EGR question For CA models and …

M30s and Z31s only run 37psi base pressure - could be an issue if you're running a stock M30 tune with even 43.5psi fuel pressure.... Just throwing that out there.

Run a gallon of denatured alcohol on a half tank of fuel in additional to the timing and new cat, should help drop the numbers significantly

We need all the info including co2 and 02. For all u know it can be a lean conditionnletting your car run rich. As well as the extra air not allowing the cat to cut the nox

He's not burning all the fuel inside the chamber, and he's running too hot into the exhaust --- this could mean his base timing is too retarded for the octane he's using, or the fuel pressure is too high, allowing fuel to continue burning poorly in the exhaust, creating all 3 conditions: high CO from improper burn, high NOx from still burning in the exhaust, and high HC from the remaining extra fuel that couldn't find anymore oxygen in the exhaust

The slightly high CO could also indicate his cat also isn't effective, or not up to temperature, the AIV is supposed to speed up heating the cat (though I'm guessing he doesn't have one), but it could be contaminated by too much fuel or oil too

When he does a retest, we'll find out how much has changed, but chances are it has nothing to do with his o2 sensor and very little to do with his cat

The M30 did not have AIV or PAIR so I did not include it in the electrical swap. My understanding is that Air Injection only happens at idle anyway so other than heating the cat while idling before the test (no idle sniffer test here) I'm not sure it would help my test scores much. It spends about 3 min at 15mph and 25mph and that's it.

​I've also been thinking about the timing thing, Yes the CR is Higher so It would need less advance (1-2 deg less through the mid range per Point CR) but since the test is 1000 rpm below mid-range (1782 rpm @ 15 mph and 1921 rpm @ 25 mph)With 14 being my base timing it should be pretty close for that rpm range.

More we talk about fuel the more I want that AFR SO I can see what its doing.
New question, would pre-cats up stream from the o2 sensor throw off the stock o2 reading? I haven't done it yet but I'm considering a pre-cat hanging off each header to make passing easier next time around....

Any catalyzing you do before the o2 sensor will affect the readings, which may adjust your mixture incorrectly, most likely always in the same direction, I don't think that's your answer

I don't believe the AIV is important in the slightest, a good highway run prior to the test is all you need, a 10min drive at 100km/h should be plenty to burn off any crud, then just keep driving above idle to the test center and don't allow it to sit or cool off if possible

If you plan to do any tuning later on, might be a good idea to invest in an egt sensor and discrete guage as well, that and a wideband will give you the full picture

I can see that, I bet it would make it run richer because the Pre-cat would be burning what the O2 is supposed to read. Highway is easy, I live ~20 miles from the nearest town and ~30 miles from all the smog stations.
Discrete Gauges? They cannot fail you because of gauges. Having gauges cannot prove one way or another that the engine is modified. They might look harder at the Visual inspection if they see gauges because they suspect modifications. I have all the the equipment listed in the vacuum diagram under my hood (1990-95 Pathfinder Vacuum Diagram to match the manifold) and its all hooked up and functioning the way it should. They suspect nothing so far and nothing has been said about my vacuum gauge on the dash either.

Well, I got the MTX-L hooked up and went for a drive targeting the speed range of the smog test. But I didn't see anything that screamed rich AFR…

First RUN,
Idle AFR ~14.5:1
~25 mph @ ~2k rpm AFR 13.8~14.7:1 but mostly stayed in the low 14 range the numbers changed rapidly, it was hard to read.

Second Run, Fixed loose wire on Fuel Temp Sensor
​Idle AFR ~14.5:1
~25 mph @ ~2k rpm AFR 14~14.7:1 but again mostly stayed in the low 14 range

Third RUN, For kicks o2 Unplugged
​Idle AFR ~13.5:1
~25 mph @ ~2k rpm AFR 12~13.5:1

Fourth Run, New engine o2 sensor
​Idle AFR ~14.7:1 sometimes floated up to 15
~25 mph @ ~2k rpm AFR 14~15:1 all over the fourteen range top to bottom but spent more time in the upper 14's than anything else. The numbers had a greater range sweep but changed more slowly than the first run.

So 2 repairs have managed to lean my AFR out by about 1/2 point on average but I have no Idea if that's going to be enough to pass me. I guess I can look into the FPR tomorrow after work and see if that will help it keep out of the low 14's when cruising.

I also need to extend my tail pipe so they can keep their sniffer in there deeper without getting a dilution error.

A fully baffled muffler helps with hc readings, the mesh/baffles help trap a lot of the soot and some of the heavier vapour, if you have one kicking around to try

No kidding? I'll have to MAKE that happen, I'm running a magnaflow with a dump pipe right now. The end of the sniffer is probably sitting inside the muffler after follows the bend inside the dump pipe.
​I'll try to find something cheap and OE like for the time being but I bet a flow master 40 with a good length of pipe after it will do the job later on, never thought an unfinished exhaust project would bite me in the ass like this.

Depending on the year z31 for federal emmisions visually there is no check engine light when you start the car. I have one and they write it down as not applicable. For california emmisions car s I have to look it up in my smog reference books. Your co2 should be above 13%. Unless ur puke stupid rich. But judging on the nox your not running that rich. If you were puke rich your nox numbers would be down. But with that high ass o2 you got a leak possibly.

Ok I Replaced the FPR with a stock one and after the ECU had some driving time to adjust the differences were slight.

​Idle AFR ~14.7:1 sometimes floated up to 15
~25 mph @ ~2k rpm AFR 14.2~15:1 very similar to my previous run except it never went below 14.2 while driving like this. I also saw 15.0 more often.

Also made a few WOT runs at reline before and after the regulator swap… WOT redline stock FPR was 10.8:1 and modified FPR was 10.2:1 Looks like I had plenty of fuel either way.

Well my 10:1 vg33e with euro cams PASSED CA SMOG TEST! So clean Its unbelievable.

HC 15 mph limit 121 actual 6
HC 25 mph limit 101 actual 3

CO 15 mph limit .70 actual 0.00
CO 25 mph limit .63 actual 0.00

NO 15 mph limit 1006 actual 0
NO 25 mph limit 606 actual 4

No limits listed
%CO2 15 mph 13.2
%CO2 25 mph 13.2

No limits listed
%O2 15 mph 2.2
%O2 15 mph 2.2

Changes since the last test:
1 Replaced glass Pack & dump pipe (found a big hole in it too…) with Flowmaster 40 & factory cat back (Thanks G-E !!!)
2 New CA model Mangnaflow Cat
3 Ran Regular 87 Octane Gas (ran premium last time)
4 Re-installed stock FPR