Just got this truck about 4 mos. ago. 15 miles in the CEL came on. O2 sensors. Long story short, the cats were empty. put on new ones then I got the P0300. Everything that Ive read to fix it has already been replaced or looks to be in working order. It stalls at highway speed on the freeway and at stop lights. It fires back up no problem. CEL flashes if I punch it and get over 3200 rpm. I checked fuel pressure and all the sensors I could think to check. I really like this truck, 2004 1500 4dr 4.7L 116,000 miles, and I want it to run right. Please help.

 

Misfire can be caused by a bunch of things... But a common failure on the 4.7 is head gasket leaks, and most people seem to want to look for a good used replacement when that happens - but 4.7s are hard to find, and when you do they tend to cost a bit more than you'd like. So I'd be looking for any evidence of that head gasket problem going on. Like a compression check and oil contaminated by anti freeze, or antifreeze contaminated by oil. Now,surely there will be some 4.7 fans replying about having 300k miles on their 4.7 and it still runs like new.

Best way for us to help, you should list out what all you've done so far. Chances are we're going to spend our time telling you about things you've already addressed. I will recommend that you get a bluetooth obd2 reader and the torque pro app so you can monitor what is going on as its showing the symptoms.

 

Oh no. When I changed the oil, there was sludge on the bottom of the fill cap. The oil i drained didnt look bad at all, just really black. The antifreeze looks right as well. Ive been driving it 18 mles each way to work 5 days a week. I changed the Crankcase vent tubes, TPS, CPS, cleaned the IAC. When I list it out, it doesn't seem like Ive actually done much...but it feels like it.

 

The sludge under the fill cap is normal. It sits so high up off the engine that it stays cooler and condensates. If you want to check head gasket, you can rent a block tester (free when you return it) from your local auto parts store. I'd be looking at sensors though. TPS can cause stalling. So can the IAC. And then there is the crankshaft sensor. Replace with Mopar sensors.

 

Some sensors are "new looking" but probably the cheapest available. Thanks for the input on the cap sludge.

 

Have you pulled the spark plugs? Check each plug general condition and gap. There are guides online to show you what normal looks like (color and build up). If the gap is wide, or they have alot of build up on them - I'd replace them. Have you run any injector cleaner? You can pull the injectors and test them to see if you've got issues there as well, plenty of online resources on how to do that as well.

 

P0300 means the misfires are on multiple cylinders. It is possible but unlikely that multiple spark plugs or even multiple coil packs could be bad. Most likely it is a single component is affecting the cylinders. Sometimes you can get away with a cheap IAC. A cheap TPS is even more likely to fail and a cheap crankshaft sensor is almost a guaranteed failure because they can't get the design exactly right. I've found decent prices buying mopar units online. With around 314K mi, I'm still on the original crank sensor... so I'm watching it.

 

No, its actually likely. Google "P0300 spark plugs". Many times that code is because someone ignored the maintenance recommendations on their spark plugs. Should always check the basics before chucking expensive parts at the problem. The PO might have even put the wrong plugs in there. You don't know until you look. Taking those plugs out for inspection costs nothing but your time.

 

I know the magnum engines would spit that code for folks if they installed rare-earth spark plugs.......

 

Not disagreeing that the plugs should be checked. Heck, you'd hope that was done before posting the problem. It's such a basic part of maintenance, that I take it as a given, especially when someone buys a used vehicle. And yeah, it costs nothing to look and is a cheap replacement if it comes to that. I'm just drawing on what I've experienced with regard to troubleshooting these problems.

Wish I had a pic of my plugs back when I got my truck. The center electrodes were completely worn down to nothing and the ground electrodes were worn to a sharp edge. I could probably have passed the entire gap tool's body in the gap. It was a wonder that it still ran. LOL