my 1990 grand prix cranks but wont start. i took the fuel line off at the injectors and there is fuel getting to the engine. i pulled a spark plug wire and there was also spark. could it be the computer ? 1990 grand prix se 300,000 km but in great condition still. starter was done recently. i sprayed quick start in the air intake and it sputtered but didnt fire.
1989-2003 Pontiac Grand Prix
Known for developing ignition problems at high mileage.
The waste-spark DIS ignition system on the 3.1L is similar to that used on other GM V6 engines.
Ignition misfire can be caused by worn or fouled spark plugs, bad plug wires, weak coils or faults in the ignition control module. No starts are most often due to faults in the crank sensor circuits (there are two on most engines). In some cases, a no start or intermittent loss of spark can be caused by wiring that is chafing near the rear exhaust manifold.
The DIS system has three coils that share paired cylinders (1-4, 6-3 and 2-5). If any of the individual coils fail, it will cause a misfire in the two paired cylinders it supplies with high voltage. Random misfires, on the other hand, are more often due to a lean fuel condition caused by intake manifold vacuum leaks, dirty fuel injectors or a leaky EGR valve.
If you suspect a bad coil, one trick is to swap two adjacent coils to see if the misfire moves to the other two cylinders. If there’s no change, the fault may be poor contact between the two spade terminals under the coil and the ignition module, or a fault within the ignition module control circuitry. You can also check the secondary resistance of each coil with an ohmmeter. A good coil should read 5,000-7,000 ohms. Also check the underside of each coil for cracks or carbon tracks that would tell you high voltage is leaking from the coil.
If the engine cranks but won’t start and there’s no spark from any of the coils, check the ignition control module supply voltage and ground connections. If both are okay, check to see that both crank sensors are producing a signal. Chances are the problem will be a bad crank sensor, but it could also be a wiring fault between the crank sensors and ignition module.
