Sudden onset Pre-Ignition Knock
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Sudden onset Pre-Ignition Knock
I have a 2010 F150 with 4.6L 3V engine & 50K miles. I have NEVER had a problem with pre-ignition knock until one day is was driving up a slight incline and suddenly the engine started making a terrible noise that was so loud I jumped and let my foot off the gas. I thought the engine blew. I realized i could make it happen again by applying the accelerator. My experience in the olden days with the cars designed to used leaded gas was that this would happen if you were in too high a gear and some load but not enough gas. The mixture was too lean and would knock but not like this. Then you could apply a bit of gas and it would go away or downshift and it would go away. That does not happen with my F150. Further, some days it happens and some days it does not. Sometimes it can go weeks with nothing then happens every day for months. I am convinced a sensor has changed and is feeding some bad information back to the computer, but which one? Every time I take it to someone, it naturally does not do it so they cannot find a problem. No check engine light at all either. Any ideas?
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Joined: Jan 2008
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From: Maine, Virginia
Welcome!
My 2004 Expy with the 4.6L would do that sometimes as well and it turned out to be one or more COP's breaking down and causing a misfiring event. It never threw a code and no one could pin point the issue but I knew that it had to be a misfire. I changed out all COP's and the issue is gone.
My 2004 Expy with the 4.6L would do that sometimes as well and it turned out to be one or more COP's breaking down and causing a misfiring event. It never threw a code and no one could pin point the issue but I knew that it had to be a misfire. I changed out all COP's and the issue is gone.
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Joined: Jul 2011
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From: Sioux Falls Area
Is this a 4 wheel drive?
if so I’d put money on the front hubs losing vacuum and trying to engage. My expedition did the same thing and it sounds exactly like spark knock or pinging from low octane fuel.
Mine was intermittent like you described and was a cheap fix to replace the check valve assembly. $15 and five minutes of time and the problem was fixed.
if so I’d put money on the front hubs losing vacuum and trying to engage. My expedition did the same thing and it sounds exactly like spark knock or pinging from low octane fuel.
Mine was intermittent like you described and was a cheap fix to replace the check valve assembly. $15 and five minutes of time and the problem was fixed.
Laughing Gas
Joined: Dec 2010
Posts: 1,200
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From: Timbuk3, MI
- Is the fuel tank routinely left low? *Issue of condensation in the tank.
- Quality of gasoline.
- Clean the MAF sensor.
- Check the throttle body and clean if necessary.
- Small vacuum leak. *e.g.PCV hose.
- Check the air filter and replace if necessary.
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