# What part of a car is a vacuum pump? **URL:** \ **Category:** Factual Questions\ **Created:** [August 5, 2011, 12:09pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580 "2011-08-05T12:09:31Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [August 6, 2011, 5:04pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/21 "2011-08-06T17:04:29Z")
I have nothing to add to the discussion about rocker covers and vacuum devices, but why did you need to have your AC recharged? Air conditioning is a “closed” system. Unless you have a leak, it shouldn’t need recharging. Hopefully, you had it checked for leaks before paying for that service. Also, car air conditioning doesn’t work all that well in many vehicles when it gets up into the 80s or 90s outside. It is often undersized and cars are poorly insulated. I thought the AC in my Saturn Vue had developed a leak, but found out it was just a piece of shit at higher temps. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 6, 2011, 5:26pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/22 "2011-08-06T17:26:45Z")
Even the best AC systems will outgass a bit over time. With new systems that use a critical charge the loss of a few ounces over a year or two can dramatically effect AC performance. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 6, 2011, 5:47pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/23 "2011-08-06T17:47:18Z")
> [@Rick](#): > > On large trucks which use air pressure not vacuum there are warning horns and a gauge for air pressure in the event of a problem. > On vacuum boost systems I have never seen any type of warning for low vacuum as vacuum is such a variable parameter. Typical readings for a non VVT /vanos engine at sea level might be 17" idle, 21" cruise and 0" at WOT. Where do you set the warning? Everywhere from 0-21 is normal. Abnormal is 0 and that is in the normal range. > It for sure won’t trip a check engine light as only items that effect emissions do that. A dead vacuum pump has no effect on emissions. I have a F-350 with a Powerstroke diesel engine. The warning indicator that the vacuum pump is broken is: no brakes. (Actually, you get one actuation, and then you need to use two feet to stop after that). ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [August 6, 2011, 6:17pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/24 "2011-08-06T18:17:50Z")
> [@electronbee](#): > > However, I am absolutely sure, that with a car with ABS, will have a vacuum pressure sensor in order to maintain the proper vacuum. I’m sorry to say that is simply not true. I’ve worked on hundreds of cars with ABS and none of them have such a sensor. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [August 6, 2011, 6:34pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/25 "2011-08-06T18:34:45Z")
> [@Throatwarbler\_Mangrove](#): > > I don’t know any specifics about your vehicle or whether you need a new one or not, but many BMWs have vacuum pumps because they don’t have conventional throttles. > > [Valvetronic - Wikipedia](http://en.wikipedia.org/wiki/Valvetronic) I just came in to say this. Valvetronic (and Fiat’s MultiAir) use variable valve lift as the throttle, and thus have no manifold vacuum. older light-duty diesel vehicles could have a vacuum pump to run the brake booster, others had hydroboost (hydraulic brake booster fed by the power steering pump.) ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 6, 2011, 6:35pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/26 "2011-08-06T18:35:25Z")
> [@Gary\_T](#): > > I’m sorry to say that is simply not true. I’ve worked on hundreds of cars with ABS and none of them have such a sensor. I’ll see your hundreds and raise you to thousands. 😃 **beowulff** yup you nailed it. If you think you vac pump is failing on a diesel I would suggest a large anchor and 50 feet of stout chain as an emergency brake. ---
**Author:** ![pullin](https://avatars.discourse-cdn.com/v4/letter/p/c57346/32.png) [@pullin](https://boards.straightdope.com/u/pullin)\ **Post date:** [August 6, 2011, 10:03pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/27 "2011-08-06T22:03:22Z")
> [@beowulff](#): > > I have a F-350 with a Powerstroke diesel engine. > The warning indicator that the vacuum pump is broken is: no brakes. > > (Actually, you get one actuation, and then you need to use two feet to stop after that). My Diesel F250 had a vacuum pump. Is that normal for diesels? If so, why do they need vacuum pumps when gas engines normally don’t? (sorry for the hijack, but I’ve been curious about this) ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 6, 2011, 10:11pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/28 "2011-08-06T22:11:12Z")
> [@pullin](#): > > My Diesel F250 had a vacuum pump. Is that normal for diesels? If so, why do they need vacuum pumps when gas engines normally don’t? > > (sorry for the hijack, but I’ve been curious about this) Because Diesels have no throttle plate - they always ingest as much air as possible, and simply vary the amount of fuel injected. This is as opposed to gasoline engines which try to maintain the “prefect” fuel/air ratio at all times. Because there’s no throttle restriction, there’s no significant engine vacuum developed. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 6, 2011, 10:11pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/29 "2011-08-06T22:11:25Z")
> [@pullin](#): > > My Diesel F250 had a vacuum pump. Is that normal for diesels? If so, why do they need vacuum pumps when gas engines normally don’t? > > (sorry for the hijack, but I’ve been curious about this) No throttle plate on a diesel, they control engine speed by injection. Gasoline engines (mostly) have a throttle plate and the engine sucks more than the throttle will allow, causing the intake manifold to be in a vacuum. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [August 6, 2011, 11:14pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/30 "2011-08-06T23:14:09Z")
some modern diesels do have a butterfly valve in the intake, but it’s not a throttle. it’s there to improve EGR ingestion. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [August 6, 2011, 11:16pm UTC](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580/31 "2011-08-06T23:16:10Z")
> [@pullin](#): > > My Diesel F250 had a vacuum pump. Is that normal for diesels? ) it is if they have vacuum operated accessories. if not, they generally don’t have one. My '84 F-250 with the Navistar 6.9 liter engine had a vacuum pump for the primary purpose of supplying the brake booster. The '00 Ram 2500 CTD that replaced it didn’t have a vacuum pump, and had a hydraulic brake booster instead. [Previous page](https://boards.straightdope.com/t/what-part-of-a-car-is-a-vacuum-pump/591580.md?page=1)