So many times there are questions as to why my car does not run or runs poorly with multiple miss-fires or kinda quits on hills with questions that relate to what needs to be changed to fix this.
The problem with that kind of question is what worked for some one else and blindly recommended as a solution may have nothing to do with the problem at hand. Following those things and the train of thought, there are any number of parts that can be changed that may or may not have to do with solving things and the costs can be astronomical when tallied up.
I have found on today's Computer controlled car with fuel injection that a very valuable tool is the fuel pressure gauge. It can tell you so many things if you know what to look for. So I suggest the following series of things to consider.
Testing with a fuel pressure gauge requires having one.
I have one similar to this one;
http://www.summitracing.com/parts/anm-cp7838/overview/
at about $50.00 or so and today I needed to use it to determine what was wrong with my car.
Now you need to know what to look for and where to look it up. A Chiltons, Mitchels or Haynes or similar service document purchased from O'Rielly's, AutoZone, Pep Boys or where ever is about $30.00 or so and it gives not only the information as to what the specs are but where to hook things up. You are now up to over $80.00 in tools and books. All which may be used over and over again. Where as if you arbitrarily with out having a clue that it is bad, change the fuel pump and it is about $200.00 or so and if you determine you do not have to replace it you are ahead of the game already.
There is a fuel rail on a port injected engine that runs down one side of the engine from the engines front and back. There will be a pressure regulator on it with a vacuum line running to it and a capped off connection the fuel pressure gauge will screw on to some where on that rail.
What does this do?
The fuel pressure at the rail generally is about 40# of pressure as it is regulated to that level by the regulator or some other value. The book will tell that.
When the engine is idling vacuum is high and the pressure will be at it's nominal value. When the engine accelerates the fuel usage is higher, the vacuum falls and the regulator will try to increase the pressure to compensate for the increased fuel usage. As the pump probably pumps out some 90# pressure the regulator will compensate by trying to increase pressure towards that value as fuel is used. How does it do that? The decrease in vacuum will cause the regulator to try to raise the fuel line pressure as read.
Thus if the pressure falls off and it might, there is a range it can run in, but if falls too far that is an indication the engine is using more fuel than can be supplied and if it starts to misfire under those conditions than that is beginning to point at the fuel pump or a plugged filter limiting the amount of fuel available and the gauge will read a very low number. What is low? Your book should tell you.
However if the engine decelerates, vacuum now is high, fuel usage is less and the line pressure will try to increase except the higher vacuum will cause the regulator to decrease the pressure.
Thus pressure read will be some where around the nominal value and I am using the number 40 as nominal because that was nominal to me today. Acceleration caused a drop in pressure to about 35 and deceleration caused an increase in pressure as measured to about 45 or a little under which seemed to be normal for operation as defined. And the engine did not miss-fire.
Also when I first installed the gauge, pressure was zero. Which makes sense, the engine was not running and the ignition was off. Turning the ignition to run mode with out starting the engine, the fuel pump turned on and regulated at 40# pressure.
The pump in my car is rated at 90#. Thus in that mode, the pressure regulator was working. Starting the engine, the pressure stayed at 40# indicating the regulator was working and the pump was adequate.
Disconnecting the vacuum line from the regulator (vacuum controls the fuel pressure) the pressure as measured increased from a nominal 40# to about 65# which indicated the regulator indeed was also working. Plugging the vacuum back in cause the nominal reading to go back to 40. Idle, acceleration and deceleration worked as indicated and engine seemingly ran o.k. however. And there was a however. The fuel pump was extremely noisey in operation and engine performance as observed seemed correct but not crisp as I expected it to be.
I had a spare new fuel pump so Installed it. This let me check the fuel filter. A very simple test for that works. If you can blow through it with about the same effort it takes to blow through a straw it is not plugged.
When the new pump was installed and operating it was;
1. quiet
2. The deviation from 40# was smaller which made me feel better. Smaller deviation means it is pumping more fuel faster
and most importantly
3. Engine performance seemed a bit crisper.
The point?
Measuring fuel pressure gave me a positive indication as to what is going on.
The measurements verified certain functions were indeed working and when I decided to change the fuel pump anyway as the nose it was making was not a good indicator of proper operation I could make measurements that said things were working better when done.
Diagnosing and measuring things is a far better way of repairing your car if it is in truth,your car you are working on and your money you are spending. You really do not want me to tell you how to spend your money and unless you are very good at telling me what is wrong with your car.
And keep in mind this thing. The engine in your car needs to have Air, that is the air cleaner, filter and throttle body, Fuel supplied by the gas tank fuel pump and fuel injectors and fire supplied by the ignition, coils, battery,wires and spark plugs.
If you can test something with a fuel pressure gauge and the reading say things are working? They ain't broke, so save your money, if they ain't broke don't fix them.
I hope this helps some one.
Merry Christmas.