I have a 2003 Dodge Neon that started getting engine light in Code is P0300 and P0303 several months ago. I have replaced the plugs, wires, spark plugs, coil pack. Swapped out the fuel injector between #3 and #4 cylinder problem got worse so swapped back. Compression at 50 lb on cylinder number 3. Other cylinders are 70 and 2 at 60. Specification is 170 to 220 so all within spec. Just tried to smog after resetting the computer emission passed with flying colors but failed due to monitor. After running the car were set error came back with 10 miles. Any idea how to proceed? Probably going to look at the cam next.

 

I re-tested the compression turns out all the cylinders are at between 120 - 130 with number 3 at 60. I pulled the valve cover and removed the rocker arm assembly. Looking for issues on number 3 intake/exhaust looking at rollers and lash adjusters to see if anything stands out. Will update based on findings initial check shows nothing outstanding. May have head/cylcinder or piston/ring issue. Not ready to pull head ths wekend.

 

Found one of the #3 Cylinder intake lash adjusters loose so I replaced and re-assembled. Will see if the code comes back wont help with the compression issue. It's strange the compression is so low on just #3 cyl but no sign of issue on the tail pipe or in the oil? This forum sure is a great place to keep notes for myself

 

Hi, I have the exact same issue on my 2003 neon. I just took off the valve cover and rocker arm assembly - also here, nothing that leads me to believe anything is wrong in that department. I had hoped I would find something because I had heard valve noise for a while before the check engine light came on.

I have not pulled the head as I am a little apprehensive. Anyway, I will appreciate any notes we can share. I am taking pictures during dis-assembly.

 

I have a misfiring cylinder issue as well. I've not had a chance to have anything checked out, but when I turn the wheel sharply it makes a smoothish grinding sound. I was wondering beforehand if there is something in specific that would be causing this noise, and if it correlates to the cylinder issue...

 

Compression sounds a bit low. 60 PSI? Do a leakdown test and see if it is the rings, intake/exaust valves. May even be leakng past the head gasket to one of the other cylinders or a cracked head.