description and tape. The stop doesn't stop the engine at TDC so touching the stop and making a mark means nothing by itself.

You put the stop in and rotate the engine clockwise until it touches and make a mark. Then, rotate the engine counterclockwise until it touches and make another mark. TDC is in between these 2 marks.

The computer does not compensate for the timing. 2* advanced means the timing is always 2* advanced compared to the programmed timing curves.

Originally Posted by Fast355

If the 02 sensor was cooling off the engine would run rich, not lean.

When I learned the 1-wire O2 doesn't work in the collector of long tube headers, the engine went badly lean at idle. It would start working correctly again once the rpm's were brought up to the 1500+ rpm range.

The engine also tended to run a little lean at cruise in the 1500-2000rpm range, but that was a lack of adjusting the loop for the headers since it still occurred with a heated O2 sensor. At cruise I could hear the engine pitch slightly change every time the O2 sensor voltage went low. Some integer delay and O2 switching point adjustments were required to fix it.

**bigmac** · 03-14-2017

The procedure you described is exactly what I did. The two silver marks in my picture were the piston stop points. The line I labeled TDC is the halfway point. The other wider black line is the one on the damper. I just guessed that the difference between those two lines is about 2 degrees. Sorry, I didn't make this clearer in my previous description. You make a good points regarding the O2 sensor and the INT adjustments. After I install the new ECM with the ASDU chip later this week, I will retest and see where things stand. If still running lean, then my next plan is to switch the single wire O2 to a 3-wire heated to perhaps compensate for the headers like you stated. If it still is running too lean, then I will probably have to make adjustments to the tables. I will need help doing that but will post the latest log file you to look at first after the above changes. Thanks for the suggestions, I really appreciate them.

Lee

**Fast355** · 03-14-2017

Originally Posted by lionelhutz

I can't follow what you are doing with the piston stop by your description and tape. The stop doesn't stop the engine at TDC so touching the stop and making a mark means nothing by itself.

You put the stop in and rotate the engine clockwise until it touches and make a mark. Then, rotate the engine counterclockwise until it touches and make another mark. TDC is in between these 2 marks.

The computer does not compensate for the timing. 2* advanced means the timing is always 2* advanced compared to the programmed timing curves.

When I learned the 1-wire O2 doesn't work in the collector of long tube headers, the engine went badly lean at idle. It would start working correctly again once the rpm's were brought up to the 1500+ rpm range.

The engine also tended to run a little lean at cruise in the 1500-2000rpm range, but that was a lack of adjusting the loop for the headers since it still occurred with a heated O2 sensor. At cruise I could hear the engine pitch slightly change every time the O2 sensor voltage went low. Some integer delay and O2 switching point adjustments were required to fix it.

2* advanced is 2* advanced over whatever has been programmed into the chip. The chip itself probably has additional advance over stock.

My experience was exactly the opposite with an unheated o2 sensor in a long tube. The o2 voltage would fall when the sensor cooled off, driving the Integrator and BLM up to their limits. It would run so rich it would actually blow black/grey smoke until the revs came up and the 02 sensor started working.