There are all kinds of problems with the diagnostics that have been done so far. The catalytic converters wont cause abrupt stalling or a failure to start. My best guess is the nail trick was to press the valve in the fuel pressure test port to see if there was pressure in the system. That is a worthless test because as little as five pounds of pressure will make the gas spray up to the hood, but the engine needs way more than that to run. Doing the test that way is similar to testing for air in a tire. It can be almost flat but will still hiss when you push the valve. You wont know the pressure in the tire unless you measure it with a gauge. A proper fuel pressure test is to attach a fuel pressure gauge and read the exact pressure while cranking the engine.
"that is it but later that day it stopped working"
What is "it"? I do not know if you are referring to the catalytic converter, the engine stalled, or something else.
"it was so changed the spark plugs still nothing"
"still nothing" does not say anything. Do you mean it did not start? It ran and did not stall? You need to be specific so I know exactly what you mean.
You can have a fouled or worn spark plug, or a bad spark plug wire, but that will cause a misfire that you can hear and feel. You know all six of them are not going to fail at the same time to cause a failure to start.
The biggest concern is blaming the timing chain. They can stretch and jump a few teeth resulting in a failure to start and run, or the engine will run very poorly, but that will not magically correct itself so the engine runs well at other times. The problem will be permanent.
If this is a permanent failure to start, it will be obvious when it is solved. By far the most frustrating problems are the intermittent ones because we can never know for sure when we have them fixed. We only know when we have not solved them when the problem acts up again.
If this is still an intermittent problem and the engine does run at times, a lot of people have a hard time understanding that no diagnostic tests can be done at that time because everything is working properly. All testing has to be done while the no-start condition is acting up. The first things to look at are whether there is spark and there is the correct fuel pressure. Both of those tests take less than a minute. Also, too many people get hung up on the first thing they find missing, but it is much more common to find spark and fuel pressure missing at the same time, so you have to look at what both systems have in common. Even that can be misleading because the fuel pump will run for one second when you turn on the ignition switch, but with this common problem, it will not resume running during cranking. That one-second burst can develop enough fuel pressure to make it appear that system is working.
You did not list the engine size so I do not know which electrical system you have, but the most common ones use a crankshaft position sensor and a camshaft position sensor. The Engine Computer needs both of their signals to know when to fire the spark plugs and the fuel injectors. It also knows the engine is rotating, (cranking or running), by the presence of those signals, and that is when it turns on the fuel pump again, (after that one-second burst). It is very common for either of those sensors to fail by becoming heat-sensitive, then they will work again after they cool down for an hour. They cause an intermittent loss of spark, injector pulses, and fuel pressure. That is why all of those things have to be checked.
When the problem occurs too seldom to do any diagnosis of value, your mechanic can connect a scanner to view live data during a test drive. The goal then is to get the stalling to occur so he can see which sensor signal is missing. Either of them should set a diagnostic fault but often the engine coasts to a stop too quickly for the engine computer to detect the problem and set the code. That is where viewing sensor data during the test drive has its advantages.
Wednesday, December 30th, 2020 AT 6:22 PM
(Merged)
