South Coast Boy

Hi Chevy Astro fans. We've had a '95 4.3 Tiara Day Van for nearly a year now and it still refuses to start. The padlock light isn't on and the previous owner swears the security system was always disconnected. The starter only cranks if you jump the solenoid to the battery. The fuel pump primes and there is a smell of fuel at the back.. There is a big fat spark at the plugs too. On YouTube is a video by a guy called "Scanner Danner" which results in a corroded connecter in the terminal behind the battery. However he shows a test sequence for the ignition system which I've run through as far as the purple/white wire in the four way plug on the ignition. The video shows an oscilloscope with a pulse from this wire when the engine cranks. I cannot get a feed with a simple test lamp, should there be a signal from that one?

The starter doesn't crank from the ignition switch, just a click from a couple of relays, one at the front and one behind the drivers seat. I was going to try shorting out the gearbox inhibitor switch but I can't find it. Anyone have any clue where it is, I can't find it on the gearbox?

Help please!!!!