VERY high 'C0' in smog check for 86' turbo...

[Tilikum Turbo]

Anyone else register a very high 'CO' on their 3.3L/930/68 1986 USA engine?, during a state exhaust test/smog test.

Right now unless I figure this out, I may have to buy a brand-new fuel metering unit for the car...hoping it may just need a WUR rebuild, but checking to see if anyone else has experienced same problem. Car also get's no better than 10 MPG in city, and about 12-14 HWY.

Car runs great, passes all other tests(CAT, 02 sensor, etc), just C0 is off the charts!

Any help...thanks

[mark houghton]

Adjust your mixture screw...you don't need to spend big bucks replacing engine components. Your MPG is way off, which says your mixture is way off too.

You'll need a 3mm allen wrench to make the adjustment (turn it out counter-clockwise to lean it out). But you'll be shooting in the dark unless you have access to an exhaust gas analyzer (for DIY folks, that means a Gunson Gas Tester, or an on-board AFR gauge).

And of course it goes without saying to make sure everything else is properly tuned up (plugs, timing, etc.).

[911boost]

Double check the o2 sensor. Is it the original? I had the same issue with CO and while the o2 sensor appeared to be working properly, it wasn't at all times, and replacing it solved my problems.

Bill

[JFairman]

You can make it pass the CO test without spending a dime if you have some experience tuning carbs or EFI idle CO by ear.

Ignore the lambda system and the oxygen sensor because you can adjust around it so it is doing nothing to upset your target CO.

With the motor idleing at operating temp turn the CO adjustment screw just a little tiny bit at a time counter clockwise with a short 3mm allen wrench until idle starts slowing down and getting just a little bit less smooth but not rough and not missfiring.
Right at that point it is a little leaner than you like for driving but it will pass the CO test easily.

15 years ago when Florida had yearly emission testing I had an '81 BMW 320i with CIS.
While waitng in the line of cars to drive through the 10 minutes of exhaust emission testing while on rollers I'd pop the hood and turn the 3mm allen screw counterclockwise until the engine idle rpms would slow down a little and become just a little rough.

Then get back in the car and wait my turn while leaving the motor running so it and the catalytic converter would stay hot.
Then take the CO test and it would pass with lower CO numbers than it needed to pass.

When done I'd drive the 20 feet out the other side of the drive through building, open the hood and turn the 3mm allen screw back clockwise and richen it up until idle speed increased and smoothed out real nice and then drive off - done for another year.

With a little experience the CO adjustment takes about 5 seconds to adjust and pass the test.

[pdx930]

If your O2 sensor is actually working, you can check the duty cycle of the pulse valve at the diagnostic connector on the fuse/relay panel in the engine compartment. Should be around 50% when the mixture screw is adjusted per spec. (which is pretty lean).

FYI, I plugged in my O2 sensor and set the mixture as above and it passed the CO spec with no cat. Once done with the test, I unplug the O2 sensor and set the mixture by ear as suggested by jfairman. I usually see an RPM gain of about 100-150 RPM from spec to running nicely.

[Tilikum Turbo]

Thanks for all the good info and help here!