Back Probing

This is a practice to be able to get a reading from a back of a plug specially in the situation where we need this plug connected but also want to get a reading while its connected to its counter part .... We do this process so that we don't damage terminals, connectors and also wires.
To do this we use a sewing pin to gently insert it to the back of the plug so there is a contact with metal so we can obtain a reading.

1. Turn the multimeter on and put the setting to it would read Ohms (resistance)
O/L : is the result when the leads not in contact with each other , O/L stands for over load which confirms that we have an open circuit and the resistance between the leads are too high for our multimeter to show hence O/L.

2. Obtaining Ohms reading with leads connected.
0.5 Ohms which tells us the internal reasistance of the Ohms meter and the leads... we need to take this resistance out of any resistance we measure with this meter so we could have an accurate reading .

3. I used a plug which had one side of the pulg and the wire still attached so I back probed the plug and measured the resistance from the plug to the end of the wire which was 1.1 ohms
so 1.1 -0.5(internal resistance)= 0.6 ohms which is the correct resistance readings

I tired to back prob my distibutor so I could get a reading but the plastic around the wire was solid due to years of extereme heat .
I back probed Toyota soarer O2 sensor so I can get a reading after it was warmed up and working , real easy because it was single wire so 1 lead to the O2 sensor and the other to the -negative battery terminal (0.7 votls)

WS8

Firing voltage : the voltage (push) that is needed for the spark to jump the spark plug gap.

Burn voltage : the voltage need ed to maintain an arc between the spark plug electrodes so it can burn all of the fuel in the combustion chamber.

Burn time : the length of time which the arc is maintained between the spark plug electrodes

this is normally used to check the secondary circuit components eg. spark plugs , HT leads , secondary ignition coil, distributor cap , rotor and king lead .

Dwell time : the length of time which the primary circuit is grounded (turned on) before each cylinder firing so it can build strong enough magnetic field so then secondary winding can create a strong enough spark to jump the spark plug gap .

Primary Ignition Pattern : It is a very good way to check our primary ciruit and also to see firing voltage and burn time ... the higher the firing voltage the shorter the burn time this uses string theory so as the firing voltage decrease our burn time inceases .

Secondary Ignition Pattern : This pettern is a reflection of the primary ignition and has the same charactristic , its produced by the primary circuit collapsing on its self and inducing a voltage very similar to the primary pattern but the firing voltage is lower . After a snap acceleration we can see the firing voltage decreases and burn time increases which proves the string theory.

Toyota corolla FXGT 4AGE

All of these readings are normal ( checked against manufactorer spec)

We can see here as I am flicking thru all 4 cylinders that they are very similar and if there is an odd one then we know there is a problem with that spark plug , lead ... a very good way for diagnosis.

We can see in the above video dwell time increases as the engine RPM increases , this is so that it still can provide a strong enough spark due to the coil being earth out earlier before the cylinder reaching TDC in the compression stroke.

In the table below we can observe the string theory in action ... as the cylinder 4 has been grounded to the body the firing voltage decreases because it does not need as much voltage as in a sprark plug but this causes the burn time to increase

Again we can see in the table below that because the gap in the tester is smaller than the spark plug gap then firing voltage has decreased , the burn time has increased

WS7

CO:

Carbon monoxide is a indicator of rich air/fuel mixture and shows there is not enough oxygen in the combustion chamber. The lower the better because it is a very dangrous gas and lethal for humans because of it properties and also indicating not a efficent combustion due to too much fuel and not enough oxygen.

HC:

Hydro carbon levels show the amount of unburnt or partly burnt particals in the exhaust. misfire due excessive lean and also rich air/fuel ratio ,misfire can also be due to ignition problems.The lower the levels of HC the more efficent the fuel is being burnt in the combustion chamber . It is also a green house gas and related to global warming.

CO2:

Carbon dioxide is a good by product and indicates good combustion inside the engine and is produced when the fuel is oxidised , a good rule is the higher the CO2 level the more efficient the engine works .Even tho this is a a good gas for an engine it is also concidered a green house gas and related to so called ''Global warming''. Air/ fuel imbalances , misfires and mechanical problems in the engine will decrease the amount of CO2 produced because ideal combustion will produce high levels of CO2 and water vapor. A good way to measure combustion effiecency.

O2:

high levels of oxygen is a good indication of lean air/fuel mixture because O2 increases as the air/fuel mixture gets leaner , it also can indicate misfire but we have to look at HC to come up with this conclusion .

CO: 5.8 HC: 521 CO2: 11.53 O2: 0.28 Cold engine idling

CO is high which shows rich air/fuel mixture because the engine is cold , High HC again indicates not an efficient combustion and high levels of fuel not getting burnt completely. in comparison with the level of CO2 when the engine is warmed up this indicated not a very efficient combustion . O2 levels are low as the air/fuel mixture is rich .

CO: 7.1 HC: 506 CO2: 10.6 O2: 0.20 Warm engine idling

CO level still high wich indicates rich air/fuel mixture, HC is also high which tells us there is high number of fuel particals not being burnt due to rich air/fuel mixture and not enough oxygen being present to help burn all the fuel off. CO2 is also low which cofirms rich mixture and finally low O2 which can also tell us rich air/fuel ratio.

CO: 0.4 HC: 123 CO2: 14.6 O2: 0.47 Warm engine 2500 RPM

Low CO shows a good air/fuel ratio , low HC which indicates more efficiency , High CO2 tells us a good and efficient combustion and a little higher O2 readings which tells us the air/fuel mixture is not as rich as the 2 readings before .

CO: 1.6 HC: 250 CO2: 13.21 O2: 2.38 Idle, Rich mixture

High CO levels and high HC reflect on the rich mixture , CO2 levels a little less than the above reading which shows not as much efficiency in the combustion and high O2 shows not all the Oxygen is getting burnt .

CO: 0.07 HC: 230 CO2: 11.88 O2: 4.9 Idle, Lean mixture

Low HC and high O2 levels indicates Lean air/fuel mixture , even lower CO2 levels shows us the effiency is decreasing .Low and good CO readings.

CO: 3.349 HC: 1188 CO2: 9.09 O2: 9.34 Blipping throttle

High CO due to very rich air/fuel mixture , High HC shows us not all the fuel is being properly burnt , low Co2 which shows the effiency of the engine is deceasing and high O2 shows us a very very rich mixture and probably the most inefficient part of a normal operation .

CO: 0.157 HC: 2672 CO2: 7.28 O2: 11.03 Disconnect one spark plug

High HC , O2 shows us the fuel and air not being burnt in one cylinder , CO2 decrease shows the combustion effiency is falling ,CO levels are a little bit high but thats because a cylinder with no spark doesnt effect the CO levels.

CO: 0.068 HC: 188 CO2: 6.94 O2: 11.72 Disconnect one Injector harness

Good and low CO reading , low HC and high O2 shows us there is too much oxygen not being burnt and even lower CO2 levels indicates a very poor combustion .

CO: 0.550 HC: 195 CO2: 14.02 O2: 1.58 under load

A little bit high CO levels due to the rich air/fuel mixture , a bit higher than average HC which is because of the rich mixture , highest CO2 level which indicates the most efficient combustion period for this engine , higher than normal O2 reading can indicate that this not too much of rich mixture and still has enough Oxygen to burn all the fuel properly.

WS6

Toyota Soarer 1994 single wire ziconia switching sensor:

I back probed the plug coming from this sensor and which was located on the left hand side of the enigne on the exhaust manifold.

After engine has warmed up and in closed loop which we can tell this as it is in nomal cycling .

Maximum voltage is around 0.8 Volts

Minimum voltage is 0.2 volts

Cross counts were 7

Below we can see as we made the air /fuel mixture rich by a couple of sudden acceleration becuase usually this will make the system pump more fuel into the cylinder and makeing mixture rich.

The highest voltage I got was 0.85 Volts which was within manufaturer specs. each division is 0.5 Volts and time is 1 second.

Below we made the air/fuel mixture lean by reving the engine up to 3000 RPM and then a sudden deceleration will make the system to go into lean mixture. the lowest point was 0.05 volts and we can see the how it is going back to the normal cycle just at the end there .

Below we want to see how quickly the O2 sensor responds to changes and the easiest way is to do a sudden acceleration and see how quickly it changes ... we can see the voltage increasing from less than 0.2 Volts to higher than 0.8 Volts in less than 100ms which I think is a very good results

We can see that this sensor is in good working condition as all the results were within the specifications and had a response time and also clearly showed us and reflected the lean or rich conditions .

WS5

MAZDA FAMILIA 2000



Above are the information we could obtain from this vehicle .

Fault codes :
I checked on the scan tool but there were no fault codes recorded .

after lecturer intoduced the faults :
1st: turn on the car and check for fault codes 100 MAF , 110 IAT this will indicate the area .
2nd: turn on the vehicle and now compare the reading with the previous reading which we did earlier ... IAT was 25.46 deg/C and now 19.85 deg/C . MAF was 1.87 V and now 0 Volts
3rd: visual check the sensors and wires and noticed MAF and IAT sensor plug was not plugged in properly
4th: Repaired the fault by connecting the plugs properly and clear the fault codes using the function on the scan tool .
5th: Recheck the live data to make sure they are back to normal IAT 25.46 deg/C and MAF 1.87 Volts .
6th: recheck the system for any faults and none were recorded .

Live data is a very important, usefull also easiest ways to diagnosis a problem specially if there is no fault codes recorded . It is a good way to check the performance of the vehicle under different conditions where some faults could be hiding in ...

Parameters are as important as the live data because how would you know if this data you are getting is within the manufacturer specs (normal) ??? you'll have to compare the live data with the parameters to make sure that they are within the parameteres that is concidered normal for this vehicle .

Scan tool can aid us to check the live data against the parameters and point us in the direction we need to be looking ... it might not pin point where the problem is but its a good start for direction and even if the sensor is faulty after checking the circuit for bad connections , bad earth ... by comparing the live reading against the parameters

WS4

First locate a fire extinguisher close by incase of an accident

There are several different ways to relieve the pressure before installing a pressure gauge , I personaly prefere this method myself ... Remove fuel pump relay then start engine till it run out of fuel and stops then to double check crank the engine to make sure no fuel is left in the fuel lines ... This is a very tidy , quick and not messy and also not dangrous to get rid of pressure in fuel lines .

Hook up the fuel prssure gauge , turn on the car briefly and stop to check for any fuel leaks. we didnt have any fuel leaks so we move to the next stage ...

Fuel pressure with key on and engine off was 284 Kpa.

After turn on the engine for a couple of minutes and the pressure was 260 Kpa.

Also with the engine running clamp the fuel return line to record maximum pressure 490 Kpa.

To similuate wide open throttle we disconnected vacuum line going to fuel pressure regulator 310 Kpa.

To check residual or rest pressure we turned off the engine and watched fuel pressure for 5 minutes 250 Kpa.

To check the flow of fuel in the fuel lines and to make sure enough fuel is getting to our injectors 2.2 L per minute and also to check if it is within manufacturer's specification because too low will cause a lean combustion and too much would make it run rich .

Now follow the same step as the top to get rid of fuel line pressure so we can disconnect our gauges and put the vacuum lines and fuel lines back where they belong . double check for leaks and make sure the vehicle is safe and runs fine.

Symptoms :

Low fuel pressure :

This will cause the engine to run rough and cause it to misfire due to lean mixture and increase emissions of HC.

Low fuel flow :

This could be caused by a blockage in the line eg. fuel filter blocked , this will cause the vehicle to have a poor performance specially under high loads or quick throttle response is poor also as the injector runs out of fuel to inject in to the cylinder

High fuel pressure :

This would cause black smoke out of the vehicle exhaust which indicates rich mixture and high HC (unburnt fuel) to enter the atmosphiere ... engine would run rough at idle. it also can be caused by faulty fuel pressure regulator .

Faulty fuel pressure regulator :

This will also result in black unburnt fuel to come out of the exhaust and very rich air/ fuel mixture . Bad fuel economy , high HC emissions . it also can damage the cat convertor and O2 sensor if this problems carries on for a long period .