Tech Tips

My friend Tim Hogan, training director of ASA-Texas/Houston, has come up with a better way to isolate faulty injectors, using an Interro Systems PDA and a low-amp probe. Setting the scope's timeframe to 500 microseconds and the range to at least 70 amps, with the low-amp probe clamped around the injector trigger wire, the screen shot pattern tells the tale. The jagged sawtooth pattern represents the jittering signal that "machine-guns" the oil control poppet off its seat, creating what Tim calls a "Bart Simpson Head" (BSH for short). 

First-generation Power Strokes only have one BSH, as seen in the '94 injector waveform screen shot. Second-generation Power Strokes apply high current to the injector coil to unseat the poppet, and then a lower current to hold it open, comprising the two BSH areas on second-generation engines. Interestingly, the second-generation PSD waveform looks almost exactly like the Duramax injector waveform, BSH included. The point is that the down slope right after the BSH should be a straight line. The ragged bump indicates an injector that needs replacing. If you don't replace every injector with this bad bump pattern, the engine still won't run right. 

The exact reason why a bad injector waveform exhibits this scratchy bump ? some look considerably nastier than this ? is something of a mystery at this point. At the time of this writing, Tim said that he has used this method on six or seven different trucks with excellent results.