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4.6K views 11 replies 8 participants last post by  Zach_cdr  
Z
#1 ·
So I posted this on Central a week ago and haven't had a single reply. It's in regards to a few steps that an admin lists off after buying a classic 900

4. You investigate or/and replace all vacuum-hoses, regardless of what the PO says.
5. You test/replace the bypass-valve, regardless of what the PO says.
6. You unplug the connector on top of the APC-solenoid (located above the radiator, with three large vacuum-hoses going out of it, and a connector on top), to check the base-boost. Drive the car warm, find an inclining road, go into third and floor it. Note the boost on the CALIBRATED boost-gauge, and adjust to 6 psi or 0.45 bar. Shorten the actuator rod for higher boost, lengthen it for lower boost.

YEEE I just purchased my first 900! She's a '92 turbo vert with 130k miles and body/top are in excellent condition, interior is in almost as excellent condition. The car has been garaged nearly its entire life and has always had full synthetic oil changes (according to the nice gentleman I purchased the car from). After inspecting and changing oil and overall engine bay quality, I'd assume this is a true statement.

Now for the questions! Where's the best place to buy new vacuum-hoses? On a side note to the hoses, I've been reading that a key component in the cruise control not working is a damaged vacuum-hose. Which one would this be? Most the the hoses appear to be in great shape.

In regards to question 5, what/where is this? How do I test?

Step 6... I am lost =[

(I hope I can get a little bit of help with this... thanks guys)
 
#2 · (Edited)
Are you having any driveability issues other than the cruise not working?

Sometimes screwing with things that aren't related to any specific problem on these cars is just inviting trouble. To test or replace the bypass valve you have to disconnect a lot of components. In doing that, there's a bit of wrestling/manhandling of nearby parts involved. Inevitably, fixing a non-problematic bypass will likely cause problems with these nearby parts--coolant bypass hoses, throttle body nipples, etc.

To answer your question, the bypass valve is connected to the rubber nipple right at the intake on the turbo compressor. It is snugged up against the motor, has a vacuum line going to it from the manifold, and is below the little "I'm old, touch me and you'll puncture me" coolant bypass hose at the forward end of the cylinder head.

#6. Again, I'd only check base boost if you are having a low-boost situation that you are trying to diagnose. Otherwise, just drive the sum-bitch.
 
#4 ·
We have 6 c900s and I think only one has working cruise control. I think it's more uncommon that a c900 has working cruise than not. I never use it so I've never tried to fix it. Someone else will have to chime in on that.

The cruise control pump is mounted on the driver's side fender toward the front. It's a black cylinder and has a little red cap on it. There are vacuum lines that connect to it. That's about all I can say about it. Obviously there are other components in the system that could fail (switch at the brake pedal, servo, etc.)

If you don't have it yet, pick up the Bentley 1979-1993 16-valve service manual. That is the best resource for the DIYer or someone who just wants to know what's up with the mechanicals on these cars. Plenty of illustrations and photos, wiring diagrams, diagnostics...
 
#9 ·
On the Cruise control - There are a lot of vacuum hoses in the dash as well, You might want to check there. I had a terrible boost leak and all the hoses seemed to be fine, and all of them held pressure and vacuum( as much as I could impart), but the only thing that fixed it was changing them out.

I could be wrong on this one, but There is a rubber diaphragm in the foot well of the drivers side that is up around the mounting points for the pedals. If that has a tear or hole, i don't think your cruise will work.
 
#11 ·
When i bought my red LPT the cruise did not work, in my case it was a faulty speed sensor (not sure about the correct name of this part?). It is mounted on the rear of the speedometer with two small PH/PZ screws. The sensor i connected to the cars wiring loom using a 3-pin connector in black plastic on newer models, MY1988 and newer. 1987 and earlier models is using a 2-pin connector in blue plastic.

This site helped me alot!
 
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