When I decelerate, I get a wicked popping and snapping sound from my exhaust. If I hit the gas and then immediately pull off of it, it gets really bad. Is my muffler too small?
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Popping exhaust sound when decelerating
- Thread starter SouthBostonFJ40
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hicruise55
IH8MUD VOYEUR
You have an exhaust leak, maybe at the manifold/header or downstream of there somewhere-collector, joint ect... check all bolts for tightness and look at gaskets as well-good luck
Cruiserdrew
On the way there
I had this for a long time in my 40, and I think it came down to the throttle positioner not working properly. The issue was entirely resolved after the desmog and carb rebuild-there, the throttle positioner is assigned a different duty. JimC would know the details.
You can also get this if your timing is not right, and I could lessen the amount of "after fire" by advancing the timing. I never understood this very well, but it helped.
Good luck, I occasionally had some really loud after fire. It was embarassing!
You can also get this if your timing is not right, and I could lessen the amount of "after fire" by advancing the timing. I never understood this very well, but it helped.
Good luck, I occasionally had some really loud after fire. It was embarassing!
If you still have the air pump and air injection, then it is a problem with the throttle positioner and air bypass valve.
If not, then you have some air leaking in to the exhaust system somewhere as mentioned above.
At deceleration there is a high intake manifold vacuum and the air/fuel ratio is too low for the spark to ignite. When the unburned fuel encounters air in the exhaust manifold, it will spontaneously combust.
If not, then you have some air leaking in to the exhaust system somewhere as mentioned above.
At deceleration there is a high intake manifold vacuum and the air/fuel ratio is too low for the spark to ignite. When the unburned fuel encounters air in the exhaust manifold, it will spontaneously combust.
Downey
SILVER Star
Or if you still have the air injector manifold, it had an anti-backfire valve mounted on the front end of it. When that valve goes bad, hello backfires?????????
Yep, check for leaks. I have headers with a couple of cracks and I get the same popping on decelleration. I have a short exhaust which makes it a little worse. Gonna fix it real soon.
Colorado Boy-74-FJ40
I may grow older but I refuse to grow up!
X3 on the gaskets. I had the same problem. I queried the crew here and they said the same thing. I thought they were full of s***. I replaced the intake/exhaust manifold gasket and wallah!. No more backfiring (popping) and it runs like my wifes vibrator. Smooth unless you bog it down.
- Thread starter
- #8
I just laughed and spit out coffee on my keyboard
I just laughed and spit out coffee on my keyboard
Classic!! I would have spit out my coffee had I been drinking some!!
No intent to hijack, I have a similar problem. Upon letting off the gas anywhere around 55 - 65 mph, (Freeway off ramp) I get a loud POW when I get slowed down to around 45, does it like clock work, every time. Dash vacuum gauge shows 25 - 26 in/hg.
So you're saying an exhaust leak will do that?
So you're saying an exhaust leak will do that?
I'm jumping on this thread. I'm popping on decel every time. I've re-gasketed the manifolds twice. On my third time with a new intake/ex manifold. The heat rise valve bushings in my old one were leaking (1982 FJ40). No more manifold leaks. I don't think I have any exhaust leaks aft of that. Still figuring easiest way to check exhaust leaks. Is it possible that adjusting the air/fuel adjustment on the carb a little would solve the issue? Raise the mixture? I notice if I give it a little gas as I decelerate the problem isn't really there anymore. Otherwise, next step is to adjust timing.
Adjusting the idle mix might help but I doubt it. The 100% solution is to reinstall the throttle positioner and the vsv that operates it because the job of the TP is to prevent the popping in the exhaust manifold. People often disconnect the TP or throw them away when they "desmog" an engine, but they do useful things other than reduce smog.
On an 82, the smog computer may actually cut off the idle fuel to prevent popping (and smog), but I don't know exactly when this was phased in.
On an 82, the smog computer may actually cut off the idle fuel to prevent popping (and smog), but I don't know exactly when this was phased in.
Cruiserdrew
On the way there
Just my take--Exhaust leaks do not produce the popping. Unburned fuel in the exhaust stream causes the popping (afterfire). Since air is being pumped in and excess fuel is present, it will ignite in the exhaust.
When I desmogged, I removed the air pump and the air rail. Plus, the throttle positioner is now only the "choke breaker". It makes for much more satisfactory carberator operation.
When I desmogged, I removed the air pump and the air rail. Plus, the throttle positioner is now only the "choke breaker". It makes for much more satisfactory carberator operation.
Would valves that need adjusted add to the problem?
Cruiserdrew
On the way there
I guess if they were way out and you were not closing the exhaust valve, it could, but then you would burn the valve in short order.
Doubt that's the problem though, as I had it with properly adjusted valves.
I guess the main reason I ask about this popping noise is when the truck does it the other drivers look at me with that "Did you just fart?" look on their faces....
ha!! thats funny!!
My rig did this as well ('69 FJ40). I had a leak at the donut, and my muffler as rotted out - been that way for years. I replaced the donut, muffler and tailpipe, and 95% of the backfire went away. It really sounds different when it runs and while driving now, having the exhaust come out of the tailpipe instead of everywhere in-between!
ABV on fender, too
Not only is there a check valve (I think that's what y'er talking about), but the ABV mounted on the fender could be going bad.
I had the wickedest backfire when my ABV went south. I'm talking about setting off car alarms coming off a highway exit and in between every shift. It was a really, reeeeeaaaalllly bad backfire. I put on the new ABV....fixed it. The PO put on a flowmaster with dual pipes out the back of it...these days, it'll pop a little, but not a "backfire" by anymeans.
Not only is there a check valve (I think that's what y'er talking about), but the ABV mounted on the fender could be going bad.
I had the wickedest backfire when my ABV went south. I'm talking about setting off car alarms coming off a highway exit and in between every shift. It was a really, reeeeeaaaalllly bad backfire. I put on the new ABV....fixed it. The PO put on a flowmaster with dual pipes out the back of it...these days, it'll pop a little, but not a "backfire" by anymeans.
I once had cops come up on me in a parkeing lot, guns drawn, in east san jose after i pulled over due to severe backfiring. People thought we were firing guns. It was due to a defective voltage regulator that killed the battery and in turn decreased the spark. I had a v8, headers and flowmasters. It was loud.
