Need help troubleshooting
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Joined: Jun 2015
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Need help troubleshooting
If anyone can help me troubleshoot why my truck won't run that would be great. I have replaced all the spark plugs and cleaned the carb and got a kit for it. It's a 78 f100 with the 351M. Problem is, when I turn the key she turns over, fires and almost gets going. But the moment I let go of the key the engine dies. It did sit all winter. But summer before it ran fine without spark plugs or carb being cleaned. Does anyone have an idea of what it might be.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Welcome to FTE!
It sounds like it doesn't have power in Run. Here are the steps I would take to troubleshoot it. And, I would do them in that order because you need to prove that you are getting sufficient fuel, that the choke is closing, and the spark is strong before jumping to the step where you check power.
It sounds like it doesn't have power in Run. Here are the steps I would take to troubleshoot it. And, I would do them in that order because you need to prove that you are getting sufficient fuel, that the choke is closing, and the spark is strong before jumping to the step where you check power.
- Fuel: Verify that it is getting fuel by pulling the air cleaner and, while looking down the throat of the carb, open the throttle. You should see two streams of gas shoot into the carb. This indicates you have fuel getting to the carb, and that the accelerator pump is working.
- Choke: When the engine is cold the choke should be closed.
- Spark: Pull a spark plug wire and put an old plug in it. Then, while cranking it over hold the plug's body against the engine and observe the spark. It should be blue or white.
- Power: With the key in Run verify that you have around 7 volts at the Batt terminal of the coil, which should be a red/light green wire, as shown here: Start, Ignition, & Carb Circuits - ???Gary's Garagemahal
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
Agree with Gary on the troubleshooting procedure.
Small clarification.
..#4 key in RUN, engine OFF. You should have no problem with that.....please forgive....just being a wise a$$.
Additionally - test the voltage on the 'I' terminal when trying to start. You should see BATT voltage there and nothing (or very little residual voltage) in RUN.
Small clarification.
..#4 key in RUN, engine OFF. You should have no problem with that.....please forgive....just being a wise a$$.Additionally - test the voltage on the 'I' terminal when trying to start. You should see BATT voltage there and nothing (or very little residual voltage) in RUN.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Agree with Gary on the troubleshooting procedure.
Small clarification...#4 key in RUN, engine OFF. You should have no problem with that.....please forgive....just being a wise a$$.
Additionally - test the voltage on the 'I' terminal when trying to start. You should see BATT voltage there and nothing (or very little residual voltage) in RUN.
Small clarification.
..#4 key in RUN, engine OFF. You should have no problem with that.....please forgive....just being a wise a$$.Additionally - test the voltage on the 'I' terminal when trying to start. You should see BATT voltage there and nothing (or very little residual voltage) in RUN.
Thread Starter
|
New User
Joined: Jun 2015
Posts: 3
Likes: 0
Welcome to FTE!
It sounds like it doesn't have power in Run. Here are the steps I would take to troubleshoot it. And, I would do them in that order because you need to prove that you are getting sufficient fuel, that the choke is closing, and the spark is strong before jumping to the step where you check power.
It sounds like it doesn't have power in Run. Here are the steps I would take to troubleshoot it. And, I would do them in that order because you need to prove that you are getting sufficient fuel, that the choke is closing, and the spark is strong before jumping to the step where you check power.
- Fuel: Verify that it is getting fuel by pulling the air cleaner and, while looking down the throat of the carb, open the throttle. You should see two streams of gas shoot into the carb. This indicates you have fuel getting to the carb, and that the accelerator pump is working.
- Choke: When the engine is cold the choke should be closed.
- Spark: Pull a spark plug wire and put an old plug in it. Then, while cranking it over hold the plug's body against the engine and observe the spark. It should be blue or white.
- Power: With the key in Run verify that you have around 7 volts at the Batt terminal of the coil, which should be a red/light green wire, as shown here: Start, Ignition, & Carb Circuits - ???Gary's Garagemahal
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