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Old 05-21-2010, 11:53 PM   #1
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vacuum problem

my 90 s10 blazer 4x4 4.3l tbi is giving me hell. it drives great and isnt throwin any codes. problem is when i take it on the highway after a while its blowin thick white smoke like i blew a head gasket. i didnt blow the gasket and it doesnt leak coolent. it only does this after 15 or so minits of highway driving. when i shut it off and start it back up there is no more smoke and the exaust is virtually clear and normal like it supposed to be. after researching everything it could be im almost positive my problem is tranny fluid being sucked into the intake manifold via the vacuum lines and burning up in the exaust. acording to my recorces replacing the 4x4 actuator and replacing vacuum lines should fix it. i dont want to do all that work to find out that something else is doing this and need advice. i just relized my 4x4 indicator light flikers on and off and when i was testing on the highway seemed like it would engauge by itself even though the lever is in the 2 hi position. this past winter, two blizzards coverd my community and i was one of the few able to venture out on the road without getting stuck. the 4x4 worked as it should. any advice or help would be great. my haynes and automotive tech books tell me nothing about this type of problem and i wish i still had access to alldata. i still havent found any vacuum diagrams after months of searching online and really need some advice
Old 05-22-2010, 12:03 AM   #2
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Re: vacuum problem

lol...spellcheck is your friend...if you've already researched it and you're almost positive you know what's wrong with it then go for it!!
Old 05-22-2010, 02:34 PM   #3
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Re: vacuum problem

Is the vac system on that vehicle very different from the 95? I assume that if the 4WD is vac actuated that you will need to check the actuator under the batt (or on fender in your case maybe)? As well, the most likely culprit would be the 3 way vac switch on the side of the trans case or encoder motor? I had a bad vac switch next to t case and it caused fluid to be sucked in to the vac modulator and HVAC system. A switch replacement for maybe $20? fixed it. I don't know if this applies to the 90 model. I bet it's a similar fix however.

Good luck and check the simple stuff before dumping big bucks. You might try putting a little controlled air (I used shop air at maybe 10psi) towards the switch from the 4WD actuator. Get behind the intake and crawl under the truck and listen for a hissing sound. If you hear a hiss, fix the hose or dead vac switch.

Good luck.
A.
Old 05-22-2010, 05:37 PM   #4
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Re: vacuum problem

thanks for the input im going to get my compresser out either today or tomarrow i really need a vacuum diagram for this specific model. i unpluged a hose i think was connected to the wrong place and now im back in two hi. i have to investigate further but still get confused with vacuum problems. i know how to rebuild and repair automatic trannies but am overwhelmed when it comes to routing vacuum lines. if anyone has a diagram i will be greatful
Old 05-23-2010, 10:54 AM   #5
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Re: vacuum problem

Quote: Originally Posted by chadfrank1983
thanks for the input im going to get my compresser out either today or tomarrow i really need a vacuum diagram for this specific model. i unpluged a hose i think was connected to the wrong place and now im back in two hi. i have to investigate further but still get confused with vacuum problems. i know how to rebuild and repair automatic trannies but am overwhelmed when it comes to routing vacuum lines. if anyone has a diagram i will be greatful
I've attached vacuum diagram for 1989 and 1991 4.3 TBI engine ... not yet found one for a 1990. Difference appears to be 91 has three port carbon canister. You might check yours and choose most appropriate diagram.

Last edited by far2grumpy; 12-27-2010 at 06:41 PM.
Old 05-23-2010, 11:24 AM   #6
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Re: vacuum problem

so t case fluid could be being sucked into the intake through the valve on the t case?

hmm interesting. and very quite possible! i dont know anything about the 4x4 systems on these trucks and the smaller jeeps etc these years. but i know the front axle was commonly electric actuated and the t case i dunno.


like the modulator valves on the old th400 and th350 trannies they used to rupture internally and cause tranny fluid to be sucked into the intake and burnt and it always did cause white smoke at idle when intake manifold vacuum is highest. 15-18 hg


so yeah....

or its burning water.... intake gasket most common failure on the 4.3 and v-8 but that would do it all the time..... head gasket on the 2.5L
Old 05-23-2010, 11:47 PM   #7
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Re: vacuum problem

Check out this thread for a decent vac diagram also - last post has attachments.

http://www.s10forum.com/forum/f13/transfercase-378818/

Good luck.
A
Old 05-25-2010, 11:54 PM   #8
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Re: vacuum problem

thanks for the diagrams what do the letters stand for?
Old 05-26-2010, 01:23 AM   #9
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Re: vacuum problem

p.s. i have been driving it without the vacuum ball since i wrecked it and lines have been open. a friend connected them when i wasent looking. it was stuck in 4x4 mode when they were connected. this winter it shifted in and out of 4x4 no problem even with disconnected lines. still trying to figure out the fundementals of vacuum modulated systems and how they work. any one with experiance want to extend their advice? help me learn something
Old 05-26-2010, 02:54 PM   #10
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Re: vacuum problem

Quote: Originally Posted by chadfrank1983
thanks for the diagrams what do the letters stand for?

No problem and do you mean, A & B by letters? They're just two sides of the vac switch that are labelled for clarity. One is on the engine (draw) and one on the vent side (venting to atmosph). I hope this helps. The main thing is to make sure the line or vac switch isn't damaged, leaking or disconnected.

A.
Old 05-26-2010, 03:03 PM   #11
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Re: vacuum problem

check Kyle's blog also - great info and lots of fixes discussed.

http://www.kylestubbins.com/node/11
Old 05-30-2010, 05:16 AM   #12
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Re: vacuum problem

thanks for the input people. i drained the transfer case and all fluids are where they should be. it hasent smoked at all im going to drive it on the highway toomarrow and hopfully no smoke. wish me luck i really dont wanna remove the cat to change the actuator
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