Hi everyone - new to the forum. Glad to be here. Please take time to weigh in on this issue as I am out of easy answers.

Couple weeks ago I stumbled onto a 92 dakota 3.9 magnum extended cab truck....with 98kmiles on it...owned by some older folks...bought it...paid only a grand for it. Truck is in pretty much immaculate shape. The owner said it had a small engine noise (before I bought it) but I looked at it and chalked that up to a bad water pump.

I changed the water pump out which made the engine noise disappear - did a complete tune up on the motor which consisted of:
-clean and inspect IAC (works now)
-shake PCV valve (works)
-replace cap, rotor, and spark plug wires
-replace spark plugs
-clean and inspect crank case ventilator (don't know exactly what it's called on this truck)
-cleaned throttle body
-replaced air filter
-replaced egr valve and vacuum controller

I have inspected all the vacuum hoses that lead to and from the engine and all 'appear' to be fine...in addition...I sprayed carb cleaner all over each and every vacuum point to see if I could get the motor to stumble...no stumble. Throttle body bolts are tight and all the intake manifold bolts are tight. No hissing.

All cylinders register right around 150lbs EXCEPT #4. #4 cylinder is 120lbs.

I have NOT taken off the throttle position sensor and looked at it or replaced it. I have not taken off the map sensor and looked at it either. I have not looked at the PCV grommet or the CCV grommet...but...the motor doesn't stumble when I spray them either. There is no check engine light on (I don't even know if this model has one).

I don't have a borescope so I can't look at the piston on number 4 or the valves for that matter.

The engine will run like a top when you are the accelerator...but when you stop at a light and the truck is in gear...it will 'lope' real hard. Shakes the whole truck. I don't think this is electrical. No light shows at night.

Can someone recommend something I might have overlooked?

Thanks folks!
Chris

 

Try the dakota section for more help, this is the 3rd gen v6 ram section. The manual for my ram states many possible causes for what you describe including:
1. vacuum leakage
2. fault in the fuel or electrical systems
3. plugged pcv valve or hose
4. fuel pump not delivering enough fuel to injectors
5. leaking head gasket
6. camshaft lobes worn