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Old June 12th, 2007, 08:52 PM   #1
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alright, our 71 bronco is miss firing. we cant figure out why. its not the ignition system up to the coil. we have good compression and dont think there is a vacuum leak. could it be the carburetor or maybe the distributor? help.
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Old June 20th, 2007, 11:43 PM   #2
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this thing is giving us major headaches. we put on a different carb, same result, new distributor, same, no valves stuck closed. wtf
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Old June 20th, 2007, 11:55 PM   #3
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check the plug wires? they can break internally.

how much of a new distributor? did you replace the cap and/or rotor? or just the base? the cap can get corrosion on where it and the rotor spark, and that will mess things up a bit.
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Old June 21st, 2007, 12:10 AM   #4
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is it timmed correctly? Is it an older engine... or rebuilt?? Timming chain could be stretched throwing the cam to crank timming off.....
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Old June 21st, 2007, 06:45 AM   #5
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Timming chain could be stretched throwing the cam to crank timming off.....
x2, had that issue on a Chevy 4.3L. we pissed with that thing for weeks before we finally gave up, pulled it AGAIN, and took it all apart. And the symptoms would fit nicely with what you describe, unfortnately.
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Old June 21st, 2007, 09:07 AM   #6
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check the plug wires? they can break internally.

how much of a new distributor? did you replace the cap and/or rotor? or just the base? the cap can get corrosion on where it and the rotor spark, and that will mess things up a bit.
we just got the distributor a few days ago. we're gonna try cap and rotor and see what that does.
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Old June 21st, 2007, 09:08 AM   #7
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is it timmed correctly? Is it an older engine... or rebuilt?? Timming chain could be stretched throwing the cam to crank timming off.....
its from a 71 bronco. the motor was rebuilt at 98,000 and now it has 121,000 on it. maybe sometime we'll have to look at the timing chain.
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Old June 21st, 2007, 04:19 PM   #8
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did it run fine after the rebuild ?? Did u purchase this engine from a guy who said it was rebuilt???
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Old June 21st, 2007, 05:21 PM   #9
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did it run fine after the rebuild ?? Did u purchase this engine from a guy who said it was rebuilt???
It was rebuilt by my grandpa before he sold it back to my dad. My dad bought it in the late 70's then in the late 80's he sold it to my grandpa, then my dad bought it back a few years later and my grandpa rebuilt it at 98k. Its the original engine too.

My dad just recently converted it from points ignition to the duraspark ignition. it was running better than it ever has until one time i was driving it and i let of the gas and it died.

BTW its not cap and rotor. checked that today.
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Old June 21st, 2007, 07:02 PM   #10
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You may already know this, there are 2 firing orders for a 302, 1 for and old school 302, and 1 for the H.O. motors. Are you using the correct one? Do you have any loose Rocker arms? Just some ideas.
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Old June 21st, 2007, 07:05 PM   #11
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hmm,,, still could be the timming chain as they can stretch... specally if its a non double roller
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Old June 21st, 2007, 09:24 PM   #12
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You may already know this, there are 2 firing orders for a 302, 1 for and old school 302, and 1 for the H.O. motors. Are you using the correct one? Do you have any loose Rocker arms? Just some ideas.
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hmm,,, still could be the timming chain as they can stretch... specally if its a non double roller
yes, we are using the correct firing order stamped on the intake. the rockers aren't loose. the valves are stuck closed or open.

were gonna convert it back to points ignition and see if that fixes it. if not we'll check out the timing chain. it should be good cus its not that old but ya never know till you check it out. Thanks for the input.


Mike
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Old June 22nd, 2007, 01:05 AM   #13
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4 things to make a motor run

Fuel - check the pressure into the carb, might have to plumb in a gauge. Also verify visually that the fuel is spraying thin (not drops) out of the carb and isn't flooding the motor. The motor will actualy idle ok a little lean, but won't idle very rich.

Spark - Timing light on the tip of each wire near the plug with show all cylinders are getting spark (timing is another issue). However a timing light on 1 cyl will show if the chain jumped.

Air- Have to assume intake is ok... anything in the exhaust that could be plugged?

Compression - run a compression test and a leakdown test.
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Old June 22nd, 2007, 09:41 AM   #14
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4 things to make a motor run

Fuel - check the pressure into the carb, might have to plumb in a gauge. Also verify visually that the fuel is spraying thin (not drops) out of the carb and isn't flooding the motor. The motor will actualy idle ok a little lean, but won't idle very rich.

Spark - Timing light on the tip of each wire near the plug with show all cylinders are getting spark (timing is another issue). However a timing light on 1 cyl will show if the chain jumped.

Air- Have to assume intake is ok... anything in the exhaust that could be plugged?

Compression - run a compression test and a leakdown test.
its getting fuel, there is plenty of pressure and the bowl has fuel in it. we checked each spark plug with a timing light and they all worked as the should. Nothing is plugging the exhaust it is coming out how it should. we ran a compression test and all the cylinders were good, around 130 psi.
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Old June 24th, 2007, 01:04 PM   #15
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pretty sure its the timing chain. we have to advance the timing really far just to get it to idle. gonna start working on it tomorrow. thats gonna be fun.
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Old July 5th, 2007, 06:22 PM   #16
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Its NOT the timing chain.
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Old July 5th, 2007, 10:19 PM   #17
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wiped out cam? is there any metal in the oil? have you pulled the valve covers to make sure all of the rockers are moving properly? You mentioned before you had to advance the timing to get it to run better, possibility the distributor is off 1 tooth? I'm sure you already checked these, just some thoughts.
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Old July 5th, 2007, 11:07 PM   #18
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wiped out cam? is there any metal in the oil? have you pulled the valve covers to make sure all of the rockers are moving properly? You mentioned before you had to advance the timing to get it to run better, possibility the distributor is off 1 tooth? I'm sure you already checked these, just some thoughts.
Thanks for the input but, took valve covers off, everything moves like it should, distributor isnt off a tooth b/c we put it back in where it was before.

I just dont get it cus it was running fine then it just went bad.
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Old July 5th, 2007, 11:44 PM   #19
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Did you happen to put the points distributor back in to see if it runs any better? I don't know alot about points, but from what I remember vehicles with points always had a resistor so they could reduce the voltage to the coil. If this resistor is still in place (if you have/had one) it could be keeping the current to low for your electronic distributor. I know a couple good ford guys, I will do a little more inquiring and see if they have ever had this problem.
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Old July 5th, 2007, 11:52 PM   #20
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Did you happen to put the points distributor back in to see if it runs any better? I don't know alot about points, but from what I remember vehicles with points always had a resistor so they could reduce the voltage to the coil. If this resistor is still in place (if you have/had one) it could be keeping the current to low for your electronic distributor. I know a couple good ford guys, I will do a little more inquiring and see if they have ever had this problem.
Once i get it all back together, its goin back to points to see if that helps.
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