What's causing my misfire?
 

1997 Dodge Ram 1500 with the 5.9l.

Codes for misfire (P0300) and misfire at cylinder 1 (P0301).

I have changed all the spark plugs and spark plug wires, the distributor cap and rotor, and the cylinder 1 fuel injector (as long as cylinder 1 is indeed the one furthest front on the driver side).

Still rough idle occassionally and same misfire codes popped back up.

What do I do next??

Getting good spark on number 1?

Also, may have cracked the porcelain of the spark plug during installation. That will certainly cause a misfire. What type of spark plugs are you using? Copper plugs tend to work best in these motors.

How manmiles on the engine? If it's over 120K, has the timing chain ever been replaced?

I'm using double platinum on all of them. I even pulled it back out and rechecked the gap.

I'm right at 121,000. And no, haven't done that....any advice on how to do it? Does it need to be done? I guess I thought with a chian I wouldn't have to worry...

The stock chain is a morse style. (stamped steel plates riveted together) and very prone to stretching.

In addition to the chain stretching, the factory cam gear is plastic coated. They tend to crack at the teeth. It would be a good idea to replace the timing chain set with a good double roller timing chain and gear set. I'm sure there are several YouTube videos that show how to remove & replace a Dodge Ram 5.9 magnum timing chain & gear set, if you're inclined to do the job yourself.

Might also want to try some copper spark plugs to see if your misfire issue clears up, as platinum plugs (especially Bosch) don't tend to work well in these motors. :icon_twocents:

Ah, good to know. While I guess I should definitely change the timing chain soon (thanks for the tips), how would I actually verify that that is my problem? I do not want to go through the chain change and still have the misfire. I do not presume it is because of the plugs since only one is misfiring (I stayed away from Bosch plugs). How do I actually diagnose where my misfire is coming from? How do I know it isn't PCM or injector wiring related?

A couple of quick things to check...

- Pull the #1 spark plug and swap it with a known good plug and see if anything changes.
- Ohm test the offending spark plug wire with a multi-meter to ensure it isn't bad.