engine bogging down
1992 Ram 150 3.9L v6, 3 speed auto trans: Engine bogs down under load, very little power, slows down going up hills. During warm idle in neutral the vacuum is 15 inches. After opening throttle valve vacuum climbs to 19 inches. However in drive the vacuum is 13 inches at idle and drops to 5 inches when the throttle is opened. Is this a motor problem or a transmission problem?
I read on another thread on this site where someone's truck would bog down for a while and suddenly clear up and run good until the next episode. Their description of the way their truck ran when it was acting up matches what my truck is doing. My truck just runs that way all of the time. It will cruise o.k. on level roads. Yesterday I was doing 60 and floorboarded it. I went about 1/10 mile like that and the speed never increased. It did downshift and stay in second until I lifted my foot. It is as if the PCM will not allow the engine to have the gas that my foot pedal is calling for. The engine does backfire into the intake manifold under load and the problem is worse when the engine is cold.
I have put numerous bottles of Sea Foam, Gumout, STP, etc. in the tank. Primarily I use 100% petroleum fuel. I am trying to locate a fuel gage now to check pressure but I don't think that is the issue. I may have a major filter failure and the injectors could be staying stopped up.
I have replaced o2, manifold temp sens., coolant temp sens., throttle position sens., exhaust system including cat., timing chain & sprkts., oil pump drive shaft & bushing, plugs, wires, cap and rotor. The only diag. code is 45 - open or short in overdrive solenoid circuit. The truck doesn't have an overdrive transmission, but could it still be a transmission problem? Can the transmission be seizing or trying to go into two gears at once or something and bogging the motor down?
I'm open to suggestions.