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deville 4.9L
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Discussion Starter #1
hi guys,

i am trying to solve the riddle of poor mpg on my base 92 deville 4.9l. so i did the usual: clean throttle body, change air filter, change spark plugs HT leads etc.
i am getting E44 code lean mixture as well so i thought of checking for vacuum leak along with the testing the pump to see if it can pull 21HG as per the manual.
As i dont have a ramp i sent it to a garage who claim they could not find the vacuum pump on either side of the chassis body.

my question is does a base 92 deville come with a pump?

and if it does can the car operate normally without a pump or would i know such as failing brakes etc

thanks

al
 

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1985 Sedan DeVille
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1,883 Posts
I don't think it has one but if it did it would be behind the front left wheel apron. You would also be able to trace the large vacuum line on the brake booster down to it. If the brake booster line goes directly into the manifold then you don't have the booster.
 

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deville 4.9L
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9 Posts
Discussion Starter #4
ok guys many thanks so where does the vacuum source come from?

is it the manifold?

the small rubber hose between the FPR to the TB looks very worn but i cant work out if it is leaking and ac delco informed me that they dont sell them from.
any idea where i can by it from.

there is an even smaller rubber hose for the transaxle modulator can you tell me what that does please?

thanks al
 

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1985 Sedan DeVille
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ok guys many thanks so where does the vacuum source come from?
Four-stroke engines operate by (1) pull piston down to suck fuel and air into combustion chamber, (2) push piston up to compress the mixture, (3) ignite the mixture with spark to push piston down, and (4) push piston up to blow out the spent gasses.

Vacuum is created in the manifold when the piston pulls air and fuel into the combustion chamber. Put your hand over the throttle body and feel the air getting sucked in... that's the vacuum source.

The vacuum pressure is the manifold is also used to drive some accessories, such as HVAC vents, cruise control, power brakes, etc. Since the vacuum pressure in the manifold changes according to factors like RPM and throttle angle, some of the Cadillac models also have a supplemental vacuum pump that helps to keep pressure levels constant. With a good engine you don't need the extra pump, it's just extra weight, but it does help to prevent things like having the HVAC change from vent to defroster when you step on the gas up a hill. Weak vacuum can also make the brakes less responsive.

If you want to know your vacuum pressure, go down to autozone or wherever and buy a gauge and some plastic tee-fittings and unions. The gauge is about $15. Cut into one of the small vacuum lines and install the tee-fitting, then let the engine get warm. Good vacuum is 15-20 hg inches at warm idle, closer to 20 is better but you can also have too much.
 

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2010 DTS
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87,430 Posts
there is an even smaller rubber hose for the transaxle modulator can you tell me what that does please?
The Vacuum Modulator monitors engine vacuum by a rubber vacuum hose which is connected to the engine. Engine vacuum reacts very accurately to engine load with high vacuum produced when the engine is under light load and diminishing down to zero vacuum when the engine is under a heavy load. The modulator is attached to the outside of the transmission case and has a shaft which passes through the case and attaches to the throttle valve in the valve body. When an engine is under a light load or no load, high vacuum acts on the modulator which moves the throttle valve in one direction to allow the transmission to shift early and soft. As the engine load increases, vacuum is diminished which moves the valve in the other direction causing the transmission to shift later and more firmly.

http://www.familycar.com/transmission.htm
 

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deville 4.9L
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9 Posts
Discussion Starter #7
Dear Hall and ranger,

many thanks for all your advice it was very helpful. So if i do not have a vacuum leak what would be the reason be behind the poor mpg and the E44 fault code.
i have checked the TB, air filter changed spark plugs, ht leads etc etc.

Should i look at a poor ground behind the wheel arch and/or replace the fuel pressure regulator as well? thanks

al
 

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Super Moderator
2010 DTS
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87,430 Posts
Check the FPR. No need to replace it unless it is leaking gas from the nipple when you pull the vacuum hose (at idle).
 

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1985 Sedan DeVille
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The older throttle bodies tend to develop leaks around the butterfly hinge, might check there. Check gaskets too.
 
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