Hummer H2. Manual — part 161

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. 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. Fig. 6 . Notice that it limits current flow to 750 milliamps.

The waveform shown in Fig. 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

Fig. 5: Injector Bank w/Excessive Current Flow - Current Pattern

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

Fig. 6: Single Injector w/Normal Current Flow - Current Pattern

Fig. 7: Single Injector w/Excessive Current Flow - Current Pattern

EXAMPLE #2 - VOLTAGE CONTROLLED DRIVER

This time we will look at a GM 3.1L V6 VIN [T]. Fig. Fig. 8 shows the 1, 3, 5 (odd) injector bank with the
current waveform indicating about a 2.6 amp draw at idle. This pattern, taken from a known good vehicle,
correctly stays at or below the maximum 2.6 amps current range. Ideally, the current for each bank should be
very close in comparison.

Notice the small dimple on the current flow's rising edge. This is the actual injector opening or what engineers
refer to as the "set point." For good idle quality, the set point should be uniform between the banks.

When discussing Ohm's Law as it pertains to this parallel circuit, consider that each injector has specified
resistance of 12.2 ohms. Since all three injectors are in parallel the total resistance of this parallel circuit drops
to 4.1 ohms. Fourteen volts divided by four ohms would pull a maximum of 3.4 amps on this bank of injectors.
However, as we discussed in EXAMPLE #1 above, other factors knock this value down to roughly the 2.6 amp
neighborhood.

Now we are going to take a look at the even bank of injectors; injectors 2, 4, and 6. See Fig. 9 . Notice this bank

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

peaked at 1.7 amps at idle as compared to the 2.6 amps peak of the odd bank (Fig. Fig. 8 ). Current flow
between even and odd injectors banks is not uniform, yet it is not causing a driveability problem. That is
because it is still under the maximum amperage we figured out earlier. But be aware this vehicle could develop
a problem if the amperage flow increases any more.

Checking the resistance of this even injector group with a DVOM yielded 6.2 ohms, while the odd injector
group in the previous example read 4.1 ohms.

Fig. 8: Injector Odd Bank w/Normal Current Flow - Current Pattern

Fig. 9: Injector Even Bank w/Normal Current Flow - Current Pattern

EXAMPLE #3 - VOLTAGE CONTROLLED DRIVER

Example #3 is of a Ford 5.0L V8 SEFI. Fig. Fig. 10 shows a waveform of an individual injector at idle with the
Lab Scope set on 200 milliamps per division. Notice the dimple in the rising edge. This dimple indicates the
actual opening of the injector (set point) occurred at 400 milliamps and current peaked at 750 milliamps. This is
a good specification for this engine.

The next waveform pattern in Fig. Fig. 11 shows an abnormality with another injector. With the Lab Scope set

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

on 500 milliamps per division, you can see that the current waveform indicates a 1200 milliamp draw. This is a
faulty injector.

Abnormally low resistance injectors create excessive current draw, causing rough idle, and possible computer
driver damage.

Fig. 10: Single Injector w/Normal Current Flow - Current Pattern

Fig. 11: Single Injector w/Excessive Current Flow - Current Pattern

EXAMPLE #4 - CURRENT CONTROLLED DRIVER

Example #4 is of a Ford 4.6L SEFI VIN [W]. See Fig. 12 for the known-good waveform pattern. This Ford
system is different from the one above in EXAMPLE #3 as it peaks at 900 milliamps and the actual opening of
the injector (set point) is just below 600 milliamps.

This is offered as a comparison against the Ford pattern listed above, as they are both Ford SEFI injectors but
with different operating ranges. The point is that you should not make any broad assumptions for any

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial