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Basic Car electric part 31:

Part 2


EGR Valve: Electronic, 5 wires, 2 to operate solenoid, outer ones, one is 12 volt positive and the other is switched to earth by computer (duty cycle), inner ones from ecu, 5v ref wire, earth and signal to ecu to tell the computer where the valve position is, you can test the wires in the normal way. The earth (via ecu) for the solenoid, if you ground that out with the engine idling the engine should die as valve opens...can test for square wave on centre wire, signal to ecu, the egr valve is a sensor and acuator all in one. The Job of the EGR valve is to put exhaust gasses in the inlet manifold, to make the exhaust hotter, at the appropriate time to reduce nitrous oxide...

EGR Valve: (2) EGR Vacuum operated, Vacuum diaphram, actuation solenoid (EVR valve), DPFE sensor. this is mostly on Fords, has a diaphram on the engine, between exhaust and inlet, as with the other types if you push that diaphram to the open position the engine will die at idle, this type has a DPFE sensor on, usually 2 rubber pipes connected to an orifice in the the pipes that comes up from the exhaust, the idea is it checks the differencial pressure across the orifice and decides whether or not to open the egr valve, in most cases that sensor unit, usually on bulkhead can be troublesome...the vacuum unit on the engine is connected to a vacuum hose via an electronic solenoid valve close to it. you can energise that solenoid and stall the engine as it opens the diaphram. If the pipes keep pushing themselves of the DPFE sensor, suspect the Catalitic converter may be blocked...DPFE is Delta Pressure FEedback. to test the DPFE sensor, check the power and ground, the 3rd wire is signal wire, if you start the car and let it idle, check the voltage at the signal wire of the DPFE sensor, now energise the solenoid to open the valve and the voltage at the sensor should rise to around 4 volts, if it doesnt move change the sensor but check wiring first. The system is of course controlled by the engine ECU...the activation solenoid is ground side switched, the sensor can also be tested by putting a vacuum pump on the small pipe and checking the voltage at the signal wire, it should rise with rising vacuum applied, from about 0.5 to 5 volts, You can test the main diaphram with a vacuum pump. The DPFE sensor usually has a 5 volt supply, the solenoid (EVR valve) 12 volts. On some cars pulling the plug off the DPFE sensor should stall the car at idle, if it does replace the DPFE sensor.

Ignition Coils: Various, Wasted spark, normal, COP, (Coil on Plug). 2 wire type, or 3-4 wire type. On wasted spark check for a common live and normally 2 switching wires on 4 cylinder cars, has two coils and two cylinders fire at once, with coil on plug there are 2 wire ones, 3 wire ones and 4 wire ones, the 2 wire is live and switched at ecu, 3 wire ones are live, earth and switched at ecu, they have some electronics in them, the 4 wire ones are the same, but 4th wire goes to ecu for monitoring any faults or misfires etc...there are multi pack ones with several wires on, maybe 5 or 6...they all work on the same principal. 12 volts in and a switched by ecu wire out, also test earth connection. If you get no switching on coil negative leads, it could be the coil, wiring to ecu either open or grounded or the ECU driver not switching to ground. Or crank or cam sensor....or both.

Fuel Pump: Live from Relay and earth, 12 volts about 8 amps. runs ign on for 2 seconds, then uses ign signal running, there are several ways to test the fuel pump, you can locate the relay, prob have 2 big and 2 small terminals, the big ones are for the 8 amps going through the pump, if you bridge those 2 the pump should run, can you hear it?, will it start, you can put an amp meter in line and see the amps its using, if zero check all the lives and earths up to the tank, the 2 small terminals are normally, live from ecu and ground, or they can be live 12 volts and grounded by ecu, in either case you should get a 2 second pulse at one of the terminals, and when cranking should be live or grounded all the time, depending on system, ground or live side switched, the pump should only run when you turn the ignition on for 2 seconds then stop, also when cranking or running, no other time, for safety reasons, if there is no current when trying to run the pump you might want to check the inertia switch, normally in the boot or under dash...
There is now a new kind of fuel pump system, it works from a duty cycle supplied by the ECU, i believe the pump has 3 wires, 12 volt supply, signal wire and earth, there might be several other wires on the pump, but they are probably for the gauge sender unit, i suspect the thick wires are for pump current...the pressure in the system is monitored by a pressure switch connected to the ecu, either in the tank or on the fuel rail, when the pressure gets too high the pump slows right down, when the pressure gets low it speeds up, done by the duty cycle of the square wave signal from ecu, i suspect at 50% duty cycle it would run at half speed, at 90+% on full speed, at around 10% on low speed...

Fly by Wire Throttle: (electronic throttle) This a dc motor on the side of the throttle body fixed to the butterfly flap through a ton of reduction gears, it's connected to the ECU and is controlled by the throttle sensor on the pedal, the throttle position potentiometer also on the throttle shaft senses where the throttle plate is. The DC motor is reversable type.

ECU /ECM /PCM, Computer not possible to test easily, eliminate everything else. check powers and grounds and 5 volt reference voltage. Most sensors these days either give out a varying dc voltage or a duty cycle square wave, you need to know how to test for both.
Code tests are always a good idea. Beware of reading codes that might have been caused by someone else running the car and pulling a plug off to see if something is working, creating a code, they will most likely have set a false code, so write them down, clear them and see if they come back.....otherwise you will be chasing your tail and fitting wrong parts, before renewing any part it's a real good idea to test the unit and wiring as much as you can, saves un-necessary work and peoples money. If you get a car that won't communicate with the diagnostic tool and the MIL light doesnt work, suspect a dead computer, which might be as easy as fitting a fuse...check powers and grounds on ECU. Running you car with the fuel cap off can create a fault code.....

from fred in Essex.
 
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