3 Way Cat Needed, but....

In reply to vazbmw :

Lean is relative.  Running a constant 15:1 is lean enough to not convert NOx.  Heck, running a constant 14.7:1 is lean enough to not convert NOx that well.  Even switching 14.5-15:1 is generally lean- that's .1 rich to .5 lean.  It should be symmetrical on either side of stoich (which is 14.6:1 for most commercial sensors, since they output the wrong thing and assume gasoline) for what the front sensor can see.

Basically, it is telling you that you are lean.  Also, you could easily have a leak that the O2 sensor isn't seeing, which really does a number on conversion.  Did you plug up the EGR passage really well?

In reply to alfadriver :

Thanks @alfadriver, this is great information! Yes, the EGR passage is welded completely shut on the intake side, and the manifold doesn't have EGR fittings (from a newer Volvo)

Ok, so my goal will be to increase fueling. 

What would be a good AFR for the lowest NOx without increasing HC or CO?

One more uninformed question:

If I splash in a percentage of E85, would that lower my combustion temps enough to clean up the NOx? Or would that make me so lean that I will have even more problems with NOx?

In reply to vazbmw :

If your car is actually running off the O2 sensors in the exhaust, as it should be, the Ethanol won't make any difference that will help.  You need to really figure out why it's not operating with proper control from the O2 sensor that should be controlling it.

It's not really about increasing the fueling- the system should do that on it's own if it's in control.  Once it's in control, it will properly balance the NOx, HC, and CO as it's supposed to do.

So find out what's not working right instead of just adding fuel.

In reply to alfadriver :

Great advice! Will do! I have had the intake off recently, so there may be a leak that I didn't notice. I will check for leaks...and if necessary I will put the intake back to stock. Stock air box and all.

Thank you again @alfadriver. I will let know ya'll know what I find, and the solutions I found.

Thanks everyone.

In reply to alfadriver :

Ok. So, here is the latest.

There is some type of intake leak, but I can't track it down exactly...since I was going back to stock intake, I didn't sweat it. I just put the stock intake back on.

So, I went back to the stock intake and that AFR is not 12.8-13.8 at idle.

It's at 13.8-14.5 cruising now (stock Intake) -- as opposed to 14.6-15.4ish with the custom intake

Do you think the change in AFR of 14.8 - 15.4ish at cruising up to an AFR of 12.8 is enough to reduce @4530ppm of NOx down to 800ppm?

Yes it will lower the NOx.  But it may raise the HC and CO too much.  Do you have any info on the O2 sensor that the computer is using?  Not the one you are reading, but the one the  computer is using.

In reply to alfadriver :

I don’t have any information on the EFI’s O2 sensor other than it’s a Bosch that’s about 2 years old. Are you meaning like a data sheet on the unit? (I can probably get that) Or actual data from the unit’s readings (I don’t have that)

In reply to vazbmw :

The reason I ask about it- it seems as if it's not working right.  You are either running a little rich or a little lean.  If the sensor is working, it should be switching around 14.6.  It's easily close enough to that point to deal with it- so it's odd that it's not.

In reply to alfadriver :

Looks like my reply didn’t make it...resending.

Some of the EFI functions can be captured on OBDII, but this is a pre-OBDII car with a OBDI diagnostic system and an OBDII port also...so not all OBDII data can be read via my OBDII. But, will see if I can read O2 sensors

i have some old spare O2 sensors, so I will swap to see what differences that makes 

alfadriver said:

In reply to vazbmw :

The reason I ask about it- it seems as if it's not working right.  You are either running a little rich or a little lean.  If the sensor is working, it should be switching around 14.6.  It's easily close enough to that point to deal with it- so it's odd that it's not.

I agree.  It seems like it's running in open loop for some reason.

Ok. So here is a video of the data stream from the EFI O2 sensor. Normally the O2 sensor’s voltage is swing back and forth right? Is 1 volt normal? I thought the voltage should be less than 1v, and would swing back and forth as it adjusted the fueling to stay at 14.6 during idle? O2 sensor video.

as I watch the video, I noticed my throttle position is at 9%, when it should be at zero. I will need to address that. That could be adding extra fuel as it idles 

In reply to vazbmw :

1 V is very not normal.  It should swing between about .2 to .8V.  Could be a little less than that, too- like .3 to .7.  Steady is not working.  For sure, a car of that vintage should be closed loop at idle- something is making the car ignore the sensor.

You bought this car already modded, correct?

Maybe a stupid question, but did the previous owner hide a O2 sensor emulator in the harness somewhere?  Sometimes a trick done to turn off a CEL on a modded car if that is all that's checked for emissions.  

In reply to Ian F :

All mods are mine. No emulator. No check engine light...although the PO removed the bulb HA! I can see if a code is thrown through diagnostic ports, both OBDI (Volvo under-good system) And OBDII (so strang e to have a car with both). I am going to see I can swap out some old O2 sensors to see if voltage changes

Something to note- if you change the sensor, and you still see over 1.0V on the signal, the problem is someplace in the circuit.  

No normal O2 sensor will output more than 1V when it's working properly.  Given the richness you are talking about- it should peak out at just over 0.8V.  It's also really odd to see a sensor output a pretty constant voltage.  One quick thing you can try- take the sensor out- it should be 0V.  If not, there's another circuit issue.

The good thing here is that we are narrowing down what the problem is without throwing a lot of parts at it.  :)

In reply to alfadriver :

Agreed on the narrowing.

I am going to test to see if there is still voltage with no sensor!

Great advice!

Update:

1. Change: I swapped the O2 sensor for an old one

Result: O2 sensor swinging to adjust more in line with a normal O2 sensor...but still a bit slow

2. I tracked down two tiny vacuum leaks. One in the vacuum tree on the throttle assembly. And, the over in the inter cooler  tube

Result: I fixed the vacuum tree because I had the part. Have not fixed the intercooler to throttle tube yet. But, car runs at 14.6 more frequently (it’s still not solidly consistent)

ODBII Video.

 It will still richen up too much — especially when first started (even when warm) but things are looking more normal. I also found a graph in my Bosch EFI book the correlates AFR To NOx, HC and CO

Unfortunately there are no hard numbers, but it gives an idea of the relationships like @alphadriver  and others were stating.

basically 14.4 - 14.6 is key to passing the Emissions test

Much better.  The swinging frequency will depend on the flow going to the engine- but figure 1 Hz +- 1/2 is good.  it will work fine that way.

Odd that the voltage drops to 0.00V every once in a while.  

It's also interesting that your new sensor was not good.  Is it a direct fit one?  3 wire or 4 wire?  It's almost as if one of the heater lines is bleeding into the return lines.  Or there's some bad wiring between it and the car.

In reply to alfadriver :

It's a 4 wire sensor. I didn't check if I could install the connector backward...but I doubt that I could

Maybe there was a short some where in the sensor's wiring? Or, like you say bad wiring in the car. I was moving a lot o things around. I could be that I moved a bad wire, and it was not the newish sensor that was the problem.

I guess more investigating is needed, because it is not consistent enough. Like that voltage drop to .000

In reply to vazbmw :

Given that the old sensor is giving you more logical numbers, it *seems* as if the issue is more in the sensor.  But check your wires none the less.

Track this all down, and you should pass just fine.

In reply to alfadriver :

happy dancing

Hi Everyone,

Wanted to update everyone on the results of this thread.

I was looking to get a new Cat in order to pass emissions, but was advised by the great folks on this thread to check into my AFRs  to make sure I was ok.

There were a few small problems that conglomerated into the overall problem:

1. Tiny vacuum leak at the vacuum tree = I fixed this leak

2. Aftermarket high flow Cat...that was 1/3 the size of the stock unit = I reinstalled that factory cat.

3.TPS sensor not in spec. Reading 10% at idle = Junkyard TPS. I still need a new one. Ordering this today

4. O2 sensor reading funny = New O2 sensor

5. Remove pod filter set up and reinstalled factor airbox

My emissions readings were:

25/25 Intial Test

• HC: 71, Allowed 117
• CO: .01, Allowed .65
• NOx: 4305, Allowed 821

25/25 NewTest

• HC: 15, Allowed 117
• CO: .01, Allowed .65
• NOx: 4, Allowed 821

50/15 Initial Test

• HC: 55, Allowed 120 
• CO: .01, Allowed .67
• NOx: 4276 Allowed 907

50/15 New Test

• HC: 12, Allowed 120 
• CO: .05, Allowed .67
• NOx: 1 Allowed 907

Thank you again everyone