First of all, you didn't say what the original problem was. Unless there was a catastrophic failure, you repair an engine. That is usually less expensive than replacing it. Second, if you went by the first shop's diagnosis and simply asked the second mechanic to do a specific job, like replace the engine, you got what you asked for and you're obligated to pay for it. Third, the first shop has no business saying the shut-down is due to the engine. I challenge anyone to tell me what mechanical part can cause that symptom.
There are temperature-related electrical failures all the time and they can be real frustrating to find but the dealer has the benefit of having a scanner that will talk with the many computers on the vehicle. Most independent shops have similar equipment but they are always a few years behind with their software. Most scanners have a record feature that allows the mechanic to take a snapshot of the sensor data when the problem occurs, then he can play it back slowly to see what changed. You could be losing spark, or fuel pressure, or both.
There should also be a diagnostic fault code stored in the Engine Computer related to the cause of the problem. That will lead you to the circuit or system that needs further diagnosis. When there's no fault codes, that usually means it's a fuel supply problem because other than for leaks, the fuel supply is not monitored.
The most common thing to fail by becoming heat-sensitive is the crankshaft position sensor. Often they will work again when they cool down. Less commonly, depending on which engine you have, the camshaft position sensor can do that too. Has anyone actually checked for fault codes?
You must also keep in mind that the battery was disconnected numerous times and each time the Engine Computer lost its memory. Until it relearns "minimum throttle", the engine will be hard to start unless you hold the gas pedal down 1/4", it won't give you the nice idle flare-up to 1500 rpm when you start it, and it will want to stall when you come to a stop. To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.
Your symptoms don't really match the need to relearn minimum throttle but it bears mentioning in case that symptom shows up too.
They way I would approach this is to trick the Engine Computer into thinking the coolant temperature is less than 157 degrees. I have a "decade box" that I use in tv repair. That allows me to switch in different resistance values to substitute for the coolant temperature sensor. Regular individual resistors from Radio Shack work just as well. The only thing you don't want to do is unplug the sensor and / or let it go open circuit, (unplugged), without having some resistor in there any time the ignition switch is on. Nothing serious will happen but the computer will detect that, set a fault code, and turn on the Check Engine light. Any code CAN cause other codes to not set and you may need that valuable information to be detected by the computer for you.
The lower the value of the resistor, the higher the coolant temperature that will be seen by the computer. By picking the right values you can actually read the coolant temperature on the scanner that the computer thinks it's seeing, then you can see if the engine still stalls. If it does stall, something else is failing from heat just at the same time as the engine gets to 157 degrees. That could be due to temperature or running time. With lower resistor values you can also trick the computer into thinking the coolant temperature is much higher than 157 degrees right after start-up when it's really still cold.
Also consider that in every Engine Computer there is the magic temperature at which it goes to "closed loop". That is when it assumes the oxygen sensors are up to 600 degrees and their readings will be accurate. At that temperature, closed loop is when it adds the oxygen sensors' readings to its fuel metering calculations from all the other sensors. It can also begin running some self-tests on the emissions systems. The oxygen sensors have heaters in them to get them up to 600 degrees within one or two minutes of start-up, but if the computer is tricked into going into closed loop when those sensors are still not hot enough, fault codes may be set related to "O2 sensors not switching properly". Since we know we are the cause of those codes they can be ignored but they must be erased so the computer can resume its other self-tests.
The computer also knows that the coolant temperature sensor and the intake air temperature sensor had better be reading the same temperature when the engine has not been running for more than six hours. If they're drastically different, the computer has to figure out which one is wrong so it can set the proper fault code. If the mechanic comes to work in the morning, sticks a resistor in place of the coolant temperature sensor, then starts the engine, a fault code is likely to set. Knowing they should be reading the same temperature is part of how it learns the characteristics of a new sensor when one is replaced. (It's also why people run into problems when they throw a lot of random parts at a problem thinking one is going to magically fix something).
If the vehicle still has spark after it stalls, the fuel supply system should be checked for pressure. If it is dropping off close to 20 psi or less, suspect a plugged pickup screen on the fuel pump. I just replaced the screen in my '88 Grand Caravan for the second time yesterday. Now I can easily hit "XX" miles per hour again and it runs really well. Your symptoms don't match this cause either but it would be the most likely suspect if fuel pressure is the cause of the stalling.
Wednesday, June 26th, 2013 AT 8:17 PM