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02-12-2013, 11:15 PM | #1 |
Truck and auto performance nut
Join Date: Feb 2007
Location: McKinney,Texas
Posts: 3,848
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Need help - Vacuum loss and can't resolve
When my truck was running this new genIV LSx motor with a carb'd setup...it ran with 15-17" of vacuum. Truck ran well but a bit rich. I also installed brake booster along with a vacuum storage tank along with other brake upgrades during the build. Brakes were awesome...could throw a passenger threw the windshield.
Then came the change to efi. Removed the carb'd setup and on went plastic efi manifold and ported throttle body, running a custom harness w/e38 ecm (t42? tcm) combo, w/4L80e trans, running a custom tune by well known tuner. That's when things went south. Vacuum has been in the 10-12" range since then and through 4-5 different tunes. Idle seems similar to when carb'd...just not making the same vacuum any more. This motor is not old, and is/was a "new" 0-hr. motor. Less then 1000mi now. Items checked off - Changed pcv setup - no change Closed off any/all ports including one for brakes to check vacuum level - no change Obtained new OEM efi intake manifold and gasket set - replaced w/o any change Throttle body - swapped from my TBSS - no change Also - Pulled the injectors and setup a test bed. All injectors fired and sprayed similar strong streams Pulled each injector connector one by one while running - each cylinder appeared to pull engine down when injector disconnected and picked back up when reconnected I need to resolve this. While the motor is running and making good power it obviously isn't right at 10-12". I have HPTuners and have tried some things there w/o any improvement. With the vacuum at this level as you might expect my brakes absolutely suck now...not a problem a carb'd to efi swap should create! Ideas?
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Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken |
02-13-2013, 03:00 PM | #2 |
Truck and auto performance nut
Join Date: Feb 2007
Location: McKinney,Texas
Posts: 3,848
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Re: Need help - Vacuum loss and can't resolve
Ah come on guys......anything?
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Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken |
02-13-2013, 06:27 PM | #3 |
Registered User
Join Date: Apr 2010
Location: Guntersville Alabama
Posts: 1,073
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Re: Need help - Vacuum loss and can't resolve
Was the cam you had in it for a carb set up. If it was then when you put the efi on it may not of liked it. I do know there is different grinds for the two. Just a thought.
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02-13-2013, 06:19 PM | #4 |
Senior Member
Join Date: Sep 2005
Location: Lewisville, Nc
Posts: 10,237
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Re: Need help - Vacuum loss and can't resolve
unplug and block off your brake booster and check your readings again
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David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube |
02-13-2013, 08:22 PM | #5 |
Truck and auto performance nut
Join Date: Feb 2007
Location: McKinney,Texas
Posts: 3,848
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Re: Need help - Vacuum loss and can't resolve
Thanks guys.
Actually, already unplugged everything and capped them all off - no change Cam is a Comp LSx cam... .223/.231@.050 .610/.617 lift and 112 lsa. Don't remember it specifying carb or efi. You may be on to something, but its not something I would have thought make a difference. I suppose it certainly could tho. Wish I had a way to know for sure?
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Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken |
02-14-2013, 08:28 AM | #6 | |
Registered User
Join Date: Apr 2010
Location: Guntersville Alabama
Posts: 1,073
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Re: Need help - Vacuum loss and can't resolve
Quote:
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02-13-2013, 09:15 PM | #7 |
meowMEOWmeowMEOW
Join Date: Sep 2009
Location: MKE WI
Posts: 7,128
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Re: Need help - Vacuum loss and can't resolve
Aside from the common stuff or maybe a crank in the plastic manifold?
HAve you tried spraying the stuff underhood with carb cleaner, then watching your fuel trims in HPT to see if the car is making up for it. This is a stupid one....got a loose valve cover gasket?
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'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD
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02-14-2013, 12:08 AM | #8 |
Truck and auto performance nut
Join Date: Feb 2007
Location: McKinney,Texas
Posts: 3,848
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Re: Need help - Vacuum loss and can't resolve
I'm almost ashamed to say, but I bought a new one....believing that it HAD to be the intake, or a gasket...and so -
no change...but I have a spare L92/LY6 intake! hadn't checked valve covers...but I will!
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Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken |
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