Sudden backfiring?
Thread Starter
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Cargo Master
Joined: Aug 2008
Posts: 2,661
Likes: 23
Sudden backfiring?
What would cause an engine to suddenly start backfiring?
My brothers truck has a 302 in it, worked fine, but today he's had some serious problems with it. While driving it starts to sputter and die off then had a massive backfire. He got it working again and it did it again, massive enough that time to literally blow his exhaust off, said it was like gun fire. Obviously he has fuel not being ignited, I'm thinking he's not getting spark, but I can't figure out why it would suddenly start getting inconsistent.
Anyone have any ideas? I'd like to be able to help more than just telling him he's not getting any spark, especially since it's an out of the blue problem.
Thanks
My brothers truck has a 302 in it, worked fine, but today he's had some serious problems with it. While driving it starts to sputter and die off then had a massive backfire. He got it working again and it did it again, massive enough that time to literally blow his exhaust off, said it was like gun fire. Obviously he has fuel not being ignited, I'm thinking he's not getting spark, but I can't figure out why it would suddenly start getting inconsistent.
Anyone have any ideas? I'd like to be able to help more than just telling him he's not getting any spark, especially since it's an out of the blue problem.
Thanks
Hotshot
Joined: Oct 2009
Posts: 16,135
Likes: 4,735
From: Burbank, WA
What Dick said was my first thought, as well. It could also be something as simple as a rotor coming apart, (yes, I had that happen to me once) where the little rivit that holds everything together comes loose and the electrode starts flopping. Also, check the condition of the spring in the points, if so equipped.
Logistics Pro
Joined: Feb 2005
Posts: 3,952
Likes: 117
From: Upper Left Coast
Mine too.......
My former 239 timing chain slipped on my F-600. It became severely retarded though.
I don't know how a timing chain could slip and become advanced (which would make it more apt to backfire) unless it slipped a LOT!
Post Fiend
Joined: Jun 2001
Posts: 7,493
Likes: 7
From: Erie, pa
I've had a cam break and sound like that but that was just before the pistons started swaping holes.
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Laughing Gas
Joined: Nov 2008
Posts: 914
Likes: 51
From: SW Missouri
As everyone has said if it's backfiring out the exhaust it very likely is getting spark with a open valve. To do that either the valve has to be opening at the wrong time(chain/gear slipped, valve stuck open, or so badly burnt it can fire past the closed head)
Or the firing has to be off enough to fire on the open valve ( rotor bad, distributor cap cracked, plug wires bad and cross-firing, possible a cracked coil tower) If it was running ok and suddenly developed this issue I would look at the valve timing, then the spark.
One other possibility is it's flooding so badly it's filling the exhaust with fuel and it's igniting from the hot exhaust. Not very likely but have seen that happen a couple times.
Good Luck
Larry
Or the firing has to be off enough to fire on the open valve ( rotor bad, distributor cap cracked, plug wires bad and cross-firing, possible a cracked coil tower) If it was running ok and suddenly developed this issue I would look at the valve timing, then the spark.
One other possibility is it's flooding so badly it's filling the exhaust with fuel and it's igniting from the hot exhaust. Not very likely but have seen that happen a couple times.
Good Luck
Larry
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Logistics Pro
Joined: Oct 2002
Posts: 4,489
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From: Valley Center, CA
My buddy also just blew his muffler apart when his 302 backfired. They thought it was the distributer causing the problem, but when they changed it out, it didn't help. 
They are trailering his 65 back to the engine builders with the thought that the cam/crank timing may be off. However, they say the compression test was good, so I'm stumped as well. Good luck, Jag
They are trailering his 65 back to the engine builders with the thought that the cam/crank timing may be off. However, they say the compression test was good, so I'm stumped as well. Good luck, Jag
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
Also, make sure none of your spark plug wires are touching or close to each other - especially #7 and #8 (back 2 on the drivers side) which fire in succession.
I had a backfire problem and there are specific warnings about those two wires. Mine had spark jumping through aluminum tubes and almost an inch between those wires.
I had a backfire problem and there are specific warnings about those two wires. Mine had spark jumping through aluminum tubes and almost an inch between those wires.
Hotshot
Joined: Oct 2009
Posts: 16,135
Likes: 4,735
From: Burbank, WA
It's funny how many problems occur "out of the blue", right after people go around "fixing" things. LOL
If only we knew your brother just gave his rig a "tune up" right before his problems started, our answers may have been much different. ;-)
Glad they figured it out!
If only we knew your brother just gave his rig a "tune up" right before his problems started, our answers may have been much different. ;-)
Glad they figured it out!
Thread Starter
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Cargo Master
Joined: Aug 2008
Posts: 2,661
Likes: 23
So my brother replaced the plugs and cleaned the air filter, didn't have anymore time till he had to go to work. He says it ran like a champ and just when he got comfortable with it it dies. No hesitation no backfire just dead.
He killed the battery trying to restart it (something he's had trouble with before. And a couple days ago the starter got stuck), he used his jumper and managed to start it long enough to rev then it remained dead.
Any ideas?
He killed the battery trying to restart it (something he's had trouble with before. And a couple days ago the starter got stuck), he used his jumper and managed to start it long enough to rev then it remained dead.
Any ideas?