Electronic Engine Management Systems

Troubleshooting Electronic Engine Management Systems
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You know them, you hate them, but do you really understand them? That's right. Thingamabobs, aka, things that are very important, they cost a lot to replace, they're hard to get to and you don't know the exact name for them or how they work. What is that thing on the side of the manifold there? It's a Thingamabob. It's a little black box. Probably some kind of sensor or something like that. It's one of those things with weird capital letters with periods behind each letter.

Thingamabobs. Yeah, there are a whole lot of them on your computer controlled car. They are things that sound important, and by coincidence, are important. Yes, I'm talking about all of those things that make your EFI or computer controlled engine run better.

Thingamabobs are the bane of the stone age mechanic and the best friend of the modern mechanic. Those who understand them know them to be powerful allies in the quest for more power, it's like having an unseen mechanic under your hood. Those who don't understand them often see them as the bitter enemy and would prefer to follow the path of the Luddite instead.

All together, the various Thingamabobs under your hood and scattered throughout your vehicle form a complex, highly technological, but not all that hard to understand system of electronic engine management. Once you jump right in and get your feet wet, well, there's no turning back and as someone famous once quoted "A mind expanded by a single great thought never collapses to it's original size again." or something like that. What this means is, once you learn what electronic engine management and all it's Thingamabobs can and will do for you, you won't ever want to look at anything other than the beauty of electronic engine management.

So, just what exactly DO all of those Thingamabobs under your hood really DO? Do you need them? Some of them, most of them, or just a few? What happens when they don't work? Can one Thingamabob shut down your whole car or truck if it fails? What do you do to fix your latest problem? Inquiring minds want to know! EFI and computer controlled engine management maintenance is not for the average dummy of the world, but if you are brave enough (and high enough on the food chain) to resist ripping out your TBI and installing a stone age carburetor ("Ah nevuh kood gets thats theres dang fooled jections to works in my dang old car..."), then you might take some comfort in the following information. If you've ripped out your EFI (TBI or TPI) for a carburetor, well, all I have to say is you have to be smarter than what you work with, and carbs take no brains to slap on or modify. Makes a statement doesn't it?

Here is a general trouble shooting chart for EEM electronic engine management. Listed below you will find several common problems, and arranged underneath each problem in simple YES or NO format is an indicator as to if the listed Thingamabob could be causing the problem. Simple enough for you?

"Know" as in this is a very general reference based on my experiences with EFI and EEM. It is a very deep and broad experience, with many years backing it up (all the way back to Cross Fire Injection when it was first introduced on the 3rdGen F-body) but I am simply a human being, and no human being is perfect. I could be wrong, but generally, I'm pretty knowledgeable about these things. I'm not perfect, but I share what I know so you're getting some great advice for free which is a price I'm sure you'll agree that you can't beat. Please don't knock my experience. If something here is wrong, let me know and I'll correct it! However, your EXACT problem and solution application MAY vary slightly or highly depending on year, make, model, and country of origin. It's been my experience that, for the most part, all of these systems work in very similar ways on all cars and trucks, regardless of year, make, model, or country of origin. That's because of the principle of EEM / EFI and the mechanical and electrical nature of these components. You could not use a Speed Sensor to read the Manifold Absolute Pressure, so I don't believe you'll ever run across an application where the VSS performs the additional duty of the MAPS, so you see, this stuff, once you become familiar with it, is pretty much easy to understand. Once you become familiar with it, trouble shooting EEM and EFI is a walk in the park, or a run down the quarter mile, which ever makes you happier.

However, be aware, there ARE some odd ball vehicles driving around out there so you could run across something not covered in this presentation. If you do, please let me know and I'll work the new discovery into the presentation. Please use this chart as a reference to trouble shoot your EEM / EFI problem in a general sense, then consult the mechanics, shop, or tech reference guides / books for your specific model to track down the exact problem and solution if required. I can get you real close (hold fingers together at the point where they are almost touching) but the last diagnosis is up to you, ultimately.

Abnormal Engine Management Problem Observed

Stalling
with no restart

Stalling with restart

Hesitation or stumble

Pinging or knocking

Dieseling or Run-On

No Torque Converter "Lock-Up"

Illuminated "Check Engine" or "Service Engine Soon" light

Backfiring

Loud Exhaust Noise

Fast Surging or Erratic Idle

Activates Temp Gauge / Light

Cold Engine Warm Up Problems

High Emissions

Surging at Highway Speeds

Poor Performance and / or Fuel Economy Observed

Black Smoke From Exhaust

Strong Exhaust Odor

No Start

Hard or Very Hard Start

Air Charge Temperature Sensor

YES

A.I.R. (Air Injection Reaction) Tube

YES

Camshaft Position Sensor

YES

Check Valve

YES

Coolant Temperature Sensor

YES

Crankshaft Position Sensor

YES

Diverter Valve

YES

EGR Valve

YES

EGR Valve Position Sensor

YES

EGR Valve Pressure Sensor

YES

EGR Vacuum Solenoid

YES

Idle Air Control Valve

YES

Idle Speed Control Motor

YES

Knock Sensor

YES

Manifold Absolute Pressure Sensor

YES

Mass Air Flow Sensor

YES

Oxygen Sensor

YES

Pick-Up Coil / Hall Effect Sensor

YES

Speed Sensor

YES

Throttle Air Bypass Valve

YES

Throttle Position Sensor

YES

EQUIPMENT MODULE	FUNCTION
Air Charge Temperature Sensor	Used by the computer to determine the temperature of incoming air in order to control the air / fuel ratio. Usually located in the air cleaner or intake manifold
A.I.R. (Air Injection Reaction) Tube	The tubing used by the AIR pump to deliver air to the exhaust manifold. This helps to reduce exhaust pipe emissions. Usually located on the exhaust manifold.
Camshaft Position Sensor	Used by the computer to determine which fuel injector or ignition coil to fire. Usually located at the front of the motor.
Check Valve	This is a simple device which prevents extremely hot exhaust gases from entering and subsequently damaging the AIR system. This device is usually located between the AIR tubes and the AIR system hoses.
Coolant Temperature Sensor	The CTS is used by the computer to determine the temperature of the coolant circulating through the engine and helps to control the air/fuel ratio, idle speed, ignition timing, and sometimes the vapor canister purge. Usually located in the coolant system or on the engine block itself.
Crankshaft Position Sensor	The CPS sends a timing signal to the electronic ignition module and the computer. This signal allows the computer to determine when is the optimum time to fire each spark plug. The CPS is usually located on the engine block or transmission housing.
Diverter Valve	This little device controls the amount of air that flows from the AIR pump to the atmosphere, catalytic converter, exhaust manifold, and / or the air cleaner array. It is usually located on or near the AIR pump itself.
EGR Valve	The EGR valve mixes a measures the air/fuel ratio with a measured amount of exhaust gas in order to determine the optimum mixture and control combustion chamber temperatures while reducing exhaust emissions. The EGR Valve is usually located on or very near the intake manifold.
EGR Valve Position Sensor	The EGR VPS tells the computer how far the EGR valve is open. It is usually located on top of the EGR valve. Duh.
EGR Valve Pressure Sensor	The EGR Valve Pressure Sensor tells the computer what the optimum EGR flow is. This device is located on or near the exhaust manifold.
EGR Vacuum Solenoid	The EGR Vacuum Solenoid is used by the computer to turn the EGR valve vacuum supply on or off. This regulates and controls the EGR valve operation. It is usually located in the vacuum line between the vacuum port and the EGR valve.
Idle Air Control Valve	The IAC valve is used by the computer to maintain the correct engine idle speed. It is usually located in the throttle or throttle body housing.
Idle Speed Control Motor	The ISCM is used by the computer to maintain the correct idle speed of the engine. It is usually located on the side of the carburetor, throttle body, or throttle body housing.
Knock Sensor	The Knock Sensor is used by the computer to 'listen' for the sound of 'knock' or detonation by detecting the vibrations from such conditions as knock and engine pinging. This allows the computer to adjust ignition timing and eliminate these conditions. The knock sensor is usually found in many various locations on the engine block or intake manifold. You may have more than one knock sensor!!!
Mass Air Flow Sensor	The MAF is used by the computer to measure the volume of air entering the engine. This helps the computer to maintain the proper air / fuel ratio. The MAF is usually located between the air cleaner and the throttle or throttle body housing.
MAP Sensor	The MAPS measures engine load by sensing vacuum and barometric pressure and sending this information to the computer. This information helps to control the air/fuel mixture and to keep the ignition timing correct. The MAPS is usually located on the intake manifold, air cleaner housing, firewall, fender well, or under the dashboard.
Oxygen Sensor	The oxygen sensor is used by the computer to measure the amount of oxygen in the exhaust stream. This helps the computer to determine the proper air/fuel mixture and adjust it accordingly. The oxygen sensor is usually located in the exhaust manifold or somewhere in the exhaust system.
Pick-Up Coil / Hall Effect Sensor	This little device provides the electronic ignition module with a timing signal. This helps the computer to determine when to fire each spark plug. Usually found inside the distributor.
Speed Sensor	The computer uses the VSS to measure direct vehicle speed and to control the torque converter lock-up and the shifting of the transmission. The VSS is usually located on the transmission housing, connected to the speedometer cable or located on the speedometer itself.
Throttle Air Bypass Valve	The TABV is used by the computer to maintain the correct idle speed for the engine. The TABV is usually located on top of or near the throttle or throttle body housing
Throttle Position Sensor	The TPS measures the throttle plate movement. The signal generated by the location of the throttle plate allows the computer to control the ignition timing, air/fuel ratio mixture, and the torque converter lock-up feature. The TPS is usually located on the sides of the throttle or throttle body housing or the carburetor.