Tech Tip - EF Falcon No Start

Hi again.
Well it has been a while since my last tip, so here's one to put in your memory bank that could save you a lot of headaches in the future!
When faced with a Falcon that has starting problems we often go for the BCM (or BEM) for the usual Smartlock issue, but on the EF model there could be something else causing this symptom... something definately outside the square!
If you are faced with an EF Falcon that fails to start and all other areas have been covered and you think there is nothing else to replace, try replacing the starter motor. Right now you are probably thinking that I am crazy because it cranks over fine so the starter must be ok! Well this is where thinking outside the square comes in.
The problem could be that the starter motor is inducing noise into the Crank Angle Sensor signal, thereby making it unrecognisable to the ECU. One tell-tale of this problem is a small kick when you release the key as if the engine wants to start. This is because as you take away the source of the noise (the starter) the ECU now can see the CAS signal and it fires the injectors and spark. Unfortunatley you no longer have the drive from the starter to get it going so all you end up with is a small kick, which is quite often not enough to start the engine.
Although it might not be the fault in your case, it's worth thinking about next time you are presented with this problem.

Until next time,

The Doctor.

Got any questions of your own?......

Commodore warning light problem

Today I would like to talk about a common fault on Commodores from VT to VY series.

The typical symptom is the dashboard warning lights all coming on and if you present your car to a workshop and they try to hook up their scanner they find that they can not communicate with anything on the car.

The fault is actually caused by the ABS control unit and we sell them by the bucketload! You can confirm the fault by disconnecting the multi pin plug on the ABS unit and if all the dash lights go out (with the exception of the ABS and TRAC OFF light, if fitted) and you now have communication with all modules (except ABS of course) then you have found the problem. It is caused by an internal fault where the serial data line is corrupted, hence the symptoms.

Just a short one this time, but hopefully it could save you a lot of time down the track.

The Doctor.

Got a question? Need an answer?...

Tech tip - Oxygen Sensors

Here is another tech tip/info article on the often misunderstood Oxygen Sensor.

Well as you may have figured, an Oxygen sensor senses oxygen right? Well, yes but more accurately put, it senses the lack of oxygen!

It is placed in the vehicle's exhaust stream and it detects and measures how much oxygen is in the exhaust gas. A quick lesson in what is actually in exhaust gas - you probably hear a lot about Carbon Dioxide (CO2) emissions but there is more to exhaust gas than this alone. You also have hydrocarbons (HC), Carbon Monoxide (CO) and Oxygen (O2) as the "big 4", as well as Oxides of Nitrogen (NOx) and other less significant gasses. However, right now we are only concerned with oxygen. Now you might be wondering why it is important for the ECU to know how much oxygen is in the exhaust? Well I'm glad you asked! This is actually a great way of measuring the fuel mixture (how rich or lean) quickly and easily. This is primarily done so that the manufacturers can meet emission standards, but the bonus for you is that is is great for your fuel economy!

Basically, when the conditions are right, the ECU has a look at the O2 sensor and if it is reading "lean" (lots of oxygen content) it slowly richens the mixture until it gets a "rich" (little or no oxygen content) reading and then it slowly leans the mixture off until it gets a "lean" reading and the process then repeats itself over and over again. The ECU is now in "closed loop" mode. When I said slowly before, I meant slow in computer terms, as this "rich/lean" cycle can repeat itself up to 3 or 4 times a second depending on the vehicle and conditions, but is usually maybe 1 or 2 times per second. This ensures that the car runs as close as possible to the ideal mixture, which is 14.7:1 air/fuel ratio (AFR). This is also called Lambda 1.

Now to briefly tell you how this sensor works! It has a zirconia coated ceramic element inside that generates a small voltage when there is a difference in oxygen content across it. Basically, when the amount of oxygen inside the exhaust is different to the amount outside, you get a voltage. This voltage is only one volt, but as long as it changes from zero to one volt the ECU can see it.

Of course there is a lot more to it than this, but this gives you an idea :)

There are also other types of sensors, such as Titania (instead of Zirconia) as well as wide-band sensors. I also have not mentioned the difference between single wire or 2, 3 or 4 wire sensors, perhaps that is for a later article.

Happy motoring!

The Doctor.

Tech Tip - Fuel Supply

Here's another quick tech tip/info article, this time on how important it is to understand your Fuel Supply in your EFI vehicle.

The fuel in an injected vehicle is delivered under high pressure, for a few important reasons. Firstly it prevents vapourisation of the fuel, especially on hot days. Secondly it allows much better control of the delivery into your engine. When it is injected under pressure it allows the fuel to atomise which makes for a more efficient burn in the combustion chamber. The less atomisation, the more unburnt fuel and hence, bad emissions.

Okay lets get to the nitty gritty. First we need to identify the main components in the fuel system, starting from the source, the fuel tank.

First in line is the fuel pump - probably the most important component in the system. It's job is obviously to supply fuel, duh! EFI pumps are great at pumping but pretty bad at sucking, in fact you could even go so far as saying they suck at sucking! For this reason they are usually placed inside the tank at or very near the bottom. There are some that are external, and you will usually find that they have a pre-pump inside the tank to feed it. At this point it is important to mention that the pump supplies volume, and this importance will be outlined later.

Next in line is the filter. This is obviously important to filter out contaminants that might wreak havoc on other components in the system. You can NOT check an EFI filter by blowing through it! Try it on a brand new one and you will know what I mean :P

After the filter, the fuel goes to the fuel rail where the injectors are mounted. The injectors are switched on and off rapidly by the ECU (Engine Control Unit) so that the precisely correct amount of fuel is supplied to the engine.

After the rail is the pressure regulator. This is responsible for maintaining correct fuel pressure and bypassing unused fuel back to the tank. Understanding this is paramount to correct diagnosis of fuel systems and you will be surprised how many "service professionals" fail to understand what I am about to tell you!

Now, the best way to test a fuel pump is to check the fuel pressure, right? Wrong! When you check the fuel pressure, all you are doing is making sure the pressure regulator is working. Granted, if you have a dud pump you may measure little or no pressure but guess what, your pump will show signs of failure long before it drops fuel pressure! What you really need to measure is return flow. This is basically how much fuel "reserve" you have in the system. Your fuel pump needs to supply volume under pressure, so free flow or pressure alone will not tell you how good a pump is. For example, lets say that the fuel reserve on your car with a good pump is 2 litres per minute, and your engine under maximum power requires 1.5 litres per minute of fuel. In this case, on the rare occasion (for most people) that you have your foot flat to the floor you still have half a litre of fuel being returned back to the tank. Hop in the doc's DeLorean (I hope that Flux Capacitor is working...) and go forward a few years when your pump has done a lot of work and is close to worn out and it has dropped it's ability to supply a good flow of fuel. It is now only returning ONE litre of fuel back to the tank, and this is okay for normal driving but you are noticing a lack of power up hills and for acceleration. This is because once your engine requires more than one litre per minute of fuel, your poor pump can't supply it anymore and your engine starves of fuel. But wait, your pressure is still okay when you check it with the car idling! If you were to check it under full load you will find that it drops as soon as the enigne's fuel requirement overtakes the ability of your pump to supply it.

This is why checking fuel supply is way more important than checking pressure, and here's the great part - you can buy the tools to do this for just a few dollars! A good quality EFI pressure guage kit could cost many hundreds of dollars, and is still an important tool for the service professional but way out of reach of most home mechanics and DIYers. All you need is some basic tools to remove the return line and a jug or bottle to measure the amount of fuel. Run the pump for 30 seconds, measure the amount of fuel captured, double it and there is your flow rate in litres per minute.

Well so much for the "quick" tech tip, but I sincerely hope that you have learnt something.

Come back for more :)

The Doctor.

Any questions?....