This is my first post but I have been lurking for a while. Figured I would mention what fixed the dreaded p0305 cylinder 5 mis fire code for my 2002 3.9L QC 4X4 Dak. I appreciate the advice I got from lots of lurking so here goes. It's a bit of a story and hopefully it will save someone wasting time and money like I did. :-)

So I get the P0305 code popping on every few days to a week so I do the following in order;
clean the IAT and throttle body, check for vacuum leaks
The code still comes on every few days and will sometimes go off by itself

replace the plugs(NGK) and wires(MSD 8.5mm)
The code still comes on every few days and will sometimes go off by itself

replace the distributor cap and rotor.
The code still comes on every few days and will sometimes go off by itself

replace #5 cylinder fuel injector
The code still comes on every few days and will sometimes go off by itself

Remove intake manifold to replace timing chain and belly pan gasket. Fix leaking valve cover gaskets at same time. While I have valve cover off I check for broken valve springs on #5 cylinder. All ok.

Haven't had the code for a few weeks so take the truck on holidays towing a 5th wheel trailer. 2 hrs into the trip the code pops on. Stop at Walmart and get a new spark plug. Clear code. Drive for 3 hrs and get the code again. Drive 1000miles clearing code every fill up.

replace the distributor cap and rotor.
The code still comes on

replace cam sensor
The code still comes on

Back from holidays so I perform compression test. All fine(135 to 150)

Ask my mechanic friend to check the International Automotive Technicians Network for any ideas as to why this code comes on. He tells me it's the lifters. There was 6 cases reported of lifters over inflating and keeping the valve/s from closing fully. I replace the lifters and the problem has gone away and not come back. It's been 5 months P0305 clear.

Just thought I would share my welcome to Dodge experience. I've already had the Evap codes too. This forum helped me to find and fix them.

Something I wanted to mention as well. If the Crank or Cam sensor or TPS is bad the computer will send a code as it tests them against the other sensors. I found out you don't have to set the voltage on the TPS by adjusting it as the computer does it automatically. Thats why they are non adjustable! You just need to let the computer know what wide open throttle is a few times. LoL

Thanks again for the help!!

 

Welcome on forume, dude!
Nice post

 

You wouldn't know which cylinder was 135 psi?

 

On this engine the lower compression cylinders were on the passengers side, 2,4,6. Cyl 5 was around 145ish.

 

The lifters will only over inflate with the engine running. Doing a compression test will not pick up over inflating lifters as there's no oil pressure.

 

Well with the engine warm and cranking the engine with no spark plugs it can create oil pressure. Well it better for the sake of the engine. I figure taking the intake out and valve covers off I can take care of several leaks especially the antifreeze around the thermostat housing.

 

There will be a little oil pressure but not enough to cause the problem. ie 100rpm vs 2000rpm

While you have the intake off check the belly pan seal. Open the throttle and shine a flashlight down the throttle body. Look for oil on the bottom of the intake. Any oil on the topside of the belly pan means an oil leak.

 

Looked down the throat yes there is a little oil , but I think might be from pcv. Did you do the lifter change yourself? Hoping it is not a valve problem. Pair of heads $500 plus doing it myself.

 

Yes, you can get some oil from pcv. Jegs sells a seperator that you can splice into pcv hose.

Lifters are easy to replace when intake is off. Just undo rocker arm nuts and lift out. I believe lifters need to go in a certain orientation so make sure to read instructions. If I remember correctly it's just a matter of torquing the rocker arm nut to spec. Not a hard job.

 

Well I got to working on the dakota . I went ahead and replaced both heads and lifters. I now have it back together. Guess what? Still have P0305 code after not more than 30 miles.