Re: GM C3I Ignitiion

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From: hotothethismailto@hotmail.com
Date: 6/15/2006
Time: 11:20:44 PM
Remote Name: 147.202.45.202

Comments

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From: Jamie Fraser
Date: 18 Dec 2001
Time: 18:09:49
Remote Name: 24.69.255.205

Comments

Ok, I found out the information I needed, but I thought I would post it here anyway in case someone else could refer to it for help in the future. If anyone can add anything or thinks something is different than I explain, please correct me. This ignition system uses 2 crankshaft sensors and one cam sensor. All sensors are hall-effect and have a 10v power supply and 5v reference which is pulled low to ground by the sensor. The crankshaft sensors are a 3x (per crank revolution) and 18x sensor. The 3x sensor uses an interrupter ring in which the windows are spaced 10, 20 and 30 degrees apart. This is coupled with the 18x sensor so that the ignition module knows which coil to fire within 120 deg of crankshaft rotation for faster starting and more accurate crankshaft position information. A 3x sensor that fails while the vehicle is running will allow the vehicle to continue running, however if either of the crank sensors fails, the vehicle cannot be restarted. The cam sensor also inputs to the module, but is output to the ECM for injection timing. If the cam sensor fails, a code 41 is set and the vehicle randomly picks an injector to start firing on, so there is a 1 in 6 chance of it guessing right each time. This is to allow the vehicle to be driven in a limp mode until it can be taken to a shop. From the ignition module the cam and crank information is sent to the ECM. Under 400 RPM the computer calculates timing according to a predetermined schedule based on engine rpm alone. Above 400 rpm the computer outputs a bypass voltage to the ignition module switching the control from predetermined settings to being controlled by the ECM based on inputs from rpm(module), cts,mat,tps,knck,vss,prndl and maf or map sensor signals. If the bypass signal is missing, the ignition system goes into base timing mode (predetermined settings). Ok, now that I knew all of this I went back to the car and tried to start it again because it should run with a missing cam signal. It took a bit of feathering the gas pedal, but it did start and run. I pulled out the cam sensor from the housing and inspected the interrupter on the cam sprocket and there it was, broken. The vehicle is now being disassembled to replace the interrupter ($14.95 from GM) and I also recommended to do the chain and sprockets at the same time which the customer agreed to. I will let you know the final outcome of this when it is back together.