(The cruise is fixed. What a nightmare!) -- Jim
March 25, 2006 Removed the test contacts in the amplifier and put it back in its case. Put together the bench vacuum pump again now that its glue has had a chance to dry. When stuffed inside its foam 'football' it's really quite quiet. It ought to come in very handy from time to time, and it's nice to finally have a use for that wretched pump I got stuck with. March 26, 2006 Reinstalled the cruise amplifier. Installed the auxiliary fan support brackets. No auxiliary fan, but this is the best place to store the brackets! Glued torn right-side door weatherstrip. Checked brown and green vacuum lines (again) for leaks, nothing. I don't know what to think. While driving it today it seems to me that the throttle pedal gyrations (which you can feel with your foot if you try) must be abnormal, and reflect an excessive consumption of vacuum by the actuator. But _why_ does it do this? It doesn't on the bench. I thought I'd better cover some bases, something I believe to be true is not. So I tried a different stalk switch. A long shot, but in theory it is possible for a contact that doesn't open-circuit all the way to disrupt the amplifier. No dice, the car drove the same. Maybe I need to swap actuators too to be sure of it. I also started the resoldering process on the two dead amplifiers I have in the box. If I can get them to work on the bench I'll try them both in the car to see what happens. ...Got one running well on the bench and took it for a drive. Exactly the same results. Definitely pointing away from the amplifier. The other spare amplifier, after resoldering, goes into immediate deceleration. Probing reveals a climbing FET output voltage, for no apparent cause. Looks like a leaky FET, probably gate punch-through damage induced during the resoldering resulting in leakage from the Drain. Be careful with those! This exercise leaves me with two spare vacuum amplifiers that seem to work, one from before and the one I just fixed. That's enough! March 27, 2006 Removed the cruise actuator and brought it in to the bench. Seems to act exactly like the one I use for testing. No abnormal appetite for vacuum in other words. Removed vacuum pump. What a PITA! Disassembling it I find no torn diaphragms, and the valves work. There was oil in one of the valves, the intake, but I suspect that this car had an oil leak into the vacuum system at a prior date that was not completely cleaned out. I suppose it could be that the puddled oil was preventing the valve from working fully? Let us hope. The cam and bearing are perfect. The rubber bits all look good. Reassembling the pump looks to be even harder than disassembling it. I put the valve cover back together and sucking and blowing on the two ports results in good behavior. No backwards leaking that I can detect. The pump requires 1" of preload on the main spring for reassembly, I used a block of wood on the floor as a spacer while standing on the pump. Awkward, but do-able. The reassembled pump went back on the engine easily enough and 'squawked' as it pumped when the engine was turned by hand. Sounded normal enough. With the engine started the brake booster pumped down in a normal amount of time. Went for a test drive. Same. Crap. That was the last major piece to look at and it looks good. Y'know, as I mentioned before when weird things happen that you can't explain then something you believe to be true is not, one of your basic assumptions is wrong. So I started a round of divide-and-conquer diagnosis. First I unhooked the brake booster and used duct tape to secure the vacuum check valve (which feeds the reservoir/doors/cruise systems) to its end, taped shut the usual tap for the accessories, and went for a drive. Perfect cruise operation, other than the lack of power brakes! The vacuum level never dropped much at all. The pump has got plenty of 'oomph'. I then hooked up all the vacuum taps to this point and tried again. Still good. I then taped off the brake fitting and moved the check valve to the usual tap, though bypassing the splitter and much of the hose and tried again. Better than usual, but not good. So that eliminates the brake booster as a leak (not that I suspected it but we are in full science mode now). At least this lets me hook up the power brakes again! I then removed the usual vacuum hose from the tap and used a section of 1/4" fuel line as a vacuum tap. This fits over a stepped portion of the body of the vacuum fitting, and should eliminate any chance of restrictions in the usual hosing causing problems. The check valve was taped into the end of the fuel line. Still not good. That leaves the vacuum tap as the only remaining potential culprit. I removed the brake vacuum line from the car and heated the plastic tap fitting with a heat gun and drove a nail down it to stretch it out. I couldn't get it in all the way. With it stretched a bit I then ran a drill down it to finish opening it up. Then I blew out the shavings and put it back on the car, using the fuel line tap system. I used a section of cruise actuator bleed line (extra large) as the thing to go between the fuel line and the 4-way splitter. Duct tape was used to seal it all up as an extra precaution. Success! On a test drive the cruise worked well, and the vacuum gauge never fell very far. Either something was caught in this vacuum tap, it was defective all along, or somebody replaced this tap (or the entire line) with one that was for a non-cruise-control car. As a bonus, when the car is shut off it shuts off much faster now, more like every other diesel we have. Something was definitely wrong, and I wasted a _lot_ of time chasing what turned out to be a very simple problem.
