Topic: Info needed on Vaccum Modulators for EGR to pass smog

[Aaronm]

My runner is not passing smog because of High Nox. After troubleshooting it and wanting to shoot it. I traced the problem down to the EGR and basically it is not opening because of the vacuum modulator which supplies vacuum to the EGR. After running my runner for about an hour you can put your hand on the EGR line which goes between the EGR and Intake manifold and it is barely warm. I checked the EGR with vacuum and it stalls the engine, the BVSV changes with the temp of the engine, and I am getting vacuum back to the modulator. After checking the modulator and cleaning it I am still not getting vacuum through it. Does anyone have info on what modulators a 86 4runner should have? I need a part number and can anyone explain how the modulator should work? I am about to modify the vacuum lines to eliminate the modulator and run straight vacuum off of the manifold to the EGR and see how this would affect the NOX. Anyone have a similar problem to mine with a way to fix it?

[Vang530]

i think you can temporarily bypass it by switching the vacuum hose on the egr valve to any vacuum nipple on the intake manifold..just for the test atleast. by doing this you are telling the egr to run all the time...all the bvsv tells it to do is to not open the egr valve when when the engine is cold, and the vacuum modulator is pretty much a vacuum switch or filter if i recall...
so instead of dealing with all that smog stuff, route a vacuum line to an intake manifold vacuum source straight to the egr to bypass all that crap to pass the smog test with the egr valve open and plug it up when you are done.. i may be totally wrong in this and someone might come and correct me, but hey its worth a shot right 

[emsvitil]

Did you change your exhaust?

The stock EGR modulators need back pressure to work correctly.

For smog tests, I temporarily add a blocking plate after the cat for backpressure

[Aaronm [OP]]

i think you can temporarily bypass it by switching the vacuum hose on the egr valve to any vacuum nipple on the intake manifold..just for the test atleast. by doing this you are telling the egr to run all the time...all the bvsv tells it to do is to not open the egr valve when when the engine is cold, and the vacuum modulator is pretty much a vacuum switch or filter if i recall...
so instead of dealing with all that smog stuff, route a vacuum line to an intake manifold vacuum source straight to the egr to bypass all that crap to pass the smog test with the egr valve open and plug it up when you are done.. i may be totally wrong in this and someone might come and correct me, but hey its worth a shot right 

I just got back from the smog shop and tried something similar to what you suggested. I plumbed in a second vacuum line into the line which runs into the EGR and it did drop the NOX to near nothing but it created an internal vacuum leak. So I passed everything except the HC part. Because I created an internal vacuum leak by opening the EGR all the time it was miss firing on the 25 mph test and dumping fuel so it ran super lean and failed the 25 mph test. At least I made improvement and I am not failing both the 15 and 25 test.

[Aaronm [OP]]

Did you change your exhaust?

The stock EGR modulators need back pressure to work correctly.

For smog tests, I temporarily add a blocking plate after the cat for backpressure

I just finished adding a restrictor in the exhaust of mine after the cat. I am trying to figure out a way to have more vacuum applied to the EGR which is measured by the modulator. I am going to lower the timing to 3 degrees and warm it up as much as possible tomorrow and give it another shot.

[Vang530]

I just got back from the smog shop and tried something similar to what you suggested. I plumbed in a second vacuum line into the line which runs into the EGR and it did drop the NOX to near nothing but it created an internal vacuum leak. So I passed everything except the HC part. Because I created an internal vacuum leak by opening the EGR all the time it was miss firing on the 25 mph test and dumping fuel so it ran super lean and failed the 25 mph test. At least I made improvement and I am not failing both the 15 and 25 test.

oh...this is a dyno smog test. that trick usually works for me cause up here in norcal we don't do dyno tests...what a headache huh..goodluck.