Failed Emissions, spewing HC’s (F.I. 2.0L)

[TimW]

I’m trying to get my ’73 2.0L stock F.I. to pass emissions in WI. This is a used motor, and has unknown miles; but it runs great, starts right up, etc.

These are the numbers from the first time I took it in:

FAIL HC 8.2494 grams/mile (7.0000 limit)
PASS CO 67.6885 grams/mile (120.0000 limit)
PASS NOx 2.6451 grams/mile (6.0000 limit)

I wasn’t so concerned about the first failure because I hadn’t done anything to tune the motor. I really just wanted to see if it would pass or not as-is.

Well, after tuning the motor the numbers are worse. I set the dwell/timing, new points, cap/rotor, plugs, plug wires, and vacuum hoses.

Here are the numbers from the second test:

FAIL HC 8.9644 grams/mile (7.0000 limit)
PASS CO 66.2308 grams/mile (120.0000 limit)
PASS NOx 3.5931 grams/mile (6.0000 limit)

BTW: in WI if I spend $450 to fix the problem I can get an exemption. Unless I take it to the Porsche dealership I don’t think that’s going to happen. I ~should~ have the mechanical ability to fix it myself .

Any ideas?

Tim
’73 914 2.0L

[Dave at Pelican Parts]

Was that at idle or at higher RPM?

If at idle, what is your idle speed?

If at idle, try tweaking the mixture control knob on the ECU. Count the number of "clicks" (so you can get back to where you started). CCW is leaner, CW is richer. You want leaner.

If at higher RPM, the knob on the ECU will have no real effect. You can try removing the resistor from the head temp circuit (if there is one). Or you can try--after warming the engine up--shorting the head temp sensor lead directly to ground. That should lean the mixture out a bit.

Or you can drop the fuel pressure. Spec is 29 PSI. Check yours first to see if it's in spec or not. Try dropping it a couple of PSI--that should also lean the mixture out somewhat.

Note that you may have some idling and/or driveability problems if you change something that affects the mixture through the whole range, like the head temp circuit or the fuel pressure. You may have to monkey with things a bit to get everything to work decently.

Kjell's D-jet Guide is still the best single resource I know of on-line: http://www.914fan.net/djet.html

--DD

------------------
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

[HMeeder]

This may be cheating, but you can install a 1K variable potentiometer in line with the CHT. This will allow you to adjust the fuel mixture yourself. I have found that there is a wide range of performance of this one little item (I have tried 4 differnt CHTs and get different charecteristics from all of them!)


Good luck!

------------------
Herb
'72 1.7 Tangerine 'Teen
'74 2.0 Red Rustmobile

[TimW]

In WI the tests are performed in two series of 0 to 60 mph tests for 2min. each (4min. total). The numbers are the average.

Looking at the nice little graph they game me it appears the HC’s drop off sharply around 25-30 mph (low emissions at high speeds). I’ll try and post those later just for giggles.

Idle is rock steady at 1100 RPM (pretty much warm or cold).

I’m becoming very familiar with the djet doc. I didn’t futz with the mixture or pump pressure, yet. I will, as well as re-familiarize myself with the CHT potentiometer adjustments. Unfortunately in WI since test are done at state facilities rather than local garages there isn’t much opportunity to make adjustments during the tests. I pretty much have one shot to get it right. Although I can go as many times as I need, I just have to pay $10 after the first three tries.

I refuse to give up!

Tim

[Jim Smolka]

I would back off the fuel pressure in the fuel rail by adjusting the fuel pressure regulator...

That should help some... Also the CHT think is a good shot.

I have also heard that you can loosen (more gap) the adj on the valves

[pbanders]

High HC and CO indicate your car is running rich. Here are the things I'd check, see my reference below for measurement values

1. Fuel pressure
2. TS2 (head temp sensor) cold and hot resistances
3. MPS coil resistances
4. MPS full-load diaphragm integrity. If you have a hand-held vac pump w/gauge ($30 at FLAPS), it shouldn't bleed down more than 5 in. Hg in 5 minutes. Cheap/fast test is to suck or blow on the intake port, any sign of leakage the thing is toast. Replace with a rebuilt unit.
5. Make sure your TS1 (air temp sensor) is connected, it will run more rich if it is disconnected.
6. Verify you have all the right part numbers using my reference below.
7. Idle ECU knob setting. There should be a mark in the plastic surround of the knob, about halfway. Use that as a starting point.

Good luck! I don't suggest adding ballast resistance to the TS2 sensor, it will only make your car run richer. As a last resort, try turning your ECU knob completely CCW, and opening up the air bleed screw to bring your idle up. Reset after the test to a good driveable setting.

Brad Anders

http://members.rennlist.com/pbanders

[Will98D]

One other thing I thought of could be a leaking cold start injector. Plus, why is your idle 1100... that sounds about 200 too high. If you need it there to keep it idling, it could be from this extra fuel you have going into the system.

[TimW]

Here are the graphs they gave me. --Tim

[Dave at Pelican Parts]

HC readings spiking like that would make me suspect something electrical.

Probably ignition-related. If a good check and going-through of the ignition system didn't improve things, then check the wires and connections that have to do with the FI.

--DD

------------------
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling