P0303 03 Chevrolet Tahoe- P0303 misfire. Please help

Question

Hello I have a 03 chevy tahoe and a couple weeks ago im driving down the road and i noticed my truck had this vibration to it when in idle/ at a stop light etc. A day later my check engine lighr came on but not flashing, another day later it started to flash when i would accelerate the gas but stay solid when in cruise control.had a freind who is a mechanic take a look at it and run the OBD to see what codes may come up. P0303 came up, show he proceeded to tell me that i needed a new ignition coil. So that was done and which it made no difference...it actually made it worse (i dont know how but it did)....so if anyone has any suggestions or may jnow whts going on please help...at this point i need all the help i can get im a mother of a 2 yr. old and know nothing about car repairs... thanks in advance...

Answer 1

Hi there,

I would check the spark plug. Swap it with the one next to it and see if there is any difference. Make sure #3 was the one that was replaced. Get the firing order and cylinder ID. If it wasn't #3 that was replaced it would leave the impression of it being worse since you swapped the coil. I suspect this is the most likely thing that happened.