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Username Post: vacuum diagram        (Topic#244221)
ggenovez 
Senior Member
Posts: 819

Loc: DFW, Tx
Reg: 06-08-05
06-21-10 07:18 PM - Post#1933906    

Hi all,

Still chasing down my demons.

Compression looks good.

Feels like I have a vacuum leak. I used to get 19" vac in park and 16 in gear. Since fighting and replacing the valve seals she runs rough.

Very rough when I first fire her up, like an old harley, and when she goes into closed loop she gets a little better.

Now vacuum slowly rises to 17 in park and idles at 13 1/2

I did manage to disconnect the vacuum brake booster when I was fighting the valve locks. I'm wondering if is cracked something or disconnected a hose.

I did spray some carb cleaner around the hoses but diddn't find anything. don't know if I hit them all though.

Is there a vacuum diagram floating around for a 90 350?

Any advice?

Thanks everyone for all their help.
1990 r-1500 suburban, 350 TBI, 2wd


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
06-21-10 09:12 PM - Post#1933957    
    In response to ggenovez

The vacuum system on any tbi truck is super basic. Off hand all I can think of is the brake booster, EGR, Evaporator and maybe one other. Either way they all come off the base of the throttle body so if this was an issue you could always check all the nipples and buy plugs and plug them all. If it gets better then it is a leak, if it doesn't then time to move on to other theories.
98 Silverado k1500 4x4 350


 
Boosted 1 
Member
Posts: 179

Loc: Downey,Ca.
Reg: 10-26-06
06-21-10 11:11 PM - Post#1933986    
    In response to ggenovez

Not knowing what we are working with Question... is the vacuum steady or floppin around ? If its bouncing readjust the valves, Also maybe check valve timing, check for flat cam
92 3500 toy hauler, 63,70,Nova,83 Shovel, Blown with N2o 90 step side


 
ggenovez 
Senior Member
Posts: 819

Loc: DFW, Tx
Reg: 06-08-05
06-22-10 05:11 AM - Post#1934029    
    In response to Boosted 1

Thx 355.

Boost, there's maybe a 1/2" fluctuation. Timing is right on 0 with the bypass. I doubt it's flat cam since I had 19" one day and after the valve seals it's 17". huge drop for "overnight". Took more than 1 night
1990 r-1500 suburban, 350 TBI, 2wd


 
ggenovez 
Senior Member
Posts: 819

Loc: DFW, Tx
Reg: 06-08-05
06-24-10 01:40 PM - Post#1935296    
    In response to ggenovez

How is the vacuum to the brake booster supposed to be hooked up?

I have a hack job on my hands.

I have a T connector in it. one side goes to the distributor vacuum, the other to the booster, and the other to a canister that looks like it connect to the fuel line.

Any idea if that's right and what the canister is?
1990 r-1500 suburban, 350 TBI, 2wd


 
someotherguy 
Moderator
Posts: 25437
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
06-24-10 01:49 PM - Post#1935302    
    In response to ggenovez

On a '90 Suburban, you shouldn't have vacuum going to distributor - it should be 100% electronically controlled. If it has vacuum advance then it's an older distributor hacked in - is this one converted to carburetor?

On your normal TBI engine setup, vacuum to the booster is provided via the tube running along the driver's side of the intake manifold, attaches to a bracket behind the driver's side head and turns to rubber line to the check valve in the booster.

Yours being a '90 Suburban, square body, will have vacuum-operated cruise control, which uses a vacuum diaphragm towards the driver's side rear of the intake. Easy to spot as it will have connection to the throttle linkage.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
someotherguy 
Moderator
Posts: 25437
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
06-24-10 01:52 PM - Post#1935305    
    In response to someotherguy

By the way, the sum total of vacuum-operated items on a stock setup would be:

PCV valve, off the front of the TBI
Brake booster, off the intake tubing
MAP sensor, off the rear fitting down low on the TBI
EGR solenoid, off the passenger side front fitting of TBI

Squarebody versions - cruise vacuum pot though I'll be damned if I can remember where it T's in.

And on early models where equipped - smog pump diverter valve, which on most I've seen that still had it, was a dual connector on the same port on the TBI that runs to the EGR solenoid.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
ggenovez 
Senior Member
Posts: 819

Loc: DFW, Tx
Reg: 06-08-05
06-24-10 02:05 PM - Post#1935313    
    In response to someotherguy

Richard, you're right, it's the large vacuum port that is in front of the distributor. It actualy goes from that port to a bunch of T's and finaly to another T for the booster.
1990 r-1500 suburban, 350 TBI, 2wd


 
ggenovez 
Senior Member
Posts: 819

Loc: DFW, Tx
Reg: 06-08-05
06-24-10 02:12 PM - Post#1935319    
    In response to ggenovez

So, the way I see it, it goes from the booster to a T that eventually connects to the passenger side vacuum port on the manifold in front of the Distributor.

The other end goes down to a canister that appears to connect to the fuel line.

If that canister is a check valve, it's probably useless because of the vacuum port. Also, what is the other side of the canister SUPPOSED to connect to.

Much appricitated...
1990 r-1500 suburban, 350 TBI, 2wd


 
someotherguy 
Moderator
Posts: 25437
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
06-24-10 03:05 PM - Post#1935350    
    In response to ggenovez

Oh jeez sorry, forgot about the charcoal cannister. Also hooks to front of TBI unit, driver's side port. On later models (94-95) there's a purge solenoid, earlier ones hook directly.

The other side of the cannister is fed by the small hard line that runs back to the tank - it's the "vent" - since this is a closed fuel system, it does not vent vapors to the atmosphere, it sends them to the cannister. It's also why you're not supposed to top off your tank; it can run up the vent line and damage the charcoal in the cannister.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
ggenovez 
Senior Member
Posts: 819

Loc: DFW, Tx
Reg: 06-08-05
06-24-10 06:05 PM - Post#1935447    
    In response to someotherguy

Got it. Thanks!
1990 r-1500 suburban, 350 TBI, 2wd


 
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