04 Jeep Grand Cherokee/ P0303-possible vaccum leak

Most likely ,even though you have a 303 code, that
it wasn't that cylinders coil that failed

Need to put the old coil back & walk new one to different
cylinder or use a professional scan tool in Mode $06 ,to see
the misfire counts on all cyl's

Unrelated,I would loose the front O2 sensors after 7 years
& 100,000 miles

Never need to do plugs to diagnose problems
Only do plugs every 3 years a preventative maintenance

Code P0303 and P0306...

A code P0303 and P0306 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.


Hope helps.

P0300 is Multiple Misfire and P0303 is one specific misfire in the cyl #3.

A code P0303 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.

Hope helps.

p0303 is a mutible engine misfire on number 3 cylinder. the best fix,

A code P0303 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
• but first of all check the wires and sparkplugs first!

focusing on the coil packs but no mention of changing or checking the injectors or wiring to those injectors

check spark plug and wire
test oxygen sensor
check compression ( valve might be at fault)
have computer checked

1.Plugs
2. Vacuum leak
3. Injector fault
4. High or low fuel pressure.
Thats the list of things to check.
This is a #3 cylinder misfire.
There is also TSB about #3 injector needing added heat protection. This could definitely be the cause. I start at plugs and go from there.
Hope this helps.
Thank you,
Lee

yah direct ignition coil pack does away for the need a a distributer cap and rotor.much higher energy ignition system where the computer tell when to fire.if that helps.not hard to change.as long as you change them one at a time so you don't screw up the order.

P0303 means misfire on number 3 cylinder. It could be a spark plug, spark plug wire, coil pack, or maybe fuel injector. What ever it is, the number 3 cylinder is the problem.

Check the cylinders Commpression. over 115 psi is good, 120 psi is normal.