#3 misfire code 303
 

My 2000 Trailblazer Edition Blazer would not start one damp dreary morning (engine was wet from condensation). Would crank but no start. Checked fuel pressure and was just below 60 psi. Ordered new Delco cap and rotor from Rock Auto but before installing tried starting and started fine and ran fine (engine was dry). Put new cap and rotor on anyway using dielectric on cap. Started fine but noticed misfire and check engine light and code 303 #3 misfire. Cleared code and started again. Check engine light and code 303 again. My son told me I should do the plugs and wires also so I ordered from Rock Auto, Delco plugs and wires. Installed and still #3 misfire. This car never misfired before replacing cap and rotor. I've owned the car 10 years and never replaced any ignition parts till now. Any suggestions?

1. Make sure that your ignition wire boots are tight at each end, especially the plug end.
2. Did you use the correct plugs/heat range?
3. Make sure the distr cap is seated right and did not crack when installed
4. Is the rotor seated correctly?
5. Make sure that the distr is not loose and rotating
6. Check your wire routing from the cap, there is one crossover
7. Mist in the dark and look for arcing
8. If you still have the problem then check CMP retard and get it in spec

George

Thanks for your reply GeorgeLG. I did not mention that one of the ears for holding down the cap on the distributer broke off. I could still snug down both sides of the cap. I did not have a miss until I put on the new cap (Delco D328A) and rotor (Delco D465). Then replaced plugs (Delco 41979) and wires (Delco 9746KK). Blazer had 70,000 when I bought it and now has 180,000. I have a new distributer ( Delphi CZ20007) on the way. All parts from RockAuto. Also forgot to mention that I checked for spark at the distributor and good spark was arcing from the wire to the distributor but later realized I was checking #1 and not #3. So I still will check with a spark tester at the plug and replace the distributor. If I still have a miss I will continue this thread. The weather is cold here in Pittsburgh right now but I will also check your list.