Jim Grant's Tech Tips

93 Pontiac Bonneville, No Spark
Q: I have a ‘93 Bonneville SE with 225k miles and the engine is as strong as it was when new. In January, I started the car and let it warm up for about 10 minutes and put it in drive, I moved about 15 feet before the engine died. It still won't start to this day. The fuel system is good, it has fuel pressure, I tested the injectors with a noid light and they are all good. So next I checked for spark - no spark. Well, the body shop that I work at had a totaled ‘93 Lesabre sitting outside waiting to be towed away, so I grabbed the ignition module and coils out of that car and tried them in mine - nothing, still no spark. For some reason the injectors pulse erratically with the key turned to the on position but it does not do this every time. When it does they will not stop pulsing until you turn the key off. Here is a list of everything done to the car so far:

GM computer - I now have four computers for this car and yes all numbers match and I'm using correct PROM. GM ignition module & coils - three sets. GM crankshaft position sensor, camshaft sensor and new timing chain. Oil pressure, fuel system, fuses, relays and even the computer chip in the key is good. Countless hours with wiring diagram and voltmeter. And there are no codes in the computer.

I desperately need help, like I said above the car ran like new and then nothing and four months later still nothing. It's like somebody flipped the power off switch, I don't understand it.....Steve

A: Wow you have a very confused computer. But why? For the fuel injectors to pulse (open and deliver fuel to the engine) they need a command from the computer. The computer gets information/signal to operate the injectors from the ignition module. The ignition module receives its information from the crank and camshaft position sensors. For the computer to pulse the injectors yet the engine is not running indicates there is an erratic signal being created. About the only way this can happen is if there is a bad ground wire. The computer, ignition module and sensors rely on a good power supply to operate. But more importantly these systems require a good electrical ground. There are several ground wires that are dedicated to these components. Failure of just one of these wires can send the system into total chaos. The result is a confusing condition much like you’re describing. Prove the condition of the grounds and you’ll likely be up and running again.