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Old 01-24-2015, 05:54 PM   #1
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Default Vacuum lines connected to ignition?

Does anyone know if there's any ignition or fuel delivery components that run on vacuum? My 97 4.6 is hesitating under load which is when there's low vacuum in the intake, wondering if I have a leaky line somewhere.
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Old 01-24-2015, 08:37 PM   #2
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Does anyone know if there's any ignition or fuel delivery components that run on vacuum? My 97 4.6 is hesitating under load which is when there's low vacuum in the intake, wondering if I have a leaky line somewhere.
Fuel delivery comes via fuel pump. Ignition would be DC current.

Vacuum , = intake/PCM/solenoid.

Vacumm leaks usually cause high idle issues with automobiles

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Yea, just post the problem someone will help you with the right path troubleshooting. You say under load. Well which load and where ? Describe the load if you want specific info.
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Old 01-24-2015, 09:50 PM   #3
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Jbrew, by "under load", I'm referring to when I'm at a lower (<1500ish rpm) and hitting the gas. Thus creating a low vacuum. Also when I'm taking off from a stop, (manual transmission) unless I rev up considerably, it shakes until up to speed, almost as if I have a bad pinion bearing or oil on the clutch, which neither are the case here.
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Old 01-24-2015, 09:53 PM   #4
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I know the supply of fuel and spark are other methods but are they maybe controlled by vacuum? Such as maybe when there's high vacuum it would tell the fuel to decrease pressure or spark to retard, and vice versa? Just a theory.
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Old 01-24-2015, 09:55 PM   #5
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I know the supply of fuel and spark are other methods but are they maybe controlled by vacuum? Such as maybe when there's high vacuum it would tell the fuel to decrease pressure or spark to retard, and vice versa? Just a theory.
vacuum controls the pressure regulator
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Old 01-24-2015, 10:01 PM   #6
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Does anyone know if there's any ignition or fuel delivery components that run on vacuum? My 97 4.6 is hesitating under load which is when there's low vacuum in the intake, wondering if I have a leaky line somewhere.
I am dealing with this exact same issue. I've tried to diligently troubleshoot but have ended up replacing a lot of stuff. Plugs, wires, ignition coil packs etc.
I set up a fuel pressure gauge and monitored it through a drive.
I've started to believe it's a TC shudder instead of a engine hesitation. With no codes I'm kinda at my wits end. Gonna remove all the injectors and check their flow pattern. If that's good I'm guessing it's the TC.
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Old 01-24-2015, 10:38 PM   #7
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vacuum controls the pressure regulator
Perhaps that's what he means? No carbs on these trucks. These systems aren't return-less.
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Old 01-24-2015, 10:40 PM   #8
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Jbrew, by "under load", I'm referring to when I'm at a lower (<1500ish rpm) and hitting the gas. Thus creating a low vacuum. Also when I'm taking off from a stop, (manual transmission) unless I rev up considerably, it shakes until up to speed, almost as if I have a bad pinion bearing or oil on the clutch, which neither are the case here.
Well, I guess it's in gear then correct ? What shakes exactly ?
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Old 01-24-2015, 10:52 PM   #9
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The engine shakes which in turn shakes the transmission and the shifter, you can even hear it, sounds like a single cylinder misfire. No codes being thrown.
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Old 01-24-2015, 10:54 PM   #10
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I too have replaced plugs and wires, fuel and air filter, all with no relief other than running smoother when it's not shuttering.
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