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Old 03-28-2008, 06:00 AM   #1
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weird vacuum problem

my car used to idle around 20-22 in hg, my engine is rebuilt with 9:1 compression forged pistons total seal gapless rings i put all new gaskets on it. when i put it back in the car it remained idling around 20-22 in hg however about 2 months after breaking it in and driving normal for about 2000 miles it now idles at 14-15 in hg. when i engine brake it doesnt get deeper into vacuum. other than this the car runs great, i do however have a problem sometimes building boost. i checked with a second gauge and it shows the same vacuum. i disconnected the supercharger and ran it n/a, still shows the same. i resealed the intake and still no change. the engine compression has to be good it runs fine never misfires. just every once in a while have trouble building boost. will only get 2-3 psi but if i give it a sec it will get to the normal 7psi, then the rest of the drive it will get to 7psi. and the car idles around 14-15 in hg any ideas

also no leaks of air are heard as in vaccum leaks, and needle stays steady at 14-15in hg it doesnt bounce around
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Old 04-05-2008, 02:24 AM   #2
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Re: weird vacuum problem

i will be checking the compression on all cylinders and double checking that the cam sensor eccentric hasnt moved since installation hopefully this will give me some answers on the vacuum being low at idle
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Old 04-10-2008, 07:27 PM   #3
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Re: weird vacuum problem

update- i figured out my boost problem, im getting boost everytime now my air filter was too dirty lol its hidden in the bumper with the sc kit. i performed a compression check on my engine all cylinders between 180 -190 psi on the compression test. still vacuum is idling between 14-16 in hg instead of the normal 20-22 in hg, when i engine brake it will not go deeper into vacuum. i know the ignition timing is set by the computer which knows where tdc is by the cam sensor thats gear driven off of the cam, that hasnt moved since i reinstalled the engine. only problem is if i get on it when i get to the light to stop it dies everyonce in a while which im assuming is either a too quick of change from rich to lean or this vacuum problem which im attempting to solve. any ideas on why my idle vacuum could be low ive checked everything i can think of
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Old 05-03-2008, 01:20 AM   #4
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Re: weird vacuum problem

ok update not sure what made me try this or why it fixed everything but i had a t-fitting on the top and bottom vacuum fitting on the drivers side front of the upper intake due to adding two extra vacuum lines, ( the one for the supercharger surge valve , and the boost gauge). both of which were on the same vacuum fitting on the intake. i switched one of the egr vacuum lines from the bottom to the top and put the surge valve on the bottom and the boost gauge stayed on the same one. so now the extra two are not sharing the same port everything is back to normal.
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Old 05-03-2008, 01:46 AM   #5
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Re: weird vacuum problem

One vacuum line loose or broken can make a huge difference in how a car runs, especially on boosted cars (LTFTs go lean, and once boost is hit car goes haywire..) I've run into this several times with the regal

Anyway..glad you seem to have figured it out
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Old 05-03-2008, 03:09 AM   #6
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Re: weird vacuum problem

neither line was broken or leaking i had no running problem, even idled normal my boost gauge just read 12-14 in hg at idle which it didnt used to. thats why i was so baffled, i made sure all lines were tight with wire ties and tape didnt help until i changed the two from the same one
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Old 05-03-2008, 10:46 AM   #7
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Re: weird vacuum problem

This prob has nothing to do with your problem but. What s/c and injectors are you running?
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Old 05-04-2008, 01:56 PM   #8
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Re: weird vacuum problem

i have the procharger running 7 psi stock injectors and pump im using the procharger chip for now its running a little rich as i found out on the dyno. but during one of my runs a couple years ago i hurt two pistons they started coming apart at the rings lands. so i fully built the engine, so i will probly go to 15 psi, custom tune, i chose procharger because of the intercooler and it has its own oil
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