need smog help

[john911sc]

i have a 1974 914 2.0.....california wants it smoged....i tried to smog it but it did not pass....the guy said it needs a new oxygen sensor....what can i do to make it pass smog????...thanks again to everyone that helps.....john

[bowlsby]

Bet the smog tech also tried to open the fron trunk to inspect the engine, huh...

The stock 74's didn't have a stock 02 sensor...and doesn't need one for the FI.

Help us help you and tell us what your failed test infdicated...hydrocarbon levels, C02 levels etc...

Also, search previous posts, this topic has been covered.

[John Rogers]

I would make a guess and say the smog tech ment the "temp" sensor in the intake since on 1974 2.0l they will make it run leaner and I'll bet the engine was too rich, probably at both test speeds? As a precaution, before I smog our 1974 2.0l, I always take it to Black Forest in San Diego and they tune it and tweek it and it has always passed. The cost has always been much nicer than the hassle of the smog techs and failing an inspection! As noted, please list the readings from the test you had as they will tell what is needed. Good luck

[campbellcj]

I can't chip in anything else at this point (except to echo John Roger's suggestion of having a local p-car mechanic/shop help you; that's what I always did with my 70 911E MFI car before it became exempt. It would NEVER pass without a lot of tweaking and/or some help from Mr. Franklin.)

Anyways, as an aside, I just had to smog my new-to-me 2000 Audi and I was shocked at how clean these new cars have become. (And this is not even an ULEV I think.) I bet the tailpipe is cleaner than the L.A. air I breathe everyday.

C02 14.9%, O2 zero; HC 6ppm; CO ZERO! Wow.

[pbanders]

Originally posted by campbellcj

Anyways, as an aside, I just had to smog my new-to-me 2000 Audi and I was shocked at how clean these new cars have become. (And this is not even an ULEV I think.) I bet the tailpipe is cleaner than the L.A. air I breathe everyday.

C02 14.9%, O2 zero; HC 6ppm; CO ZERO! Wow.

Modern FI cars with engine management systems and 3-way cat converters have remarkably low emissions, as the 3-way eliminates nearly all of the CO, HC, and NOx emissions. The FI system's job is to keep the mixture from the engine in the extremely narrow lambda range where the 3-way cat operates at peak efficiency. This degree of control is possible by accurate mixture feedback provided to the ECU from the oxygen sensor. Note that the O2 sensor is in front of the cat converter as it's purpose is to control the lambda factor of the gasses TO the cat converter - too rich, and the cat coverter heats up, too lean, and NOx goes way up.

Interestingly, modern FI systems operate in open loop (eg. ignoring the O2 sensor) in one mode - wide open throttle. The reason is that WOT is usually held for only a short period of time and is the "full power" condtition, requiring a richer mixture. The ECU is pre-programmed with this injection condition and ignores the O2 sensor telling it that the mixture is too rich. That's why it's a really good idea when you're going on a long steep grade to shift to a lower gear and maintain part throttle instead of running in a big gear with wide open throttle for extended periods, otherwise, you run a rich mixture (lambda of 0.85 or so) and the cat converter heats up like a bomb.

Brad Anders

[pbanders]

Originally posted by john911sc
i have a 1974 914 2.0.....california wants it smoged....i tried to smog it but it did not pass....the guy said it needs a new oxygen sensor....what can i do to make it pass smog????...thanks again to everyone that helps.....john

As others have said, your '74 doesn't have an O2 sensor. '75 and '76 914's had cat converters, but these were first-generation single-bed cats with oxygen injection (smog pumps) and did not have O2 sensors for ECU feedback and mixture control.

If you're in Fremont, I'd suggest you drive across the Dunbarton and go to High Performance House in Redwood City. Rich Bontempi and his staff there are experts at getting 914's into smoggable condition.

Brad Anders