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Introduction
This section will cover all the electrical issues. It starts with
the standard ZETEC engine as it came in the Escorts, Fiestas, Mondeos
etc and will cover fault finding and fixing problems.
It then moves on to cover wiring diagrams for the EDIS and standard ECU.
Finally, the section has usefull information you will need to for the ZETEC to Mk 1/2 Escort transplant.
Getting started
Before you even think of starting any electrical work on you car I strongly reccomend you purchase the following:
Digital Multimeter - Amps, V, Ohms, Dwell
Bosch 2 pin Noid light
LED test light
Various crocidile clips
Spark Plug tester (or make your own)
Standard ZETEC Fault Finding.
The engine managment and sensors on the ZETEC are generally
reliable and the ECU is capable of running the engine even with faults
on things like the MAF, or even an injector fault. What follows
is a series of guides on how to check the functionality of the
different sensors on the ZETEC.
Mass Air Flow (MAF) Sensor
The ZETEC should run even with the MAF unplugged as it will use the
Throttle Postion Sensor for load information. The MAF on a ZETEC
is of the hot wire variety. There are 2 wires in the MAF, one is
outside the airflow the other is in it. The ECU feeds power into
both wires and tries to keep both wires at the same temperature.
The wire in the airflow will be cooled by the airflowing into the
engine, the more airflow, the more it is cooled. Therfore, the
ECU has to adjust the voltage going to the wire constantly, this
varying voltage is used as the load value for the ECU ignition and
fuelling maps.
The wires can get dirty, especially if an aftermarket filter/induction
kit has been fitted. This will alter the thermal properties of
the wire and therefore the ECU will get false readings. So the
first logical step is to check for dirt on the wire and clean with carb
cleaner as required. The next stage is to voltage check the wire
with you multimeter. First turn the igntion on and let the
wires warm up before taking a reading, it should be around 5v.
Next start the engine and rev the engine at idle an watch for the
voltage to change at the MAF. The voltage changes should be
linear, and readings out of the ordinary will reveal a fault in the MAF.
Throttle Position Sensor (TPS)
The the TPS is basically are varieable resistor and is simple to
check with a multimeter. The TPS has 3 wires going into it, one
is a 5v volt feed (once ignition is on), 1 earth wire and the return
wire to the ECU. By doing a resistance check between the live
(igntion off) wire and signal wire and moving the throttle you will be
able to see if the TPS is giving any false readings, as with the MAF is
should give nice linear readings.
Charging Circuits
With the engine switched on check the voltage across the battery, it
should read in the region of 13.5 to 14.5v. If this is more like
11-12.5v turn off and check the following:
Visually check the fan belt is tight.
Check all wiring plugs are connected.
Check the battery as a worn out battery may not charge at all from
the alternator and will need trickle charging with a decent battery
charger, or replacing.
Check you have an ignition light on the dash board (normally red, and will go out once engine is running)
Positive feeds to alternator, they should read approx 2.2 volts less than the battery voltage (or very close)
Check the ignition switch feed should read the same as the battery (or very close too)
If any live feed is missing the likely problem is an open circuit
to that wire. If it is the ignition feed a likely cause is the dash
warning light bulb has gone.
Next check for voltage drop with the engine running between the
alternator body and the battery negative, any voltage suggests an earth
problem.
If dash light is not lit earth the alternator using an ammeter or wire and see if it now comes on, if so suspect a bad earth.
Next, with the engine running check for voltage drop on the main
live input and the battery positive. If there is voltage over 05.v
suspect a brush problem.
Remove brushes/regulator pack and look for signs of uneven brush wear.
If even wear change module and test voltage on battery.
If brushes unevenly worn the alternator is worn out and needs replacing.
If the bushes look ok it is worth trying a new module, if it is still not charging, suspect a worn out alternator.
Simple Battery Test
Disable the car so it will not start, ie remove CPS plug, king HT lead or something.
Connect your multimeter up across the 2 battery terminal. It needs to
read over 12.2v (50% charged) and less than 12.9v (fully charged)
before you start. If it shows more than 12.9v (surface charge) turn
your lights for a minute or 2 to get it below 12.9v.
Get a mate to sit in the car and turn the engine over for 15 sec
(time it, don’t guess) while you watch the multimeter. If the battery
is good as the engine cranks the voltage should not drop below 9v. What
you should see after a few seconds is the voltage stabilize around 9.5v
(approx). Once the voltage has stabilised, as long as the voltage does
not then drop by more than 0.3v until you stop cranking your battery is
good.
Only do this test once, if you are not sure about your reading, re-charge
Idle Speed Control Valve (ISCV)
The ISCV don't normally fail, they just clog up. Before buying a new
one try cleaning your old one with carb cleaner, let it soak over night
if need be. Loads of people change them for no real reason.
To check you ISCV is working bridge the signal wire (ISCV is
normally earthed through the ECU) wire to a good earth (only for a
second or two) with the engine running, you should hear the engine note
change. Remove the earth it should adjust back, if you get no change
remove and clean the ISCV (or in extremes you have no live feed to it,
should be 5v)!!
Vehicle Speed Sensor VSS
This is normall attached the the gearbox or a drive shaft. It uses a
Hall Effect chip, so treat like a Hall Effect distributer (see above).
Fuel Pump
The first check is are you getting power to the relay, pin 30. If
not check fuel cut of switches, immobilsers etc. If you have power
going to the relay carry out a quick resistance check between pin 87
and a good earth. You are looking for less than 10 ohms. Any more than
10 ohms next resistance check the actual pump. If that is less than 10
ohms resistance check the earth wire from the pump to a good earth adn
so on until you find what is causing the resistance (Volt Drop works
here to).
If your resistance check and volt drops all come back ok check the
actual relay. Can you hear it clicking as you turn the ignition on
(MFI) or as you crank (EFI)? For MFI cars check pin 1/TD with an LED
flash test light, it should flash as you crank the engine. If it does
not suspect a broken circuit between the pin 1/TD and the coil -ve. If
you still have not solved the problem try a different relay, even on
MFI cars you can use a normal 4 pin relay as long as the pin numbers
match up.
If your pump runs, but you suspect it may causing problems
reistance check as above. You are looking for less than 10ohms
resistance, and no voltage on the earth if volt dropping. If that is
all ok carry out an amps test. The average fuel pump will draw around 4
amps. If it is more like 2 amps fuel is not getting into the pump so
check the internal filter. Around 6 amps and you probably have a
clogged (or nearly knackered) pumped so flush your tank with fuel
system cleaner.
Crank Position Sensor (CPS)
A quick and easy test to see if your CPS is working is to connect a
Noid light to one of the injector plugs. If it flashes as you crank the
engine your CPS works. For non-injected cars you can use a NOID light
on the coil pack beween pins 1&2, or 2&3. Agian if the Noid
light flashes your CPS works. The CPS often suffers from getting dirty.
The simple test for this is a resistance check. The reading should be
around 300 ohms, any more remove and clean. Another test you can do is
connect a volt meter set on AC volts to the CPS. Then turn the engine
over, you need to see more than 0.5v (more rpm, more volts) for the
ECU/EDIS/DIS to read the CPS.
Another problem related to the CPS is a situation were your engine
just cuts out at random and will not restart straight away. This is
ofen caused by interference on the CPS wires. Some cars had a 3rd wire
(people then claim the have a Hall Effect CPS!) for the CPS that goes
to earth for this reason. If you are getting problem, engine has cut
out and wont restart. Then disconnect the CPS for 20 seconds and then
reconnect. If you car now starts you have found the problem. To solve
this issue buy some copper braid and wrap it around the 2 CPS wires and
connect it to earth.
Coolant Temperature Sensor (CTS)
On ealry fuel injected (and some with ECU conrolled ignition) cars
a CTS fault can actually stop the engine running. If you ever suspect a
problem disconect the CTS and see if your engine now runs, or runs
better. The CTS is just a resistor the varies resistance with heat. To
test, remove sensor and check with a multimeter as you heat the end of
the sensor (boiling water, cigarette lighter etc).
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