j2the-e

Perhaps you dont understand what I said. The vsv is ALWAYS on when temp is above 126 F. It does not shut off for any reason other than temperature, regardless of load or throtlle position etc...Egr operation is controlled by the vacuum modulator. The vsv simply turns the system on when its warm enough

jgrant721

That is what the manual says, but if you read the discussion in the early part of this thread I have tested this carefully and either my ECU is doing strange things or the manual is not correct (or is simplified). In my testing the ECU/VSV definitely disabled the EGR completely until the engine came up to temperature. However the ECU/VSV continued to control the EGR operation after the engine warmed up based on other sensor inputs.

If you want to check this, connect a low wattage bulb across the EGR VSV leads and let it poke out from under the hood while you go for a drive. You will see it going on and off under different engine load conditions. I would be very interested to have someone else confirm this on another vehicle.

Jim

j2the-e

Sometimes sensors can fail intermittently, either due to a bad sensor or high resistance at a connector, etc. I recently had a situation in my truck in which the vibrations of the engine would cause my temp gauge to read extremely erratically. Light accell it was fine, cruising it was fine, but medium to heavy accell above 2500 rpm the temp gauge would go haywire. It was all over the place. As soon as I let off the gas, it would go back to normal. I traced the problem to a loose pin at the body harness connector in the right kick panel. Of course, its a different temp sensor running the gauge. What you may try is checking the coolant temp signal at the ecu while driving and see if it acts up. Should be a fairly simple non-intrusive test. As you already know, according to the service manual, the vsv should remain on when warmed up. EGR flow is then controlled by the throttle position and the modulator.

jgrant721

j2the-e,

I understand what you are saying but please believe that I have checked the temp sensor and have also spent many hours carefully observing/measuring the way this system is working on my truck, both in the garage and on the road. The EGR/VSV behaves entirely consistently while driving, opening and closing the VSV under various load conditions in a completely repeatable pattern, so in my experience this is unlikely to be a random circuit/connector problem. Unfortunately the conditions under which it allows the EGR to operate seem to be so limited (only with the engine warm and under medium load/acceleration) that it isn't doing anything under the light load of the 25mph driving emissions test.

All sensors that feed the ECU are operating within spec according to the shop manual (temp, throttle position, air flow, O2 sensors etc). More importantly, the general operation that I see is exactly as described in the Toyota technical article here. The article details how the ECU overides the EGR operation under specific conditions including cold engine, heavy load, or high RPM.

I realize this is not what the 4Runner service manual says, which is why I had the same confusion as you when I started this thread (and included a copy of the specific page in that first post). As the discussion went along and scope103 pointed me to the Autoshop101 articles (which are Toyota documents) it became obvious that the service manual wasn't telling the whole story.

The real problem is to figure out why the ECU is not allowing the EGR on my truck to operate when it seems that it should be (under light load) during the emissions test.

In my research I have seen quite a few references on various websites where people have had high NOx problems after installing a high-flow header/cat/muffler exhaust system. Perhaps the lower back-pressure is affecting the engine sensors and leading to odd behavior of the ECU.

The next steps are:

- to determine if the EGR not operating during the emission test is the main culprit. I'm pretty sure this has a significant negative impact on my NOx test results.

- or is the Magnaflow cat (now newly replaced under warranty) a significant factor due to insufficient ability to process NOx.

Tomorrow I'm going to do another run through the test station with the VSV shutoff disabled. This will make sure the EGR is operating during the test. The results will hopefully be much better.

I will post results.

Jim

jgrant721

OK, went thru the test station again this morning and PASSED! The only change I made to the vehicle was to unplug the connector on the EGR VSV (the green vacuum valve at the front of the group of three mounted on the passenger wheel arch in the engine compartment).

This confirms that the main problem causing high NOx was the ECU disabling the EGR under the conditions present during the emissions test.

Here are the results for the three test passes done in the last couple of weeks along with the changes made (in order, fails are in RED):

1. HC = 84, CO = 0.51, NOx = 1838

2. HC = 17, CO = 0.01, NOx = 1281 (Notice all results are a bit better. Only change: new Magnaflow cat)

3. HC = 22, CO = 0.00, NOx = 435 Pass! (NOx significantly reduced. Only change: unplug EGR VSV)

Looking at these results it seems pretty clear from result 2 that the original Magnaflow cat had been degraded, probably by exposure to "sensor safe" sealant. Then looking at result 3 where the EGR was actually operating during the test it's clear that this was the major factor.

It's still quite possible that the Magnaflow cat may not have as much of the reactant that reduces NOx as the factory unit, which gave a result of 91 but I am happy with this result that gets me a pass.

I don't know if I will ever be able to determine why the ECU has been confused into incorrectly controlling the EGR operation due of the install of the high flow exhaust system but at least I know I can pass emissions by simply disconnecting one plug on the VSV.

If anyone has any theories that might explain this strange behavior I would be very interested in hearing from you.

Cheers!

Jim

scope103

Congrats!

Are you driving around with the VSV disconnected? Notice any drivability issue? (you might not until the temperature drops.)

Let us know.

jgrant721

I did take the truck for a 20 minute warm-up drive with the VSV disconnected before hitting the test station, just to see how it acted. The truck is kept in my garage which is currently at about 55 degF so it wasn't that cold when I started it. The only thing I noticed was maybe a very slight hesitation when under medium acceleration at low RPM for the first couple of minutes.

I have reconnected the VSV now though so I shouldn't have any driveability issues when the weather gets colder. I am thinking about how I could separately control the VSV, perhaps starting by putting an extra temp sensor/switch on the engine to control the VSV instead of letting the ECU control it but this doesn't address the problem of disabling the EGR at high load/RPM. Still pondering...

Jim

j2the-e

Right on!

4xmtntoy

I have a similar problem... modified high flow exhaust system (LCE header, Magnaflow cat and muffler and KN intake), but still running stock exhaust pipe. Just moved to Colorado so now I have to smog and I get high NOx, CO is moderately high but still within acceptable range, HC minimal. I replaced the EGR valve (easy to do but wasted $160), fixed an exhaust leak after cat before 2nd O2 sensor, replaced a crack vacuum hose, cleaned the MAF and throttle body. Still the exact same high NOx level. I found this thread and I'm going to try Jim's solution.

The EGR VSV isn't easy to get to in the 2.7L because its in the cave created by the air intake plenum so I bypassed the VSV valve by hooking the EGR line that comes from the VSV directly to the throttle body. I did this today and test drove it; ran fine and idle was normal and outside temp was 40F. But I now get a pending P0401 code (insufficient EGR flow) which could be related to the VSV not getting any vacuum signal. Jim said he just disconnected the vacuum line. Any suggestions? Colorado apparently allows vehicles with pending or active trouble codes to pass so this may not be an issue for me. I'm going to test again tomorrow to see if this worked.

j2the-e

You probably have a bad egr modulator. The round plastic thing with 3 vacuum hoses going to the top of it/ Remove the cap and see how much carbon is present in the filter. P0401 doesnt care about the vsv getting vacuum. Computer looks at egr flow based on temp sensor in the egr valve(if yours has a temp sensor, cant remember off hand).

KistCustoms

I'm glad you passed. I have HEARD that not enough catalyst idea several times. I have also heard that high-flow cats don't retain enough heat to properly catalize. My answer to my clients, and the world is, stop bolting on long, expensive, cop-magnent exhaust systems and just get headers and an electric-swing valve cut-out right in front of your stock cat. That will give you the free-est flowing exhaust on a switch at your finger tip

KistCustoms

Didn't mean to wonder off-subject guys, sorry.

Gamefreakgc

I second the cat as being the overall culprit. Although messing with the EGR can help reduce some emissions, the only part of the emissions system that reduces all three harmful emissions is the catalytic converter. A high-flow cat allows the exhaust to exit faster which also gives less time to break down the harmful emissions into harmless carbon dioxide, nitrogen, and dihydrogen oxide (water).

The OP's tests prove this. All three categories jumped when nothing else in the emissions system was changed. So, perhaps a high-flow cat is not recommended in California where emissions are strict. Other states might be ok but just look into it first or keep the old cat on hand in case you need to swap them out!

KistCustoms

The gases moving to fast! I totally agree. That is definately not one I thought of. Good thinking Gamefreakgc.

Gamefreakgc

Who knew that I would actually use things I learned in Chemistry?

j2the-e

Actually the proper scientific term for water is dihydrogen monoxide. lol

4xmtntoy

So I retested today with the VSV bypassed and the EGR functioning at all times. It made the NOx worse but did lower CO about 20%. I know my EGR was working because the pipe gets hot without the VSV connected and stays cool when the VSV is connected.

Here's the scores in gal/min Reading/Allowable
HC .37 / 1.2
CO 8.57 / 15.0
NOx 3.47 / 2.5

NOx was running at 3.1-3.2 and CO was 10-11 when the EGR was not functioning.
Here's a log of my O2 sensors. Does this look normal (for a lean running vehicle)?

j2the-e

Your egr is NOT functioning if your NoX went up. When you bypassed the egr vsv, did you also bypass the modulator? And according to you picture, you have a bad catalytic converter. The rear o2 sensor should be a flat line. However, I would fix the egr issue before messing with the cat. Your truck will set a p0420 when the cat fails. Why do you think its running lean? Your truck won't run lean unless the front oxygen sensor is bad.

j2the-e

One more thing, what RPM did you get the snapshot of the o2 sensors at? If that's at idle, its normal. To properly check the cat, you need to hold it at 3k rpm to heat it up. Thats when the rear o2 should flatline.