Pete L

Posting to this board for first time in two years! Hope somebody can help me. My 86 flunked CA emissions last week. NO was high; 1590 vs 1106 std at 15MPH and 1238 vs 936 std at 25MPH. HC was a bit high as well. 244 PPM vs 128 max at 15MPH and 112PPM vs 103PPM std at 25MPH. CO2 was 12.2 and 13.1% respectively. O2 was 2.8 and 2.2 respectively.

I am doing a step by step process to take care of the problem, starting with vacuum leaks. Then will check O2 sensor and all LH sensors at the computer.

Found several vacuum leads including a badly cracked fitting at the air injection diverter valve (hopefully this will fix majority of the problem). THis leads to following questions.

Looking at the fuel path in manuals on 24-208 the vacuum thermo switch located at passengers side rear of engine is connected to the charcoal canister air bleed valve. The air bleed valve opens with vacuum on it from the line from the thermo switch. Does the thermo vacuum switch close (no vacuum) hot or cold? Which is it? When cold, mine is open, have not run car up to temperature yet to check hot. Seems like if the engine is hot, you would want the bleed valve closed to keep there from being a big vacuum leak allowing the fumes in the charcoal canister to be sucked into the engine into the intake manifold (I think?).

There is a vacuum diaphragm valve at the front of the motor that I presume controls the amount of “suction” from the canister into the intake manifold. The vacuum line for this device comes straight from the vacuum spider behind the MAS. Does this open under high vacuum thus allowing charcoal canister venting or close? I am all confused!

Thanks in advance

Pete Loedding
1986 928 5-speed black/black
Now 170K young and loving Willow Springs here in SoCal

PorKen

Pete L,

The air injection diverter valve diverts air from the cats and dumps it into the airbox when you lift off the throttle suddenly. This is to cut down on 'popping' on decelleration, from unburnt fuel.

The control-valve regulates the purging of the vapor sytem during part-throttle cruising, but only after the engine has warmed up. (The vacuum thermo switch is connected to ported vacuum.)

This post may help: >Gas Vent System<.

Pete L

Today my 86 5-speed early passed emmissions. Here is what I did to get it through:

1. Checked all inputs at computer like temp sensor 2, throttle switch, etc per FSM section 28. All checked out.

2. Checked all vacume lines and hoses. Found J connection on top of air injection diverter valve badly cracked, so probably limiting the injection of air into the cats. Possibly this is why O2 increased on second test and NO went down. Replaced the vacume line. Replace oil filler and dip stick o rings as well. They were hard. The vacume thermo switch that controls the charcoal canister output line air bleed valve was leaking. Did not replace but nippled off to get through test.

2a. Checked air pump diverter valve with vacuum pump to see if valve inside was moving. It was. Started car with air line dissconnected from diverter valve to check output of air pump. It was pumping a good deal of air thru the line so OK

3. Checked MAF. All items checked except one test with range of 3.6 to 4.1 ohms I got, 4.3 ohms and on other test with range of 0 to 1000 ohms I got 982 ohms. Had a spare MAF and installed it with new O rings (large and small). Reconnected MAF ran car to 2000 RPM and looked to see if wire burn off feature (red hot 4 seconds after turning off ignition) working. It was.

4. Replaced O2 sensor with three wire universal sensor from 928 International. May not have had to do this as old sensor seemed to work properly except a little slow when computer was in closed loop. Checked with a volt meter

5. New air filter using factor instead of my K and H.

6. New plugs, used bosch wr7dc

7. Container of Guaranteed to Pass emissions in the tank and 100 hard miles of driving.

8. Fresh tank of gas and was hot prior to the retest

Results are below:

HC 01June Limit 16May
15MPH 126 128 244
25MPH 72 103 112

CO
15MPH 0.39 0.80 1.03
25MPH 0.08 0.60 0.13

NOX
15MPH 916 1106 1590
25MPH 788 936 1238

O2 3.0 2.8

In summary, the things that probably fixed the problem were repair of vacuum leak at diverter valve, MAF and running the fuel cleaner thru the injectors and getting the car good and hot prior to test. Surprised it passed since I did not get the CO reset to 0.6% per spec after replacement of MAF

So, got it all done for 9 hours of my time and $150 in parts. Still weird about high HC at 15MPH. I went back and looked at my last 8 years of inspection tests in VA and CA and they all had HC between 90 and 126 at 15MPH. I think I have a lean miss in the car that causes this. THe miss has been in the car since I purchased it in 1994

Pete L
1986 928 S 5-speed black black
170,000 miles

PorKen

Good job!

Regarding your miss, maybe you have a goofy injector?

Also, I've had corrosion problems (especially after pressure washing the engine) with the fuel injector connectors, which caused poor running.