2000 Dakota 4x4, 3.9L reg cab

New Guy here,
P0303
Got the above mil code, #3 cylinder misfire.
Reset puter a couple of times, keeps coming back. Done the look see and poked around. Engine only misfires when hot and at idle. When accelerating and cruising no misfire. Just when waiting for a light, a toll booth etc.. Motor runs a little ruff and you can hear the misfire in the exhaust. I tried putting something around the injector to deflect heat, did not help. Truck just passed 40,000 miles.
I 've pounded the internet, why I tried the heat shield, and I can not trust the mechanics where I purchased truck. They earned my distrust, could not even put right amount of oil in crankcase.
Installed my own, DIY ram air solution. Use HALO sparkpugs and Dixie Caps. "Highly Recomend Both" Use K&N air filter. Split exhaust from cat back. Done a couple of other minor mods. Gets 19 to 20 mpg Highway.
Made most of changes before 15,000 miles and it runs nice.
So any help with the hot soak misfire?
Got this code last fall after having coolant change.

The 1763,
Had those parts replaced once already at 20,000 miles. The code is showing up again at 40,000+.
Any ideas why these parts are failing again?
Its my get away truck. Why the mileage is so low, just glad I'm not dependant on it for work.
As you know, it will not pass inspection with the mil light on, I got 6 months to solve the problems.
Its not the injectors, I do not think its the crank sensor, but............

ty

 

No Help?
I had high hopes for this forum, please do not disappoint.

 

Well,
I'll keep hunting.

 

Well a P0300 is not a #3 misfire. It's a Multiple cylinder misfire. Check your fuel supply. Possibly clogged fuel filter, fuel pump going bad, clogged fuel line, etc.
However, a P0303 would be a cylinder #3 misfire.

Try getting a bottle of Chevron Techtron and putting that in the gas tank. It can help clean out the system and it's the best stuff out there, within a reasonable price.

Sorry about the replies being late. Sometimes we don't always catch threads. I know I didn't see this one before.

 

TY for responding and the clarification.

 

Does it stall or hard to start sometimes? It might be the crank position sensor.

 

So I had to edit original post.
Mis-remember the code. I have a ODB II scanner in cab and I had wrote down the codes, originally. Should have looked at the paper before post. I had just remembered it being a #3 cylinder misfire.

Fires right up. No stalls, when engine is hot and at a stop light, you can feel the miss. Engine just a little ruff. You hear the miss in the exhaust as well. But, when driving or when motors cold, all works fine. Gets good spark, I replaced the plug once. Listen to the injector, via screw driver ear method, and metered the injector. All good.
It accelerates great.
Code popped soon after a coolant change??????
I need to deal with it because it will not pass inspection with the mil light on. Thermostat is stock and motor temp when hot is 190F to 200F.
Very annoying.

 

Do a compression test. Compare the number to the rest of the cylinders. Also do a leak down test, if your compression comes up short. You have spark, and you have fuel. Only things missing are Air and compression.
Also check the plenum. I think the 3.9 has a plenum gasket, never had a 3.9 so not sure.

I think the coolant change may happen to be a coincidence. I highly doubt it's related.

 

It has a plenum issue too but not as prone as the 5.9's since they run hotter/v8's

Compression sounds right. Have you checked the Spark plugs? Looked at them too see any difference in color? You might even have a faulty wire that is arcing once it heats up. I don't know. But it does sounds like a head gasket issue with it only happening at warm.

 

Gents,
As I stated above, I replaced the plug, no difference, No discoloration.
Now I'm not a professional mechanic, but I do not believe its a compression issue. This misfire only happens at "HOT IDLE", the truck accelerates fine and theres no misfire toodling down the rode.
Please check out the link provided, same type issue with my truck.
http://www.naxja.org/forum/showthread.php?t=1017684

Is there away to convert the fuel system so that it recirculates back to the tank?
Is there a better fuel injector? or a proper heat sink that I can add to the injectors port in the manifold?
Whats the best way to check if the injectors seal in the manifold is leaking? soapy water work?
If the injectors seal is bad, wouldn't that affect it at all times and not just idle?
Is there an injector design that deals with heat better to stop it from vaporizing the fuel?

Please, I do not want $1000 suggestions, truck runs to good for it to be a major problem.

TY

ps: not in a position to do a "leak down test" no compressor available. If I have to do I can go buy a compression test guage, but I'm trying to keep from buying stuff for a poke and hope. Please read what my symptons are, I get dam near 20mpg.