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  #1  
Old 03-29-2010, 12:54 PM
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Default Backfire

So i have been trying to eliminate things on my list, almost done with the brakes still have the heater core but here is another problem.

My car backfires or pops when under acceleration it idles fine but when i give it gas it seems to hesatate a little and begin to pop or backfire. So steps i have tried to take to correct this, I replaced the points used a dwell meter to get them right, replaced plugs and checked the plug cables where on right cylinder (guy i bought it from didnt have them on right cylinder, tried to adjust mixture. The only thing i havent gotten to is checking the timing (but its on the list haha), i also replaced the fuel pump filter, but id be willing to bet the tank is probably bad so i might have to replace the filter again.

So any suggestions on what to do
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Old 03-29-2010, 04:54 PM
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Quote:
Originally Posted by 1965TbirdMan View Post
So i have been trying to eliminate things on my list, almost done with the brakes still have the heater core but here is another problem.

My car backfires or pops when under acceleration it idles fine but when i give it gas it seems to hesatate a little and begin to pop or backfire. So steps i have tried to take to correct this, I replaced the points used a dwell meter to get them right, replaced plugs and checked the plug cables where on right cylinder (guy i bought it from didnt have them on right cylinder, tried to adjust mixture. The only thing i havent gotten to is checking the timing (but its on the list haha), i also replaced the fuel pump filter, but id be willing to bet the tank is probably bad so i might have to replace the filter again.

So any suggestions on what to do
Loosen the dist. a bit so you can move it, but it doesn't move on it's own. Start playing with the timing after the motor is warm. Set it where it wants to idle the best and back off just a tick. Go drive the car see if she pings under load, if it does back it off a bit more till it doesn't ping.

I rarely use a light to set timing fwiw...

Do you have a filter before the fuel pump?
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Old 03-29-2010, 04:55 PM
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Backfire is most always a timing issue. Yes, having the wrong wire on a spark plug is a timing problem. First thing, check your firing order (I know you did, but do it again). I trust you have a Shop Manual.

Backfire happens when fuel mixture, just after the carburetor, gets ignited. It happens because the intake valve is still open when spark (or heat) is introduced.

If your distributor cap has carbon trails, spark may be diverted to the wrong wire. Carbon is a great conductor and usually found in cracks in your cap. When a spark plug won't fire or a spark plug wire goes bad, the high voltage follows the path of least resistance.

Wait until dark and open your hood. Use a paint stick to move your spark plug wires around. The insulation breaks down on old wires, causing an arc to jump to another wire or to ground. It usually shows clearly in the dark.

I don't have enough info about your engine. How many miles on it? Has the distributor ever been removed? Could the distributor be off a tooth on the cam? (Be sure your rotor points to #1 spark plug tower @ TDC.) Ignition timing can cause backfire if it is too far off, so can a timing chain that has jumped a tooth. Badly worn valves can cause backfire, too. A compression checker will show worn valves, so will an air hose (pressurizing a cylinder with the valves closed, you can hear it hiss).

Hesitation is caused by a sloppy timing chain. I guess this enough 'things to check'. Let us know what you found. - Dave
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Old 03-29-2010, 08:06 PM
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Also;

1) Vacuum advance canister,

2) Accelerator pump diaphram
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Old 03-29-2010, 08:43 PM
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Feel free to correct me if I'm wrong but I think there are two kinds of backfiring: through the carb and through the exhaust. The word "backfire" , if taken literally, seem to imply the latter.

In 2005, I was getting ready to rebuild the motor from my '58 in a neighbor's garage. Just prior to that, I removed the hood and put it in my own garage, and left the air filter there as well. I then fired up the car to drive it to his house. It was January, cold and dark; the motor was worn out with some 150,000 miles or more. As I began to accelarate the cold motor down the road, it hesistated significantly and then let out with this most impressive backfire through the carb!! A neat ball of flame! I had heard this in cars before that were running poorly - hesitation and then a "poof" but never seen it.

Back in the old days, the bikers used to enjoy an occasional backfire for fun and entertainment. They did it like this: go along at a decent speed, hit the Kill switch with the throttle wide open. Wait a second and then, with the carb still wide open, turn the Kill switch back On. BOOM!! Done correctly it could break a window nearby.... This, of course, was unburnt gas vapors down the exhaust pipes suddenly ignited.

John
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Old 03-29-2010, 09:12 PM
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Quote:
Originally Posted by JohnG View Post
Feel free to correct me if I'm wrong but I think there are two kinds of backfiring:..
Actually, there are three (according to Webster)... My wife backfired last night, and made the curtains flutter.
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Old 03-29-2010, 09:52 PM
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Thanks for the help so far hopefully this weekend i get to look at it more. But to answer some questions and ask some more
Yes I have to the shop manual, your distributor cap has carbon trails, spark may be diverted to the wrong wire. Carbon is a great conductor and usually found in cracks in your cap. When a spark plug won't fire or a spark plug wire goes bad, the high voltage follows the path of least resistance.

Wait until dark and open your hood. Use a paint stick to move your spark plug wires around. The insulation breaks down on old wires, causing an arc to jump to another wire or to ground. It usually shows clearly in the dark.

How many miles on it? Odometer reads under 52000 i belive and that is orginal miles on car, Has the distributor ever been removed? Not to my knowldege the guy i bought i plan to replace the cap and the rotor just to be safe and i did replace the point already. But it Could the distributor be off a tooth on the cam? This is very possible i have loosened the dist a think (is that what holds the distributor in place, sorry not a total expert on technical names. it turns alittle but havent taken off the vacuum advance line again since i replaced it so i think its hitting on a few things limiting my turn ability of the distrubtor to really tinker with the timing.

Also you said the Accelerator pump diaphram i got a new one of those when i got my carb back which was rebuilt so i replace it just to be on the safe side, seeing how i dont believe they changed it when the rebuilt it. It is possible that the vacuum advance is bad itself but i am open for suggestions as to what where i should start and if that doesnt fix it what to move on to next __________________
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Old 03-30-2010, 12:25 AM
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Justin, you are certainly welcome and thanks for the details. 58,000 miles is not an old engine. Which engine do you have?

Take your distributor cap off, and watch the bottom plate while you pull a vacuum on the hose. The points-plate should move quite a bit. If it doesn't, buy a new diaphragm and screw it in.
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Old 03-30-2010, 12:27 AM
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Seems like either new plug wires might be in order, or check the ones you have with the multimeter.

If you carefully read the Shop Manual, you will find some comments by Ford about correctly laying out and arranging the plug wires so that no "cross firing" can occur (one wire inducing another). There are two specific cylinders they mention (too lazy to go look it up...). You might get an extra pair of looms to help with this.

Dave, if Backfire Type #3 is occurring, perhaps you now have an answer to Mr. Iacocca's question . . .
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Old 03-31-2010, 11:02 AM
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I have the 390 i believe z code also what is the backfire type you are refering to, i will check the plug cables could just buy new never hurt and your saying make sure they arent laying on each other possibly causing a cross fire? also would you recommend just to be safe putting a new cap and rotor, and new wires and diaphragm ? I have a shop manual but didnt see anything about the cylinders to check where is that located?

So starting with those and working up is a good start i assume, also just moving the distributor around till the timing seems like is probably a good move as well i assume, thanks again
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