mystery part

[veggiesub]

I have a 95 6.5l GM Suburban. While digging around in the engine bay I found a vacuum line with one end not connected to anything. The other end is connected to a softball sized black plastic thing mounted on the drivers side firewall. This platic ball is connected to the oil pressure swith via another vacuum line. I have stared at all the photos in the parts thread but do not see anything similar to my black ball.

Sorry for my ignorance, but 1) what is the black ball, and 2) what should the vacuum line be connected to?

 

[gmctd]

That is a vacuum reservoir off a gasser (patooie!), back when they had vacuum-operated hvac systems - no possible connection to the 3-wire electrical OPS - possibly someone was trying to compensate for a failing vacuum pump, which operates EGR and Boost systems

BTW - welcome to the forum....................

 

[veggiesub]

Hmm. Interesting. No possible connection to the OPS? Then I have misidentified something. I'll take a pic. There is some kind of plastic solenoid on the firewall connected to this black ball by a vacuum line. Another vacuum line disappears into the underworld. I dig around and find where it goes. As I originally posted, another vacuum line comes off the ball into nothing.

 

[gmctd]

The firewall-mounted piece is likely the EGR sensor, or the Baro sensor with "F" engines (they look alike) - the vac resevoir plumbed into the circuit would seem to indicate you have the "S" EGR engine, the other ends going to the pump and the EGR vent solenoid - you should have three solenoids: EGR, EGR Vent, and Boost - scheme may have been for failing vacuum pump, or some manner of not-well thought-out EGR fooler (was only fooling himself)

At any rate, if it's not symptomatic, remove it, and go in peace, my son............

 

[gmctd]

Anybody see this thread as "closed"?

 

[HighSierra86]

I thought all suburbans had the "F" engine. Is the vaccum canister something that is seen more overseas? I seem to remember a similar question from a guy in australia

 

[gmctd]

Here is the rest of the parry and riposte, in hopelessy inverted and possibly non-sensical format, all for your reading enjoyment:

Ahhh, this explains why my 4WD doesn't work. I connected the reservoir line to the vacuum line and now the turbo actuator bar doesn't move, as it shouldn't, when idling. I will proceed with the vacuum check just to see if everything is OK. Thanks again for the help.

Did you close the thread, or did I accidentally do it?

Quote:
Originally Posted by gmctd
That would be the vacuum-actuated axle disconnect motor for 2wd-4wd operation - may be a solenoid on the firewall that controls that actuator
- still need to check the vacuum pump output for 25"HG, see if it even works
- in any event, the vacuum pump line should connect to the wg solenoid, the EGR solenoid, and the 4wd solenoid, then if desired, to the reservoir
- a separate line goes from the EGR to the EGR vent solenoid
- a separate line goes from the EGR vent solenoid to the EGR sensor on the firewall

Quote:
Originally Posted by veggiesub
Thanks for the help. The vac line leaving the reservoir is currently not connected to anything. There is, however, a T in the yellow line connecting the WGS to the vac pump. One port in that T is open.

The EGR has two vac lines connected to it. One goes to the reservoir. The other comes from something mounted to the axle. I don't know what this is, but it looks like some kind of small pump. However, I don't see any power going to it.

Quote:
Originally Posted by gmctd
It should definitely not go in the wastegate line - PCM vents that to atmosphere at @ 30times\second via the wg solenoid to quickly control Boost

Trace the lines from the reservoir to their final destination, see what is connected\disconnected

Find the vacuum pump supply line, starting at the vacuum pump, trace it to first connection at the solenoids - you could tee it in there, but first check the vacuum level with a guage: should be ~25"HG at idle and 2000rpm - if so, you won't need the reservoir - if way low, the reservoir won't help, as that 25" level is required to operate the wg solenoid to provide factory Boost pressures

If there is no vacuum pump, remove all that extra paraphenalia - the resultant lighter vehicle weight will net you better fuel economy.................

Quote:
Originally Posted by veggiesub
For some reason I have lost to ability to reply to threads.

Thanks for the information. The vac line coming from the reservoir that is not connected to anything must have been spliced into the vacuum line somewhere. Correct?

I found a 3 way rubber connector in the vac line between the wastegate acuator and wastegate solenoid. One of the ports has nothing in it. My guess is that the abandoned vac line should go there. But you think I can just remove the whole thing? What would the vac lines from the EGR be connected to?

 

[veggiesub]

Problem solved. The mystery part is actually part of the vacuum controlled 4wd system. I found a vacuum line in the 4wd system that had become disconnected. Connecting it solved what I thought were several separate problems: low power, black smoke, intermittent engine rattle, and no 4wd.