I'm not familiar with how the OBD-I systems operate, but on the OBD-II the ASD relay controls the entire fuel/ignition system. shuts it down in the case of a crash to turn off the fuel pump and reduce risk of spark from charged electronics.

On OBD-II as soon as the computer sees the crank is not turning, it turns everything off after about 2 seconds. you can confirm it works by turning key on. you should hear the fuel pump prime for 2 seconds, then shuts off until the computer sees crank rotation.

9 times out of 10, when the ASD stops working, it's because the crank position sensor is no longer working, or there's a short/bad ground in the harness somewhere, so start checking sensors and wires.


Personal story: took the wife out in the truck for a date night. before we left she asked "is it reliable? it won't break down on us?" this is after a new engine had been in for months, driven to New Jersey and back, and never had a hiccup. At midnight on the way home, everything went dead. gauges wouldn't respond, scanner couldn't even read the computer. Turns out on assembly, I pinched a wire on the crank position sensor in the distributor cap. while the insulation was not broke or cut, it eventually grounded out against the distributor body and killed everything. as soon as I un-pinched the wire (after hours of checking sensors, computer, etc.) a buddy of mine told me to check the wires to the crank sensor. truck started right up like normal as soon as the wire was un-pinched. I replaced the sensor for good measure and it's been fine since.

Another time, a small, 12 ga wire from the core support to battery negative had worked itself loose in the crimp. truck would randomly not start. found it while holding the key in 'start' while someone was wiggling wires and when they touched that one, it fired right up.

Also I've seen where every ground was connected but the ONE ground by the power steering pump. it was off to remove the intake and I was trying to do a compression test. hooked that wire back to ground and it worked flawless.

So...moral of the stories...on these fuel injected, computer controlled trucks, check everything on the harness and sensors, and check for all your grounds!

it can be frustrating and take a lot of time, you'll start to feel helpless like you'll never find it. Then it's usually dumb luck, you find it, and you get a rush of relief, followed by "I can't believe something that simple took me so much effort to find and fix"

Good luck!