Petrol Fuel Injector Testing - Toyota 4AFE
Check voltage to injectors with key on .
Battery voltage 13.77v
injector voltage :
Cly #1 = 12.85v
Cyl #2 = 13.00v
Cyl #3 = 13.24v
Cyl #4 = 13.44v
With the engine idling, watch the injector firing by using a LED test light.
http://www.youtube.com/watch?v=0IBjL8W7Pfc
With engine idling, watch injectors firing by using a multi-meter set to read %(duty cycle)
Cyl #1 = 96.5%
Cyl #2 = 96.5%
Cyl #3 = 96.5%
Cyl #4 = 96.5%
These reading represents the time the injector was closed.
With the multi-meter still set to read %(duty cycle) accelerate the engine with short, fast throttle openings and note the readings.
Cyl #1 = 84.4% at 3500 rpm
Cyl #2 = 86.2% at 3500 rpm
Cyl #3 = 84.2% at 3500 rpm
Cyl #4 = 86.2% at 3500 rpm
Set the multi-meter to Hz, and with the engine idling, record the readings for each cylinder.
Cyl #1 = 9.2Hz
Cyl #2 = 9.1Hz
Cyl #3 = 9.2Hz
Cyl #4 = 9.1Hz
So the injectors were opening 9.2 or 9.1 times per second wile idling.
With the multi-meter still set to read Hz, increase the engine rpm and watch how the Hz changes and record your results.
Cyl #1 = 21.6Hz
Cyl #2 = 20.4Hz
Cyl #3 = 21.6Hz
Cyl #4 = 20.4Hz
These readings were taken at 3500 rpm.
Using the formula "pulse width ms=(%duty cycle/100)/frequency" calculate the pulse width of each injector both at idle and when the engine is reved up.
Cyl #1 At Idle : Cyl # 1 at 3500 rpm
(96.5/100 )= 0.96/9.2 (84.4/100) = 0.84/21.6
pulse width ms = 0.104 pulse width ms = 0.038
Cyl #2 at idle : Cyl #2 at 3500 rpm
(96.5/100) = 0.96/9.1 (86.2/100) = 0.86/20.4
pulse width ms = 0.105 pulse width ms = 0.042
Cyl #3 at idle : Cyl #3 at 3500 rpm
(96.5/100) = 0.95/9.2 (84.2/100) = 0.842/21.6
pulse width ms = 0.104 pulse width ms = 0.038
Cyl #4 at idle ; Cyl #4 at 3500 rpm
(96.5/100) = 0.965/9.1 (86.2/100) = 0.862/20.4
pulse width ms = 0.106 pulse width ms = 0.042
I don't think testing injectors this way is very efficient, using a multi-meter to measure duty cycle then Hz then doing calculations seems quite long winded and clumsy. Specially when you can use an oscilloscope to get an accurate picture all this information almost instantly.
WS2 : Flash Codes
For this test I used a toyota corsa with a 4AFE engine. First we bridged the TE1 and E1 terminals to get test mode. Then some faults were created.
The first flash/blink code I got was 4 flash then 1 flash this = code 41 = Throttle position circuit
The 2nd flash/blink code was 2 flash then 1 flash this = code 21 = Oxygen sensor circuit
The 3rd flash/blink code was 3 flash then 1 flash this = code 31 = Vacuum sensor circuit
Next I did a visual inspection under the bonnet and found the plug connectors for the three sensors were disconnected so I plugged them back in. Then I cleared the codes by disconnecting the negative of the battery for a couple of minutes. Then I rechecked for codes and got one flash which means system normal.
How could the faults found affect engine performance?
Faulty oxygen sensor would make engine run rich, this would use more fuel and have higher harmful emissions.
A faulty TPS would cause flat spots when accelerating.
A faulty MAP would cause rough idling or engine might stall.
Discuss what other tests you should do once you have found the fault codes :
You could back probe the connector plugs and check supply voltages and signal voltages. Check the earth connections make sure the are good and clean. Do a scan tool test and get active readings and check these with manufactures specifications.
