You are still fixated on the computer, but that should be your last suspect after all other potential causes have been eliminated. You need to start by determining what goes missing when the stalling occurs. As ASEMASTER6371 said, you need spark, fuel, compression, and correct timing for the engine to run. Compression and timing will not be intermittent, but loss of spark and fuel commonly are. In fact, loss of spark causes perhaps three percent of stalling and crank/no-start problems. Loss of fuel pressure causes maybe another two percent of those problems. Loss of spark and fuel pressure is responsible for a good ninety five percent of stalling problems.
A good suspect on all car brands other than Chrysler products is the mass air flow sensor. They do not cause as many problems as they did back in the late 1980's and early 1990's, but sometimes if you tap on them while the engine is running, that will cause the stalling to occur. Same with the Engine Computer. If it has broken solder connections inside, tapping lightly on it can cause the problem to occur.
Another cause of stalling I read about quite often is corroded ground connections, particularly inside the car. They are tight and secure, but unbolting them and shining up the terminals seems to cure a number of issues.
If you connect a fuel pressure gauge to the fuel rail and find pressure drops when the stalling occurs, and you still have spark, suspect the fuel pump or the strainer attached to the pump's housing. Chrysler fuel pumps almost always fail by failing to start up, leaving you sitting in the driveway. Once running, they rarely stop running while you are driving. GM pumps are just the opposite. They almost always start up, then fail later while you are driving, leaving you sitting on the side of the road. To my knowledge, time is not a good symptom in diagnosing a bad fuel pump, meaning it will fail after ten minutes one time and maybe it takes twenty five minutes to fail the next time. Therei s no regular pattern like you observed.
A real big cause of stalling on all car brands is the crankshaft position sensor or camshaft position sensor, and those commonly fail by becoming heat-sensitive, then they work again after cooling down for about an hour. The typical symptoms are the engine runs fine as long as you are driving and natural air flow keeps those sensors cool, then, once you stop for a short time, as in when filling with gas, heat from the engine has time to migrate up to the sensors, causing one to fail. On most cars, a failed sensor will result in no spark, no injector pulses, and no fuel pressure. Fuel pressure can be misleading because the pump will still run for one second when you turn on the ignition switch. That keeps the pressure up, but it will not resume running when you are cranking the engine.
The first thing you should have done was to have the diagnostic fault codes read and recorded. A code can be set related to one of those failed sensors, but by disconnecting the Engine Computer, that valuable data was lost. Disconnecting the battery in a misguided attempt at resetting something is another way people loose this information. Very often a fault code for a failed sensor will not set again just from cranking the engine. They need more time to set, as in when a stalled engine is coasting to a stop. At this point, I would find a code reader to see if any fault codes have set, but if there is none related to those two sensors, that is not conclusive the sensors are not failing when one gets hot.
The next thing is to connect a scanner to view live data. The two sensors will be listed under the "Inputs/Outputs" menu with some way to show if their signals are showing up at the Engine Computer. They will both be listed as missing once the engine has stopped rotating, so you have to watch if one switches to missing just before the engine stalls, or if it is listed as missing while cranking the engine.
The scanner also has a test mode that allows you to command the Engine Computer to fire ignition coils and injectors, and turn on the fuel pump. If one of those does not respond appropriately, you have to decide if the circuit needs to be diagnosed or if it is being caused by the computer.
If you do need to replace the Engine Computer, the engineers at GM have designed in a number of tricks to separate you from your money after the sale. One of those is requiring you to buy a new computer from one of their dealers, and having them program it to your vehicle's ID number. They sure do not do that for free. That can be done by independent shops for many other car brands, but from all the complaints I hear from GM owners, it is likely you will need to visit the dealer for that. Of course they will not want to reprogram a computer you found at a salvage yard, and in fact, there are some computers that can only be reprogrammed to different vehicles three times before that no longer works. That prevents mechanics from having used computers on hand to try on multiple vehicles as tests.
Sunday, June 10th, 2018 AT 8:28 PM
