1999 5.2L misses at idle, stumbles at +2,800 RPM's
 

My 2003 Ram went down from electrical issues so I pulled my toy out. My '99 Ram fired right up and I started to work, after about 15 miles I came to a stoplight. The light turned green. and I went to take off. She started spitting and bucking and shut down about half a mile later. My dad tried tow starting me, and after a little bit I could get her to run if I kept throttle on her, although she was smoking and backfiring. I thought it was water in the fuel, so I bought two bottles of HEET and five gallons of 93 octane fuel. I put the fuel and one bottle of HEET in the tank and got towed again to start home. I forced her to make it home, fighting and backfiring all the way. I pulled the timing cover and found she had jumped time, so I replaced the chain and tried cranking her. Nothing. I figured I had warped the valvetrain, so I pulled a spare set of working heads and good pushrods and installed them, with all the appropriate gaskets. She cranked up, but ran poorly, and I got a code P1391, intermittent loss of cam or crank sensor. I had replaced the crank sensor not too long ago, so I bought a new cam sensor from Mopar. Still the same thing. I read an article about cam/crank sync and how to rough set it, which I did. That got her drivable, but still not right. I went to the dealership today to have the sync set. It was off by -18 degrees. But she still exhibits much the same behavior. Idling rough, a brick wall at 2,800 RPM's, except now I have misfire codes for cylinders 7, 3, 2, and 6, along with a random misfire code. These were not there before.

I was told it might be a MAP sensor, but I wonder if all that raw fuel escaping fried my 02 sensors? The truck ran great until she jumped time, and I thought I had replaced anything mechanical that might have been damaged......

What do your spark plugs look like, especially on those cylinders? Also the wires, cap and rotor? First thing I would do is check wires and plugs are good and correctly routed. Then check compression and see what you get.

Almost sounds like a restricted cat issue . Can you pull the upstream 02 at the cat and try running it w/o to test ?

Check fuel pressure with a gauge . May be too high

As asked , nice to know if the plugs can tell anything from a visual

It's NOT the cat, don't ask why :)

Working on the fuel pressure now.

If the pressure tests out, I'll pull some plugs.

I noticed today, that if you back way off the throttle or in lower gears, I can exceed the 3,000 RPM mark. Its only on moderate to heavy throttle that it bucks and stumbles. Any thoughts?

Alright, I finally got my fuel pressure gauge hooked up in a makeshift way. By makeshift, I mean I had to remove the schrader valve and band clamp a piece of rubber to the test port. I had a friend crank her up while I watched the gauge. It held a steady 50 PSI all through cranking, the rough idle, and the unwilling rev-up. It still stumbled at idle, and yet, still held a steady 50 PSI.

Could be a tps, A bad plenum gasket is synonymous for misfires.

Sounds like a coil issue I had years ago with another vehicle. It would idle, but put a load on it and it didn't want to run.

Just saying....

How old are your O2 sensors? Although, I would think those would cause issues at smaller throttle openings, as opposed to larger...... Tried some fuel system cleaner?

I replaced my O2 sensors and the idle problem almost disappeared. I pulled the positive cable, waited about 30 minutes, touched the positive to the negative, then hooked it back up and drove her about four miles. The low RPM issue is solved (so far), but it did not affect the upper RPM issue. Any thoughts?

Cam or crank sensor would be my first guess. (assuming the rest of the ignition parts are up to snuff.)