• Test Procedure
1. Connect the CH A lead to the injector control signal from the PCM and its ground lead to the injector GND.
2. Start the engine and hold t hrottle at 2500 RP M for 2-3 minutes until the engine is fully warmed up and the
Feedback Fuel System enters closed loop. (Verify this by viewing the O
2
sensor signal, if necessary.)
3. Shut off A/C and all other accessories. Put vehicle in park or neutral. Rev the engine slightly and watch for the
corresponding injector on-time increase on acceleration.
1) Induce propane into the intake and drive the mixture rich. If the system is working properly, the injector on-
time will decrease.
2) Create a vacuum leak and drive the mixture lean. The injector on-time will increase.
3) Raise the engine to 2500 RPM and hold it steady. The injector on-time will modulate from slightly larger to
slightly smaller as the system controls the mixture. Generally, the injector on-time only has to change from
0.25 ms to 0.5 ms to drive the system through its normal full rich to full lean range.
4. Use the Glitch Snare mode to check for sudden changes in the injector on-time.
• Reference Waveform
VEHICLE INFORMATIONS
YEAR
: 1993
MAKE
: Chevrolet
MODEL
: Suburban 1500
ENGINE
: 5.7 L
FUELSYS : Throttle Body Fuel Injection
PCM_PIN : A16 DkBlu
STATUS
: KOER (Key On Running)
RPM
: Snap Acceleration
ENG_TMP : Operating Temperature
VACUUM : 3-24 In. Hg
MILEAGE : 55011
• Troubleshooting Tips
Spikes during on-time or unusual high turn off spikes indicate the injector driver’s malfunction. On GM and some
ISUZU dual TBI systems lots of extra oscillations or “hash” in between the peaks indicates a faulty injector driver in
the PCM.
6-35
When the Feedback Fuel Control System controls fuel mixture properly, t he injector
on-time will modulate from about 1-6 ms at idle to about 6-35 ms under cold cranking
or Wide Open Throttle (WOT) operation.
The injector coil release spike(s) ranges are from 30 V to 100 V normally. The turn off
spikes less than 30 V may indicate shorted injector coil.
Initial drive voltage should go close to 0 V. If not, injector driver may be weak.
• Reference Waveform
VEHICLE INFORMATIONS
YEAR
: 1993
MAKE
: Ford
MODEL
: F150 4WD Pickup
ENGINE
: 5.0 L
FUELSYS : Multiport Fuel Injection
PCM_PIN : 58 Tan wire
STATUS
: KOER (Key On Running)
RPM
: Idle
ENG_TMP : Operating Temperature
VACUUM : 19 In. Hg
MILEAGE : 66748
• Troubleshooting Tips
Spikes during on-time or unusual high turn off spikes indicate the injector driver’s malfunction.
Peak and Hold Type (TBI) Injector
• Theory of Operation
Peak and Hold f uel injector drivers are used almost exclusively on Thrott le Body I njection (TBI) systems. These
drivers are only used on a few selected MFI systems like GM’s 2.3 L Quad-4 engine family, Saturn 1.9 L, and Isuzu
1.6 L. The driver is designed to allow approximately 4 A to flow through the injector coil and then reduce the current
flow to a maximum of about 1 A. Generally, far more current is required to open the pintle valve than to hold it open.
The PCM continues to ground the circuit (hold it at 0 V) until it detects about 4 A flowing through the injector coil.
When the 4 A “Peak” is reached. the PCM cuts back the current to a maximum of 1 A, by switching in a current
limiting resistor. This reduction in current causes the magnetic field to collapse partially, creating a voltage spike
similar to an ignition coil spike, The PCM continues the “Hold” operation for the desired injector on-time, then it shuts
the driver off by opening t he ground circuit complet ely. This creat es the second spike. Under acceleration the
second spike move to the right, while the first remains stationary. If the engine is running extremely rich, both spikes
are nearly on top of one another because the PCM is attempting to lean out the mixture by shortening injector on-
time as much as possible.
• Symptoms
Hesitation on throttle tip in, rough idle, intermittent stall at idle, poor fuel mileage, emissions test failure, low power on
acceleration.
6-34
When the Feedback Fuel Control System controls fuel mixture properly, the injector
on-time will modulate from about 1-6 ms at idle to about 6-35 ms under cold cranking
or Wide Open Throttle (WOT) operation.
The injector coil release spike(s) ranges are from 30 V to 100 V normally.
MAX = 35.3 V
MIN = -2.00 V
DUR = 3.92 ms
PCM turns
circuit off here
PCM turns
circuit on here
MAX = 83.5 V
MIN = 0.00 V
DUR = 5.51 ms
Straight line here (just below
battery voltage) indicates
good injector driver.
