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Q: Nonstop backfiring

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I am replacing a few parts on my truck. DPFE sensor, camshaft position sensor and fan shroud. Since I have to replace the cam sensor I put a socket on the crank shaft and wanted to see if it would move and it did. But I couldn't get to the bolt that holds down the camshaft position sensor because it's behind the engine so I decided to leave it for now. I installed the new DPFE sensor hooked everything back up and went to start the vehicle. It is now backfiring nonstop and even blew the hoses off themes DPFE sensor. So I put the old one back on and it is still backfiring. Did I throw the truck off timing by moving the crankshaft? What could be causing it to backfire this way.

My car has 160000 miles.
My car has a manual transmission.

A: Backfiring occurs when the air fuel charge ...

Backfiring occurs when the air fuel charge in a cylinder(s) fires at the wrong moment often when the exhaust valve is opening. There are backfires into the intake manifold, too, however. If during your work on the engine you moved the distributor, yes, you could have altered the engine timing. However, merely turning the crankshaft, using the harmonic balancer bolt only, clockwise is harmless. The possibility of the ignition timing being off is easy to check with a timing light...just check the basic ignition timing at idle and check the advance function, too.

It is possible that the distributor cap is cracked and/or the plug wires have carbon tracking. In working on the engine, you may have sort of "tipped the balance" on already old, failing parts and set the stage for this backfiring you are getting. Backfiring is also possible is the fuel to air ratio is too high (rich); that means there is too much fuel to create an explosive, fast-burning flame. When too much fuel, the fuel burns slower, and isn’t complete before the exhaust part of the engine cycle. When the exhaust valve opens on the affected cylinder(s), the extra air allows the unburned fuel to explosively burn and the popping noise of a backfire is heard. Check for a dirty air filter by the way which can cause too little airflow. A certified Mechanic can be dispatched to determine the causes of the backfiring in your engine.

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