Failed emissions

[porschedavid]

2005 Porsche 996 c4s
46000 miles
Took car for mot today after being sat for 6 months and failed emissions.
Before i took her i filled it up with new fuel and gave it a few blasts up and down the road to get cats hot.Its only done 429 miles since last mot which it passed emissions ok.

[JFP in PA]

Failed for what exactly?

[porschedavid]

co too high

[JFP in PA]

High CO levels normally result from over rich air fuel ratios, which could be anything from a dirty air filter to a sensor issue. If you have access to a Porsche specific scan tool like the Durametric system, check you fuel trims for over fueling.

[porschedavid]

A few months ago i installed a low temperature thermostat would that make a difference.As they run hot because of emissions

[yelcab1]

Originally Posted by porschedavid

A few months ago i installed a low temperature thermostat would that make a difference.As they run hot because of emissions

That is the problem. The lower temperature thermostat is telling the CPU to enrich the mixture in order to warm the engine up some more. Since it can never do that with the new lower thermostat, it will not pass … smog.

Options are to …

1. Reprogram the CPU, Hard
2. Replace with stock thermostat to bring the engine operating temperature up, easier
3. Give the car a tune up while you are at it. Change the air filter, spark plugs, oil, and drive it aggressively for a few days then take it to test again.

[JFP in PA]

Originally Posted by yelcab1

That is the problem. The lower temperature thermostat is telling the CPU to enrich the mixture in order to warm the engine up some more. Since it can never do that with the new lower thermostat, it will not pass … smog.

Options are to …

1. Reprogram the CPU, Hard
2. Replace with stock thermostat to bring the engine operating temperature up, easier
3. Give the car a tune up while you are at it. Change the air filter, spark plugs, oil, and drive it aggressively for a few days then take it to test again.

Sorry, but that is utter nonsense. We have a couple hundred customers running 160F thermostats, and NONE of them have ANY issues. The factory DME tune has more than enough flexibility to adjust for the coolant temp change.

[yelcab1]

Originally Posted by JFP in PA

Sorry, but that is utter nonsense. We have a couple hundred customers running 160F thermostats, and NONE of them have ANY issues. The factory DME tune has more than enough flexibility to adjust for the coolant temp change.

Then your experience is different from mine. I will believe it when you can dis-assemble the CPU code and show that the CPU is programmed to deal with 160F water temperature.

[BYprodriver]

Originally Posted by yelcab1

Then your experience is different from mine. I will believe it when you can dis-assemble the CPU code and show that the CPU is programmed to deal with 160F water temperature.

Yes JFP's experience is very different from yours, he knows every one of your cars far better than you do mechanicly speaking !

[JFP in PA]

Originally Posted by yelcab1

Then your experience is different from mine. I will believe it when you can dis-assemble the CPU code and show that the CPU is programmed to deal with 160F water temperature.

Let me make this simple, so that you can understand it: If the DME was unable to cope with the mixture conditions at 160F, your car would code every time it warmed up with the factory thermostat and reached 160f on its way to its 205-210F normal operating range. Obviously, that does not happen, or every Porsche owner would be coding every day..........

[porschedavid]

What about where it as sat for a few months,IE would it need a good run

[996AE]

I have a low T in my 996 replaced along with WP a few months ago. Just passed CA SMOG Star Station testing with flying colors.

[JFP in PA]

Originally Posted by porschedavid

What about where it as sat for a few months,IE would it need a good run

If it sat for "a few months", particularly without fuel stabilizer in it, I would dump Techron in the tank and take if for a hard run before checking its fuel trims.

[JFP in PA]

Originally Posted by 996AE

I have a low T in my 996 replaced along with WP a few months ago. Just passed CA SMOG Star Station testing with flying colors.

There is absolutely no reason a car with a 160F stat would do otherwise.

[996AE]

Winner!

[Rodsrsr]

Are not the CATS more effective the hotter they get? I was always told to make sure the car is at least normal operating condition before testing.

[JFP in PA]

Originally Posted by Rodsrsr

Are not the CATS more effective the hotter they get? I was always told to make sure the car is at least normal operating condition before testing.

The cats are heated by exhaust gases, which do not change much in temperature as a function of coolant temperatures, they are more a function of air/fuel ratios.

The reasons for getting the car up to "normal operating conditions", or steady state as it is known in the trade, is to allow everything to come to equilibrium. Good examples of why this is important are the misleading results you get when you check cam deviation values or engine sump vacuum levels on a car that is not steady state.