Just an interesting blurb on the 6.5 injection system

[great white]

Ran across this somewhere, just a good read for those who don't know:

GM 6.5L engine

The distributor type Stanadyne injection pump on the GM 6.5L engine regulates fuel quantity with a solenoid valve controlling the amount of low pressure fuel entering the high pressure pumping chamber. The solenoid driver on the side of the pump housing operates the solenoid on command from the PCM, much like gasoline injection. The solenoid is not pulsed, but fully opened and fully closed. The driver senses when the solenoid is fully closed to tell the PCM when injection has ended.

With this system, there is no mechanical governor, no lever, cable or linkage connecting the accelerator pedal to the pump. A pedal position sensor inside the vehicle, much like a throttle position sensor, supplies data on pedal position and movement to the PCM. It then operates the fuel solenoid accordingly. This drive-by-wire system (sometimes called fly-by-wire because it was first developed for aircraft) is also used on some gasoline engines. As things like traction control and anti-skid control become more common, drive-by-wire may eventually replace direct throttle linkage in all vehicles.

The Accelerator Pedal Position (APP) sensor contains three separate potentiometers, each with its own 5V reference and distinct return signals. The triple redundancy is because this is the one signal the PCM absolutely must have to run the engine. If one or two sensors fail, the vehicle can still be driven but with limited power. The PCM will set a code and turn on the ‘Service Throttle Soon’ light. If all three fail, the engine will run only at idle. Using a scan tool and the diagnostic procedure in the factory service manual, you can look at each APP signal. Further, with a scope you can look for the same drop-outs that would indicate a bad throttle position sensor.

Another unique feature on the Stanadyne pump is the Optical/ Temperature sensor on the pump itself. It consists of a standard thermistor type fuel temperature sensor and two optical pick-ups that share a housing and a 5V reference signal. The optical pick-ups read tone wheels that rotate with the cam ring inside the pump. One pick-up provides a high resolution signal, generating 64 pulses per cylinder firing stroke. Along with fuel temperature and the crankshaft position data, this extremely fine position signal makes it possible to trim the fuel quantity for each individual combustion stroke. The other pick-up has only eight slots and reports pump cam position to locate the start of injection for each cylinder and to index cylinder No. 1. Along with the crankshaft position signal, this information is used for pump timing, idle speed control and other ‘real time’ events in power train control.

Injection pump timing is controlled with a stepper motor on the side of the pump. By changing the position of the cam ring, first movement of the high pressure plunger (plunger lift) can be varied relative to crankshaft position. With mechanical governors, this is a function of hydraulic pressure in the pump housing, increasing with rpm to advance timing as speed increases. On this system, the PCM operates the stepper motor.

Most of the other inputs to the PCM are things you’ve likely seen before, including sensors for coolant temperature, crankshaft position, intake air temperature, barometric pressure or manifold pressure (turbo), vehicle speed, brake switch, A/C, cruise control and the automatic transmission sensors and signals. Outputs include the ‘Service Engine Soon’ and ‘Service Throttle Soon’ lights, A/C, cruise control, glow plug relay, automatic transmission and, of course, the injection pump driver and timing stepper motor. EGR was added to this engine in 1997, using a standard vacuum operated EGR valve and a duty cycled solenoid valve to control the vacuum. Troubleshooting all of these with a scan tool is similar to the procedure for gasoline engines.

 

[Acesneights1]

Think that is in my 6.5 GM book.

 

[ak diesel driver]

egr was added before 1997

 

[iamdave0887]

egr was added before 1997

I was going to say, EGR's on the 6.x IDIs has been around much longer than 97. My 85 6.2 had an EGR on it.

 

[ak diesel driver]

even before 87

 

[jmiller]

That's a very good description of how things work.