Sudden Acceleration 6.5 Turbo Help!

[kjf]

I own a 1998 K3500 Dually with the 6.5L diesel engine. I have been unable to diagnose this problem, so the vehicle is getting no use for the last year. When you start the engine, it goes into a very fast (1500 rpm), rough idle. Kind of oscillating. It will keep going like that even after warming up. The moment you shift into drive or reverse, it goes back to idle and behaves normally, until you press the accelerator pedal, where it accelerates severely. It doesn

[More Power]

Are any codes present? Is the MIL (Malfunction Indicator Lamp) on?

How long as this problem been present? Was there a transition period where the engine ran normally, then...

Jim

[kjf]

The problem became worse with time. I thought that it was related to the bad connector on the previous PMD. Once I replaced it, I had very fast starts but the acceleration problem persisted. I can't remember the code, so I will have to scan it. I do remember that the only code in memory had to do with the "security". After not starting the unit for some time, I usually have to recharge the batteries and the truck will not start until I lock and unlock the doors with the beeper a few times.

It then starts immediately but will the misfire and acceleration problem described earlier. :confused:

[arveetek]

Is there possibly a high idle switch installed? On the '96 and newer models, if the high idle switch is engaged, the engine will revert to normal speeds once the brake pedal is pressed and/or the gear selector is moved out of park.

Here is info on the high idle modifications:

http://www.kennedydiesel.com/FastIdleSetup.cfm

Otherwise, I would suspect a failing PMD/FSD. I have personally seen them fail where there is idling/RPM issues, and have heard of them failing and going to wide open throttle, which can be scary.

Casey

[Kennedy]

Sudden unwanted acceleration (touchy pedal) tends to be more in the pump metering control not moving freely in my experience. I don't know enough about the mechanics inside, but I would probably relate it to rusted/corroded or varnished hard parts from sitting or lack of lubricity.

The misfire is likely the ECM trying to drop cylinders to reduce the RPM to target.

[ronniejoe]

There are a few ways that sudden uncommanded acceleration can occur. Some are electrical and some are mechanical.

Here is a shot of the back of the pump with the solenoid cap removed.

http://www.schoolcraftpowertrain.com/Pictures_&_Data/2014-09-02 21.22.52.jpg

What you see here is the armature sitting against the coil. The next shot is of the armature removed from the solenoid. Notice the wear indication near the end of the pin. It's a little out of focus, I apologize.

http://www.schoolcraftpowertrain.com/Pictures_&_Data/2014-09-02 21.27.45.jpg

The armature pin slides in and out of the coil based on commands from the PCM through the fuel solenoid driver.

The next shot shows the pump rotor in the stator distributor. The solenoid actuated metering valve is in the rotor.

http://www.schoolcraftpowertrain.com/Pictures_&_Data/2014-09-05 21.00.17.jpg

The rotor and metering valve are shown separately here.

http://www.schoolcraftpowertrain.com/Pictures_&_Data/2014-12-08 21.17.08.jpg

The metering valve is held open (slid aft in pump orientation) by a spring in the valve bore. When the solenoid is energized, the armature pin pushes the valve against its seat to close. The milled slot in the rotor outer surface (top in the photo, aft in pump orientation) with a drilled supply hole from an axial hole is the fuel feed hole to the individual injectors. The other hole that is visible in the outer surface is the inlet feed to the main four plunger pressure pump. There is another hole like this 180 deg away.

The larger hole at the bottom of the image (front of rotor in pump orientation) is a through hole with another through hole the same size 90 deg away. These holes are where the four plunger pistons operate.

The next shot is of the distributor stator with the rotor removed.

http://www.schoolcraftpowertrain.com/Pictures_&_Data/2014-09-06 13.20.39.jpg

The holes in the bore toward the rear (nearest in the photo) are the main supply distribution holes. These holes feed directly into the visible holes for the injection line fittings. The milled slot in the rotor mentioned previously rotates past these holes in sequence. When the holes are lined up, fuel can flow from the rotor to the stator and to an individual injector based on how long the solenoid is energized. The other holes seen toward the front of the bore are the inlet feed holes for the main pressure pump.

The amount of fuel delivered to an individual injector is based on the the pressure generated at the main pump and the length of time that the solenoid is energized to close the metering valve. Excess volume from the main pump is spilled into the return circuit when the solenoid is de-energized.

If something in the electrical controls causes current to remain on to the solenoid coil, the metering valve will be held closed causing the full volume of the main pump to be delivered to the injectors in sequence, interrupted only by the fact that the hole in the rotor moves out of alignment with an individual distributor hole in the stator. Likewise, if either the armature pin or the metering valve seize or stick in their bores, the same thing will happen. That is why a failing FSD (PMD) can sometimes cause a runaway. The wear seen on the armature pin in the earlier photo may have caused the metering valve to stick closed or not close at all intermittently, causing surging, stumbling, etc.

I retain copyright for the photos in this post. I am sharing them for informational purposes only.

[Kennedy]

http://www.kennedydiesel.com/images/totpow_ol.gif