Chevy Vortec Misfire 1996 to 1999

I had a 96 tahoe 5.7 that gave me hell with the Distributor sparking to the wrong terminal. These Vortec engines use computer controlled timing, but still use a rotating distributor to determine which cylinder the coil's spark goes to. Twisting the distributor does not set the timing like it did for older engines, instead it just sets where the rotor is pointing relative to the cap when the computer decides to fire the coil. Aligning the rotor to the cap's electrodes at the instant of spark is called having the cap "indexed" to the rotor.

In my case the distributor was a few degrees off after an intake gasket change. The engine ran fine for a while, but was always sparking off to one side of the electrodes in in the cap due to mis-alignment. After a while, that side of each electrode became corroded, and rather spark around to the far side of the electrode, it was actually a shorter path to the clean side of the next electrode over. This resulted in stumbling and misfires.

I rotated the distributor a few degrees toward the corroded side and changed the cap and rotor. The next cap and rotor went about 10k further before acting up. I rotated towards the corroded side again, and the same cap and rotor have been running ever since.

Scribe a mark on your distributor and intake for reference and twist the distributor a few degrees towards the corroded side of the electrodes in the cap as the cap sits on the distributor. Don't forget if you take the cap off and flip it upside down, then you need to reverse the direction you twist. You want to twist the distributor cap towards the corroded side with the cap sitting in place on the distributor. This will help move the cap's electrodes closer to the center of the spark-range (as the computer jockeys the timing around, where the rotor electrode points at the instant of spark moves).

all codes will show the same results
Symptoms Symptoms may include:

• the engine may be harder to start
• the engine may stumble / stumble, and/or hesitate
• other symptoms may also be present

Causes A code P0304 may mean that one or more of the following has happened:

• Faulty spark plug or wire
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector
• Burned exhaust valve
• Faulty catalytic converter(s)
• Running out of fuel
• Poor compression
• Defective computer

Possible Solutions If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

A P0300 diagnostic code indicates a random or multiple misfire
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back
Symptoms may include:

• the engine may be harder to start
• the engine may stumble / stumble, and/or hesitate
• other symptoms may also be present

A code P0300 may mean that one or more of the following has happened:

• Faulty spark plugs or wires
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector(s)
• Burned exhaust valve
• Faulty catalytic converter(s)
• Stuck/blocked EGR valve / passages
• Faulty camshaft position sensor
• Defective computer

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders ( spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open

Hi, multiple cylinder misfire, is when the engine cylinders do not fire in the correct order, and do not do it constantly. There is no particular pattern to it. My experience with this condition is that it is usually caused by a faulty ignition coil that is beginning to burn out. It could also be bad wires pluds rotor or cap

Causes Include.

• Faulty spark plugs or wires
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector(s)
• Burned exhaust valve
• Faulty catalytic converter(s)
• Stuck/blocked EGR valve / passages
• Faulty camshaft position sensor
• Defective computer

Possible Solution:
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
Random misfires that jump around from one cylinder to another. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.

our van did this also. only when it rains. we did 2 things to cure it. 1 expensive but huge difference. use GM oem cap, rotor, ignition module. 2 make sure your windsheild seal is watertight. we were getting water into our firewall junction under the dash board.