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Exhaust leak on a 4.9

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Old 12-27-2017, 05:36 PM
bigyellerdawg1991
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Exhaust leak on a 4.9

Would this cause a moderate miss and a slight loss of power? While going thru my checklist of wtf could be causing my miss, I not only heard the exh leak this time, but I saw where it was coming out-#2/#3 cyl area. There was a slight hesitation when I goosed the butterfly, like the rpms dropped a 100 or 2 for a split second, then would catch itself and increase normally. But if I just eased into it, it wouldn't hesitate. Its also about 30-40 degrees colder out now compared to last time I drove the truck, and this diagnosis was done during initial startup. Would I be ok putting around 800 miles on her this weekend/next week without having to worry too much about something catastrophic happening with this exh leak?
 
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Old 12-28-2017, 01:08 PM
jason832
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An exhaust leak shouldnt do much. It'll make some noise, and possible crackle or pop from any unburnt fuel mixing with fresh air then burning in the exhaust pipe. If its a small leak drive it and fix it when you can.

A vacuum leak on the intake side however could cause cylinders to lean out and overheat parts and cause tuning issues.
 
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Old 12-28-2017, 01:15 PM
jason832
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if this is a carbureted motor the cold could be causing running issues when you snap on the gas. Carburetors have an accelerator pump that squirts extra fuel when you press the pedal down.

When you open the throttle the air can speed up faster than the fuel and the accelerator pump squirts the extra fuel in to compensate. A broken or mistuned accelerator pump, plus denser cold air can cause the air fuel ratio to lean out for a split second causing bogging or bad running when hitting the gas.
 
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Old 01-02-2018, 12:33 PM
arse_sidewards
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Originally Posted by jason832 View Post
An exhaust leak shouldnt do much. It'll make some noise, and possible crackle or pop from any unburnt fuel mixing with fresh air then burning in the exhaust pipe. If its a small leak drive it and fix it when you can.

A vacuum leak on the intake side however could cause cylinders to lean out and overheat parts and cause tuning issues.
The (non-MAF) EFI system is very good at handling vacuum leaks as long as they're relatively uniformly distributed. A single runner with a gasket that's just barely failed enough to suck air on the intake but not enough to feed air to the other cylinders will pose a problem.

A failing fuel injector can also cause a misfire.

Either way you have to pull the top half of the intake to get to the problem.
 
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Old 01-02-2018, 07:07 PM
jason832
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If the engine is an EFI one....

Classic example of the original poster needs to include more details.
 
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