Porsche-noob-91

Almost one year after my failed MOT inspection, I'm almost ready to go back. To do so, I have to request special plates that give me the right to drive around for 20 days. After these 20 days, I'm out of luck and will have to find other means (trailering/waiting another year) to move the car to inspection. This is a very limited amount of time to get the car in order if something is wrong.

So that explains the time sensitive nature, and also my rather pre-emptive question as I don't want to waste time asking for possible solutions if I fail the inspection again for the same reason. Last time, the car failed because of high CO (measured +- 7, should be no more than 4).

This led me to change a host of things:
- New crossover pipe + gaskets + extra LR copper gaskets + nuts and bolts
- New exhaust headers (second hand) + gaskets + studs + nuts
- New intake header gaskets
- New AFM
- Reinstallation of OEM air filter + new air filter element
- New O2 sensor
- New turbo to intercooler hardpipe (smoke test found leak)
- New fuel rail (leaked)
- New engine oil + filter
- New spark plugs (Bosch WR7DC)
- Checked Fuel Quality Switch position in DME (Pos = 0)

Before I will go to the inspection, I'll also change the fuel filter and add new fuel (fuel is from november 2022). I'll also make sure to ride 30 mins or more on the freeway so I can get the car good and hot before the test.

My question, with all this background info, is now clear: what can I do to lower my CO emissions if you know all this?

My own ideas would be:
- Manipulate the air bypass screw on the AFM - turn it counter clockwise
- Manipulate the FQS in the DME - set it on position 2 (-3.1% fuel)

Hope to see some tips here and even better, hope I won't need them in the coming weeks!

Nowanker

CO is burned fuel, from rich mixture.
Some readings would help, where you are vs. allowed would be great... Assume the car runs well, other than the high readings?
The O2 sensor system can adjust for minor variances, but does have a range. Without the cat, it should hold approx .5-.6% CO.
Lots of possible causes to be too rich
Excess fuel pressure: Test that with a fuel pressure gauge
Bad DME temp sender or wiring: If you unplug it, the mixture should go very rich. If it doesn't change, look at the wires...
Leaking fuel pressure regulator
Shorted O2 sensor circuit. Does the engine respond if you unplug it?
AFM bypass screw bottomed
Off the top of my head.

Porsche-noob-91

The car runs fine as far as I can tell during my limited driving.
The test revealed my CO levels were "7" instead of the allowed "4". Not sure if that is PPM, % or some other measurement.
The car has its original cat.

That are some great suggestions already, I'll definitely test the fuel pressure before I head to the MOT as I do have a fuel pressure tester that's waiting to be used, so I'll do that ASAP.

Thank you!

kev951

If it is % that is way rich. What is the oxygen percentage? There are different settings in the dme that can help some but if they were never touched your problem lies elsewhere.

Nowanker

Hope it's some me other measurement besides %.
4% is already way too rich, and point7% seems pretty tight for a maximum. Not unfeasible, though. Running well, and with a functioning cat, should be well below that.
Even without a cat, not impossible.
Best of my recollection, even Kalifornia allowed 1% out the tailpipe, but I've been away for awhile.
Just out of curiosity, does anyone have current limits to post?

Porsche-noob-91

No idea. I'll make sure to write the measurements down when I go again. The DME didn't seem like it was touched, FQS was still on position 0. But even if it was stock, putting it in pos 2 would mean -3 % less fuel, so that would theoretically help circumvent a rich condition right?

It's possible the guy at the DMV said 7 and 4 but meant point 7 and point 4. As above, I'll make sure to write down everything when I go for the test again.

Nowanker

If it's reading .7% CO out the tailpipe, it might be running within normal range, but the catalytic converter might not be working.
Make sure it's good and hot before the test.
Wouldn't hurt to try the FQS.
Good luck!

Droops83

Your eyes would be watering while standing behind the car while it's running if the CO level is 7.0%. That's about a 10:1 air-fuel ratio, so pig-rich. The cause of such a rich AFR is beyond any "normal" adjustment like FQS of the idle mixture. It would be something like a kinked fuel return line (high fuel pressure), bad NTCII/coolant temp sensor or wiring, etc, that would cause such a thing.

Check if you can get a printout of the emissions figures and maybe we can help from there.

Porsche-noob-91

I contacted the National Belgian oldtimer association to inquire about the emission test. They said (and sent me documentation) that my car needs to be below 4.5% CO while running stationary. So I guess I did have 7% CO... Maybe our emission tests are different in Belgium (Europe) than in the USA? I'll test the fuel pressure coming Monday to check if there's a problem there...

Nowanker

7% is a major problem! Rich enough that it should be repaired regardless of test requirements.
Even 4.5% is too rich.
Back in the old hotrod days, even cars with nasty cams would generally idle below that. Carbureted cars with normal cams usually 2%-3%.
Fuel injection is typically well below that. O2 sensor feedback tries to hold it somewhere .5 to .6ish, before the cat.

Fuel pressure regulator leaking fuel into the intake
Dead DME temp sender
Something bad happening.

Porsche-noob-91

This thread is making me anxious.

I just called the DMV and they don't save any info beyond pass or fail and the reason for it. So no actual CO value I can retrieve before going again.
So stuff to check before going:

- Fuel pressure
- FPR fuel leak into intake
- Dead DME temp sender
- Fuel line kinked somewhere (I already changed the lines going over the exhaust manifold, no kinks there)
- NTCII/coolant temp sensor
- Shorted O2 sensor circuit
- AFM bypass screw bottomed


Edit: if my CO levels are this high, the car should blow black smoke out of the exhaust right? Last time I checked, it didn't. Just some white smoke from sitting. It does blow out some black sludgey droplets though. Not sure this disappears when riding, but on startup, definitely there.

Edit2: I did notice that my turbo to intercooler hard pipe smells of fuel

slivel

Here in California we have very strict emissions standards. Offending exhaust parameters are, CO, hydrocarbons, and NO levels. High hydrocarbons indicate misfires and can be spark issues with plug, wires, cap and rotor or DME issues or even a leaking head gasket. High NO usually indicates excessively lean condition. High CO indicates a rich mixture as was previously mentioned. CO and NO levels usually travel in opposite directions relative to stoichiometric mixture (one goes high and the other goes low). CO and hydrocarbon levels tend to travel together. Unburned fuel in the exhaust will usually have high CO as well.

if you have verified good vacuum integrity of your intake path and all vacuum lines, then it might be a good idea to weld in a bung on the down pipe and install a wideband sensor. The data from a wideband can simplify your troubleshooting.

Nowanker

EXCELLENT idea on the wideband. The high CO might have multiple causes, and fixing the gross one won't always be enough.

Porsche-noob-91

Happy to announce that my preliminary questions were indeed preliminary. I passed the DMV inspection with flying colours! CO was 1.75 now (previously it was 7 something).
I'm good for two years!

Nowanker

Congratulations on the win!
Those numbers must be something other than percent...