Vacuum pump for cruise control? FIXED, lesson learned

[Barry Babcock]

Thanks all for the help in troubleshooting this--

It seems I had a bit of a procedural error in my testing-- the vacuum 
pump has a short bypass hose that prevents the pump from generating 
vacuum unless an internal relay in the pump housing is energized.  
That's why none of my pumps were moving the linkage at all when they 
were running.  I think all of the vacuum pumps I acquired probably 
function adequately.

When I ran +12v to that relay, the servo pulled the throttle body 
linkage all the way back, as it should.

The problem, as it turns out, was the column switch.  I replaced mine 
with one out of a junker, and that seems to have done the trick...

Anybody need a working cruise vacuum pump?  Cheap!

Whelp.... on to the next inoperative item, trying to find out why my car 
never goes into closed-loop operation.  Never ends, does it?

-Barry

-PS Thanks also to Tony for offering to check the amount of vacuum 
required to operate the servo.  I'd have told you directly, but your 
mail server has my ISP blacklisted.


Huw Powell wrote:

>
>
>
>> Still trying to fix the ailing cruise control on my 87 5kcstq.  Tony 
>> Hoffman suggested that my vacuum pump might be weak, because it won't 
>> pull the throttle body linkage all the way open--  This sounded like 
>> a very reasonable suggestion, so I tested it. (thanks Tony).  The 
>> linkage will open all the way using a hand pump- it takes between 5 
>> and 6 in Hg to pull it all the way open (Is this right?).  The servo 
>> isn't leaking, I let it sit with the linkage retracted for quite 
>> awhile and it held the vacuum just fine.
>>
>> I'm using a new, leak free vacuum hose for all these tests.
>>
>> I went to a junkyard this afternoon and pulled two other vacuum pumps 
>> from wrecked 5000's, one turbo and one nonturbo (part number is the 
>> same it appears).  NEITHER of these pumps was able to do any better 
>> than the one that was previously in the car.  Maybe I just got two 
>> other bad ones, but I did the "run soapy water through the pump" 
>> trick and got the same results.
>> The sides of the servo "suck in" but the linkage doesn't move.  I 
>> don't think it's a sticky valve-- if I compress the servo with my 
>> fingers, then release it, the spring will pull the linkage closed 
>> even with the vacuum pump running.
>>
>> Do these little vacuum pumps fail with alarming regularity like that? 
>> Were they not up to the job to begin with?  They don't suck, and yet 
>> at the same time it appears that they do suck very much.
>
>
> When I was rebuilding the cruise on  my coupe to eliminate all its 
> little quirks, I dug about 7 pumps out of my spares box and tested 
> them to pick one to use.  What I did is run each one on a little power 
> supply, and time how long it took them to comletely "suck in" the servo.
>
> Times ranged from 10 seconds or so up to two minutes, with at least 
> one not even capable of doing it.  They were all different.  I used 
> the fastest one, of course.
>
> I was going to suggest you clean and lube the TB mechanism, but then I 
> read above where you retract it all manually and the pump still can't 
> keep it in place.
>
>> Do I need to just bite the bullet and pay Rod at "thepartsconnection" 
>> the $140.00 for a new pump?
>
>
> Depends on how many junkyard ones you can try out.  If they let you 
> get them cheap, bring them home to test them.  If not, go in with a 
> little harness and a battery booster for power and time them like I 
> did (or test them 'in situ' against their TB linkages).  If you can't 
> find a "good" one then, I guess, yeah, a new one is called for.
>
>> 1) Should a good pump be capable of easily retracting the linkage (I 
>> take it the answer to that question is yes).
>
>
> I've never tried that in place, but it would seem pretty obvious that 
> it should, yes.  Whether it should be able to get beyond the first 
> butterfly or not might not be an issue.
>
>> 2) How much vacuum (inches of Hg, psi, whatever) should be required 
>> to pull the linkage back?  I don't know if you even can adjust the 
>> spring tension in the throttle valve.
>
>
> I think you can only clean and lube them.
>
>> 3) Is there any way I can make one of these pumps work by 
>> replacing/refreshing some commonly worn out internal part, or should 
>> I start looking for yet another pump, new or used?
>
>
> I've never seen or heard of a kit to repair them, they don't seem to 
> be "openable" - but you never know.  Why not bust one open and see 
> what it looks like?
>