Hi all,

I have a 1990 e350 ambulance (box truck type) with the E40d. my vacuum pump went out so I have to drive it without a vacuum pump till I get a new one (a month)

in the meantime, i have installed a electric vacuum pump connected directly to the brakes to provide my vacuum. Does this truck need vacuum anywhere else? I dont know if this transmission needs it or not. this is only temp till i get a new pump. Thanks!

Mark

 

E4OD does not use vacuum (hint - what does the "E" stand for.... ). HVAC controls are the only other thing that use vacuum.

 

There are more.

If that ambulance has the rear AC, then the rear heater core shut off valve uses vac. As you said, the climate control selector uses vac. There are handful of other things that use vacuum depending on what options you have.

Instead of connecting it just to the brakes, why not connect your e vacuum pump to the vacuum hub? Or did your mechanical vac pump go out because of a leak somewhere?

You might want to stick with the e-pump. I know guys that use the e-pumps for hyper miling, since you can kill the motor and still have vacuum to have the brake assist. One less belt to steal mpg and hp.

 

Isn't that part of the HVAC?...

I was wondering if an electric pump could handle all that. Then again, the brake boost is the biggest "draw", so if he found an e-pump that can run the booster, it should be able to handle the rest. Another option (project) - hydroboost for the brakes, e-vacuum for "the rest" (that could be a pretty small pump).

 

Ok guys, ty for the reply. the e-pump came from a drag car that is used to power master cylinders when you have no vacuum so I assume it has the power to run all the things. Iam just doing it temp till i get money for a pump. The motor puts out a constant vacuum, where I assume the manual pump would be variable to the engine speed. would that make a difference in other things like the rear heater core valve? hopefully ill get one by the time it gets cold.

mark

 

The belt-driven pump must have some sort of limiter in it, because it pulls about the same vacuum revved up as it does at idle. Nothing that's vacuum-driven requires "variable" vacuum anyway. As said, the electric pump may be a good permanent solution; one less belt-driven thing to fail.

 

Regardless, If your mech vacuum pump went bad, you might want to do a full system check to see if there are any leaks. If there was a leak, it could have put some strain on your pump. that could affect your new pump and shorten its life.

The heater core valve is only if you have rear heat and AC. When you are not running the AC, then the valve stays open, allowing hot coolant to the rear. The valve is located on the underside of the engine bay roof. Let me find a pic.



www.nickpisca.com/hypermax.htm


Engine rpms don't affect the performance of a vac pump. I've installed a replacement vac pump before, and I went mechanical. but if I had to do it all over again, I'd lose the belt and install an e-pump.

 

well, i dont know if the electric vacuum pump was designed to run constantly I guess Ill hook it to the main vacuum block and see how well it does. It does have a high idler computer that uses vacuum too , it will put the engine in a high idle when battery amps and volts drop when its in park to speed the alternator up. ty for all the replies!
mark

 

Get a vacuum switch to control it, and hook it up with a reservoir -- You can use the stock one(looks like a coffee can), but make sure of how you hook it up -- it has a check-valve in the incoming side, so it won't drain down if your mech vacuum pump stops.

As far as vacuum usage, the brakes are the main usage by far, then comes the cruise control(and all of the cruise servos I've found leak slowly, even when off). The HVAC actuators are a /tiny/ draw, and only draw vacuum while moving(i.e. when you move the lever).

You can pick up a mini vacuum pump which will run the HVAC off a newer truck -- I got one at the JY from a ~2000 F350 diesel, and in my case it is enough to run the cruise as well(I've added a small reservoir for it too -- 3" piece of 1" pipe with caps on both ends and a nipple threaded in one end -- just a little can), though the cruise comes on a little sluggish as it has to pump the vacuum.
The pump in those trucks also has a vacuum switch built in, so it only runs when the vacuum level drops below a preset amount. If you need a bigger pump, you might try using just such a small pump simply for the vacuum switch -- I found it cheaper than a standalone vacuum switch -- by just putting the motor leads in series with your relay coil(enough current to drive the relay will flow through the motor without turning it, and when the pressure switch turns off, your relay will turn off).

 

Ok ty for the picture of it. thanks guys for all the ideas, I will indeed rig it to the vacuum cannister and get a vacuum switch to control it automatically. Can somewon link me to a type of vacuum switch they would use? Id appreciate it. I dont have much experiance in this department. I kinda changed my mind and will hold off replacing the mechanical pump since this will work, and I like the fact that I will have power brakes even if the motor shuts down. thanks all
Mark

 

The vacuum pump self-limits by the design of the diaphragm, at a certain point it just flexes instead of displacing air and that's the maximum vacuum.

 

Would I have a leak if I loose all vacuum completely as soon as I shut off my key in my club wagon?


It's never had strong vacuum, if I pump the brakes more than twice, it starts getting hard.

My cruise doesn't work, i've always wondered if my leak was a busted diaphragm inside the cruise control... taughts?


I've checked all the hoses real quick, the ones I can see, and they all look good.

 

John, sounds like either a leak or the pump is barely working.

Try testing the pump by itself and see how much it sucks...