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Failed smog, high NO and HC
Hi guys,
New to the forum and just purchased an out of state 87 911 Carrera coupe. I went to go get the smog done and it failed ![]() Any thought on what I should look for and recommendations of a shop in San Diego if anyone is local to the area. ![]() |
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Registered
Join Date: Jan 2011
Location: Gulf Coast FL
Posts: 1,485
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#1 is oxygen sensor disconnected or faulty
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Under the radar
Join Date: May 2007
Location: Fortuna, CA. On the Lost Coast near the Emerald Triangle
Posts: 7,129
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BLACK FOREST will take care of you.
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Gordon ___________________________________ '71 911 Coupe 3,0L outlawed #56 PCA Redwood Region, GGR, NASA, Speed SF Trackrash's Garage :: My Garage |
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Thanks guys, I was also searching the forum and came across this old post too in regards to connecting the brown wire under the seat. I did that as mine was disconnected, then went on a good warm up drive to go retest but the shop was closed already. Perhaps tomorrow if they are open during the holiday.
I'm also going to check the O2 sensor to see how old it looks. Black Forest looks good as near Kearny Mesa and the 163. Failed smog, high NO, help! Last edited by calidude; 02-17-2019 at 12:32 PM.. Reason: forgot to add link |
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Senior Member
Join Date: Feb 2000
Location: Lacey, WA. USA
Posts: 25,308
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If you just reconnected a wire that is part of the fuel metering system, then it might make sense to just do another smog test.
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Man of Carbon Fiber (stronger than steel) Mocha 1978 911SC. "Coco" |
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I'm reading from the other thread that it's a bridge ground wire?
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Do a complete tune up including valves, Put 40 pounds of air in the rear tires , change the oil, get it hot as hell before smog test!!!
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Join Date: Apr 2013
Location: SoCal
Posts: 893
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With that much variation something is off
See this thread when mine fails a few years ago https://forums.pelicanparts.com/porsche-911-technical-forum/922792-smog-failed-high-co-low-speed-test-ideas.html Things to check O2 sensor Valves adjusted Plugs and ignition good Stock tune Connect the wire next to ecu (it is stock) With mine it was the afm base idle running rich. Based on how out yours is, suspect the cat or badly out of tune engine. Did it pass ok last time? Black Forest is a good shop |
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Still here
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That Guy
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Whats the mileage on the cat? High NO is either lean mixture (vacuum leaks) or a bad cat. CA legal replacements are available.
Even your CO numbers are high. When was the last tune up? Plugs, cap, rotor and wires if needed. Weak ignition will raise your HC readings also.
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Jon 1988 Granite Green 911 3.4L 2005 Arctic Silver 996 GT3 Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1 |
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Car has 128K on it and recently brought from Atlanta, GA where on 1/22 had the full service tune up including, oil change, plugs, cap and rotor, fuel filter, fuel lines and fuel pump replaced.
I don't think the O2 sensor was changed. Going to get it retested tomorrow after hooking the wire up today. Appreciate everyone's help as glad to join a great community of owners. ![]() ![]() ![]() ![]() |
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Join Date: Jan 2012
Location: Melbourne, Australia
Posts: 377
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I bought an 88 from Atlanta, and it didn't pass smog in CA either. Ended up needing a new cat. That was with the brown wire connected. So, just a data point that a 30 year old cat can be good enough for Georgia but not California. A replacement was about $850.
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Join Date: Apr 2013
Location: SoCal
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Pretty sure that wire will not do it. It just runs timing a little more aggressive.
O2 sensor is easy But given recent tune i suspect cat is shot See of station will do a pretest |
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That Guy
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The brown wire retards ignition. It will lower your cylinder temps which will lower NO. I dont think it will lower it enough to pass on NO with your numbers.
Another thing is check the fuel quality switch is set at zero on the DME. After 30+ years it’s worth checking that it hasn’t been adjusted. Invoice shows plugs but no cap, rotor or wires. If they were inspected and reused that’s fine.
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Jon 1988 Granite Green 911 3.4L 2005 Arctic Silver 996 GT3 Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1 |
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Yeah your right, looking at the cap I thought it was new but it's not on the invoice. The spark plug wires look original as the protective sheaths where they bolt over the fan are cracked with age.
I'll pop the cap off and look and run at a resistance check on the wires with an ohm meter but probably should replace them anyway. I was reading another article about how poor ignition or neglect over time will clog a cat ![]() I'll post a photo of the cap and rotor later. Sounds like getting an O2 sensor out is an act of God too - Looking for Tips for O2 Sensor Removal Is the fuel quality switch inside or outside of the DME? |
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Here's some info on the fuel quality switch (internal DME):
911Chips.com - Fuel Quality Switch fuel quality switch 8 position switch on D.M.E.??
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Very likely the CAT is bad.
But the slightly high NOx could also be one or more faulty injectors. A lean running cyl can cause NOx to go up. Then the O2 sensor sees the average O2 content from all 6 cyls, if one cyl is running very lean because of a clogged injector that will increase NOx and it will also cause the other 5 cyls to go slightly rich because the O2 sensor sees a slight lean condition because of the one lean cyl, the DME will then richen the other 5 cyls and then HC also goes up. Usually if NOx is high HC is low, but the above explanation is something to think about. A faulty clogged injector could result in both NOx and HC going up.
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Sal 1984 911 Carrera Cab M491 (Factory Wide Body) 1975 911S Targa (SOLD) 1964 356SC (SOLD) 1987 Ford Mustang LX 5.0 Convertible |
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calidude..also on your 911 change your wipers the one on right should go on left and vice versa...
Also your hand brake need to be adjusted.... otherwise...congrats ,nice 911.... Ivan
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1985 911 with original 502 191 miles...808 198 km "The difference between genius and stupidity is that, genius has its limits". Albert Einstein. Last edited by proporsche; 02-18-2019 at 11:04 AM.. |
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That Guy
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O2 sensor is not hard to get off with the proper tools. Leverage is everything. Take the wheel off and you will have plenty of access. Cut the connector off and use a box end of a wrench, tap with a dead blow mallet and it will come off. If the wire connector is still in good shape, get a universal O2 sensor and splice it on. This is cheaper than the O2 sensor with the Porsche plug... but the original connector can crumble with age and is not always reusable.
If the insulation on your wires is cracking, its time to replace them.
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Jon 1988 Granite Green 911 3.4L 2005 Arctic Silver 996 GT3 Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1 |
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Quote:
![]() Agree on the brake adjust too as on the list of to do |
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