gas in plenum brake booster?
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From: CALI
Car: 85' Trans Am !best car ever!
Engine: 305tpi 215hp LB9 two bolt,
Transmission: th-700r4
Axle/Gears: stock (3.27)
gas in plenum brake booster?
i was thinking a hole in the diaphragm of the fuel pressure regulator.. i cant test for pressure drop because the hose in the tank is leaking so the pressure just drops.. im going to vacuum test the FPR and possibly narrow it down to stuck injector because i do get a slight miss when accelerating but it goes away sometime.. damn two stroke oil gas from last month i bet grrr..i just built a moped too. haha
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Joined: Apr 2010
Posts: 4,337
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From: Aurora, OR
Car: 87 IROC Z28
Engine: 355 cid TPI
Transmission: Custom Built 700R4 w/3,500 stall
Axle/Gears: QP fab 9" 3.70 Truetrac
Re: gas in plenum brake booster?
To test for a broken regulator diaphram, just remove the vacuum hose from the regulator with the engine running. If the diaphram is broken, fuel will run out of the vacuum port.
Thread Starter
Senior Member
Joined: Mar 2006
Posts: 926
Likes: 1
From: CALI
Car: 85' Trans Am !best car ever!
Engine: 305tpi 215hp LB9 two bolt,
Transmission: th-700r4
Axle/Gears: stock (3.27)
Re: gas in plenum brake booster?
MAN!!! that sucks. YEAH it is the diaphragm. ughh...no wonder my gas milage is shitty... damn it. i have to remove the plenum and fuel rails now huh.. so o-rings plenum gaskets what else..gaskets do i need. i built a moped but no handle bars ugh.
Supreme Member
Joined: Apr 2010
Posts: 4,337
Likes: 29
From: Aurora, OR
Car: 87 IROC Z28
Engine: 355 cid TPI
Transmission: Custom Built 700R4 w/3,500 stall
Axle/Gears: QP fab 9" 3.70 Truetrac
Re: gas in plenum brake booster?
You'll need runner gaskets and a fuel pressure regulator diaphram. Don't stress, the job isn't that bad. Just loosen the runner attaching bolts at the lower intake. Then remove the runner to plenum bolts and lift the plenum out. Be sure to disconnect all wirng and vacuum lines as you go. The MAT sensor is on the bottom of the plenum and you want to be sure you get it plugged back in before you bolt up the plenum. The diaphram is held to the regulator by six screws. Remove the screws and diaphram. With the plenum off, remove the runner to lower intake bolts and replace the gaskets. Then reverse procedure to reassemble.
Thread Starter
Senior Member
Joined: Mar 2006
Posts: 926
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From: CALI
Car: 85' Trans Am !best car ever!
Engine: 305tpi 215hp LB9 two bolt,
Transmission: th-700r4
Axle/Gears: stock (3.27)
Re: gas in plenum brake booster?
i need the size for the torx bolt head for plenum
Thread Starter
Senior Member
Joined: Mar 2006
Posts: 926
Likes: 1
From: CALI
Car: 85' Trans Am !best car ever!
Engine: 305tpi 215hp LB9 two bolt,
Transmission: th-700r4
Axle/Gears: stock (3.27)
Re: gas in plenum brake booster?
deleted
Last edited by transam85dudeman; Jan 12, 2011 at 05:03 AM.
Thread Starter
Senior Member
Joined: Mar 2006
Posts: 926
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From: CALI
Car: 85' Trans Am !best car ever!
Engine: 305tpi 215hp LB9 two bolt,
Transmission: th-700r4
Axle/Gears: stock (3.27)
Re: gas in plenum brake booster?
deleted post
Last edited by transam85dudeman; Jan 12, 2011 at 05:03 AM.
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Thread Starter
Senior Member
Joined: Mar 2006
Posts: 926
Likes: 1
From: CALI
Car: 85' Trans Am !best car ever!
Engine: 305tpi 215hp LB9 two bolt,
Transmission: th-700r4
Axle/Gears: stock (3.27)
Re: gas in plenum brake booster?
after minutes of searching i guess t-40 is the right size. laters
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From: vacaville,ca
Car: 1988 camaro z28,1997 camaro lt1
Engine: 355 afr 195 heads,tpis big mouth
Transmission: 700r-4 built by me 3-4 z pack
Axle/Gears: 3.42
Re: gas in plenum brake booster?
T-40 is right and for the regulator bolts its a t-10 tamper
Thread Starter
Senior Member
Joined: Mar 2006
Posts: 926
Likes: 1
From: CALI
Car: 85' Trans Am !best car ever!
Engine: 305tpi 215hp LB9 two bolt,
Transmission: th-700r4
Axle/Gears: stock (3.27)
Re: gas in plenum brake booster?
well i replaced it last night, 
it works
it works Last edited by transam85dudeman; Jan 14, 2011 at 06:01 AM.
Supreme Member
Joined: Apr 2010
Posts: 4,337
Likes: 29
From: Aurora, OR
Car: 87 IROC Z28
Engine: 355 cid TPI
Transmission: Custom Built 700R4 w/3,500 stall
Axle/Gears: QP fab 9" 3.70 Truetrac
Re: gas in plenum brake booster?
LOL. Thanks for the props man. It makes feel all warm and fuzzy. I see you took a short cut on the lower runner gaskets. Its okay though. Im sure they're fine. You can pull the plenum without loosening the lower runner to manifold bolts. I just like to reseal everything while Im in there. Good job and happy motoring.
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Joined: Jan 2011
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Car: 89 Iroc z camaro
Engine: 350 TPI
Transmission: Auto
Axle/Gears: stock
Re: gas in plenum brake booster?
Ok i read this and im kinda a newb so i halfway understood all that haha, so im getting horribal mpg and i cant figure it out so i wanna know what hose to do to test this? like i need it in very basic terms haha 
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