I posted several topics and I've done a lot of work to figure this one out. When this started, I thought I just needed a tune up. So I did plugs wires, cap, and rotor. It seemed to perk it up for a short while but the problem came back.
At startup, it only takes a crank or two to start but it stumbles (misses a cylinder or two) for about 1 second and idles smooth. It seems to run OK but lacks power at the low end. High end power seems to be pretty good. I'm only getting about 11 mpg when I should be getting 15. I tried a bunch of other things; TPS, front O2 sensor, new cat & muffler, IAC clean and reset, injector cleaner, compression test (150psi on all eight), vacuum test (steady 16in/Mg at idle). I replaced the plenum pan gasket because the #8 plug was oil fouled. After the plenum replacement, I reset the computer and cleaned up the #8 plug and put it back in. I ran the truck for about a week with the same plugs and then pulled them out. All plugs look like they're running lean. With new champion truck plugs in, I got 12mpg highway (stuff on the roof and loaded inside) and still the same start issue. Looks like I'm getting 12 to 13mpg on this tank, will know for sure in a couple days.

With a previously fouled #8, should I have reset the computer after the plug replacement?

I am also suspecting a leaky injector causing my O2 sensor to tell the PCM to run leaner. A leaky injector would explain a miss at startup and lack of power at low end.

I want to test my fuel pressure but I'm not sure how. I was thinking of taking the valve stem out of the fuel rail and plumb up to my gauge. Are their easier ways to test FP?

I'm running low on ideas and I'm looking for others. I may just take it to the dealer. The guy there said that he could definitely diagnose it for ~$70.

By the way, the only CEL I got was for a rear O2 before my cat replacement. Even that code cleared itself before I actually replaced the cat.

 

I took my D into the dealership to have the injectors thouroughly cleaned for $119. Since then, the engine starts very smooth and my MPG improved a little. The over the counter cleaners aren't the same as the can they install into the actual injector fuel rail to clean the injectors. Otherwise, some people that knows how, says remove the injectors and soak them in cleaning solution for a while to really dissolve the gunk.

 

I've had and injector cleaning in my T/A only to have my problem come back in the next gas tank. I finally replaced all my injectors and the problem went away. This was 3 years and 40000miles ago and I'm noticing that its starting to miss here and there. Subtle but I can tell. I'd like to figure out a way to test for it so I can know for sure before I spend any more money.

This $120 cleaning.... couldn't we do something like that ourselves for much cheaper? Or is it done with some special adaptors and pumps?

 

You can actually buy the bottles from any auto parts store such as Napa, but I have no idea what it cost to buy the hoses and adaptors to hook up the bottle to the fuel rail.

 

I'd say you have a faulty O2 sensor. Most likely the front/first one.

I would recommend a Mopar replacement and not the aftermarket Bosch ones. The Mopar seem to last/work longer and better. I have heard of Bosch failures within weeks of the install. Funny too since most of what they make are top notch stuff.

IndyDurango

 

Seems like it could be the front O2 but I had this problem before and after I replaced it. Also, I don't think a faulty O2 sensor would cause a rough start unless the mix is so lean that there isn't enough fuel in some of the cylinders. I think that, with my plenum leak, my #8 was fouled and probably missing randomly. The misses were probably causing my O2 to think I'm running rich sending a signal to the pcm to lean out the system. I then replaced the plugs but did NOT reset the computer. Is it possible that it would take this long for the PCM to learn that I'm running lean? I put about 500 miles on since the new plugs and the problem persists.

 

Could be a crank shaft sensor. Also you might be out of timing. The computer can only compensate for about 12 degree's. If your out your gas milage will decrease. Also power robbing. At high RPM you won't notice it as much. The only way to time our motors is to hook it up to a computer. Maybe a pickup coil in the distributor.