Replaced CAS, coil packs, plug wires, and spark plugs. Checked fuel pressure and it puts out 40 PSI at idle and with just the pump primed. Even when the car does it's thing, the fuel pressure stays around 40 PSI at idle. The FPR is pulling a good vacuum and there is no gas in the vacuum line. About 50% of the time, after just priming the fuel pump to check pressure, the pressure will start to drop slowly after about 15 minutes, and after that 15 minutes, I came back to see it was at about 10 PSI. Tried to start the car back up, and it immediately starting to idle super rough between 800-1700 RPM, but fuel pressure was fine. The injector resistance was fine as far I could tell at 17.2 Ohms. The only codes being thrown are P0300, P0302, and p0304. Also lacking power due to these misfires when driving the car around, especially when under load going up a hill.
It isn't wise to get too preoccupied with fuel pressures - ok the pump needs to maintain the right pressure but it is also important the pump delivers sufficient volume of fuel that the pressure is maintained under full throttle conditions with enough reserve circulating back to the tank to keep the system cool and prevent vapour locks.
A healthy pump will fill a half gallon jug in a few seconds and that test is the essential other half of the fuel system test.
A reduced volume or pressure could indicate a dirty fuel tank...
The pressure test isn't complete until the peak pressure has also been tested and the pressure regulator vac on and vac off proved ok. The rail pressure should be maintained with the pump off and the supply closed - if it doesn't, it indicates a leaking regulator or a dribbling injector.
Once the fuel delivery has been passed ok, the fuel injectors should be removed and tested. An injector has a useful life on average of 70/80,000 miles, after which the spray patterns deteriorate - a poor spray pattern has larger droplets that burn much slower and behave like a lean mixture.
SOURCE: rough idle but at runs good higher speeds ok ,engine misfire codes intermittent
Does this have a spider injection? I don\'t know if this will help but can you take your mass air flow sensor off and look at the little wires that are inside of it. I don\'t know what these stupid little wires do but they build up stuff on them. Your supposed to clean these every so often but i don\'t remember how often. I use some kind of electrical contact spray cleaner. People say the mass air flow sensor will make your truck run poorly, but i never had one fail so i don\'t know for sure. Anyway it\'s weird to have so many misfires only sometimes. I\'m not to knowledgeable about dodge so i don\'t the firing order. If you can find out the firing order it would be easier to find a solution. It could be an oxygen sensor but i would i would make sure before i buy one cuz they not cheap and my truck has four of them so you have to make sure which one it is. But i was asking about the spider injectors because if the injectors get clogged up they stay open and constantly give it gas instead of pulsing the gas. That could be an easy fix with injector cleaner. Good luck not sure if this helps or confuses you.
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