1986 Ford F-150 backfiring thru the intake

  • 1986 FORD F-150
  • V8
  • 4WD
  • 117,000 MILES
My truck is backfiring thru the intake under a load I have checked the compression the lowest cyl. Is 130 psi and the highest is 145 psi, fuel pressure is 45, I replaced the plugs, wires, ign. Module and the pickup in the dist. Also the tps. Checked the timing right on at 10 deg. Had the valve covers of and it appears all rockers are moving the same distance( though maybe a flat lobe on the cam) I need help could this be a flat lobe? Dished lifter? Timing chain? It smells like it is running a little rich. I have also scanned for codes and the only code is no knock sensed but I cant find a knock sensor, it did sit for a while before I purchased it and it had some bad gas although I have added about 10 gallons of good gas
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have the same problem?
Thursday, November 5th, 2009 AT 8:05 PM

1 Reply

Most causes of backfires in the exhaust system can be addressed by troubleshooting the reason for the air to fuel ratio imbalance. The solution usually involves checking for vacuum leaks, changing the airflow sensor, oxygen sensor, or fuel filter to ensure the fuel system is functioning properly.

A common backfire situation occurs when there is a small leak in the air injection system that feeds the exhaust system. This can cause unburned fuel to explode suddenly. One of the most common causes is a stuck or faulty air intake or gulp valve near the exhaust manifold.

Backfiring can also occur with a sudden drop in fuel pressure. This may be due to a faulty fuel pump or a plugged fuel filter. Correcting problems in the fuel system usually resolves these issues.

Incorrect ignition timing to the spark plugs is another cause of backfire. Adjusting the ignition distributor, if the engine is so equipped, may resolve this problem. Adjusting engine timing is not difficult and can be done with a timing light by following the timing adjustment procedure for your car. If you do not know your car's ignition timing procedure please visit our car repair manual page. A vehicle that is not timed properly will not idle, run or operate correctly and will often backfire rapidly. On newer cars you will need to scan the pcm to check for CKS (crankshaft angle sensor) and CMS (camshaft position sensor) related trouble codes.
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Thursday, November 5th, 2009 AT 8:12 PM

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