Q: Truck is running rough engine light. Keep call code

The rotten egg smell out your tail pipe is the catalytic converter working to hard. It is doing this because raw unburned fuel is being pumped into it. This can damage it. If your Check Engine Light is flashing, this means there is a danger of the catalytic converter catching fire. So don’t drive it far.

With a tune-up you should have replaced the spark plug wires and the spark plugs. If it ran normally before you gave it a tune-up, I would first begin by checking the firing order. Even the best of us will mix up the spark plug wires from time to time. If the firing order is correct, I would suspect a broken spark plug. It is not uncommon for the porcelain to crack when we are tightening the spark plug. You should be using a spark plug socket. If you are not, you are lucky you didn’t break more.

If you have covered all that, then the next thing I would do is a compression check. If cylinders 2 and 8 have lower compression than the rest of the cylinders, you have leaking valves or piston rings.

Your A/C system, fuel pump, catalytic converter, fuel filter or throttle body won’t cause only two cylinders to misfire. It is possible you have injector problems, but this is unlikely with the rotten egg smell because this is an indication of unburned fuel being pumped into the exhaust.

If you’d like some assistance with this, consider YourMechanic, as one of our mobile experts can further diagnose your trouble codes and help you fix the problem accordingly.

Good luck!