Hi all,

Looking for some advice.

1993 non-EGR 945 turbo.

I recently installed a air/fuel meter. The meter shows lean at WOT. In addition, I have a recent emissions report that shows high HC and NOx.

From reading the FAQ it makes sense that I would see the combination of lean and high HC and NOx, my problem is I do not know how to find the problem.

First I will give you the numbers:

Measure Max Allowed Result
HC(PPM) 130 113
CO (%) 0.70 0.15
NOx (PPM) 1522 1513


Ther are no codes stored on the OBD.

I checked all air intake today to check for leaks and found none, although I doubt this would be a problem as I have a turbo and at WOT I figure I would be losing air instead of gaining.

The O2 sensor is only about a year old.
I changed the fuel filter about a year ago too.
The Cat is only about 6 months old.

That leaves fuel pressure?

One thing I can't find in the FAQ (except that it is difficult) is how to measure fuel pressure. Anybody got a walk-through? If it is fuel pressure, does that mean a bad fuel pump?

Any other ideas?

Thanks,
Ian

Check out ths site

http://www.interro.com/techgas.html

The common thread between the two points to your ignition system, plugs, wires, etc.

High hydrocarbon (HC) readings usually indicate excessive unburned fuel caused by a lack of ignition or by incomplete combustion. Common causes include a faulty ignition system, vacuum leaks, and fuel mixture problems. Circumstances that can lead to a high HC emissions are:

* Incomplete combustion due to fouled spark plugs.

* Improper timing or dwell

* Damaged ignition wires

* Poor compression

* Vacuum leak

* Ineffective or faulty air management system (ECM control of air/fuel ratios)

* Catalytic converter intervention and HC concentrations
High HC readings at the tailpipe are an clear indication that there is a problem in at least one part of the system, but an HC reading that appears within "normal" ranges or is only modestly elevated is not necessarily a reliable indicator of proper or even acceptable system performance. HC readings at or near "normal" are possible, and not uncommon. From a malfunctioning engine equipped with a properly functioning catalytic converter. In such circumstances, truly elevated pre-catalytic converter HC levels will be masked by the catalytic converter and the potential for an HC problem must be further evaluated in the context of other readings of abnormal gas concentrations and AFR / Lambda readings.
__________________________________________

Circumstances that can lead to abnormally high NOx emissions are:

* Malfunctioning EGR valve

* Lean fuel mixture (AFR above 14.7, Lambda above 1.0)

* Improper spark advance

* Thermostatic air heater stuck in the heated air position

* Missing or damaged cold air duct

* Combustion chamber deposits

* Malfunctioning catalytic converter
--
Bob K

Hi Bob,

Thanks for the excellent link.

It remains a mystery.

Incomplete combustion due to fouled spark plugs.

High HC
* Improper timing or dwell
Isn't this set by the computer. I thought you could not set timing on 940's?

* Damaged ignition wires
Put in new wires. Still lean.

* Poor compression
Have not checked yet.

* Vacuum leak
Not that I can find.

* Ineffective or faulty air management system (ECM control of air/fuel ratios)
ECM=Computer? I have not heard of many computer failures on this car. Maybe I should see if I can find a known good one for swap?

High NOx
* Malfunctioning EGR valve
No EGR on this car

* Lean fuel mixture (AFR above 14.7, Lambda above 1.0)
Well, I know it's lean. Can't figure out why.

* Improper spark advance
Isn't this related to timing above?

* Thermostatic air heater stuck in the heated air position
No hot air intake on this car.

* Missing or damaged cold air duct
What's a cold air duct? Checked the air-filter and housing...all good.

* Combustion chamber deposits
Recently ran Techron so this should not be a problem.

* Malfunctioning catalytic converter
Cat is new.

Also replaced spark plugs and distributor cap -n- rotor since I had them laying around.

No change.

Swapped in known good Knock sensor.

No change.

That leaves -

1. Compression
2. ECM
3. Fuel pressure?

Funny thing is that the car runs great. No obvious symptoms of lean running.

When I pulled the (Volvo) spark plugs there was obvious blistering of the ceramic part.

???

I recently failed a NOx test and my mechanic diagnosed the problem as the knock sensor, if that helps any.

Thanks for the knock sensor tip.

Do you know if your mechanic determined the knock sensor based on codes set on the OBD?

Thanks,
Ian

Re. your question re. diagnosing knock sensor -

For what it's worth,
The knock sensor retards the timing some (apparently up to 10º) when it detects knock. I'm told it's basically a block-mounted microphone.

Timing changes will strongly affect emissions. Sensor reading incorrectly could certainly affect emissions.

Exactly how the mechanic knew? Good question!
--
Formerly Sophie's Maintainer. Sven: '89 245, IPD sways, E-fan conversion, 28+ mpg - auto tranny. 850 mi/week commute.

Toruqe down a knock sensor past the 12lbs will render it useless, and cause problems.
Poolman