backfiring under high rpms
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Senior User
Joined: Aug 2003
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From: Minnesota
backfiring under high rpms
my friends 1994 f150 5.0 auto, and he is noticing a backfiring at high rpms. he has had the timing checked and it was good. i was just wondering what we should do... any ideas will be appreciated. Thanks Seth
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Joined: Jun 2006
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Oooh myyyy.
Search for my post regarding plenum intake leaks. Apparently, this is more common than realized on the 5.0L EFI's. Is it just during high RPM, or when it's pulling load up a hill? Lean burn will spit, sputter, cough and wheeze when you start climbing a hill, and even make you think it's backfiring. The backfiring would be very hard to hear, though. Pulling the throttle body isn't that difficult, neither is pulling the plenum for that matter.
I have a '92 5.0L M5OD short bed. Just finished a plenum job last night. Only took 10 hours to do the job, including the test drive, dinner, and frequent smoke breaks AWAY from the truck. The only special tool you might need will be a T40 Torx bit for 1/4 inch drive. 3/8 drive sockets won't slide through the access slit in the plenum.
Seriously, check the vacuum. If it ain't 20 inches, then disconnect and block all lines except the MAP and FPR lines. You won't need to move to run this test, so yeah, go ahead and disconnect the brake booster. All lines can be disconnected at the tree on the plenum. Also, look under the curl in the plenum. If you see oily residue along the edge of the plenum where it meets the intake manifold, do the job. You won't regret it, I promise. Mine's still in the learning phases from disconnecting the battery for so long, but it's already 1000% better, and getting better the farther I drive. Getting it's first long burn tomorrow when I head to work.
Search for my post regarding plenum intake leaks. Apparently, this is more common than realized on the 5.0L EFI's. Is it just during high RPM, or when it's pulling load up a hill? Lean burn will spit, sputter, cough and wheeze when you start climbing a hill, and even make you think it's backfiring. The backfiring would be very hard to hear, though. Pulling the throttle body isn't that difficult, neither is pulling the plenum for that matter.
I have a '92 5.0L M5OD short bed. Just finished a plenum job last night. Only took 10 hours to do the job, including the test drive, dinner, and frequent smoke breaks AWAY from the truck. The only special tool you might need will be a T40 Torx bit for 1/4 inch drive. 3/8 drive sockets won't slide through the access slit in the plenum.
Seriously, check the vacuum. If it ain't 20 inches, then disconnect and block all lines except the MAP and FPR lines. You won't need to move to run this test, so yeah, go ahead and disconnect the brake booster. All lines can be disconnected at the tree on the plenum. Also, look under the curl in the plenum. If you see oily residue along the edge of the plenum where it meets the intake manifold, do the job. You won't regret it, I promise. Mine's still in the learning phases from disconnecting the battery for so long, but it's already 1000% better, and getting better the farther I drive. Getting it's first long burn tomorrow when I head to work.
