94-98 12 Valve Cummins Low Power, Sputtering, White Smoke.
In this article we’ll troubleshoot low power, or the engine just not running right.
If the engine doesn’t want to start at all, go here: Engine Not Starting
Is it normal?
If you start the engine, and immediately floor it, it will get to about 2000 RPM, and then pop, sputter, white smoke, and RPM won't climb. This is somewhat normal. Same goes for when asking for much power when the engine is cold. There are a couple things that compound the issue:
- Cold Weather.
- Dysfunctional Grid Heaters.
- Disconnected Intake Plumbing.
- Turbo Removed.
- Low Fuel Pressure or Air in the fuel.
Basically, If you are starting the engine on a test stand, it is perfectly normal.
Things to check:
FSS (Fuel Shutoff Solenoid).
Symtoms: Engine Low on power, No Sputtering/misfire/smoke. Engine runs normally, just runs out of power quick.
The FSS is an electrical solenoid that lifts a lever on the injector pump. If FSS isn’t adjusted correctly, or is full of grime, it will limit the amount of fuel the injector pump injects and thus limit power. For more information, Go To: Fuel Shutoff Solenoid (FSS)
Low Fuel Pressure/Unhealthy fuel system.
Symtoms: Possible Hard Starting, Possible Misfire at idle, Possible White Smoke, Especially when engine is powering out.
If the engine takes a couple cranks to start after sitting overnight, check for air in the fuel. Go Here: Checking For Air In Your Fuel
It is highly recommended that you install a fuel pressure gauge to avoid blindly throwing parts at the problem. Go Here: How to install Fuel Pressure Gauge
Fuel Pressure should stay above 20 psi at all times, if it goes down to 15 psi, you know you have a problem, to diagnose the cause. Go Here: JoeG's Fuel System Write-Up
Slipped Injection Timing
Symtoms: White smoke, Engine Knocking, Low Power.
Warped Injector Pump Plungers.
Symtoms: Runs normal when cold, Misses and Dies once warm.
To test, once the engine starts to misbehave, pour a bucket of water over the injector pump to cool it down. If the engine starts running fine again, look into getting a new injector pump.