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EEC Handbook - Version 6 / HTML

First time through? Please read (or at least skim through) this chapter. There are notes that will help you to understand the EEC system and to use this manual to diagnose problems. There are also some reference sections at the end of this page.


Transmission in Park or Neutral and the driven wheels off the ground or chocked when cranking/running the engine.
Check fan blade for cracks and do not stand next to the fan when engine is running.
Use caution when working on fuel systems, which can remain pressurized for a long period after the key is turned off.
No smoking around fuel.
Watch for electric fan which can come on at any time.
Watch out for hot and/or moving parts.
When working on a no-start vehicle, use a neon spark tester to check for spark and ground the coil wire to prevent accidental starting if spark should occur while testing.
Watch out for high voltage secondary circuits.
If you are not sure of the safety of any operation DO NOT DO IT. ASK SOMEONE!


In this chapter:
[Engine Codes]
[Vehicle Year Codes]
[Vehicle Identification]
[EEC System Overview]
[Code Diagnosis Overview]



This booklet is intended as a supplement to the authorized repair manuals for Ford electronic engine control systems.
The Ford service procedures, if different from these, take precedence.

The user should insure that he is conforming to any applicable state and federal emissions laws when performing any adjustments or repairs.
If in doubt, consult a Ford or Lincoln/Mercury dealer or other state authorized repair facility.

Although we have tried to be as accurate as possible, there are no guarantees as far as this booklet goes. The authorized repair procedures can change daily.
See Ford service publications and technical service bulletins for the latest procedures/parts etc.

Again, the Ford Motor Company publications have the final say.


There are various warnings throughout this book and the Ford manuals.
Pay attention to them.
We can warn, but YOU have the responsibility of making all operations safe.
If you are not sure of the safety of any operation DO NOT DO IT.


Most EEC system parts are covered by mandatory 5 year 50,00 mile emission warranties.


Refer to the emissions/vacuum diagram under the hood for any engine settings (plug gap, base timing specifications, idle speed).


The engine calibration sticker should be on the front of the engine or on one of the valve covers.
On 1988 and up vehicles it is located on one of the left side doors or door jamb.

Look for the words Cal or Calibration. Some typical calibrations are:

6-25F- R10, 7-25F-R00, 7-54Z-R05.

The first part of the calibration is the year; but you may see 1986 vehicles with 5- calibrations, 1985s with 4- calibrations etc.
The second part is the base calibration and the third part is the revision number.

If the calibration sticker is illegible or missing a dealer can get the calibration on the Ford online service network by referencing
the vehicle identification number (VIN, or serial number).


This is the HTML version of "EEC Handbook - Version 6" originally published on paper by Dali Design (me).
Dali is the name of one of our cats, and I liked the way it sounded with design.

There are some salary people that can spend 8 hours finding an intermittent problem but most of the people I know work flat rate.
In order to pay the bills you have to produce. For these people I will try to give some easier suggestions to some problems.
These will be in the form of FLAT RATE boxes.

There are a number of problems with the easy approach. First, there aren't always easy answers.
Consider some of the things that can make a vehicle not start.

FUEL SYSTEM: fuel pump, fuel pump relay, processor or any of the wires to each
IGNITION SYSTEM: spark plugs, module, pickup(s), coil(s) or any of the wires to each
EEC SYSTEM: Processor, MAP sensor, throttle sensor, or a lot of different wires
BASIC ENGINE: Camshaft, timing chain, distributor, rings

I can recall a Taurus no-start that drove a few people crazy. It turned out to be the EEC VPWR wire to a transmission solenoid rubbed through inside the transmission. The main problem was that the wire only shorted and blew the EEC fuse when the engine was cranking. For a long time we thought it was a starter circuit problem.

This is why it is so hard to say "here is where your problem is". It requires a lot of knowledge and detective work on your part.
Experience and a bit of luck help also.

So when a FLAT RATE box says it's best to replace the EGR valve when you get a code in memory it's because that's what experience has told me was usually wrong in the past so I'll try it again. Once in a while it doesn't fix the problem or I get a comeback but 9 out of 10 times it works.

Just remember that you may get burned. You have to balance the comebacks against the ones you do fix. Your only alternative is to not do anything to the vehicle unless a problem shows up. Then the customer will take his car to another shop that WILL hang a few parts on. After 2 or 3 parts they'll nail the problem and then the customer is convinced you didn't know enough (but THEY'RE GREAT!).

So use the FLAT RATE boxes but also keep your wits about you.
LOOK CAREFULLY at wiring etc. and check for special notes on the vehicle or engine you are working on.


Sometimes it helps if you try to think like a computer. A computer is just a set of circuits that can switch one way or the other.
It makes "this" or "that" decisions based on data it is receiving.

Fuel system control is a good example of how this works.

Say the oxygen sensor (O2S) signal line was grounded. The PCM says "the O2S is lean (0.0V) , so I'll richen the mixture".
The O2S line is still grounded so the PCM keeps on richening. After a bit of this the vehicle is blowing black smoke.

The Manifold Absolute Pressure (MAP) sensor which reads manifold vacuum is another example:

When the driver accelerates, the vacuum to the MAP drops off and the frequency it outputs starts going higher.
The PCM says "MAP frequency up = acceleration = richen mixture" and richens the mixture for acceleration.

Now suppose the MAP line develops a leak and the vacuum drops to the MAP. The PCM again says "MAP frequency up = acceleration = richen mixture" and richens the mixture. Now you have a vehicle with a vacuum leak blowing black smoke.

This is why, when the customer complains about fuel mileage and black smoke you may get a lean code, or no code.

In the case of the lean code, the rich mixture is just the PCM trying to compensate. In the case of the MAP problem, the PCM didn't see a problem.
It saw what it thought was acceleration and it acted correctly according to its rules.

Keep this in mind when you are trying to figure out a tough problem. Try to put yourself in the place of the PCM and figure out what type of INPUT would give you the REACTION you are getting.


Most of this handbook concerns hard fault codes. That means a problem that is present at this moment.

If the code you are receiving is a memory code, you will have to duplicate the problem to find it.
Try wiggling wires and tapping solenoids and sensors while you check them.

There are hints to help find intermittent problems for certain codes but not all the possibilities can be covered.

EEC wiring should only be unplugged with the key off. On vehicles equipped with an idle speed control motor wait 10 seconds for the time delay relay to turn off.

All connector drawings are vehicle harness ends (looking into the end that plugs up) unless otherwise noted. Wire colors when listed are typical. Numbers in parentheses (34) are TYPICAL processor pin numbers. See the PINOUTS AND WIRE COLORS chapter for actual pin numbers.

When directed to "Wiring Tests" refer to the link. SOME WIRING TESTS ARE DIFFERENT. For instance the wiring tests for Electronic Ignition systems have different techniques than the wiring tests for most other components.

Farther down is an overview of the EEC system and a link to a typical wiring diagram.

At the end of this section there are some vehicle/engine identification charts.

There is a glossary to help you with terms you don't know.


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Below is the basic procedure for diagnosing an EEC system code. At times it is easier to use a different procedure but this will give you an idea of what to aim for.


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[Example EEC wiring diagram]

Ford's Electronic Engine Control EEC IV is basically the same as the earlier types of EEC systems.
The differences are a memory, easier diagnosis and some redesigned parts.

The "brains" of the system is the Powertrain Control Module (PCM) also known as the processor. It contains a microprocessor which reads various input signals and controls the fuel and emissions systems to try to obtain the best performance while maintaintaining good mileage and emissions output.



The Throttle Position sensor (TP) mounted on the end of the throttle body or carburetor shaft tells how much demand the driver is asking for both by how far it opens and by how fast it opens.


The EGR valve position sensor (EVP) or pressure feedback EGR sensor (PFE) gives an indication of how much EGR gas is flowing.


The exhaust Oxygen sensor (O2S) outputs a voltage in proportion to the air/fuel ratio. In Closed Loop operation the PCM reads the O2S and then decides if it should richen or lean out the mixture. In open loop operation (e.g. engine cold or Wide Open Throttle) the PCM uses preset fuel/air mixture ratios.


A manifold absolute pressure (MAP) sensor normally measures the manifold vacuum. When the throttle is wide open it also measures barometric pressure. A similar sensor (BARO) measures only barometric pressure. At higher altitudes the air contains less oxygen so the engine requires less fuel.


The engine coolant temperature sensor (ECT) is self explanatory.
The ECA will deliver a richer mixture to a cold engine.

The Inlet Air Temperature sensor (IAT) located in an air passage in the intake manifold measures the incoming air temperature.
Cold air is denser, contains more oxygen, and therefore requires a richer mixture.

Sensors used only on specific models include:

A Knock Sensor (KS) outputs a voltage when it detects engine ping. The PCM can then retard the timing slightly to compensate for it.

An air metering box includes a Vane Air Flow (VAF) sensor to measure the amount of air going to the engine and a Vane Air Temperature (VAT) sensor to measure the incoming air temperature.

A Mass Air Flow (MAF) sensor may be used to measure the amount of air going to the engine.

Other inputs that may be used:

Vehicle Speed Sensor (VSS)
Power Steering Pressure switch (PSP)
Brake On Off (BOO)
A/C demand (ACD)



The EGR solenoids (vent and control) regulate the vacuum supply to the EGR valve to get the desired flow rate. The Electronic Vacuum Regulator (EVR) performs the same function with one solenoid. The ECA turns the solenoid on and off rapidly (dithers it). If the on time is longer than the off time, more vacuum is output and the EGR valve opens farther. If the times are equal, the valve will hold it's position.


Secondary air injection bypass (AIRB) and diverter (AIRD) solenoids direct the secondary air injection system downstream to the catalytic converters, upstream to the exhaust manifold or bypass it to the atmosphere depending on engine mode. They simply put vacuum to the appropriate vacuum operated valves when they get a signal from the PCM.


Carburetor feedback solenoids mix extra air into the fuel mixture to control the air to fuel ratio.
The solenoid is dithered on and off by the PCM to get the correct ratio.


Fuel injectors are solenoids that "fire" along with the ignition system. When current flows through the coil inside, a needle is pulled off of it's seat allowing fuel to flow out. To change the air/fuel ratio the PCM varies the amount of time the injector is energized. vThis is measured in milliseconds (1/1000 second - abbreviated ms). The longer it stays open when it fires the richer the mixture.

Some engines use a single injector in a throttle body (Throttle Body Injection or TBI), some use 2 in a throttle body (also TBI) while others use individual injectors for each cylinder (Multiport Fuel Injection or MFI).

MFI vehicles fire either in banks of 2 (e.g. a 6 cylinder firing 1,3,5 at the same time and 2,4,6 at the same time) or use Sequential Fuel Injection (SFI) where each injector fires in the firing order.

A fuel pressure regulator insures constant fuel pressure.

The Canister Purge solenoid (CANP) is controlled by the PCM to vent fumes from the charcoal canister only when the engine is running.


EEC IV can adjust idle speed in one of three ways.
1. A throttle kicker solenoid (TKS) which sends vacuum to a vacuum motor to boost the idle a set amount.
2. An idle speed control motor (ISC) which physically moves the throttle lever.
3. An air bypass valve which allows air to flow around the throttle plate(s).

The last two systems (which are the most used) allow the PCM to fully control the engine idle speed.


Some late models EEC IV systems control the transmission also.

Solenoids in the transmission allow the PCM to control shift points, shift feel and the lock up torque converter.


All EEC IV systems control the ignition timing. Later systems also do away with the distributor and distribute the spark electronically.
This gives the PCM total control and also does away with misadjusted timing problems.

See the TOOLS AND TECHNICALITIES chapter for a description of the EEC IV ignition systems.


Don't say this is an odd place for these charts. It was hard enough finding a place for them.

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These are the Ford and Mercury full size vehicles.

These models are mid-size vehicles with rear wheel drive. You may see the LTD referred to as a "Ford" in this book.

Front wheel drive models produced since 1986.

Front wheel drive models similar to a small Taurus/Sable. Produced since 1984.

Small front wheel drive, American style. Produced since 1981, the EEC equipped versions started in 1984 with the Escort GT, 1.6L MFI.

Small front wheel drive, Japanese style. Produced since 1991. The only ones with EEC IV are equipped with a 1.9L MA engine. The 1.8L uses a Mazda engine control system.

Mid size rear wheel drive vehicles.

Front wheel drive, Japanese version. The only version covered here is the 1990-1992 3.0L MFI.

Mid-size rear wheel drive vehicles.


Full size pickup.

Full size all purpose vehicle similar to the Ford F-series pickup.

Van style truck also available as a window van or a stripped chassis for add-on bodies.

Small pickup. Some versions equipped with the 2.0L engine with MCU engine control system but most are EEC IV equipped.

Small all purpose vehicle.

1990 replacement for the Bronco II.

Small wagon style truck available since 1986


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The year is the 10th position of the VIN (serial number).
F = 1985
G = 1986
H = 1987
J = 1988
K = 1989
L = 1990
M = 1991
N = 1992
P = 1993
R = 1994	
S = 1995


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The engine code is the 8th digit of the VIN (serial number).



3       1987-88     3.8L TBI
4       1988-93     3.8 MFI/SFI
5       1988-90     1.6L MFI
6       1991-92     1.6L TC
9       1987-93     1.9L TBI
A       1986        2.3L OHC 1V
        1987-90     2.3L OHC MFI
C       1990        3.8L MFI SC 
        (Note: see code "R")
D       1986-90     2.5L HSC TBI
E       1987-93     5.0L MFI/SFI HO
F       1986-91     5.0L MFI/SFI
G       1986-91     5.8L HO VV CARB
J       1986-92     1.9L MFI
M       1991-92     2.3L MFI
N       1991-92     2.5L MFI/SFI
R       1986-87     2.3L HSC 1V CARB
        1990-92     3.8L MFI SC
        (earlier models code "C"
T       1986-90     2.3L TC
        1991-92     5.0L HO
U       1987-93     3.0L MFI
V       1987-90     2.9L MFI
W       1986        2.3L MFI TC
        1991-93     4.6L SFI
X       1986-87     2.3L HSC TBI
        1988-93     2.3L HSC MFI
Y       1990-93     3.0L SHO
Z       1991-92     1.6L MFI



1       1986-87     6.9L Diesel
A       1986        2.3L OHC 1V
        1987-93     2.3L OHC MFI
B       1986        2.3L TC
C       1986-87     2.0L 1V
F       1986        5.0L 2V
G       1986        5.8L 2V
        1987-93     7.5L MFI
H       1988-93     5.8L MFI
M       1988-93     7.3L Diesel
N       1987-93     5.0L MFI
S       1986        2.8L 2V
T       1987-92     2.9L MFI
U       1987-93     3.0L MFI
X       1990-93     4.0L MFI
Y       1986        4.9L 1V
        1987-93     4.9L MFI

Copyright 1987-2005 Dali Design. No part of this document may be reproduced without written permission from the author.

Dali Design, Berlin, MD

Remove the brackets to email: jthorsse[@]gmail[.]com