94 1500 5.2 backfires and stalls under load when warm

[JakDodge]

Need help please. If there is a thread that addresses please point me in the right direction as I did not see one.

Experience: Just purchased a 94 Ram 1500 with 5.2L. Check engine light comes on and the truck will stutter and stumble with backfires on acceleration or under load - it does seem better if acceleration is very light but have to lift pedal and drop rps for it to shift. Black smoke out of pipe when this occurs. Have to shift to N and apply pedal to prevent shut off at lights etc...that is my experience...

Observation: Both ICTs and crank sensor look recently replaced. Valve cover gaskets and trans pan have recently been replaced - all fluids look recently changed. Vacuum line on pass side engine that splits to a T has two leaks. Oil filter housing or pass valve cover leaking (poss rear main) and trans pan leaking. Vehicle appears to have cat delete - o2 sensors and wiring??

Diag: Consistent codes in this order 12, 37, 21, 15, 55 (I understand 12/55 are start/stop). Temp repair on vacuum leak noted above - no significant change in drivability.

Plans: check cap/rotor/wires and plugs but looks like a recent tune up done. Seems like fuel to lean but with cat/o2 non existent not sure what to do about that.

Should I check fuel pressure? Is there an external fuel pressure regulator/filter? Will induction service help? Thoughts on codes 37 and 15? and any other tips or advice. I am ok with this being a around town truck for light hauling but I want to know it won't shut off in front of oncoming traffic...etc.

Thank you!

 

[Dean2]

Is it backfiring out the exhaust or into the throttle body? Exhaust backfire is caused by unburned fuel in the exhaust, heat from the exhaust fires it off. Unburned fuel can be caused by timing, poor ignition, over fueling by PCM due to head gasket leaks, vacum leaks, O2 sensor issue's, vlaves etc. Start with your error codes, chase each one of those down, then move to the more complicated/expensive issues.

Final point, make sure all sensors are OEM MOPAR. NAPA et al sensors cause WAY, WAY more problems than they have ever fixed.Many issues have been completely cured by just swapping out sensors for OEM.

 

[18CrewDually]

The engine needs an O2 sensor. You need to install one if it was removed. It should be in the Y-pipe upstream from where the cat was.
The black smoke and stumbling are indicators of misfire. Either flooding injector or bad ignition wires or plugs. If it looks like it was changed recently, triple check check Firing Order and placement of the spark plug wires. The last guy very well could have say wires 3&5 or 4&6 for example mixed up. Check them all.
Also does the speedometer work? It may have a bad speed sensor or harness issue.

 

[JakDodge]

Interesting analysis as I neglected to mention that the speedo does not work.

 

[JakDodge]

Drivers behind report black cloud out of exhaust but I hear the misfires in the engine and at least once or twice, I heard a backfire in the intake but usually it is out of the rear. The misfires never go away but they are much worse under any load or harder acceleration. The rest of the time, even at highway speeds and the lightest acceleration, I can hear the staccato misfires.