QuestionQUESTION: The car has 40,000 miles it starts and seems to run fine but while driving it will just die. You can almost immediatelt restart the car, then it happens all over again. Have had it in the shop and checked fuel pressure, replaced throttle body switch adjusted timing yet it still stalls. It does not ever run rough
ANSWER: Hi Jeff,
The fact that it quits narrows the problem down to only a million things. It is no use testing when it is running correctly so you need to see what is missing at the time of failure. It will get expensive to keep replacing parts in the hopes that you happen to hit what ever is failing.
So you need to do some testing. All engines need only three things to run, Compression, fire and fuel with conditions on each. It is unlikely compression because if you loose compression it is not going to come back. So that means it is fire or fuel. Fire (spark) is the easiest to test. So connect a timing light to any spark plug wire and tape the trigger down so the light flashes all the time and run the wires out form under the hood and put the light under a wiper arm and if you are going to run this test in daylight you may need to tape a piece of cardboard over the end of the light on to the windshield so you can see the flash as you drive. Then just drive the car until it quits again and watch the flash to see if the flash stops first or it keeps flashing as the engine slows down to a stop. This tells you if it is an ignition problem. If it is then you need to go to some place like Radio Shack and get a 12v LED and connect it to the negative side of the coil and again run the wires out and tape the LED to the windshield so you can see it flash when you drive. This tells you if it is the primary of the ignition system that fails. LEDs are cheep so you may want to do this at the same time you do the timing light test. Then you will be testing the primary and the secondary of the ignition system at the same time.
If neither fails when the car dies you need to get a fuel pressure gauge and run it out from under the hood so you can watch to see if you have fuel pressure at the time of failure. Checking pressure when it is running is useless information, you MUST see pressure at the time of failure. If all these are good at the time of failure the next set of tests are a little more difficult as you need to know if you have injection pulse at the time of failure.
Let me know and I will tell you how to do that after you complete these tests.
Howard
---------- FOLLOW-UP ----------
QUESTION: Howard, is there anyway it is the cars computer? that was one area or excuse the mechanic had. He has already run the test on the fuel, while the car was being driven/stalling and that was not the problem. I have had someone else say it might be the ignition amplifier or the coil or both. Using your analogy of either compression, spark or fuel it must be spark or ignition. Does the timing light test show you what in the ignition is wrong?
AnswerJeff, the timing light test tells you if it is in the ignition and the LED test tells you if it is in the primary section or the secondary section. The primary section is the amplifier, primary winding in either of the coils and the secondary is the secondary winding of the coil and the cap, rotor, coil wire, plug wires or plugs. Once you know the section a problem is in you can then test each component.
An ECU is a possible but only after you eliminate all the other stuff, unless you have deep pockets and like to spend money on lots of parts you don't need.
Lots of mechanics don't like doing all the tests too, they just keep putting parts on until it is fixed. They make a lot more money that way.
Howard
