Hummer H2. Manual - part 157

Clutch 

Ticking Or Screeching As 
Clutch Is Engaged 

Faulty Release Bearing, Uneven Pressure Plate Fingers 

Click Or Snap When 
Clutch Is Engaged 

Worn Clutch Fork, Worn Pivot Ball, Worn Or Broken Front 

Bearing Retainer 

Transmission Shifts Hard 

Clutch Not Releasing, Incorrect Gear Oil, Shift Mechanism 

Binding, Clutch Installed Backward 

Will Not Shift Into One 
Gear, Shifts Into All 
Others 

Bent Shift Fork, Worn Detent Balls 

Locked Into Gear, Cannot 
Shift 

Clutch Adjustment, Worn Detent Balls 

Transmission Jumps Out 
Of Gear 

Pilot Bearing Worn, Bent Shift Fork, Worn Gear Teeth Or 

Face, Excessive Gear Train End Play, Worn Synchronizers, 

Missing Detent Ball Spring, Shift Mechanism Worn Or Out 

Of Adjustment, Engine Or Transmission Mount Bolts Loose, 

Transmission Not Aligned 

Shift Lever Rattle 

Worn Detents Or Shift Lever, Worn Shift Fork, Worn 

Synchronizer Sleeves 

Shift Lever Hops Under 
Acceleration 

Worn Engine Or Transmission Mounts 

(1)

Most units use spur cut gears in Reverse and are naturally noisy.

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Manual Transmission Trouble Shooting

  

GENERAL INFORMATION 

Waveforms - Injector Pattern Tutorial 

PURPOSE OF THIS ARTICLE 

Learning how to interpret injector drive patterns from a Lab Scope can be like learning ignition patterns all over 
again. This article exists to ease you into becoming a skilled injector pattern interpreter.  

You will learn:  

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How a DVOM and noid light fall short of a lab scope.  

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The two types of injector driver circuits, voltage controlled & current controlled.  

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The two ways injector circuits can be wired, constant ground/switched power & constant power/switched 
ground.  

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The two different pattern types you can use to diagnose with, voltage & current.  

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All the valuable details injector patterns can reveal.  

SCOPE OF THIS ARTICLE 

This is NOT a manufacturer specific article. All different types of systems are covered here, regardless of the 
specific year/make/model/engine.  

The reason for such broad coverage is because there are only a few basic ways to operate a solenoid-type 
injector. By understanding the fundamental principles, you will understand all the major points of injector 
patterns you encounter. Of course there are minor differences in each specific system, but that is where a 
waveform library helps out.  

If this is confusing, consider a secondary ignition pattern. Even though there are many different 
implementations, each still has a primary voltage turn-on, firing line, spark line, etc.  

If specific waveforms are available in On Demand for the engine and vehicle you are working on, you will find 
them in the Engine Performance section under the Engine Performance category.  

IS A LAB SCOPE NECESSARY? 

INTRODUCTION 

You probably have several tools at your disposal to diagnose injector circuits. But you might have questioned 
"Is a lab scope necessary to do a thorough job, or will a set of noid lights and a multifunction DVOM do just as 
well?"  

NOTE:

This article is intended for general information purposes only. This information 
may not apply to all makes and models. 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

  

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

  

In the following text, we are going to look at what noid lights and DVOMs do best, do not do very well, and 
when they can mislead you. As you might suspect, the lab scope, with its ability to look inside an active circuit, 
comes to the rescue by answering for the deficiencies of these other tools.  

OVERVIEW OF NOID LIGHT 

The noid light is an excellent "quick and dirty" tool. It can usually be hooked to a fuel injector harness fast and 
the flashing light is easy to understand. It is a dependable way to identify a no-pulse situation.  

However, a noid light can be very deceptive in two cases:  

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If the wrong one is used for the circuit being tested. Beware: Just because a connector on a noid light fits 
the harness does not mean it is the right one.  

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If an injector driver is weak or a minor voltage drop is present.  

Use the Right Noid Light 

In the following text we will look at what can happen if the wrong noid light is used, why there are different 
types of noid lights (besides differences with connectors), how to identify the types of noid lights, and how to 
know the right type to use.  

First, let's discuss what can happen if the incorrect type of noid light is used. You might see:  

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A dimly flashing light when it should be normal.  

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A normal flashing light when it should be dim.  

A noid light will flash dim if used on a lower voltage circuit than it was designed for. A normally operating 
circuit would appear underpowered, which could be misinterpreted as the cause of a fuel starvation problem.  

Here are the two circuit types that could cause this problem:  

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Circuits with external injector resistors. Used predominately on some Asian & European systems, they 
are used to reduce the available voltage to an injector in order to limit the current flow. This lower voltage 
can cause a dim flash on a noid light designed for full voltage.  

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Circuits with current controlled injector drivers (e.g. "Peak and Hold"). Basically, this type of driver 
allows a quick burst of voltage/current to flow and then throttles it back significantly for the remainder of 
the pulse width duration. If a noid light was designed for the other type of driver (voltage controlled, e.g. 
"Saturated"), it will appear dim because it is expecting full voltage/current to flow for the entire duration 
of the pulse width.  

Let's move to the other situation where a noid light flashes normally when it should be dim. This could occur if 
a more sensitive noid light is used on a higher voltage/amperage circuit that was weakened enough to cause 
problems (but not outright broken). A circuit with an actual problem would thus appear normal.  

Let's look at why. A noid light does not come close to consuming as much amperage as an injector solenoid. If 
there is a partial driver failure or a minor voltage drop in the injector circuit, there can be adequate amperage to 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial

  

fully operate the noid light BUT NOT ENOUGH TO OPERATE THE INJECTOR.  

If this is not clear, picture a battery with a lot of corrosion on the terminals. Say there is enough corrosion that 
the starter motor will not operate; it only clicks. Now imagine turning on the headlights (with the ignition in the 
RUN position). You find they light normally and are fully bright. This is the same idea as noid light: There is a 
problem, but enough amp flow exists to operate the headlights ("noid light"), but not the starter motor 
("injector").  

How do you identify and avoid all these situations? By using the correct type of noid light. This requires that 
you understanding the types of injector circuits that your noid lights are designed for. There are three. They are: 

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Systems with a voltage controlled injector driver. Another way to say it: The noid light is designed for a 
circuit with a "high" resistance injector (generally 12 ohms or above).  

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Systems with a current controlled injector driver. Another way to say it: The noid light is designed for a 
circuit with a low resistance injector (generally less than 12 ohms) without an external injector resistor.  

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Systems with a voltage controlled injector driver and an external injector resistor. Another way of saying 
it: The noid light is designed for a circuit with a low resistance injector (generally less than 12 ohms) and 
an external injector resistor.  

If you are not sure which type of circuit your noid light is designed for, plug it into a known good car and check 
out the results. If it flashes normally during cranking, determine the circuit type by finding out injector 
resistance and if an external injector resistor is used. You now know enough to identify the type of injector 
circuit. Label the noid light appropriately.  

Next time you need to use a noid light for diagnosis, determine what type of injector circuit you are dealing 
with and select the appropriate noid light.  

Of course, if you suspect a no-pulse condition you could plug in any one whose connector fit without fear of 
misdiagnosis. This is because it is unimportant if the flashing light is dim or bright. It is only important that it 
flashes.  

In any cases of doubt regarding the use of a noid light, a lab scope will overcome all inherent weaknesses.  

OVERVIEW OF DVOM 

A DVOM is typically used to check injector resistance and available voltage at the injector. Some techs also use 
it check injector on-time either with a built-in feature or by using the dwell/duty function.  

There are situations where the DVOM performs these checks dependably, and other situations where it can 
deceive you. It is important to be aware of these strengths and weaknesses. We will cover the topics above in 
the following text.  

Checking Injector Resistance 

NOTE:

Some noid lights can meet both the second and third categories 
simultaneously. 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Waveforms - Injector Pattern Tutorial