Common emmission test failure items

[Eric Hahl]

Hi all,

I just got back from an emissions test with my 85 3.2. I barely passed the CO % limit at cruise speed but failed miserably on the same test at idle speed.

What should I look at replacing to remedy this type of failure? O2 sensor? What else could be the cause?

Thanks

[rusnak]

You should tune up the motor, then take the car out on the freeway, drive it for about 50 miles and then take it in to get tested. I betcha it passes, especially if you passed your last emissions test. It doesn't hurt to add a can of BG 44k to the gas tank either.

There is a good section in the Bentley manual for testing the motronic components.

[Eric Hahl]

Thanks, I'm gonna have to read through that section of the Bentley. Whats BG 44k, some kind of fuel injector cleaner?

[88911coupe]

My '88 recently failed and at the suggestion of the tech I replaced the plugs and it passed. My car is in need of valve guides though so the plugs were a little fouled.

[Mark Mcgarry]

Thank goodness its not required in fl anymore.

[mthomas58]

My 87 is in need of valve guides too....had one plug foul out completely last week. Changed them along with new rotor and cap....runs great now.

BUT, approx three weeks ago, I also failed the emissions test on the third attempt.

First test car started to travel on the dyno and test had to be aborted but it was passing up til the abort.

Second test the computer locked up before a report could be printed but it was passing

By the third attempt car had been idling now for over 30 minutes in 90 degree ambient temps and was getting hot. Front oil cooler was on. IT FAILED this time!

Took car out and ran it on the hwy for 20 minutes......pulled back in to the test station an it passed! Had me a little nervous though! They suggest running the car to get it up to normal operating temp before the test which I did not do at first b/c I live < 1 mile from the test station.

[jester911]

If you don't know the age of the O2 sensor you probably should change it. Also make sure the sensor is plugged in at the connector at the firewall. Also before you pay the absurd price for the "Porsche sensor" do a search here for the model numbers that will work.

There are 4 or 5 different Bosch models that are compatible with the car. I bought one that I believe was spec for a Ford car and it was only 30 something bucks on fleabay.

Passed my emissions a couple months ago with it.

[mthomas58]

Originally posted by mthomas58
..had one plug foul out completely last week. Changed them along with new rotor and cap....runs great now.

Here is the condition of the plugs used in the test......#6 [top right] fouled out completely 4 weeks later.

[rusnak]

You should change the O2 sensor only if it fails the test outlined in the Bentley manual. Why throw money away? If you need to change it, then there is a 3 wire O2 sensor that is commonly used on the 3.2 liter 911. You have to re-use your old motronic plug, cut the old wires and solder the new wires and install the heat sheild protective covering, but it works well. It's way cheaper than the Porsche one which you have to order from Germany and takes a month to arrive. One thing I have to stress is that when you are going in for a smog test, you have to tune the motor up with new plugs, cap, rotor, valve adjust, new oil etc. To not do so is just asking to fail.

I passed smog with a new cat. My motor has almost 300k miles and passes California smog, probably the harshest smog test anywhere in the USA. The cat is a "sport cat" that supposedly is less restrictive, and is definitely cheaper, smaller, and lighter than stock.

BG 44K is a great fuel system cleaner. It works well and seems more concentrated than Techron. It cleans dirty intake valves, fuel injectors, fuel lines, etc. I run a can through the tank a month before the emissions test, then a second can just before the test. I then go in for the emissions test when I run down to a half tank. Never failed yet.

[88911coupe]

Just a frustrating anecdote on my first failed attempt. While sitting in the waiting room I thought I heard a car being started over, and over, and over again. Finally someone opened the door and I clearly heard MY car being started, stalled and started about 15 times, mayber more. I "briskly" walked out and as calmly as possible asked what appeared to be the manager just WTF was going on. I think he was trying to get some newby to learn how to move a car with a standard tranny and decided he needed to learn on a Porsche. Needless to say, I was pissed but I was still hoping for it to pass.

[velomann]

Eric,
start with your standard tune up (plugs, filters, oil). Follow the advice of getting it out and burn it up a little with a nice drive up the 205 at 65 MPH to Woodland and back, then the test. I passed mine about three weeks ago with flying colors with a motor that is running BIG jugs, and some pretty sick cams....needless to say it was because it was burning very clean! If you have not ever replaced the O2 sensor, that will also get you closer. Good Luck!

[Eric Hahl]

Thanks all, that gives me some idea of what to look for and items to check/replace.

[Emission]

Mine only passed with a new CAT (140,000 miles on her).

Before you do that, run her nice and hot before the test!