1977 EVAP System Challenge (1 Viewer)

[MidLife1977]

I recently replaced my fuel tank and fuel filler tube, and while in there replaced all of the fuel hoses and decided to take a shot at restoring the EVAP system, including:
- new check valve (mine was missing, just had a line from the fuel vapor container to an open-ended hard line that led to the engine compartment.
- installed a used oem charcoal cannister (appears to be a CA version, model year correct). also missing when I purchased my FJ40. The cannister tested correctly as per the emissions manual using 40 lbs of air pressure.
-installed a model year correct VSV and connected it to the original harness plug on the driver side fender. The VSV appears to pass on ohms, voltage, and air flow testing as per the 1977 emissions manual.
- replaced my original emission controller with a restored replacement unit, same part #. Not sure if the inside was restored.
- ohm tested the speed sensor signal to the controller, which appears to be functioning.
- voltage tested the controller harness which showed just under 12 volts on pin #4 when ignition was turned on.

Now the challenge. While the vehicle is in motion, I'm not reading any vacuum when reaching the speed thresholds that should activate the VSV. I put the original controller back in, but same result. With the controller harness unplugged from the controller, the engine cranks and stops correctly with no apparent difference. The vacuum routing is exactly as listed in that great diagram from Subzali several years ago. Currently there is no TP unit, so that outlet is capped on the VSV. Are there any solutions out there I'm overlooking? I'd like to have the EVAP system fully functional, but wondering if it is possible.

 

[Engineer8000]

The VSV can get stuck, will it pass air when energized? Make sure the harness between the VSV and emission computer is in tact. Those pretty restored emission computers are probably not functionally checked. I can do that for you, and repair if necessary.

 

[MidLife1977]

The VSV can get stuck, will it pass air when energized? Make sure the harness between the VSV and emission computer is in tact. Those pretty restored emission computers are probably not functionally checked. I can do that for you, and repair if necessary.

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Thanks for responding! Based on those photos it sure looks like you know what you're doing!
VSV does activate, even at 11 volts, and it did pass the air test when activated. So that said, I may send that pretty on the outside controller to you and see if you can check it out. The tabs don't look to have ever been opened!
For the speed sensor pulse, how many ohms should it read at the controller harness, and should it be the same amount each pulse, or one strong and one weaker?
Also - what method should I use to test the harness between the VSV and the controller?

 

[Engineer8000]

I would unplug the emission computer and the vsv, check for continuity from pin 4 and 6 in the emission computer connector, should be open circuit. Then jumper the two pins at the VSV and check for continuity again at pins 4 and 6, should be 0 ohm or close to it. If its still open circuit, that might explain some of what you are seeing.

As far as the speed sensor (VSS) you will see some voltage at pin 1 of the emissions computer when the VSS is open, and 0V when it is closed. It is a square wave. I worked out the exact wave form frequency, amplitude and offset to mimic the VSS input to the computer. This is hard to test with the truck not moving.

I just set up two function generators to mimic the rpm and vss inputs.

 

[Engineer8000]

Send me a PM if you want me to check those modules out.

 

[GA Architect]

Just for those special occasions you may have the 'High Altitude' version and you want to desmog, here's the Jim C's diagram: