OK, this is what I've done so far, Checked starter and solenoid - good, replaced ignition tumbler and bypassed VATS with resistors, I have #4 key so I used 1/4 watt 900 ohm resistor, still no crank, have power to everything else.
There are a few other electrical gremlins but i don't believe they have anything to do with it as they've been around awhile. I've checked for bad wires and loose grounds and haven't found any. Any ideas will help. 1992 LT1 auto.

 

Have you check for codes ? My 92 has had starting issues. based on the symptoms (checked codes and also checked for spark) and help from the guys here on the Forum, I have narrowed it down to the ECM. gonna order one tomorrow. good luck.

 

The #4 pellet resistance must be between 850 ohms to 942 ohms. You need to first measure your 1/4 watt resistor to see if it is within these limits. Next, if resistance is correct, find your clutch safety switch (gear selector sw at base of gear shift if automatic), unplug it and jump the wiring harness plug. Measure the voltage on the jumper when you hit crank position, it should be 12v and the starter should crank. You can check the starter by jumping 12v to the jumper. If no 12v, then the start enable relay is not closing or the relay is defective or the VATS module is defective.

 

Is the fuel pump running 2 seconds when you turn the key on?
W/key on, did you check for power at the starter and relay?

 

If you could give details on jumping the wiring harness plug it would be greatly appreciated

 

I just used a test light to check neutral safety switch. There is one hot wire (blue) when I turn the ignition switch on. There is no "outgoing" power on any of the other wires when I turn the ignition switch to start. Does this mean the nsw is bad or is this where VATS would disable the system?

 

Power comes through the firewall, to the ign sw, "crank", contacts, to the start enable relay contacts, to the gear selector sw, back through the firewall and to the starter solenoid. This is the order that you should test for 12v after each device to find out where 12v stops on its way to the starter solenoid. You should be able to hear the start enable relay click, and measure the voltage across the relay coil showing that the VATS module is measuring the correct resistance and is closing the start enable relay. If the relay closes, then you should measure 12v after the relay contacts and through the gear selector sw and on the starter solenoid. The start enable relay closes when the ign sw is in run and the VATS module detects the correct resistance.

 

I have power to the neutral safety switch but none leaving to the starter when I turn ignition switch to crank. I believe its the maroon wire that goes to the starter solenoid.
I don't hear a click from the starter enable relay.

 

I don't know the color of the wires to 92's (I own an 87), but if you will jump across the gear selector switch and see if it will crank, then you prove that the gear selector sw is defective. Relays are fairly quiet and you may not hear it close.

 

Jumped the neutral safety switch. IT CRANKS!! Now to replace the switch and put this mess back together. Replaced the relay switch for good measure

 

Well so much for that idea....replaced switch, same problem, power is still being cut off somewhere, engine only cranks when I jump the switch, doesn't start. I don't hear the fuel pump engage when I turn the switch on.

 

I recently purchased a 90' with no key, connected a VATS Interogator, and no code works! Trying to build a vats bypass unit, suspecting a bad CCM. If I can fool the ECM with as bypass unit, and provide a ground for the starter enable relay, then it should start. I am frustrated, have half the dash apart, trying to figure the system out. The signal from the CCM to the Engine ECM is blue wire, connector B wire 6 Drk Blue, and thats where we connect the bypass circuit. My first attempt at that circuitry failed and will try again, or order a pre made bypass. Good cars, but a little tricky!
Eric
hpranch@interx.net

 

Read my post, sixth one up and trace the 12v power through your starting circuit. Somewhere 12v is interrupted on its way to the starter solenoid.

 

I have 12 volts "all the way" to the starter solenoid. However it doesn't get passed the gear selector switch unless it is jumped, the switch was replaced with a new one, same problem. If switch is jumped the motor cranks, indicating power all the way to the solenoid. Relay contacts show 12 volts when switched to crank. If i ground the small black w/yellow stripe wire on the relay it will crank also.??

 

You aren't making any sense! You say you have 12v all the way to the starter solenoid and in the next sentence you say it doesn't get past the gear selector sw. Both can't happen at the same time!!!!!!!!!!!!!!!!!!!
The gear selector sw gets plugged in from a plug on the wiring harness. You might have a defective connection on one or both spade lugs on the wiring harness plug, or the gear lever isn't moving the switch all the way to make connection. You can use a needle to pierce the insulation on the two wires on the plug to see if you get 12v on both wires on the plug in park position.
The VATS module grounds the coil on the start enable relay if it sees the correct pellet resistance. You can ground the start relay coil wire, but the gear selector switch is after the start relay, so forcing the start relay on won't do you any good if the gear selector switch is open circuit.

 

Been awhile but I'm back. Haven't had time to mess with it much. Sorry about the confusion. The car will crank if I jump the wires on the gear switch or if I ground the starter relay but it won't start. There is no fire to the plugs and I don't hear the fuel pump kick on prior to cranking. I've replaced the ignition tumbler, new key w/#4 pellet, starter relay and neutral safety switch and the ccm has been rebuilt. Still nothing.

 

The VATS module generates a 30 Hz square wave if it sees the correct ign sw pellet resistance and that goes to the ECM which tells the ECM to pulse the injectors. The VATS module also grounds the start enable relay which connects the ign sw, "crank", contacts to the gear selector switch. If the gear selector switch is in PARK, then it completes the circuit through the firewall connector to the starter solenoid terminal on the starter motor. It appears that your VATS module is reading the correct resistance and is closing the start enable relay but you have a problem with the gear selector switch. To prove that the ECM is pulsing the injectors during cranking, you should get a noid light (available at auto parts stores), or make one with an LED (light emitting diode) and a series 680 ohm resistor. Even 910 ohm resistor will be ok. Unplug an injector and connect the noid light to the injector socket and crank the engine, you should see the light pulse during cranking. If no pulsing, check the two injector fuses with an ohmeter and if ok, then you need to see if the VATS module is supplying the 30 Hz squarewave to the ECM. You can do this with an oscilloscope or even an a.c. voltmeter which you have if you have a VOM (voltmeter, ohmeter, milliammeter) test meter. The homemade injector test light must be connected with the proper polarity on the inj socket to work.
If you don't hear the fuel pump, use a fuel pressure gauge on the shrader valve on the right side fuel rail to see if you have fuel pressure. It should be between 35 to 42 psi. Check the 10 amp fuel pump fuse in the fuse block. Engines will not start without fuel, air, spark, compression. If you have no spark, then you need to find out why. Auto parts stores may be able to test your spark module. The spark module gets a signal from a pickup coil in the bottom of the distributor, measure the resistance of the pickup coil, it should be low. You could also have a defective spark coil.

 

Checked the injectors with noid light, injectors not working, both fuses are ok. No spark to plugs, all ignition components are relatively new and "should" be ok but I'll check asap. I don't currently have a fuel pressure gauge but I've always been able to hear the pump kick on prior to starting but I don't now, just replaced the pump last year. I just got the ccm rebuilt so i believe I should be getting all good signals. What's the diff between CCM and ECM? I can place the gear selector in park or neutral and then ground the starter relay and it will crank, doesn,t that mean the gear switch is OK? It's new. Another small note, may be relevent , maybe not but my courtesy lights don't work when the doors are opened, only when rear hatch is opened, the switches are working because the "door ajar" dash light comes on. This started at the same time as when the car wouldn't start.

 

Your gear selector sw is ok. ECM is the computer board used in early C4's, CCM is used in later C4's. Your injectors aren't working because VATS is not measuring the correct resistance on the pellet of your ignition key, or the VATS module (may be incorporated into the CCM) is defective. Spark may be included in VATS on 92's, it isn't on 87's (my vette). Door jam switches ground the courtesy light delay timer and if they are defective, no courtesy lights when doors open. The hatch switch doesn't go through the courtesy delay timer relay, it operates the courtesy lights by itself. A separate door jam switch on the drivers door goes to the warning and alarms circuit that lights the door ajar light on the dash. Fuel pressure gauges cost about $12. I doubt you have pressure issues, but you can't beat a gauge for proving what pressure you have.
You need to find out why VATS isn't closing the start enable relay, isn't allowing the injectors to pulse and maybe not allowing spark (I'll see if 92's VATS controls spark tomorrow).

 

92 Vettes do not have a VATS module, that circuit is inside the CCM. Also VATS, if it doesn't see the correct pellet resistance within about 4% of the assigned value, will not allow the start enable relay to close, preventing cranking, won't allow injector pulses, and won't allow spark.
Also, you cannot full time connect a resistor in place of the ign lock contacts because VATS expects to see the resistance to become infinity (removal of ign key) between starting. I am beginning to suspect your CCM rebuild.