This is on a 90 coupe, 92,000 miles.

Went for a short drive yesterday, was running well until engine just shut off and would not restart. Had it flatbedded home and started diagnosing today. Security light goes out as it should with switch on and I get no SYS light.Chck engine light not on.I have spark and fuel to rail (came out the schrader valve). Used a jumper to get the codes and it has code 46.I followed the troubleshooting in the FSM. I cant find a open or short in ckt 229, so went on to check the ccm. It has no codes,which I thought would have a code 54...fuel enable failure. At this point I am stuck. Is there any way to make sure of why this will not start, before I have to replace the ccm, which is what the FSM says is next? I'm assuming that if the engine will turn over then its not a bad key or ignition problem that I could bypass with the available bypass harnesses. I'm also assuming that if it is a vats problem, its at the fuel enable circuit. I know I'm doing a lot of assuming here and would not be hurt to be corrected. I have searched this forum for this but most posts deal with non cranking issues and the rest I find dont help to much. Thanks for any input and suggestions

 

A small update...I just pulled the connector to a injector and probed with a test light. I get power at both terminals with key on, but no change when I'm cranking. Shouldnt the light blink on and off when cranking?

 

Saying you can't find a short is not the same as saying you know for sure there is NO short.

You have to test an entire length of wire at each link in the circuit - from PIN TO PIN. Not the easiest task, but it's pretty cheap to do electrical diagnostic, as opposed to buyin' parts blindly.

I have to do this wiring diagnostic stuff in the morning...

 

please check the injectors themselves for dead shorts.. use an ohm meter and report the values of each injector

 

If you can give a brief explanation how to do this I will do tomorrow. Can you tell me if I seem to have power to the injectors by my follow up post. Should the test light be blinking on and off when cranking the engine? Would bad injectors cause the engine to go completely dead at a cruising speed and make it impossible to restart?

 

since the batch is wired all + injector to each other and all negs back to the ecu. If you have a dead shorted injector the 12volts will feed through the injector thats shorted and put 12v into the ground circuit thats insulated in the ECU. Its not chassis ground untill the ECU connects it to ground to fire the injector. This will cause the Ecu to not function. The FSM does not take into consideration a dead shorted injector because I don't believe they ever thought an injector would short. But the design of the multec has a flaw in it that will let it short. Think of it this way. If you put the 2 wires going into an injector togeather. What would happen? The injector fuse should Blow. But if it had 5 ohms resistance would it still blow the fuse or back feed the ECU. All I know is that cars with shorted injectors act exactly like yours. All you have to do is get an ohm meter and disconnect the injector plugs.. Put a lead to each of the injector terminals and read the meter. Anything under 10ohms I would consider shorted. If you find a shorted injector keep it unplugged and try to start the car. try it, its a free test.

 

OK I will do this tomorrow after work and post my results. I hope it is something as simple as this as injectors were next on my list to replaced anyway. This would just move up the schedule a bit. Let me ask this though...by the way I understand the FSM, the injector connectors have voltage all the time(with switch on and to make them "fire" the circuit goes to ground,hence a test light would "blink" when the engine is turned over. Mine is not doing this, making me think that the ccm has the fuel "disabled". Thanks for your reply and help!

 

i don't exactly know what happens to the CCM when it sences voltage going back through the ECU via the injector ground. I can't find anyone that has ever even toyed with the idea. All i know is many people change the CCM to no avail. Dealers change them all the time, and still same problem untill the bad injector is taken out. Will this be your problem, I hope so.

 

Injector readings#1-16.5,#3-16.6,#5-16.5,#7-16.6,#2 -16.7, #4-16.4,#6-16.7,#8-16.4

 

they are all within specs. To bad that would of been easy, now you might have to look to the CCM..

 

Thanks Jon for your help...Any one else have any ideas? Is there a way to find out IF the ccm is bad? I'm really not one to just throw parts at a car unless all else fails

 

There is a condition that will disable injectors (on a '94 anyway), so that the engine does not flood. DTC41 open ig control circuit, which I'm workin' on now... (workin' on me is more like it )

Check your '90 FSM to see if ig control circuit problems will disable injectors.

 

This gives the start sequence of the '90. http://www.corvettebuyers.com/c4vettes/l98.htm.As far as I can tell, on a 90 a flooding condition will not disable the injectors. If I understand the FSM (which believe me, I may not understand) correctly If the injectors are enabled (by the ecm or ccm...not sure which) then if I hook a test light to an injector harness it should have power with the ignition on, which it does. But when cranking, the light should blink on and of....which it does not. IF this is correct, then something has the injectors disabled. I just dont know what. Thats what I'm trying to determine...if the injectors are being disabled