what if??
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i would say it is either a carb, vacuum, or timing issue
eric
eric
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·What?!?!!! A dramatic drop in back pressure will lean a carb out. Is it a carb model? Especially if it's running with already lean OEM calibrations, further leaning will definitely cause backfiring. This would indicate a dangerously lean condition. Did it start immediately after the exhaust change? It could easily be any of the things already mentioned in this thread, however, so a lot hinges on just when it started, and what you've done. Retrace your steps. That'll help narrow it down.
OK forget it.....
I am the one with the brand new exhaust.... but this problem of backfiring is somethig that has been going on for awhile....
I think it is my distributor pickup's
as I have changed the plugs, plug wires, coil, I have new pickups and reluctor for the distributor......I have just replaced the carburator as well.....
I thought maybe it was the timing chain jumped..... But I can still time it with my light it just runs really bad....It hasno pick up no go if I give it gas it just backfires and sputters and dies.....
If I ease the pedal down she runs ok until it get halfway down then starts backfiring... and has very little get up and go.....
Now this started out about a month ago and has gotten gradually worse.... before it was there but hardly noticeable....but now it barley runs it idles great but backfires when the gas pedal is touched....
Please help before I take a 25lbs sledge hammer to her as I am getting really frustrated with her....
thank you to everyone in advance,
Keven
I am the one with the brand new exhaust.... but this problem of backfiring is somethig that has been going on for awhile....
I think it is my distributor pickup's
as I have changed the plugs, plug wires, coil, I have new pickups and reluctor for the distributor......I have just replaced the carburator as well.....
I thought maybe it was the timing chain jumped..... But I can still time it with my light it just runs really bad....It hasno pick up no go if I give it gas it just backfires and sputters and dies.....
If I ease the pedal down she runs ok until it get halfway down then starts backfiring... and has very little get up and go.....
Now this started out about a month ago and has gotten gradually worse.... before it was there but hardly noticeable....but now it barley runs it idles great but backfires when the gas pedal is touched....
Please help before I take a 25lbs sledge hammer to her as I am getting really frustrated with her....
thank you to everyone in advance,
Keven
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4,027 Posts
It really sounds like timing. Does it take a while to rev the motor when you step on it? Or does it instantly rev with no load, just with backfiring?
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4,672 Posts
Sounds like a fuel problem to me. Even though you replaced all that stuff, you need to double check your work. Did you replace metal line with metal line? Don't ever use rubber over long distances. Don't assume that since your fuel pump is new that its working properly. I have a shelf full of fairly new fuel pumps that don't work very good. The stock replacement pumps you buy at a store are poor quality now days. Make a tee and tie into your fuel line after the pump and see what the actual fuel pressure is. I generally take the filter out for a little bit and install a tee there. Needs to be abotu 5-6 psi.
i have a 84 360 stock i have true duals i belive - my exhaust on each bank runs straight back to the muffler alone on each side- no cat's
i also have the heavy duty model i think
what carb are u running? 2 or 4 bar ? thermoquad?
i'd say recheck ur timing and ur carb
mine was backfireing like ur's was 2 months ago , i just reset the timing and cleaned out the carbon build up the 360's get
also what octane gas r u running? i found that i never have any problems running 90 plus octane , if i run lower i get carbon build up , crappy idle's ect
just my 2 cents
i also have the heavy duty model i think
what carb are u running? 2 or 4 bar ? thermoquad?
i'd say recheck ur timing and ur carb
mine was backfireing like ur's was 2 months ago , i just reset the timing and cleaned out the carbon build up the 360's get
also what octane gas r u running? i found that i never have any problems running 90 plus octane , if i run lower i get carbon build up , crappy idle's ect
just my 2 cents
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The heat cross over in the intake could be clogged with carbon build up, when they do this they run like sh*t.
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I'm assuming your back firing out the carb right?
It revs really good and snappy when it is in drive or nuetral... but under load it just coughs and sputters and backfires through the tailpipes....
Something else when I rev her up the rpm's fall kinda slowly back down instead of being real crisp...
No air pump/smog pump in the truck there is very little emmissions that were on her to begin with but even less on her now...
ok fuel line is metal, When a pressure guage is put on the line after the fuel filter it has 5.8 psi consistantly to the carb.
I have the 4bbl thermoquad brand new. IT has headers to true duals with dyno thrush mufflers they turn 90 degrees and exit right before the rear wheels.... no cats...
It back fires through the tail pipes..... and every now and then throught the carb if I retard the timing too much....
What is the intake heat crossovers? where are they? what do they do and where are they
?
"I would say it is either a carb, vacuum, or timing issue
eric"
I have ruled out carb problem..... I was really concentrating on timing ignition system as she misses slightly even at idle..... but I just know it is some stupid little sensor, relay, or vacum switch that should not really be on a vehicle any way.... I am slowly making her engine, plug wire, and vacum to cruise and heater plenum boxes only.....I do not want any of this unessential crap under the hood.....
I am rebuilding my distributor today with all new parts. If this does not fix it I am thinking the ignition module??
Something else when I rev her up the rpm's fall kinda slowly back down instead of being real crisp...
No air pump/smog pump in the truck there is very little emmissions that were on her to begin with but even less on her now...
ok fuel line is metal, When a pressure guage is put on the line after the fuel filter it has 5.8 psi consistantly to the carb.
I have the 4bbl thermoquad brand new. IT has headers to true duals with dyno thrush mufflers they turn 90 degrees and exit right before the rear wheels.... no cats...
It back fires through the tail pipes..... and every now and then throught the carb if I retard the timing too much....
What is the intake heat crossovers? where are they? what do they do and where are they
?"I would say it is either a carb, vacuum, or timing issue
eric"
I have ruled out carb problem..... I was really concentrating on timing ignition system as she misses slightly even at idle..... but I just know it is some stupid little sensor, relay, or vacum switch that should not really be on a vehicle any way.... I am slowly making her engine, plug wire, and vacum to cruise and heater plenum boxes only.....I do not want any of this unessential crap under the hood.....
I am rebuilding my distributor today with all new parts. If this does not fix it I am thinking the ignition module
??
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1,274 Posts
ijust went through this EXACT same thing on my 71 dart... turned out i had a MAJOR vac leak at the intake, fouled plugs, and toasted wires... now she runs smoother than a babys butt!
Sorry It was a faulty pickups in the distributor....
I went ahead and replaced the ballast resistor , rebuilt the distributor new pickups and reluctor, new coil , control module, wires, plugs , cap and rotor......
all new ignition for about $69.00 from autozone..... she runs better than 1984 when she was new...
except the primarys are not opening all of the way so I spend allot of time on the secondaries drining allot of gas..... but that is a carb adjustment....
I went ahead and replaced the ballast resistor , rebuilt the distributor new pickups and reluctor, new coil , control module, wires, plugs , cap and rotor......
all new ignition for about $69.00 from autozone..... she runs better than 1984 when she was new...
except the primarys are not opening all of the way so I spend allot of time on the secondaries drining allot of gas..... but that is a carb adjustment....
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just for future reference, it may not have an ESA, but if it aint got an ECU you wont be starting itkev said:
eric
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