So I got hold of a 4 gas analyzer and am putting it to good use here.


For a car with cats, what do you guys think of these numbers?

O2 sensor on the analyzer is curently malfunctioning (I think I need a new sensor), but for a car with cats, what would your opinion be of these numbers.

900 rpm, in park:

HC => 10 ppm
CO% => .03
CO2% => 15.4


700 rpm in drive:

HC => 20 ppm
CO% => .05
CO2% => 15.2


This is way WAY better than when the misfire was there. But it still has a little roughness that I KNOW I can get rid of. I suppose I need to get the O2 operating again to see the whole story. But what do you guys think of these numbers? I also want to tap in ahead of the cats and put the probe there to get unfiltered numbers. But what do you guys think of these numbers?

 

Not bad.
But, it's all so relative.
NOX is also a real good combustion indicator.

Having the numbers stay so stable for light load to no load, looks good, IMO.

 

Those numbers look decent. As a comparison here are the numbers from a '92. This is a 15 or 20 MPH tread mill test. At 1741 RPM:

CO% 0.04 (upper limit .71%)
HC 20 ppm (upper limit of 41 ppm)
NO 56 ppm (upper limit of 312 ppm)
Dilution 15.4% (is this CO2??)

RBob.

 

Grumpy, I also managed to finally defeat the Miniram split BLMs by making an "external" IAC passage (very similar in construction to an under-manifold NOS cheater setup). The IAC motor only supplies a very small fraction of the incoming air. The throttle blades are almost completely closed, allowing for 90% of IAC air to come in through my external IAC setup. With that, all of my exhaust tube temps (using an infared temperature gauge) are within ~150° of each other (raging from ~400° to ~550°) and my BLM's are 128 driver side and 126 passenger side.

With this data, you'd think this thing would be idling like glass (considering my cam has only 212° intake duration at @.050 on a 112 LSA). But it's rougher than one would expect. Maybe I just need to play with the O2 centering voltage and my ignition timing a little more.

I guess I need that O2 working on the gas analyzer to tell me if I'm rich or lean. The CO I know can tell that too, but the O2 will complete the picture.
----------
Rbob, that last number looks like CO2 IMO. Looks like I'm in the ball park.

 

Was wondering, what spark plugs are you using?

RBob.

 

I forget the part number, but they're Delco's and are the ones that come on a factory L98 Corvette.

 

I am so glad i don't have to do the smog test on mine oh how i like canada for the 20 years and older no test thing hehehehe

 

It depends on what part of Canada. The Lower Mainland of BC has had emission testing for 16 years and I believe the Greater Toronto Area is also subject ot emission testing. But, with all the out-cry for greener emissions and the Liberals committment to Kyoto - don't be too surprised if not only emission testing becomes a reality for the entire country but you may also find certain cars are no longer eligible for purchase in Canada.

 

OK, the '89 - '91 Corvettte plugs are the correct ones (3/4" reach, flat gasket seat).

RBob.

 

Just curious do you have pics of your IAC setup also what was the origirinal miss problem? I am running about 24-30 counts at idle after opening up my TB IAC bleed hole. I ended up using about .16 as the hole size which is probably a bit smaller than most due to the size of my motor. So far that appears to be pretty good.

 

This is what my 1983 G20 Van looks like with the HT383 cammed 350 TBI in it at the time. This is loaded on the dyno smog machine at 15 and 25 mph. The RPM is not shown, but it is at 1,200-1,300 rpm. The standards are for the original carbed HO 305.

Low Speed (15 MPH)

Pollutant-------Reading------Standard
HC(PPM)--------50------------332
CO(%)----------0.10----------1.89
CO2(%)---------14.5
O2(%)----------0.00
NOX(PPM)-------72-----------2490
Dilution---------14.6---------->6
High Speed (25 MPH)

Pollutant-------Reading------Standard
HC(PPM)--------42------------326
CO(%)----------2.62----------0.03
CO2(%)---------14.5
O2(%)----------0.00
NOX(PPM)-------47-----------2320
Dilution----------14.5-------->6%




RBob- Dilution is a reading that the smog machine takes to ensure that the machine is actually getting a sample and not just sitting on the ground.

 

I'll have to shoot a few photos...

But basically, roughly 90% of the IAC air does not even come through the throttle body anymore. I have a metered orifice on an intake tube that feeds the NOS cheater-style IAC manifold that's mounted and concealed under the Miniram. The orifice size was determined by trial and error in order to get the idle speed where I want it and very few IAC steps (when the car is at full operating temperature). The throttle blades can remain almost entirely closed.

It's in somewhat of a "prototype" phase right now and I hope to refine it a little later. But for now it's getting the job done.


The original miss problem was an incorrect grounding where I had the main engine ground routed to the serpentine bracket. While showing a good DC resistance to the battery, I speculated that at voltage vs frequency, the inductance of the connection started coming into play and the overall impedance that the spark discharge was seeing on its way back to the battery was too high. It manifested itself in a nice little light show when I ran the car at night. When I moved the ground strap to the cylinder head, that solved about ~80% of the misfire/rough idle problem.

Since then I've also speculated that if I can solve the split BLM problem, I'd take care of the remaining ~20%. I racked my brain trying to figure out how to duplicate the LT1/LT4 IAC passages and the thought of an under-manifold-NOS system popped into my head. It was then just a matter of how to feed the mini-IAC-manifold. My BLM's before were off by 15-20 points right to left. Now they're only off by 2 at the most.

I have some pictures of the underside already that I'll have to dig up, but I'll shoot some of the top side and post it all together.

 

nice numbers there ULTM8Z

RBob, the dilution is CO + CO2.
if CO2 is = to 10.50 & CO is = to 1.0, you have a dilution of 11.50.

you can see it in what Fast355 posted, he did swap the CO actual & standard readings in the 25 MPH part.

 

It is good you solved the problem I still think a threaded tube into your plenum would do the trick also. BTW that is why I went with a LT1 intake over a Stealth for my car. As for the ground I have a factory serpentine setup that I think I am going to run some extra ground straps after hearing about this.
BTW the numbers can also indicate how well your CATS are working. I just sold my old Jeep that I replaced the CAT on a few years back. The new owner failed the NOX test while I passed 2 years ago I barely did it. Long story short the CAT was replaced. The high flow CATS are suspect and this one was from CATCO that was about 3 years old. Always go with a good one like Dynomax or the factory. That is why they cost more....

 

I tried that already. It didn't work. The problem is, you're still dumping all the air into the main plenum no matter what you do. I had to completely bypass the main plenum (like the LT1's) altogether in order to slay the split-blm beast.

I'm still attempting to figure out the remaining roughness (like I said in my original post), but I'm hoping it can be tuned out. I'm actually surprised that it's rough at all with emissions numbers like these.