Took the 88 S4 (SE) for it's emissions test today - first step in getting it registered for the road here in OZ.

The test done was an IM240 test which is a 240 second (4miinutes) test done on a dyno simulating an urban cycle and covering about 3kms - about 2 miles. This test gives results that correlate with the result from a US 1975 FTP test

In all likelihood it has failed, by a long way if it needs to meet the tests for a cat equipped car but also fails the earlier non cat test.
Results were
THC 2.77g/km
Cat pass = 0.93
Non cat pass = 2.1

NOx 1.38g/km
Cat pass = 1.93
Non cat pass = 1.9

CO 43.4 g/km
Cat pass = 9.3
Non cat pass = 24.2

CO2 298.7 g/km
No pass requirements

The worst offenders are THC and CO which suggests it is running rich, The NOx reading is low which would confirm the running rich theory.

Smog pump is connected and working, MAF is three years and no more than 10,000 miles old. Car runs brilliantly. Had full service only 200 miles ago.

I pulled a plug to check and the central electrode and outer electrode look clean like new - I don't think the plugs have been in long enough to get the normal light brown colour. But if it was running rich you'ld think they'ld get sooty and black very quickly.

I'm stumped. Why is the CO so high - I thought 928 engines were relatively clean.

Oh the other bit of data was the calculated fuel consumption was 16L/100km. approx 17.8 mpg imperial or 15mpg US - a bit low I think.

 

Does it have a good o2 sensor? (wild guess)

 

No O2 sensor - no cats. Like most of the pre 90 Euro cars.

 

Just talked to a vaguely automotive knowledgeable pal of mine who remembered that the SE hadn't actually been driven anywhere since it was shipped here in June - Before the test this morning I filled the petrol tank from half full to full with Super UNleaded. so it was running on a mix of half new petrol and half 5 months old petrol - could this have made a difference?

 

Hi Jon
Have you adjusted the CO pot for 1% CO at idle ? (Air pump disconnected)

Are you running it with the airpump ?

 

Air pump should be disconnected during test. If its not it will mess up numbers. Local yearly MOT requires measurement while all emission gear is on and working. As test is done from end of exhaust result is wrong. It should be done from small pipes in engine bay. More than one owner has had serious problems passing inspection because of this while in reality their cars were running perfectly.

 

HI John

CO pot was adjusted to about 0.8k ohms IIRC when I first installed your MAF back in 2003? - Car seemed to run OK so I never got around to checking it with a CO meter - maybe that is my first step.

It would be nice if that would get things back in tune

yes I'm still running the airpump, and I'll get the mixture adjusted without it runnning

 

Erkka

On the non cat cars the airpump pumps to the exhaust manifold - Would this change the results of the test I just had done ? The measuring device was a big pipe taking all of the exhaust gases from the car for analysis not a probe stuck in the RMB.

I think (I may be wrong) that it doesn't matter how much air my air pump put into the exhaust the numbers would have been the same ?

 

Hello jon
800ohms is too high for a "new" MAF. The nominal Bosch setting is 382ohm. Personally, I try 300 ohms and then then measure it with a CO meter and gradually adjust the pot to get to the 1% set point.

 

Hi John

That may explain it.

I checked and it was still around 0.8k ohms on pins 1 and 2 of the pot. Pin 3 doesn't appear to be connected.

I'll be up with the Lark in the morning to do some serious pot screwdrivering IIRC it's about a million turns from one end to the other. Then off to find someone with CO meter.

Further thoughts - does the idle mixture setting affect partial load mixture, or WOT mixture or is that all governed by the LH mapping? My memory of chats with you says idle only but memory being what it is ??

Cheers

 

On another point, the fuel consumption is quite high .... unless that represents quite aggressive driving around town. My (ex) euro S4 would average 10l/100km on any highway average up to 140Kmph - after that, it would increase.
Having said that, it may also be worth checking the vacuum system on the fuel regulator/damper diaphrams for 'unmetered' fuel.
Hope the CO pot is the answer ..

 

When ever something is added it must have some effect on result. Air is diverted to intake at rews so it might not cause what you are seeing. Though it wouldn't hurt to try measuring pump disconnected also to see what diference it makes.

 

Wait a minute, I thought high THC was a good thing!! (*puff* *puff* *pass*)

 

Chaad, THC is basically measuring unburnt fuel - if it was burnt completely there would be no Hydrocarbons.

Garth
Fuel consumption as measured was quite high - I am guessing that because the equipment used was measuring both the total volume of exhaust gases and the gaseous content it is reasonably accurate. Although it seems higher than I have actually experienced around town, and like you I have found most economical speed is around 3k rpm in 5th gear - approx 10l/100km or approx 30mpg.