EVM (electric vacuum modulator) Operation

WWDiesel · **Posted:** Mon Oct 14, 2013 7:50 am

Does anyone know if the EVM is supposed to bleed vacuum all the time through the little air filter? Did the bypass test while the engine was off and noticed I heard vacuum being sucked into the filter very slowly as soon as I swapped hoses. The vacuum chamber seemed to have plenty of vacuum in reserve as this leak down lasted for about 10 seconds. I started the engine and let the vacuum build back up with the hoses still swapped in the test position, shut the motor off, turned the key back to on and the vacuum being sucked into the little air filter became a lot faster, vacuum depleted in a couple of seconds. Could this be the cause of my occasional P0299 code? Does this mean that the the EVM has a problem and needs replacing?
Is there a bench test for the EVM?
I have checked everything else, boost hoses, vacuum lines, turbo diaphragm rod movement with a Mityvac, all seems to be well. Motor runs great, no visible black smoke, code usually sets when at idle.. :banghead:

Thoughts from all appreciated

papaindigo · **Posted:** Mon Oct 14, 2013 9:10 am

I could be wrong but I think you have it backwards if you were doing the boost pressure solenoid bypass test (viewtopic.php?f=5&t=70602&p=757348&hilit=boost+solenoid#p757348). I don't exactly know what that filter does but the purpose of the solenoid is to hold vacuum in the chamber so I would assume if you pull the solenoid then what you were hearing is outside air leaking into the chamber and replacing the vacuum. If you do that test then you should drive for a while and see if any boost problems (remember to allow time for vacuum to build on first crank up) go away. Of course if you are having intermittent CEL issues you could just replace the solenoid (PN 4606226AC) and see if doing so solves the CEL as the part only runs ca. $46 from ID Parts.

On the other hand P0299 can be viewtopic.php?f=5&t=61240

WWDiesel · **Posted:** Mon Oct 14, 2013 5:48 pm

Bypassed solenoid #2 (as shown in picture http://i.imgur.com/L0jqo.jpg) and noticed the vacuum tank bleeding down through the little filter under the EV modulator. This may be normal and that is the question I was posing. If it is not, then the EV module may have a problem and need replacing? After doing a few tests with the solenoid bypassed, I noticed it bleeds down a whole lot faster with the ignition switch in the on position as opposed to being in the off position. Again this may just be a normal modulation of the amount of vacuum applied to the turbo vane operator diaphragm by the EVM when in the off position or at idle.
Wondering if anyone else had ever noticed this when doing the bypass test.... :?:

EVM (electric vacuum modulator) Operation

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