1998 Ram 1500, 5.2L, 4x4 158,000

I've been lurking for the past few weeks trying to track this problem down, but I think I need more direct help. It's a bit of a story, so strap in for the ride.
The engine misfires after it gets warm (over 130), sometimes bad enough that I need to pull over. Symptoms are no response/choking out when I give it throttle. Just recently it seems to have an uneven idle at start as well.

About 5 months ago while driving, I got a severe misfire, felt like I was running on marbles, truck almost died when I tried to give it gas. Pulled over, turned it off and gave it a few minutes to recover and it ran fine after that until about a week later the problem returned and happened whenever I drove the truck. Took it in to the mechanic and he found a vacuum leak (AC, on the T junction on the passenger side) Fixed that and it ran great.

About 1 month ago, I went to start and had no fuel to the rail. Replaced the fuel pump (Delphi) and it worked great for a couple days, then the misfire came back.
Since then, I have:

-Replaced the fuel pump locking ring, thinking it may have a bad seal and a vacuum leak.
-New TPS (NGK)
-Switched TB, MAP, and IAC for different used parts.
- Not installed, but I do have new PCV and CCV grommets and fittings on the way as well.

I don't think that the plenum gasket is the problem, as when I disconnect and seal the PCV and CCV hoses (as per TSB 09-05-00) I get slight positive pressure from the CCV hose. Any thoughts on what I should look at next? I'm thinking the O2 sensors are my next possible culprit, but at this point I am open to any ideas.

Thanks!

 

I would replace the coil first. If you bought pats from a chain store, they may not be working properly. Cheap sensors don't communicate properly with the computer. Get Mopar, Standard Motor Products, or ACDelco. Avoid BWD, Duralast, etc.
You could also have a severely stretched timing chain. It affects ignition and fuel timing.

 

I think timing chain would be a perpetual problem, that would show up as soon as you started it, and never go away.

Unplug the O2 sensors, and see how it goes. (just the front sensor.... I think you only have one, unless you are cali emissions.

Also, what plugs are in there, and how old? Cap? Rotor? Wires??

 

I'll try unplugging the sensor.
Autolite AP5224 Platinum plugs, redid the cap, rotor, and wires with the United motor products 17815 (brass contacts) kit along with plugs in October 2018.

 

Platinum plugs are going to be a problem as well. These trucks simply don't like 'em. Just plain jane copper plugs.

 

Alright, I'll find a new set.

Just ran without the O2. Still idles rough. Interestingly, my truck is not a CA truck, it was from Alaska originally, but it does have 2 O2 sensors.

 

Yeah, should be one before the cat, and one after....

 

Yep, got both of them. Should a CEL come on immediately or does it need to enter closed loop first? Because I did not get a light when I let it idle for about 2 mins.

EDIT: Any particular plug recommendations?

 

I have used autolites, and a/c delco with good results. I think I have NGKs in my 8.0 at the moment. Some folks like Champion. (I am not one of them. )

PCM can be really fickle about when/if it sets O2 codes. It *should* whine almost immediately about the lack of voltage on the O2 heater circuit..... but, that's just me being logical. No guarantee that Dodge agreed with me.

 

Here's the NGK #NGK 4291 {Click Info Button for Alternate/OEM Part Numbers} V-Power Info
Gap 0.040"

The Autolites or AC Delco are good too.