WAVEFORMS - INJECTOR PATTERN TUTORIAL
Article Text (p. 17)
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 09:26PM
However this is not the case because as the injector windings
become saturated, counter voltage is created which impedes the current
flow. This, coupled with the inherent resistance of the driver's
transistor, impedes the current flow even more. So, what is a known
good value for a dynamic current draw on a voltage controlled bank of
injectors? The waveform pattern shown below indicates a good parallel
injector current flow of 2 amps. See Fig. 4.
Note that if just one injector has a resistance problem and
partially shorts, the entire parallel bank that it belongs to will
draw more current. This can damage the injector driver.
The waveform pattern in Fig. 5 indicates this type of problem
with too much current flow. This is on other bank of injectors of the
same vehicle; the even side. Notice the Lab Scope is set on a one amp
per division scale. As you can see, the current is at an unacceptable
2.5 amps.
It is easy to find out which individual injector is at fault.
All you need to do is inductively clamp onto each individual injector
and compare them. To obtain a known-good value to compare against, we
used the good bank to capture the waveform in Fig. 6. Notice that it
limits current flow to 750 milliamps.
The waveform shown in Fig. 7 illustrates the problem injector
we found. This waveform indicates an unacceptable current draw of just
over one amp as compared to the 750 milliamp draw of the known-good
injector. A subsequent check with a DVOM found 8.2 ohms, which is
under the 12 ohm specification.Fig. 4: Injector Bank w/Normal Current Flow - Current Pattern
