No Subject

[Alan Cordeiro <cordeiro@avlna.com>]

>>From: "Al Powell" <APOWELL@agcom.tamu.edu>
>Date: Mon, 23 Sep 1996 09:13:24 CDT
>Subject: Cruise No Workum
>
>Still fiddling with the cruise on my 1990 200.  I tracked the vacuum 
>lines fron the brake pedal switch, and discovered there IS a vacuum 
>pump inside the left front fender, just behind the radiator overflow 
>tank.  Interestingly enough. that was where a vacuum leak was.  
>

Yes, there is SUPPOSED to be a leak, that's how the throttle position
is controlled.

The vacuum pump comes on whenever the cruise is "activated" ie
on AND supposed to be controlling the throttle. If you touch
the brake or clutch, it switches off till you "resume"....

Since the vacuum pump has two modes, ON and OFF, something needs to
bleed in some air to keep the vacuum from going to "full", from
what I saw, about 8-10 psi of vacuum. Hence your "air leak".

>Has anyone played with the vacuum pump?

Yes,

>There is a large open port next to the vacuum hose coming in - which 
>allows air to exit when you blow in, but holds when you pull vacuum 
>against it.  I assume that it's an overpressure valve.  But next to 
>it is a small port - which has a small hose going to the other side 
>of the vacuum pump - where it connects to another small port.  Go 
>figure.  Next to the destination for this small hose was ANOTHER open 
>port - and it leaked vacuum when I sucked on the hose from the cruise 
>actuator end...so I capped it.  I figured it might have had a rubber cap 
>which fell off.  Thought plugging that leak might ffix the problem.
>
>But still, I have no cruise!.  And the Bentley has NO troubleshooting 
>section for the cruise control, AT ALL.  Frankly, this is all too typical of 
>the Bentley.  I know, it's the best we have, but sometimes it has 
>GLARING omissions.  Hmmph.

Use the Bentley manual, and do the following,

1) Check the pin that has power when you turn the cruise ON, does it
   come on when you switch the cruise on.

2) Feed a +12 to the line that goes out to the vacuum pump, or perhaps
   there is a ground you need to connect to ground to turn it on, I don't
   remember exactly. See if the pump works.

3) Now block off the air bleed inlet. You should see the throttle go to
   FULL. If it doesn't, you have a leak in the system ( brake, clutch
   pedals, perhaps a pipe somewhere, even the actuator diagraphm ).

4) There is a signal from the back of the instrument panel that feeds
   pulses to the cruise to tell it what speed the car is doing. You
   can actually see this signal on a "logic probe" or even on a sensitive
   analog meter. Drive at 5 MPH, and you will see pulses.

5) If everything above works, it may be your cruise computer .....


Good luck,

Alan