Need some help tracking down a vacuum leak in my truck


Tman5293

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I have a 2004 B2300 that is experiencing vacuum loss on acceleration. Symptoms include the blower direction changing from dash vents to defrost when I accelerate indicating no vacuum pressure and a high/rough idle. The engine idles anywhere from 900-1100rpm but usually sits just below 1000rpm.

I have checked the ball shaped vacuum reservoir that is bolted to the passenger frame rail beneath the air box and found that it holds vacuum pressure using a vacuum gauge. From what I can tell, both of the lines that run to the resovoir, one from the intake manifold and the other into the firewall, are intact. I'm not sure what else or where else to check for this. If someone could steer me in the right direction that would be awesome.

If anyone has access to an accurate vacuum system diagram for the 2.3L DOHC motor that would be extremely helpful. I can't seem to find a decent one.
 


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Dirtman

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I have the diagram, will scan it from my workshop manual whe I get home. HOWEVER, there is no vacuum on acceleration. Vacuum drops to almost nothing on acceleration. Totally normal. Which is why the reservoir ball exists. It stores vaccum so you can still change vent position when the engine is running with no vacuum. Default setting is defrost when theres no vacuum which is is why it goes to defrost.

Normal idle for the duratec is 860 when warm around 1,200 when first started. There is a vacuum check valve in the ball which if not working properly bleeds off vacuum during acceleration and then you loose vent control (goes to defrost).

My guess is the vacuum leak is inside the cab at the splitter or one of the actuators.
 

Tman5293

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I have the diagram, will scan it from my workshop manual whe I get home. HOWEVER, there is no vacuum on acceleration. Vacuum drops to almost nothing on acceleration. Totally normal. Which is why the reservoir ball exists. It stores vaccum so you can still change vent position when the engine is running with no vacuum. Default setting is defrost when theres no vacuum which is is why it goes to defrost.

Normal idle for the duratec is 860 when warm around 1,200 when first started. There is a vacuum check valve in the ball which if not working properly bleeds off vacuum during acceleration and then you loose vent control (goes to defrost).

My guess is the vacuum leak is inside the cab at the splitter or one of the actuators.
That makes sense. So if I'm losing vacuum on acceleration when there is no vacuum could that indicate an issue with the resovoir? Another piece of information that I feel I should add is that if I turn the ignition to ON without starting the engine, air will only blow out of the defrost vents. I can't change the direction at all.
 

ericbphoto

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That makes sense. So if I'm losing vacuum on acceleration when there is no vacuum could that indicate an issue with the resovoir? Another piece of information that I feel I should add is that if I turn the ignition to ON without starting the engine, air will only blow out of the defrost vents. I can't change the direction at all.
If the engine is not running, there is no vacuum. Therefore, default flow to defrost.

You either have a leak somewhere in the lines or actuators for the HVAC system or the check valve in the reservoir is bad. I would suspect a leak somewhere. It's a common problem.
 

Dirtman

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if I turn the ignition to ON without starting the engine, air will only blow out of the defrost vents. I can't change the direction at all.
Yes because you have zero vacuum power to the actuators. The system spring loads back to defrost with no vacuum and wont allow any change without vacuum power. If the ball isn't broken the leak is in the cab.
 

Tman5293

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If the engine is not running, there is no vacuum. Therefore, default flow to defrost.

You either have a leak somewhere in the lines or actuators for the HVAC system or the check valve in the reservoir is bad. I would suspect a leak somewhere. It's a common problem.
Yes because you have zero vacuum power to the actuators. The system spring loads back to defrost with no vacuum and wont allow any change without vacuum power. If the ball isn't broken the leak is in the cab.
Okay so I ordered a new resovoir ball. Going to change that out when it comes in and see what happens. If that doesn't resolve the issue, what exactly should I be checking for under the dash/behind the glove box?
 

ericbphoto

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Leaky vacuum hoses/broken fittings.
 

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You can use a piece of rubber vacuum hose to listen for the leak. stick one end in your ear and go over vacuum lines one at a time and listen for a hissing sound. For this you will need to have the truck running because you need to have vacuum to hear the hiss. Surprisingly it is fairly easy to hear it with the hose and is why I am suggesting trying this to find it. Yes you will still need to tear into the dash to access the hoses but it will help you find it if there is no obviously broken hard hoses.


Don't worry everyone looks odd with a hose coming out of their ear....
 

Bird76Mojo

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There are TONS of versions of these DIY smoke machines you can make for less than $20 to find vacuum leaks..

 

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might have a failed check valve or missing check valve....or...backwards check valve......


or bad brake switch valvinator thing...or something.
 


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