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Q: truck runs great for about 3 minutes and dies for about 2 hours and then I can start it for another 3 minutes and it dies again

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my truck runs great for 3 minutes and dies for 3 hours and then I can start it again after I just change the spark plugs cleaned out the carburetor and change the fuel failter why is it dieing

My car has 219000 miles.
My car has an automatic transmission.

A: Usually this is because of an electrical co...

Usually this is because of an electrical component failing once it warms up. This is a common problem on many vehicles. In the case of your 1994 Blazer, the first thing I would suspect is the ignition module and or the pickup coil in the distributor. The ignition module can be replaced independent of the distributor, but the pickup coil is easiest replaced with a new distributor. If you purchase the entire distributor, which is common on this vehicle, it will likely come with the ignition module, pickup coil, cap and rotor. Not always, but most of the time that is how they are sold.

The distributor is the most commonly replaced part that could cause your symptom, but a few other suspects are the crank sensor and the powertrain control module (PCM). It is very rare for a PCM to fail, but crank sensors also fail when they warm up. Also, you mentioned it had a carburetor; the information I have says it should have throttle body injection. This looks like a carburetor with wires running to it. If at sometime a carburetor was fitted to it, this could cause some uncommon problems that will be hard to pinpoint.

If I were diagnosing this vehicle, I would have a fuel pressure gauge hooked up, spark tester and I would be shining a light down the throttle body to confirm fuel was spraying out the injectors. There should be two injectors. Once the car quit, I would take note of what wasn't working.

Does it have fuel pressure? If not, test the fuel relay and fuse. Knock on the bottom of the fuel tank with a hammer while someone cranks the motor. If the motor begins to run, it's a fuel pump issue.

If there is fuel pressure but no fuel is spraying, then you need to check for an injector pulse. This is easily tested with a simple tool called a noid light. If there is fuel pressure and a noid light does not flash when cranking, suspect the crank sensor.

If there isn't any spark, it is most likely a ignition module or distributor pickup issue. Replacing the entire distributor is the best repair in this case. Coils can fail, but not nearly as often as the distributor components. Have the coil tested before purchasing a distributor. It is also common for cap and rotor issues. Check for spark coming directly out of the coil. Sometimes the spark will stop inside the distributor and not make it to the spark plug wires.

Bad electrical connections on both the ground and positive side of the electrical system can behave in this manner. Just because a wire is touching something, doesn't mean electrons will flow. Wiggle wiring harnesses and connectors and see if something changes. These will be clues as to where the problem lies.

Last, engine coolant temperature (ECT) sensors are known to act in this way as well. Temperature senders can be resistance tested with a multi-meter. The resistance of the coolant temp sensor should be 177 ohms at 212 degrees Fahrenheit, 3520 ohms at 68 degrees Fahrenheit, and 25,000 ohms at 23 degrees Fahrenheit.

Good luck.

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