Backfire/pop through carb on hard acceleration?
#99317
08/03/08 10:08 PM
08/03/08 10:08 PM
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Joined: Jan 2003
Posts: 9,838
Detroit, Michigan, USA!
peelerboy
OP
master
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OP
master
Joined: Jan 2003
Posts: 9,838
Detroit, Michigan, USA!
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Alright guys, I need some input as to why this weird thing may be occuring with my car.
I'm talking about my Challenger. Freshly rebuilt (and essentically stock) 383, 4spd, 750 double pumper, MSD ingition, newer 8.8mm Accel wires. The car runs, idles, drives beautifully.
But just recently it started doing something unusual during hard accleration. Around 4,500rpm a backfire(?) "pop" sound comes through the carb. Sometimes it only does it once in one of the gears, sometimes it'll do it a few times in rapid succession ("pop! pop! pop!"), sometimes it doesn't do it at all. When it "pops" there is a split second loss of power, of course.
I was thinking fuel starvation (vapor lock?), but it didn't have this issue earlier in the year when it was just as warm out. It only started doing this recently and there's been no changes done to the car.
Any ideas or suggestions as to where to start looking first?
Dale
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Re: Backfire/pop through carb on hard acceleration?
[Re: wildman340]
#99319
08/03/08 11:06 PM
08/03/08 11:06 PM
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Anonymous
Unregistered
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Anonymous
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An engine will surge on a lean condition before you'll have anything like this.
You either have a cam going flat, something wrong in the valvetrain, or something going sour in the igniton. This could be a number of things, including cross-firing problems (electromagnetic energy causing adjacent wires to gain enough energy to fire when they are not supposed to) cracks/ carbon tracks in the rotor / cap, a coil going weak, one or more plug wires with intermittent opens (internal burns) or even a cracked plug which, because it allows spark voltage to climb, may cause cross fireing.
It could also be ANYTHING which is causing the spark energy to deteriorate to a borderline level, including (if electronic) problems in your "box" weak coil, bad condenser, or even primary feed problems (12V supply)
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Re: Backfire/pop through carb on hard acceleration?
#99320
08/03/08 11:17 PM
08/03/08 11:17 PM
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Joined: Jan 2003
Posts: 9,838
Detroit, Michigan, USA!
peelerboy
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master
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OP
master
Joined: Jan 2003
Posts: 9,838
Detroit, Michigan, USA!
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Thanks for the input, guys.   I only had time to do a quick "once over" when checking to see if all the wires & plugs were okay... and didn't actually inspect them properly. More careful investigation into my ignition & related components to take place as soon as I get home from work tomorrow.  After I verify all is cool there, then I'll consider valvetrain. I always check the cheap/easy stuff first, plus the engine doesn't have but a couple thousand miles on it since being rebuilt. I know that doesn't clear it from the possibility of a lobe being wiped or valves hanging open, but I'm saving those for last since the car runs fantastic the majority of the time.  Thanks again for the feedback, and if you can think of anything else... don't hesitate to share! Dale
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Re: Backfire/pop through carb on hard acceleration?
[Re: peelerboy]
#99323
08/04/08 09:37 AM
08/04/08 09:37 AM
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Joined: Dec 2006
Posts: 507
Northern Indiana
capac
mopar
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mopar
Joined: Dec 2006
Posts: 507
Northern Indiana
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Mine did the same exact thing when I had a vacuum leak. Check for cracked hoses, and spray the intake-to-head area with carb cleaner (while car is idling). Mine ended up being a hairline crack under the EGR valve, good luck!
edit: I just realized that you are using a holley carb.... power valve? Never ran a holley before so I don't know how to check it...
Last edited by capac; 08/04/08 09:39 AM.
'64 390 Valiant Signet Convertable (WIP...)
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Re: Backfire/pop through carb on hard acceleration?
[Re: autoxcuda]
#99324
08/04/08 03:00 PM
08/04/08 03:00 PM
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Joined: Jan 2003
Posts: 9,838
Detroit, Michigan, USA!
peelerboy
OP
master
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OP
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Joined: Jan 2003
Posts: 9,838
Detroit, Michigan, USA!
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Quote:
Didn't you have a problem with the voltage regulator recently? Overcharging I think. I was a bad ground?? Can't remember exactly.
Yep! Good memory. I had a bad ground(s) and that has since solved my overcharging issue.
And Ron... I definitely have to sort this out pronto cuz the cruising scene is getting pretty heavy here in the Motor City with the Woodward Dream Cruise around the corner.  I'll be checking all main connections, along with the plug wires, cap, etc. tonight. As a matter of fact, my engine wiring harness is original, so I plan on picking up a new one of those at the Nats this weekend. Can't go wrong for only $105. (that's the price through Year One, anyway)
Dale
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Re: Backfire/pop through carb on hard acceleration?
[Re: peelerboy]
#99325
08/04/08 05:53 PM
08/04/08 05:53 PM
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Joined: Jan 2007
Posts: 1,668
Mi,U.S.A.
mike s
top fuel
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top fuel
Joined: Jan 2007
Posts: 1,668
Mi,U.S.A.
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Sounds like low fuel pressure problem esp since it does it at higher rpm.You want 5-6 psi @ wot peak power speed.Check the float levels also.
Last edited by mike s; 08/04/08 05:56 PM.
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Re: Backfire/pop through carb on hard acceleration?
[Re: peelerboy]
#99326
08/04/08 07:14 PM
08/04/08 07:14 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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blame it on the carb.slap your spare[or a buddys]on and try again.elimination by process is tried and true.
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Re: Backfire/pop through carb on hard acceleration?
[Re: 383man]
#99327
08/04/08 10:14 PM
08/04/08 10:14 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Quote:
It sure sounds like an ign miss to me Dale. Come on and get that cool Challenger running right. But I would check the ign primary and secondary real good first. Good luck , Ron
 Had the same problem with my 360 a couple of months ago. Turned out to be the electronic distributor pickup coil.
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Re: Backfire/pop through carb on hard acceleration?
[Re: peelerboy]
#99328
08/04/08 10:20 PM
08/04/08 10:20 PM
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Joined: Jan 2003
Posts: 12,861
Gloucester,VA STOP MOVING HERE
RangerDan440
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 12,861
Gloucester,VA STOP MOVING HERE
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could be a lean condition too, maybe you need to dump some more fuel down the carb Dale
68 Valiant 408
69 Charger 318
69 Cougar 351W
70 Torino GT 351C
71 Country Squire 351W
71 Road Runner 440+6
71 Satellite sedan 318
73 Duster 318
73 Challenger 383
77 Grand Prix 455
83 Malibu 9C1 383
84 Delta 88 403
87 Grand National
96 Ram 360
09 Crown Vic
10 Challenger R/T M6
15 Challenger Hellcat M6
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Re: Backfire/pop through carb on hard acceleration?
[Re: peelerboy]
#99329
08/05/08 12:46 AM
08/05/08 12:46 AM
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Joined: Jan 2003
Posts: 27,483
So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,483
So Cal
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Quote:
Quote:
Didn't you have a problem with the voltage regulator recently? Overcharging I think. I was a bad ground?? Can't remember exactly.
Yep! Good memory. I had a bad ground(s) and that has since solved my overcharging issue.
Can overcharging hurt a MSD box? Or other ignition parts. I sort of doubt it, but I don't know/run a MSD box. 
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