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Turbo vacuum modulator
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=85443		 Page 1 of 1
Author:  akklingler [ Sun Oct 16, 2016 7:24 pm ]
Post subject:  Turbo vacuum modulator
How much vacuum should I see going to the turbo at idle and at other times?
Author:  flash7210 [ Sun Oct 16, 2016 8:24 pm ]
Post subject:  Re: Turbo vacuum modulator
I cant give you exact numbers but...
High vacuum = high boost
no vacuum = no boost

At idle, vacuum is high.

With everything connected normally and engine running at idle, look down between the engine and turbo to find the rod connecting from the actuator to a small lever on the turbo. Pull the vacuum line off the actuator and watch the rod drop. Reconnect the vacuum line and watch it pull up.

A boost gauge is an easy way to know how well the turbo is performing.
Or you can use an android phone/tablet + torquepro app + elm327 bluetooth adapter to read sensor data.

A too high or too low boost condition will result in a check engine light and appropriate code. It may even result in a limp mode condition.

If you suspect a boost problem...
1st, remove, inspect, and clean or replace the MAP sensor
2nd, bypass the small vacuum solenoid
3rd, replace large vacuum solenoid

It also cant hurt to remove the turbo inlet hose and inspect the turbo shaft for excessive play.
Author:  akklingler [ Thu Oct 20, 2016 9:32 am ]
Post subject:  Re: Turbo vacuum modulator
I would like to know numbers, or if it can supply the full 25 in. at idle? What for boost numbers should I see when?
Author:  flash7210 [ Thu Oct 20, 2016 11:35 am ]
Post subject:  Re: Turbo vacuum modulator
Does the book say it should be 25 in at idle?
If so, then 25 in is max boost.

Cant really say what it should be while driving. The computer modulates vacuum (via the solenoid) to control boost. This is determined by MAP sensor signal, throttle position, engine load, etc.
If the MAP signal indicates low boost, then the computer will adjust vacuum modulation to increase boost to the appropriate level.
If the MAP signal indicates too high boost, then will adjust modulation appropriately.

If the MAP signal indicates too low boost and the computer is unable to modulate to increase boost, a underboost code will be set.
If the MAP signal indicates too high boost and the computer is unable to modulate to lower boost, a overboost code will be set and you will get limp mode.

This is why a boost gauge or some method of reading the MAP sensor is better than a vacuum gauge.

Are you having turbo problems? If so, what are the symptoms?
Author:  akklingler [ Thu Oct 20, 2016 9:26 pm ]
Post subject:  Re: Turbo vacuum modulator
It's lazy, when I get on it it hesitates, If I lift and slow down and get back on it it is sluggish. I'm trying to figure out if the turbo is working properly or if the issue is elsewhere.
Author:  xhizzous [ Thu Oct 20, 2016 11:55 pm ]
Post subject:  Re: Turbo vacuum modulator
akklingler wrote:
It's lazy, when I get on it it hesitates, If I lift and slow down and get back on it it is sluggish. I'm trying to figure out if the turbo is working properly or if the issue is elsewhere.


I am having a similar problem on my 05. No engine lights but severe hesitation and poor throttle response. It has the Hot tune on it as well.... so I assume Boost Issues .. Stuck vanes ?
Author:  flash7210 [ Fri Oct 21, 2016 8:31 am ]
Post subject:  Re: Turbo vacuum modulator
Do all the easy stuff first.

Check turbo inlet and intercooler hoses for cracks and tears
stick your fingers in the turbo inlet and try to wiggle the shaft
remove, inspect, and clean or replace the MAP sensor
bypass the small vacuum solenoid
replace large vacuum solenoid and filter

And remember that turbo performance is directly related to exhaust flow

without a boost gauge or some way of monitoring the MAP sensor you will never know for sure how well your turbo is performing
Author:  akklingler [ Fri Oct 21, 2016 9:47 am ]
Post subject:  Re: Turbo vacuum modulator
I have checked the hoses and turbo. I have cleaned the MAP. I have bypassed the small vacuum selinoid. I would like to know how to test the large selinoid before I just buy another. I can monitor boost, I would like to know what numbers I should be seeing and when.
Author:  WWDiesel [ Fri Oct 21, 2016 10:54 am ]
Post subject:  Re: Turbo vacuum modulator
I think you should be seeing around 22-24 psig boost at full throttle in final gear in lockup... You will only see these numbers for a very short amount of time till the engine starts building HP & torque and the EMC will start backing off the turbo boost.
If the boost is low, do as others have suggested and check all things connected to the turbo:
Air filter, air intake boot and hose to turbo, both boost hoses to and from the inter-cooler (CAC), all vacuum lines feeding the vacuum solenoid and vacuum canister, vacuum line from vacuum control to turbo diaphragm controller. Anywhere you could loose boost pressure or vacuum control to turbo!
Note: One member on here found his plastic vacuum line between the turbo and vacuum control solenoid had a small crack in it loosing vacuum to turbo, a.k.a. low boost!

Other items to consider if none of the above are found to have a problem:
Does it still have EGR valve and flow control valve (FCV) on engine? If so, EGR can be stuck partly open and loosing boost through it (blowing boost back into exhaust). FCV gears could be broke, stuck partly shut not allowing full flow from turbo into engine intake manifold.
Last but not least: CAT (catalytic converter) could be partly stopped up not allowing adequate exhaust flow to leave turbo and exit to build full boost...

Check all these things starting at the air box.
Good luck! Keep us posted... :wink:
Author:  flash7210 [ Fri Oct 21, 2016 10:58 am ]
Post subject:  Re: Turbo vacuum modulator
On a stock tune I've seen boost peak at 22psi under hard acceleration.
I'd say that normally boost is 18-21psi under hard acceleration.
At idle boost will be near zero.

I dont know how to test the solenoid. But when mine was bad it was making a loud buzzing noise.
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