2005 Dodge Ram 1500 5.7 P0300 - All cylinders misfiring


Asked by Oct 14, 2013 at 03:02 PM about the 2005 Dodge Ram 1500 SLT Quad Cab SB

Question type: Maintenance & Repair

My truck started to misfire a short time ago.  Before the issue, I replaced the plugs (copper), ran SeaFoam through vacuum tubes a couple times and it ran fine for months.  A couple months ago I noticed sluggish acceleration around 2000 RPM and then started throwing P0300's.  I replaced the EGR, cleaned the Throttle plate and sensor.  Today, I had a computer hooked up to it to show all 8 cylinders misfiring randomly.  The mechanic said I need new plugs, another mechanic said it was a ignition coil going.  

What could cause all cylinders to misfire?  Any and all help is appreciated!

My truck:
165k miles
K&N filter
Super Chip
Amsoil for past 100k

Scott R

19 Answers


Hi Scott, nice truck! My guess is when you Seafoamed it the plugs got fouled and is causing the misfiring. Could be a coil failing but unless you have one coil for all the cylinders, which I doubt, it wouldn't cause them all to be misfiring. Try a new set of plugs. Inspect the old ones. Black sooty deposits mean an overly rich air/ fuel mixture while white deposits on the electrodes mean an overly lean air/fuel mixture. HTH. -Jim

5 of 5 people found this helpful.

***UPDATE*** I read a little more on this issue and even though I installed a new EGR, I unplugged it. My truck runs perfect now, minus the CEL. No more misfiring and my MPH is going back up... Any ideas on what could be the issue?

6 of 6 people found this helpful.

Some vehicles need to "learn" the closed position of the EGR valve. To do this, leave it unplugged then using a scan tool clear the computer. Then switch off the ignition and plug the EGR valve back in.That should work. HTH. -Jim

5 of 5 people found this helpful.

Thanks for the response again. How long long shall I leave it unplugged? Scott


You're welcome. Just long enough to clear the computer with the scan tool. Then switch off the ignition and plug the EGR valve back in. Then start it up. Hopefully that'll reset it. HTH. -Jim

2 of 2 people found this helpful.

Could it be valves sprngs

2 of 2 people found this helpful.

What is it

1 of 1 people found this helpful.

Weak valve springs will cause an engine to misfire. To determine this run a compression test. If some cylinders test low, squirt about a teaspoon of motor into each cylinder, one by one, and retest. This is called a "wet" compression test. If the readings improve the piston rings are worn. If the readings remain low, it's a valve problem. You should be getting readings of at least 150 PSI. Around 180 is better. At 150 the cylinders will fire but the motor is tired. Does your truck have high mileage? HTH. - Jim

1 of 1 people found this helpful.

*a teaspoon full of motor oil, sorry.


So your saying egr valve and plugs ..I just did mine a month ago ... I was gonna also do the coils

1 of 1 people found this helpful.

I'm having same problem multiple misfire after new plugs and wires light flashes for three or four seconds skips then stops light goes out and runs fine any help would be appreciated


I unplugged my egr valve after replacing it 3 times. Runs fine buck light stays on. Ran many test's and no one could tell me. Someone said it could be not the egr itself, but a sensor connected to it. Been a couple years running as it. Try unplugging.


Does it still get inspected ok and where is the egr valve on my engine I have the 2500 5.7 mechanic said I don't have a egr valve

1 of 1 people found this helpful.

Im just frustrated because it just started right out of the blue I was told it could be the battery


I moved to FL, so no emissions. I don't know anything about 2500s. Sorry!


I have a 2004 Dodge ram 1500 5.7 hemi that about three weeks ago I went out to start it cold and was miss firing horribly let it sit for about five minutes went back out started it it was fine about a week later it did it again sat for a few minutes and then started running fine and I went out today and it did the same thing but took about 20 minutes of trying to start it let it sit and then it finally came out of it again and it's only kick the engine light on one time and and the only thing it showed was multiple misfires any help would be appreciated

4 of 4 people found this helpful.

And also the truck has 84,000 miles

1 of 1 people found this helpful.

I have a 07 Dodge Ram 5.7 Hemi started bogging on the highway and then ruff idiol when I stop and sometimes turns off. Went to Autozone and Orielys to get a idea what it is and got p0300, p0306. Cylinder 6 misfire, multiple misfire. So I put New coil pack on cylinder 6 and change all plugs and still running like shit. I have no idea what it can be. Any suggestions?

2 of 2 people found this helpful.

I just replaced the head gaskets on my 2005 5.7, new plugs and wires, all new gaskets. Now I can get it to start, but I think the timing went out of whack. It'll only stay running for about 5 seconds. It doesn't have a knocking sound but it definitely sounds like it's fighting itself. Extremely rough running. Thoughts, ideas, I'm really needing to get it back on the road, I'm borrowing my dad's truck and he needs it back.

3 of 3 people found this helpful.

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