Vacuum question
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Posting Guru
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Vacuum question
My trucks been having all the signs of a bad vacuum pump, the brake are okay at the first touch but get hard if i hit them twice, such as coming up on a red, to stop you have to stand on the brakes, and the cruise control is out. I just replaced the brake booster but to make sure it wasnt bad i hooked up my vacuum guage to it. It holds steady at 22HG at idle. When I increase RPMS it goes up to about 24-25HG. But when I floor it, shouldnt the vacuum go to 0-2?
Posting Guru
Joined: Dec 2005
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From: Peterborough, Ontario
I can never tell vacuum numbers. Do your defrost/vent selector controls work? If you take the main line off the vacuum pump, does it suck your finger hard against it, or so-so?
Cruise on the earlier 7.3's worked with vacuum, later it switched to electronic.
Cruise on the earlier 7.3's worked with vacuum, later it switched to electronic.
Logistics Pro
Joined: Dec 2005
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From: Moro Bay, AR
No. Throttle position has no effect on vacuum on a diesel engine. There is no connection between the vacuum pump and the throttle.
i ain't rite
Joined: Mar 2005
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From: Marlboro Mental Hospital.
you need to have the vacuum gauge in line, and step on the brakes twice. see how long it takes for it to draw back down to 22 inches. if it draws down almost instantly, the pump is good. but i bet it takes a while to draw back down.
Elder User
Joined: Mar 2004
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From: El Dorado Co., CA.
I'm having some issues too. my brake light is coming on during my afternoon commute home. With the light, i get a firm pedal. It's not as firm as when i lost my vacuum pump belt (that was a scary drive), but firm nonetheless. I just bought a vacuum test kit/brake bleeder and i'm going to test in the morning. Since i'm not having the trouble in the morning, i'm thinking a vacuum line may be colapsing in the heat. (I live near Sacramento and it's been warm). According to what i've read, the BRAKE light on our diesels come on when low vacuum is detected. The strange thing is my rear anti-lock light comes on too. I'll let you guys know what I find.
Posting Guru
Joined: Dec 2005
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From: Peterborough, Ontario
Actually the brake light in these trucks comes on for several reasons. Low vacuum sometimes, low fluid, the proportioning valve and a couple more iirc. (I think 4 or maybe 5 things can trigger it?)
Elder User
Joined: Mar 2004
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From: El Dorado Co., CA.
You're right. I'm going to start with the easy troubleshooting and then move on the hard stuff.
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Posting Guru
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First thing tomorrow im going to go pick up a vacuum pump testor. 30 bucks at Oriellys. Ill post back and let you know the final verdict. Im 99% sure its the VP but I'd rather know for sure.
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Elder User
Joined: Mar 2004
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From: El Dorado Co., CA.
If it is your vacuum pump, they have them on rockauto.com for about 79 bucks. i've had good luck with that site and have saved a lot of money. They ship pretty fast. good luck. i'm off to check mine too!
Posting Guru
Joined: Feb 2011
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From: Princeton MN
Push the brake pedal a few times at idle and see if the light comes on, my pump is a few years old now but I never run out of vaccum no matter how much I use the brakes(within reason)
Elder User
Joined: Mar 2004
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From: El Dorado Co., CA.
I'm off to a bar-b -que and will re-test tomorrow and report back.
Lead Driver
Joined: Apr 2008
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i have the same issue here, i just assume its the pump, i dont have a leak, i can shut it off for 3 hours go out and still have lots of vacuum. But, if i hit the brakes twice, same issue, good the first time, hard the 2nd.
Logistics Pro
Joined: Sep 2010
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From: Victor, MT
Wierd, I always get good stopping now matter how much i stand on the brakes (tested and proven, lost trailer brakes going DOWN a pass with 2 horses in the back, damn thing came unplugged) I always have bad luck OUT on the road, never in-town or in the driveway. That and I had brand new brakes when I bought my truck. That can be scary haha, trust me on that. I get a little nervous letting it go downhill with good brakes, I was REALLY REALLY nervous going down that hill haha....