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Discussion Starter #1
Hello all, I'm a new poster but I've been using the forum as a resource to get my truck running.

It's a 1988 with the TBI'd 2.8 and automatic, it was free to me and I want for a spare /picking up lumber/takin trash to the dump vehicle. It seems to run fine (haven't driven it...needs new tires first). I have removed the A/C and A.I.R. pump and now I'm in the process of replacing/fixing the vacuum system.
The vacuum lines are a rotted and jumbled up mess. I have the diagram, how ever my truck is missing the "Purge VTS" between the TBI and the canister...any one have a pic of where it should be and a part number? Also, where does the vacuum reservoir tie into the system (I don't understand why it is absent from the diagram :unsure:)?

Thanks
 

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The vacuum diagram is primarily emissions vacuum routing. There is a separate couple of lines for the HVAC and 4wd (if applicable) which includes the reservoir. Basically non ported vacuum to the HVAC with a tee to the reservoir.

Don't have an 88 so I can't help on the Purge valve.
Some were electrically operated and some were vacuum. 3 hoses to it. 1 in 1 out and 1 control above a small diaphragm.
Since the truck is 32 years old, I suspect a junk yard will be your only source. And then only if you can find one that one of the previous 10 owners hasn't "fixed". Might also look at Firebirds of that year and other small GM's with the 2.8. Probably all used the same valve since they were trying to meet the same emission rules with the same engine.
 

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Discussion Starter #5
That helps, thanks.

I assume that the reservoir plugs into "ACC Vacuum" on the diagram along with the HVAC vac line.
 

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Discussion Starter #6
So another question...

At what temperatures should the IAT open and close the flapper in the snorkle tube?
 

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Awww..you ain't got shit!
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Ah...the infamous purge valve. My truck is an 84 but it has a 1991 TBI system on it. Being originally carbureted I "think" it had one on it at one time. Lately, I've been having some driveability issue with my truck. It's a 3.4L crate with the aforementioned EFI system. I found that the tank is actually plumbed wrong since they swapped a couple of the lines around on the carbed trucks to where unless you swap the stuff around you will be returning fuel into the vent and the vent will then flood the charcoal canister sometimes . I thought this was the source of my problems, but turns out, it isn't. Off subject, but it's probably the aftermarket fuel pump that sits outside the tank and the need for tuning because it pings like a mother on 87 octane.

Anyway....All the diagrams I find for the TBI trucks seem to differ and the information seems to be impossible to tell if it is accurate or not. It appears that 2.8 trucks didn't have them and it plumbed straight to the the air cleaner. That's what I think anyway. I cannot confirm nor deny it, but I also can't find a part for it anywhere to prove it actually existed.
 

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Discussion Starter #8
Lol, that's about what I found looking for more info on it. I think there actually is supposed to be one on SOME of the 2.8s and it's in the manifold near the CTS. It's temp activated similar to a thermostat.

Mine has this thing in the manifold.
335840


I'm pretty sure that is what's left of it, not available as a new part and they all seem to be broken like that in the junk yards, lol.

Anyways, I ended up just getting a vented gas cap and eliminating the charcoal can and a few other unnecessary things and cleaned up the vacuum line mess. It idles great now:cool:
 

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My truck had that thing too. Snapped off on the carbed intake. I didn’t bother installing it again. My truck has an electric fan on it, so that’s where my sensor for the fan goes. So my guess is that purge valve would open at operating temp? Makes sense sorta...
 

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Discussion Starter #10
Hey, you got a parts list for the e fan controller? I've got an electric fan in the garage but need a controller unit for it.
 

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I got the fan controller with the 190 degree thermostat from Jegs years ago. I actually used a v6 Cavalier fan for mine. Been in there for more than a decade. Works terrific. I got a write up on that too. Somewhere.
 
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