FredR

Just took my Cayenne for its first annual inspection- something required over here when a vehicle reaches the age of 10 years from when it was built [not registered].

For the first time the authorities have seemingly introduced exhaust emission measuring kit - probe up the exhuast type of thing- taken at idle speed only- the Cayenne passed no issue. However I am now worried about what will happen when my 928 is due for testing come next October. The thing has always seemingly had lots of emissions compared to my other vehicles and quickly gets unpleasant in a confined space. I presume they will be measuring CO content but I suppose they could also be reading CO2 and hydrocarbon emissions.

I can tweak the air fuel ratio at idle using ST2. As I understand the car emits 0.5% CO at an AFR of 14 to 1 so I tune for that AFR. I do not have an air pump fitted and as I am aware those things were intoduced to blow air into the exhaust and thus reduce the CO content- something of a bodge to get around legislation of the day. As I understand the CO content can be reduced by increasing the amount of fuel added at idle.

Much appreciate any thoughts based on those who have specific experience of pollution control. Obviously if they are only measuring CO I can tweak the AFR a bit- just do not want to do something stupid and make matters worse. The authorities here are pretty decent and I do not want to fall foul of them. At the moment I do not know what the impact of having no air pump is.

Rgds

Fred

joejoe

In the states if no air pump = instant fail and no test is even performed. Othr than that I have had cars (not my P cars) pass with de-veined air pump and one with an obviously gutted cat. It depends on how observant the tech was. It is much more strict now, but it seemed many cars can pass with some faults in system.

Strosek Ultra

In Sweden they do not know if there should be an air pump or not. The technicians are not very well informed of a rare car like the 928. I have removed the air pump on all three cars. On the two S4 cars, being privately imported from Germany, I removed the catalytic converter before the Swedish registration. I got them approved as non-catalytic cars which made me very happy.
Åke

alex70

Agree with the above comments. Most techs will not even know about the air pump. They'll look under the hood, hook the 'sniffer' up and if that and the gas cap pressure test works out, you'll probably be fine.

FredR

I am not expecting any awareness of what should or should not be there but I would like to know what parameter they are likely measuring [CO] and the likely acceptance criteria. I have asked a friend to look into the matter and beyond that I want to minimise whatever it is they might be looking for.

Previously they asked you to rev the car and they would make a visual looking for a smokey exhaust- now it is going to be more subtle but I suspect nothing like the smog tests in the States for instance.

Tomkat80222

Having no idea what the standards are, I would think that having a cat will get you a pass unless the car is running poorly.

FredR

Ha ha- we were still running leaded gasoline when these cars were new- ironically [and thankfully] they phased out lead just before I became the chief engineer at the local refinery in 1994. Thus my heap is a non cat with open loop CO control.

Indeed now you made me think a bit if the thing did fail on the day I suppose I could ask them to let me tweak the adjustment pot to suit whatever might be wrong- the local constabulary are generally very friendly and helpful believe it or not.

alex70

Here are worldwide standards with regional breakdown. I think this can give you some direction. Quite detailed.

http://delphi.com/docs/default-sourc...uty-2016-7.pdf

cheers and hope it helps

Speedtoys

A moderately well maintained 928 on stock tune and HW will pass no problem.


I just ran a 3yr parked 83 in california across emissions, and with goopy leaking intake donuts (spider intake) and everything else in the path of hydrocarbons clearly leaking and collecting dirty (all goopy too), AND an audible, we think, intake leak from a cracked intake boot...

Speedtoys

THEY dont need to know, the sticker on the hood says it's there.

Just depends if they look...or you live where there's reasonable enforcement of the smog shops exist.

dr bob

Fred--

More fuel = more CO. Not enough fuel gives higher HC as you get to the point of lean misfire. Not enough fuel will also spike NOx as you start having local hot-spots in the chambers. With no cats originally fitted, I'm not sure what they really expect. Leaded fuel is tough on oxy sensors too, FWIW. So after you get the mixture lined up with your ST2 and WB sensor, probably a good idea to plug the sensor hole until you are actively looking for data again.

PorKen

Fredo-san - like the CIS cars and S2s before it, the air-pump originally on your non-cat (non-O2 sensor) ROW S4-up injected air into the headers to after-burn extra fuel in the exhaust. Assuming the engine is in a decent state of tune and a properly adjusted CO pot, you should pass the CO and CO2 tests easily. (NOx tests are unlikely unless the car is put on rollers to simulate load, AFAIK.)

The air-pump on the cat cars injects extra air into the cats and is only needed during cold start. Unlike other makes with electric pumps which run only for a short time (or older Mercedes with clutched air-pump pulleys) the 928 air-pump is just a parasitic drag most of the time for O2 sensor equipped cars.

FredR

Indeed- I inadvertently got the CO/HC thing the wrong way round-NOx increases with leaness, CO with richness. I always plug the sensor hole after removing the WBO2.

I suspect they are really looking for wrecks that chug all kinds of gunge out to avoid accusations of impartiality. Maybe I will set the idle AFR at 14.7, then note the adjustment to get it to 14 so I can adjust on the fly as it were. If that does not do it then I will be well and truly in the smelly stuff.

FredR

Ken,

I have often wondered why they would fit an air pump on a non cat vehicle. The air pump on mine made some suspicious noises about 15 years ago and my friendly chief mech suggested I might consider "deletion" but my decision of course.

Rgds

Fred