Bill Ball

I removed the supercharger (SC) to get my car smogged. It passed. It passed 2 year ago before the SC as well. Then and this time the numbers seemed to be higher than I remember them being on earlier smog tests. HC and NO are above average. The cats are original and the car has 175 k miles.

-----------------------------------HC (PPM)--------C0%-------------N0 (PPM)
Test-----RPM--%CO2--%02--Max-Ave-Meas--Max-Ave--Meas--Max--Ave--Meas
15mph--1351--15.1----0.7--110---31---75--0.71-0.10--0.10---772--237--586
25mph--1391--15.1----0.5---85---20---62--0.59-0.09--0.19---711--199--331

So, my HC and NO are about twice the average. Both HC numbers are nearing the limit and NO is getting close in the lower RPM range. My understanding is NO is from running lean or running high combustion temp. HC should be from running rich. I would say bad cat, but I thought these cars run clean without one. Maybe this is how clean they run with a bad cat.

Car is running great back in stock form. I even did a surprisingly nice burnout leaving the test facility.

danglerb

Did you get the cat nice and hot prior to the test without too much cooling down time?

How old are the O2 sensors?

I called up the BAR to get some info on putting on a X pipe, and started out with the need for cats due to the high numbers on my last test, and the guy asked for my lic plate and looked up the test history and gave me this pep talk on replacing the O2 sensors.

Now I KNOW nobody here would do this, but just in case. If you get a calif reg that says "smog test only station" and fail the test with no evidence of tampering, you can fill out a simple request form and go to a COP station pay a $100 deductible and get the next $500 of getting the car to pass smog paid by Arnold.

Bill Ball

The car was fresh off the freeway and the guy ran it for a while before doing the tests. The 02 sensor is brand new and the 928 part, not a subsitute Bosch from eBay.

So, is high NO and HC likely the aged original cat?

GregBBRD

Yeah, try and imagine a regular smog station mechanic messing around in your 928 engine compartment......and doing something good! I can't get there from here.

Bill: the higher HC means that there is more unburned fuel than is desireable....which is designed to detect a missfire condition. Doesn't mean it is rich....that is the CO number. It means that one (or more) cylinders aren't doing a great job of combustion on what is available to burn. Could be a slightly fouled spark plug, a wire that is shorting out to ground part of the time (take a close look at night in the dark), an intake leak, etc. It can also be a small piece of carbon or other crap stuck under a valve when they tested the car. Check the compression, the plugs, and the wires. Check the wires where they connect at both ends for corrosion (if you don't find something in the dark.) Don't forget the coil wires. Check the caps and rotors. Pull off the plastic covers on the caps and see if they are jumping spark to other places....this is very common! Chances are, as soon as the HC goes down, the NOX will follow.

greg brown

greg

Bill Ball

Greg:

That's good advice. Thank you.

The wires, caps and rotors are fairly new, but I did have a problem with one plug wire that I thought I fixed. I got the "economy" wire set from 928 Intl and I really don't care for them, as they reuse your sparkplug caps and boots. I had intended to order the full Beru, but they sent me this instead, and I thought, what the heck, I'll use them. I'm just going to go ahead and get the loaded Beru set. Maybe that will help.

I did a compression check right after the SC was installed, but I will do it again. Heck, I have a leakdown tester I've never used, so here's my opportunity.

Daniel Dudley

I can't help but think that running some techron every few months is good PM. I would be interested in seeing if the SC would make it through the sniffer, even if it wouldn't pass visual.

Let us know what the plugs look like. Inquiring minds want to know.

John Speake

Have you had the injectors cleaned/flowtested Bill ? The O2 sensor will only read the average mixture of all cylinders.......

IcemanG17

Bill
When I get home I'll look up my last smog test.....where I barely passed....but the car was fairly cold when it tested too.....my test numbers went up quite a bit too......

Gonna put the S/C back on this weekend?

perrys4

Good to see you lurking here Greg!! We can always use good advice, thanks.

Bill Ball

Yeah, it is good to see Greg watching over us.

As to the other questions:

Ken: MAF is about 3 years old.

Daniel: I was running colder plugs with the SC. When I removed them to put back in the stock plugs, they looked textbook perfect - light tan and in new condition after 20K miles or so. It's running fresh Bosch coppers now. I'll pull them for a look when I do the spark plug wires. I have a case of Techron. I should run a few bottles through. I'm pretty sure it would have passed smog with the SC. I did have a hot idle miss that I think was due to a slight manifold leak, but they don't test at idle anymore, and everything else about the way the car ran was perfect, including outstanding gas mileage.

John: The injectors are original, never serviced. I suppose I could pull them and send them out, but I have ZERO problems with the way the car starts, idles, accelerates, etc.

Brian: I was planning on reinstalling this weekend, but I need to re-do Andy's restrictive oil filler and oil filler breather setup. That is causing a lot of oil blowby at sustained high speed. So, I want to make a wider filler with some baffles, opening up the filler cross-section to reduce the breather velocity so that oil strays in the engine rather than clogging the small breather Andy made. Something like what Tony cooked up but simpler. I wish I knew how to weld. Anyway, that will hold up the reinstall. I have all the parts to install the intercooler but hoses. The car is still fun to drive stock, so let's hold off until the Xmas holidays. I'm taking some time off at the end of the year.

ZEUS+

The high hc was probably due to the manifold leak, leaning it out at higher rpm. Have a great day !!!Looks like the rain is going to freeze here.

MBMB

This is the opposite of my understanding, which is that high NOx generally indicates lean running, and high hc generally indicates rich running.

???

Bill Ball

I guess it's not that simple...

ZUES - Sorry, but my story is convoluted. I no longer have the SC with its custom manifold installed. Took it off for CA smog testing and am back to stock with a new manifold gasket and refreshed breather and vac lines. Doubt there are any leaks. The SUSPECTED leak was when I had the SC on and was attempting to explain an idle miss. I never actually found that leak. And it's funny that the miss was only apparent at idle. Cylinder 7 would completely drop out, but come back on as soon as gas was provided and the car ran fien except at idle. That's another story.

My smog results are from before the SC and now after the SC was removed and are worse than the original smog results when I bought the car. BUT now it occurs to me that a contributing factor is that the last 2 smog tests are DYNO at 15 and 25 mph and not the old static test.

SharkSkin

Bill, have you had your maps changed at all, e.g. sharktuned? That might account for some of the change.

IIRC Tony didn't weld his breathers, they are sweat-soldered common copper pipe fittings like you would find at OSH. That's something you could learn to do in minutes if you don't already know how, and is a very forgiving process. It's just about impossible to screw things up, unlike welding.

ZEUS+

If it leans out engine management will try to richen up. Looking at all the results is how to interpet what is going on. High hc with low co indicates a lean condition or misfire. It really looks like contaminated oil. Was the oil changed prior testing ?