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Re: Cruise Control Malfunction
Posted by David Prantl (more from David Prantl) on Sat, 22 Jun 2002 17:31:45
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

>  Haynes manual says there are two types (vacuum actuated  and stepper 
>motor activated).

They couldn't spend the extra two minutes to find out that the stepper-motor 
type first appeared in the 9000 in model-year 1995...

The standard cruise system in a '93 is a vacuum-pump-based system, nearly 
identical to that found in all earlier 9000 cars and 900 cars going back as 
far as about 1985.

But even that isn't the whole story.  The majority of USA '91-'95 9000 turbo 
models came with an electronic throttle system (ETS), whereby the gas pedal 
talks to a computer brain which opens the throttle via an electric motor.  
This enables the traction control (TCS) feature.

So, if your '93 CS has a turbo engine with Traction Control, you do not have 
the vacuum type cruise system.  In fact, you have no cruise system at all !  
Cruise control functions are built into the ETS system.

>  Followed the single cable from the throttle cam on the intake  manifold 
>back through the false firewall.

The fact that you have a throttle cam means you don't have ETS, and you 
therefore have the vacuum cruise system.

A common problem with the vacuum system is old vacuum hoses drying up, 
cracking, and not sealing properly.  The resulting loss of vacuum means you 
lose the system's speed-holding and accelerating ability.  The vacuum pump 
that generates vacuum in the system is located in the right-hand part of the 
'aquarium' area - which is the compartment between the true firewall and the 
false firewall panel in the engine bay.  Remove the plastic panel at the top 
of the aquarium, and check the vacuum hose connection at the pump.  Better 
still, pull the hose off the pump and apply a vacuum to it.  If the rest of 
the system is fault-free, the throttle cam will open as you apply vacuum.  
Other common sources of vacuum leaks are the pedal switches.

>  Aside from the typical loose vacuum hoses and ill  positioned switches, 
>any other failure modes of note?

If the problem is not with vacuum, then it has to be electrical.  The pedal 
switches are dual-function vacuum/electrical switches.  The cruise ECU gets 
a signal fro the brake light switch, and must otherwise have proper positive 
and ground connections.  A wiring diagram an a volt/ohm meter would be in 
order.

Unfortunately, '92-'94 9000 cars (and '92-'93 900 cars) got a different 
cruise ECU (part number 41 08 650 for 9000, 41 08 643 for 900) that seems to 
have earned a reputation for being less reliable than the earlier versions, 
while adding ZERO functionality.  The earlier versions of the ECU can be 
retrofitted, but they use a different connector so it's not plug-and-play 
(wires must be cut and spliced - wiring diagrams are a must!).  FWIW, our 
'93 9000 is now equipped with an '88 ECU (95 26 757), which is working 
beautifully.

David Prantl
david_prantlno39sdcx6spamx782hotmail.com
'84 900S, 5M, 210kMi, RIP as of 2/98
'89 900, 3A, 116kMi, restored and SOLD on 3/24/01
'86 9000T, 5M, 200kMi
'88 9000S, 5M, 142kMi
'90 9000S, 4A, 141kMi
'93 9000CSET, 5M, 75kMi  -- FOR SALE in the TSN Classifieds --
'97 9000CSET, 5M, 60kMi
'68 97 Sonett V4, 4M, 76kMi, #000467

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