Hummer H2. Manual — part 160

occur after the slope has ended and the voltage has stabilized, it is because the pintle is slightly sticking because
of a faulty injector

If you see more than one hump it is because of a distorted pintle or seat. This faulty condition is known as
"pintle float".

It is important to realize that it takes a good digital storage oscilloscope or analog lab scope to see this pintle
hump clearly. Unfortunately, it cannot always be seen.

Fig. 2: Identifying Voltage Controlled Type Injector Pattern

INTERPRETING A CURRENT CONTROLLED PATTERN

NOTE:

Current controlled drivers are also known as "Peak and Hold" drivers. They
typically require injector circuits with a total leg resistance with less than 12
ohm.

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

z

See Fig. 3 for pattern that the following text describes.

Point "A" is where system voltage is supplied to the injector. A good hot run voltage is usually 13.5 or more
volts. This point, commonly known as open circuit voltage, is critical because the injector will not get sufficient
current saturation if there is a voltage shortfall. To obtain a good look at this precise point, you will need to shift
your Lab Scope to five volts per division.

You will find that some systems have slight voltage fluctuations here. This could occur if the injector feed wire
is also used to power up other cycling components, like the ignition coil(s). Slight voltage fluctuations are
normal and are no reason for concern. Major voltage fluctuations are a different story, however. Major voltage
shifts on the injector feed line will create injector performance problems. Look for excessive resistance
problems in the feed circuit if you see big shifts and repair as necessary.

Point "B" is where the driver completes the circuit to ground. This point of the waveform should be a clean
square point straight down with no rounded edges. It is during this period that current saturation of the injector
windings is taking place and the driver is heavily stressed. Weak drivers will distort this vertical line.

Point "C" represents the voltage drop across the injector windings. Point "C" should come very close to the
ground reference point, but not quite touch. This is because the driver has a small amount of inherent resistance.
Any significant offset from ground is an indication of a resistance problem on the ground circuit that needs
repaired. You might miss this fault if you do not use the negative battery post for your Lab Scope hook-up, so it
is HIGHLY recommended that you use the battery as your hook-up.

Right after Point "C", something interesting happens. Notice the trace starts a normal upward bend. This slight
inductive rise is created by the effects of counter voltage and is normal. This is because the low circuit
resistance allowed a fast build-up of the magnetic field, which in turn created the counter voltage.

Point "D" is the start of the current limiting, also known as the "Hold" time. Before this point, the driver had
allowed the current to free-flow ("Peak") just to get the injector pintle open. By the time point "D" occurs, the
injector pintle has already opened and the computer has just significantly throttled the current back. It does this
by only allowing a few volts through to maintain the minimum current required to keep the pintle open.

The height of the voltage spike seen at the top of Point "D" represents the electrical condition of the injector
windings. The height of this voltage spike (inductive kick) is proportional to the number of windings and the
current flow through them. The more current flow and greater number of windings, the more potential for a
greater inductive kick. The opposite is also true. The less current flow or fewer windings means less inductive
kick. Typically you should see a minimum 35 volts.

If you see approximately 35 volts, it is because a zener diode is used with the driver to clamp the voltage. Make
sure the beginning top of the spike is squared off, indicating the zener dumped the remainder of the spike. If it is
not squared, that indicates the spike is not strong enough to make the zener fully dump, meaning there is a
problem with a weak injector winding.

If a zener diode is not used in the computer, the spike from a good injector will be 60 or more volts.

NOTE:

This example is based on a constant power/switched ground circuit.

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

At Point "E", notice that the trace is now just a few volts below system voltage and the injector is in the current
limiting, or the "Hold" part of the pattern. This line will either remain flat and stable as shown here, or will
cycle up and down rapidly. Both are normal methods to limit current flow. Any distortion may indicate shorted
windings.

Point "F" is the actual turn-off point of the driver (and injector). To measure the millisecond on-time of the
injector, measure between points "C" and "F". Note that we used cursors to do it for us; they are measuring a
2.56 mS on-time.

The top of Point "F" (second inductive kick) is created by the collapsing magnetic field caused by the final turn-
off of the driver. This spike should be like the spike on top of point "D".

Point "G" shows a slight hump. This is actually the mechanical injector pintle closing. Recall that moving an
iron core through a magnetic field will create a voltage surge. The pintle is the iron core here.

This pintle hump at Point "E" should occur near the end of the downward slope, and not afterwards. If it does
occur after the slope has ended and the voltage has stabilized, it is because the pintle is slightly sticking. Some
older Nissan TBI systems suffered from this.

If you see more than one hump it is because of a distorted pintle or seat. This faulty condition is known as
"pintle float".

It is important to realize that it takes a good digital storage oscilloscope or analog lab scope to see this pintle
hump clearly. Unfortunately, it cannot always be seen.

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

Fig. 3: Identifying Current Controlled Type Injector Pattern

CURRENT WAVEFORM SAMPLES

EXAMPLE #1 - VOLTAGE CONTROLLED DRIVER

The waveform pattern shown in Fig. Fig. 4 indicate a normal current waveform from a Ford 3.0L V6 VIN [U]
engine. This voltage controlled type circuit pulses the injectors in groups of three injectors. Injectors No. 1, 3,
and 5 are pulsed together and cylinders 2, 4, and 6 are pulsed together. The specification for an acceptable bank
resistance is 4.4 ohms. Using Ohm's Law and assuming a hot run voltage of 14 volts, we determine that the
bank would draw a current of 3.2 amps.

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.

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial