Question about 2001 Pontiac Montana
A shotgun parts changing approach will waste a lot of time and money. This calls for using instrumentation to try to catch the failure.
1. You say it appears it is not getting any gas. Can you attach a fuel pressure sensor to the system? I don't know about this vehicle, but many fuel injection systems have a Schrader valve for a pressure gauge or relieving fuel pressure for service. If the pressure builds rapidly when you start the engine, then falls until the engine quits, you may have a clogged fuel filter or other obstruction in the system. If it holds steady for while, then rapidly drops just about the time the engine quits, something is telling the engine computer to turn off the fuel pump (a safety feature).
Check for normal exhaust flow out of the tailpipe, and take a gentle sniff for abnormal odor (strong gasoline odor, smoky, or otherwise dirty exhaust). Your nose is a good instrument for detecting abnormal combustion. Low flow indicates an obstruction such as a foreign object in the tailpipe or melted or clogged catalytic converter. Flow with interruptions indicates misfiring.
2. What does the engine computer readout say? Sometimes it will tell you directly, for example, a bad connection in the ignition module that opens when it gets warm will probably set a code identifying a failed ignition module. On the other hand, sensor errors can have multiple causes. Try to get the values measured by the various sensors and compare them with normal parameters. This will help to make sense of the fault code(s). You'll need an ODB II diagnostic readout tool to get this info. Some car parts stores will provide the use of one for free or a nominal rental in hopes of selling you repair parts.
"A minute or two" is just about long enough for the engine to start "closed loop" operation, when the oxygen sensors are warm enough to send mixture adjustment information to the engine computer. You can check that out by blowing cold air on the oxygen sensors after the engine stalls to see if that significantly reduces the time before the vehicle will restart. If that works, you'll know a look at the airflow sensor was not a bad guess. Focus on that, the oxygen sensor and the throttle position sensor readings first.
3. If you haven't identified the problem by this point, measurements with basic instruments (voltmeter, oscilloscope) are next. The engine computer supplies one or more regulated voltages to power some of the sensors. Make sure these are within tolerance.
Very few manuals refer to the use of an oscilloscope because it's an expensive instrument, and some knowledge is required to interpret the display, but, properly used it is one of the most efficient tools there is for checking electronic sensors and fuel injector problems. If you can get an oscilloscope probe into the engine computer connector (you can slide a short piece of 24 AWG bare solid wire into the wire pocket and hook a 'scope probe to that), you can view the waveforms for the fuel injector drive and ignition pulses, and check for sensors opening up (voltage suddenly goes to zero or maximum voltage) or having very noisy output or other anomalies. Don't forget to verify the ignition switch connection while you're looking at the computer connectors (assuming the previous oxygen sensor cool-down had no effect).
I recommend measuring at the computer even though it access is awkward because the wiring harness in the engine compartment is made to be sealed against a harsh environment, and it is difficult and awkward to probe there without either making temporary adapter connectors or damaging the wires by poking holes in the insulation (a bad practice used by some shade tree mechanics). Professional technicians often use a "breakout box", which is inserted between the firewall connectors and the engine wiring harness. This provides convenient exposed points for electrical measurements.
I wish I could give you a specific answer, but this is the reality of modern engine service. Many of the traditional tests are still useful, but sometimes you have to get into combustion chemistry and electronic diagnosis.
Posted on Nov 03, 2010
Is the check engine light on? Seems like it need a tune up or bad fuel pump, If you have a little mechNIC SKILLS .. You can try this to let you know if its fuel related or electrical.. Get some staring fluid. Start the car and after it dies and wont start. Spray the starting fluid in the breather or throttle body for 3 seconds. If it starts it will be an electrical problem...Good Luck!!!
Posted on Nov 03, 2010
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Posted on Jan 02, 2017
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