I just got the smog inspection report back and it wasn't pretty. Any way to tell whats wrong before having diagnostics from A-Z done?

Model 928, year 1980. California Car.

Test results: Gross Polluter

15mph RPM 1587 co2 9.0%, o2 3.4%,
HC 280ppm, CO 6.24%

25mph RPM 1597 co2 9.0%, o2 3.4%,
HC 278ppm, CO 6.2%

There have been no modifications to anything. All factory Porsche everything from stem to stern. OXS light just came on at just over 100K miles last week. The fuel injectors are all less than 2 years old, new spark plugs 6 months ago. Always run premium 92 octane, timing is right on.

Is there any particular thing that may be causing such a dramatic change in measurements since I passed this test a year ago? No adjustments have been made under the hood to my knowledge. I was told the car is running "rich." I hope the car running rich isn't going to make me "poor" trying to fix the problem! Two weeks until the registration is due....any ideas?

 

OXS light means that the oxygen sensor is not functioning properly & mixture is affected, me thinks. Check mV signal from OXS, maybe?

 

Do a search of "SMOG"
I went through all kinds of fun.

Can't figure out how to link you to the string I had going but the search should get you there.

Good Luck

 

The oxs warning light is merely telling you it's time for a new sensor based on the mileage counter. It does not tell you anything about the sensor operation.

How is the car running? does it feel the same?
Have you noticed an increase in fuel consumption? With those figures the engine should have a noticable decrease in power and ability ot idle. Pull the plugs and check condition. If there anything to guess at, I would check the fuel pressure and see if the pressure regulaotr has failed.

 

Regarding your registration, go ahead and pay it... you can pay it before you pass smog. At least that way you'll avoid late fees on the registration. (Yes, you'll be in some kind of weird registration limbo because you won't have stickers, but you gotta start somewhere). BTDT.

Regarding what to do... here are some suggestions, YMMV.
a) take it to the dealer or a reputable independent who knows 928's (the usual advice), they will have the tools to figure this out. For some problems, hiring someone to figure it out *can* be the cheapest solution!! YMMV!!

b) Since this appears to be a mixture/sensor issue, you could always verify whether the mixture really IS rich or not by buying one of those little mixture analyzer thingamabobs. I think they're only about $100. Of course, the type I'm thinking of runs off the O2 sensor and if that's failed, then the mixture analyzer won't function properly! (You could also purchase a tailpipe emissions analyzer but I believe they are quite expensive... goto option (a)).

c) If it were me I'd just buy the darn O2 sensor and eliminate one variable from the equation, then try the test again. It certainly won't hurt and is also arguably the number one most likely culprit since it's so old, you passed last year, and nothing else appears to have changed. On the other hand, I'm not an expert and can't tell you the expected mixture behaviour for a malfunctioning/nonfunctioning O2 sensor (though going rich would be an appropriate default behaviour).

My 2C of BS grasping at straws...!!
Rick

 

Bernie,

Find the string you want and right click. Choose "open frame in in new window" and when the new browser opens showing the string, cut and pase the address usung the "URL" tool in your post. viola.

Greg

 

Thanks for the replies....

The only strange things that I've noticed with the car in the past year is:
(1)twice the car has stalled while at a stand still...very rare occurance but did happen causing me some concern (did this several weeks BEFORE the OXS light went on) other than that idles fine, power ok.
(2) I've heard some funky noise when starting in the morning and when the car shifts gears at times (3 spd auto tranny)...I'm told that is a hydraulics plumbing issue...car still works so I'm leaving it alone for now.
(3) I've heard some whining in the right rear near what I am told is a secondary fuel pump. The car doesn't appear to have much difficulty starting hot or cold and when I stomp on it, it takes off without any noticeable delay....unless you consider that its underpowered at 240HP, but that's a whole 'nuther' issue...the fuel filter was replaced with the spark plugs.

One of you suggested checking spark plugs. Although I'm convinced there is a need to replace the plug wires (one was replaced 6 months ago due to being faulty) I had all the spark plugs replaced at that time. The old ones were actually in pretty good shape according to my mechanic but I had them replaced anyway to be sure.

Regarding the OXS light, my owner's manual says this is a "reminder" light for service. There is a separate section in the manual it refers me to, discussing warning lights, and in that section it says if the light goes on and stays on, it is malfunctioning. What is unclear is if they mean the light itself or the oxygen sensor. I would figure there would be a light that simply says "service" instead of a "OXS" if it were just a service issue but go figure....
I tend to believe this is actually the oxygen sensor gone bad. Apart from some nicks and scratches and some leather wear on the drivers seat the car is in amazingly good condition and I've poured thousands of dollars into it to keep the car in good shape. I know there's a main seal leak and a freon leak but apart from that the car is in as good a shape as they come for 23 years of age. I'll try to look up some of the previous threads to gain more insight since it'll be a few days before any competent mechanic I trust can take a look. I plan to run it over to either ROBERT's in Pacific Beach or Mind Over Motorsports by Costco
(Randy V....do you have any suggestions otherwise? I don't know the guys at Roberts anymore but they've been competent with my RX7 and Jeep in the past and seem to have a specialist for most model cars...I know M.O.Motorsports lives and breathes Porsche but they are younger guys around my age and probably have more experience with factory Carrera RSRs than 928s. BTW - my car is the Schwartz Metallic one with the "2ND OF2" plate and turbo twist 18s...maybe you've seen me around? I have yet to see your ride around La Jolla, only another white one with a roof....too bad about the guy with the Ferrari...I guess that new dealership in town is going to coax a few more rich guys with weak car handling skills into red rockets)

 

Just to address the O2 sensor issue - per the wiring diagrams and the venerable Wally P, there is no connection, physical or performance-monitoring, between the sensor and the warning light.

Nothing but power, ground, distance reading from the speedometer, and connection to the light. And a reset button, if memory serves.

 

Once again: The oxygen sensor light has NOTHING WHATSOEVER to do with the performance of the oxygen sensor. It is a mileage counter, nothing more.

Here are some possibilities:

The engine is running rich. Possibilities include bad Oxygen sensor, idle switch not operating, fuel pressure too high, leaking diaphragm in fuel regulator or dampener, idle mixture too rich.

One cylinder (or possibly more) is not firing some of the time or at all, dumping unburned fuel into the exhaust. Possibly a bad plug wire.

The cat is dead.

The AFC injection system, combined with the oxygen sensor, should control the fuel/air ratio. If something is dumping too much fuel into the system, the sensor should tell the injection system to lean out.
To run too rich, either the oxygen sensor is not working so that the system is running open-loop, or there is too much fuel coming in for the system to compensate.

Replacing the oxygen sensor might be a good first step - but not because the light is on!

 

If it were my car --- and this is just my 2 cents -- I'd replace the O2 sensor, the plug wires, make sure all cylinders were firing and finally, dump a bottle of Fuel Injector cleaner in the tank and run the whole tankful through. I'd also shake and rattle the catalytic converter and see if I heard any crunchy rustling in there... as of platinum honeycomb rattling about.

good luck

Thaddeus

 

Thanx Greg,

Learn something new everyday

 

here is the string

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=14&t=002763" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=14&t=002763</a>

Cheers

 

Interesting reading in that thread, Bernie. What ended up being the problem, at the end of the day? <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

 

Don't forget to check the output of the O2 sensor with a mVoltmeter before you buy another one. If memory serves me, it should hover around 1 volt +/- a bit. The floating voltage correlates with the mixture. I would tend to test it before replacing, but maybe that's just me. <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

 

Well, the main culprit was the O2 sensor. It was completely toasted and when replaced, my NOX dropped to a liveable quantity.
I also found, during my recent project, a test pipe that was broken completely in half. Means that there was more fresh O2 getting to the sensor than was being run through the engine. Did this have an effect as well??? - dunno....
I bet I also still had air/vacuum leaks to contend with.
Stuff like this can usually manifest itself as the sum of the little problems.
It all worked out well for me in the end and I passed my smog no problem.