Failed emissions...Need help

[aribop]

Hi all,

Took my car to get the required emissions test and it failed the NOx piece. The guy was real helpful and re-ran the test using a lower gear...no help. We then unhooked the vacuum line going to the FPR hoping it would dump more fuel into the engine...no help. Basically, he said the car is running too lean?? I thought it was running too rich per the inside of my tailpipe is black!! The CO-% was 0.00 on both runs. He said I have no unburned fuel in the tailpipe...I thought that was a good thing?? I am very confused.

Here are the stats: First Run

HC-ppm 0013 - 162 allowed
CO-% 0.00 - 1.04 allowed
NOx ppm 1388 - 1163 allowed
RPM 1935 - 1500 to 3000
CO+CO2% 12.7 - 6.0 min

Second Run

HC-ppm 0008 - 167 allowed
CO-% 0.00 - 0.94allowed
NOx ppm 1611 - 1273 allowed
RPM 2752 - 1500 to 3000
CO+CO2% 13.4 - 6.0 min

Do I need an adjustable FPR so I can crank that sucker up during the test?
I have a small exhaust leak where the catback section bolts to the cat...could this be contributing?

Any help / opinions will be greatly appreciated. This car needs to pass as it is my only transportation.

[aribop]

Sorry, I forgot to post my specs in the signature.

The car is a 1989 944 S2. Recent(less than 3k miles) engine rebuild. The only things I changed/added. New FPR and Damper. Had injectors tuned. Fixed all the vacuum leaks. SFR catback.

They checked the CO+CO2%. Yes, the only thing it failed is the NOx.

Thanks,
Albert

And..I used your procedure from your site to remap the tracking arms on my AFM.

[UconnTim97]

Mine had similar numbers when I got it tested last month. I was fortunate to be just under the limit for the NOx.

I am curious to see what was causing that too...

[Porsche-O-Phile]

I agree - I'd start with the catylitic converter. The O2 sensors are kind of notorious in these cars, but yours sounds like it is behaving properly. Good luck.

[aribop]

I should not have any carbon buildup in the engine at all.

So I suppose the cat is probably at fault. I was hoping I could get by with a new O2 sensor...oh well. I guess now would be a good time to upgrade to a high flow cat....any suggestions?

Oh, and my DME is not chipped. I want to chip it but have not found a good compromise between price and actual improvement.

[aribop]

Thanks! I will definitely try that.

How does that work? I thought the hall sensor was tied to the knock sensors some how? I'm still trying to learn the electronics part of this car...

Also, if the car consistently runs lean, isn't that more of a problem than it running rich? and what can I do counter??

[Makis]

I think NOS emission are high when the engine is running hot. So increasing fueling may help and/or retarding the ignition. The following information may help you in trying to sort out the NOX emission problem. Extra fueling should also improve performance, so I would try that only before altering ignition. Also swithing to higher octane gas may help.


Extract from clarke garage
http://www.connact.com/~kgross/FAQ/944faq12.html



13.8 Aside from chips, is there any adjustment I can make to my car's DME?
There is a provision on the Motronic cars (944 and 911) to make small adjustments to the fuel mixture (injection pulsewidth) and the ignition timing in order to compensate for the quality of fuel available in your particular country or region.

There is an board-mounted eight-position rotary switch accessed through the little hole in the back side of the DME box. These adjustments can be made without opening the cover of the DME box, unless you have a California vehicle, which will probably have a metal plug over the hole instead of a plastic fitting. The switch has a triangular-shaped recess in which to insert a special adjustment tool — I just whittle down a golf tee to make mine.

The switch has detent positions so you can count the clicks to tell where you are set. All the DME boxes I’ve ever seen have been set on position #1, so I call that the stock position. The adjustments can be found in the following table:

switch position fuel mixture adjustment ignition timing adjustment
stock 0 0
2 +3% 0
3 +6% 0
4 -3% 0
5 0 -3 degrees
6 +3% -3 degrees
7 +6% -3 degrees
8 -3% -3 degrees

[Don 944 LA]

2 things.

1st... that table is for the 911. try FR_Wilks site for the 944 tables.

2nd ... the FQS will retard timing and adjust fuel ( in euro NON-O2 sensor cars ). On US cars ( non-euro chip ) it will just adjust the timing.

I believe I am correct on this.. correct me if I am wrong.

[Makis]

Originally posted by Don 944 LA
2 things.

1st... that table is for the 911. try FR_Wilks site for the 944 tables.

2nd ... the FQS will retard timing and adjust fuel ( in euro NON-O2 sensor cars ). On US cars ( non-euro chip ) it will just adjust the timing.

I believe I am correct on this.. correct me if I am wrong.

1. FR_Wilks site does not include 944S2 information. Some experiments I did with my S2 suggest that the 911 tables are applicable to S2.
2. Even if FQS retards the timing, that should be enough to help pass emissions, so is definetelly worth a try.

[Eli K]

Where exactly is the hall sensor located?

[Brando]

In/On the distributor.

[aribop]

Hi all,

The clutch went out shortly after I posted this and that is why I am just now getting around to an update.

I took FRWilks suggestion of unplugging the Hall Sensor and went back to the emissions station.

The car passed with flying colors!

Thanks to everyone for their input.