Is there a trick to removing the servo? I pulled my battery out, and undid the bolts in the battery tray (in the bottom and in the side) and I couldn't get the tray to come out.
You found those nuts 'n' bolts, but you missed the nut behind the wh... errr, the two nuts in front of the wheel (between the splash liner and the body). Then you have to disconnect the battery temp sensor and the servo connector.
Then the battery tray will come out right nicely.
I took mine apart today. Fixed a bunch of oddities. But still no joy.
While you have the battery tray out, you'll see a connector that has a bunch of black wires going into it. This is a 'ground tie'. It's worth undoing that and cleaning it. I didn't have much of a servo ground until I did (54K ohms is a very poor connection).
(Note: when checking for 'closed' circuit, the ideal is zero ohms. However, in practice, don't be dismayed if you see as much as 5 ohms; this is still pretty close to a short circuit. )
Use a DMM and check your various grounds (making sure the meter probes are well connected to the metal). If you see around 2-4 ohms or less, consider the ground OK. If it's hundreds or thousands of ohms, *something* needs cleaning. Ensure servo connector pin 4 is well connected to ground.
Next, with the brake switch disconnected, jumper its connector pin 4 to ground. Then check the resistance of servo connector pin 3 to ground. You should, again, see 2-4 ohms or so. If it's higher, or open, you have more checking to do.
Disconnect C134 (the large connector under the dash by the brakes). Pin 48 (for my '98, IIRC) on the loose connector goes to pin 4 of the brake switch connector. You should see a short circuit between these two pins. Pin 48 on the fixed connector goes to pin 3 on the servo connector. This, too, should be a short circuit.
Once I verified that the wiring was as it should be, I put it back together. Then the CC wouldn't turn on. @#*$&#! Checked servo pin 3: millivolts. Checked brake switch position: OK. So I loosened C-134 and snugged it back down a little less this time. Now the CC light turns on. OK. Time for a test drive. ... No joy. It doesn't work.
So, if the weather holds tomorrow, I'll take it all apart again and see if I can operate the servo manually. I'll apply 12V to pin 3, ground pin 4, then short the other pins in the right manner and see if the servo moves at all. I *think* the PCM just grounds these two pins to actuate the solenoids inside the servo (just as it grounds the intake heater solenoid controls to actuate them; this 'grounding' is another reason the PCM needs to have very solid grounds). I wish I had a small vacuum pump so I can hear what's happening. Hmmm. Maybe I can use a large vacuum pump: Dad's Town Car; it's got a quiet motor.
I do need to make sure the vacuum check valve is working. While the engine is running, the pump *should* be producing a constantly 'large' vacuum. But, at 9. 5 years, maybe it's getting tired, and the check valve is needed anyway.
And I didn't bother applying 12V to the servo's pin 3 to look for 12V on the other three pins (the Sadist's Manual's sole test for the servo)
Because the Sadist's Manual doesn't really describe the operation of the servo, here are my guesses. I think the 12V and ground pins set up the solenoids in a 'safe' mode: vacuum closed off, vent open to atmosphere; this way the servo cannot interfere with accelerator operation. When CC is engaged, the vent is closed off, and the vacuum is pulsed open to bring the accelerator to 'speed'. Once at speed, the vacuum is left closed again. When the vehicle slows, the vacuum is pulsed open again to bring it back to speed. All this while, the vent has been held shut. When the vehicle is moving too fast, the vacuum is left shut and the vent is pulsed open to let the accelerator decrease fueling. When the vehicle is back down to speed, the vent is held closed again.
If the servo doesn't seem to work, I'll just have to take it apart. It would seem the electronics are held in by a couple screws (rather than epoxy, plastiwelding or rivets).
Hmmm. This could make a really nice journeyman's throttle stick: flip a switch to power the servo and close the vent. Then tap the vacuum momentary-contact switch to increase RPM. Tap the vent momentary-contact (or momentary-break) switch to reduce RPM. Turn off the power to return the engine to idle. Add a simple controller that reads RPM from the CCD bus and you could have an RPM-based cruise control, a minimum idle speed control, or even a constant RPM stationary operation control. Just think: no more futzing around with the P-pump's hidden, hard-to-reach idle-speed adjuster: let the cruise control servo do it for you!
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