jgrant721

Looking for a smog gear expert to help with this one.

When I installed Doug Thorley headers and Magnaflow Cat and muffler on my 3VZE a few years ago all of the smog readings degraded significantly for some reason.

Test Results
25 mph
Test / Before / After
HC / 8 / 84
CO / 0.0 / 0.51
NOx / 91 / 1000+
Idle
Test / Before / After
HC / 6 / 33
CO / 0.0 / 0.2

All of the smog gear was left intact and I have been over it a number of times to test that it is operational, per the procedures in the manual.

If anyone has a good explanation for this overall degradation I would love to hear it.

My other question is more specific to the EGR and in particular the VSV ;

Since the NOx level will more often than not be high enough to cause a smog test fail and since NOx is primarily affected by the EGR I have been researching its operation.

I checked all the vacuum lines, valves and modulator per the manual and they tested OK. The odd thing that I found is with the EGR VSV.

According to the manual (* on chart attached) the EGR VSV should be open at any time the coolant temp is over 118F. When I hooked up a test light to my EGR VSV and went for a drive I noticed that, once the engine is warm, the valve opens and closes depending on throttle position and engine load. In particular, contrary to the chart in the manual for the #3 situation where the throttle is open more (past the R Port) the EGR VSV opens and prevents any exhaust gas recirculation.

Anyone know if this is correct or should I be looking at this as the cause of my high NOx?

Thanks!

Jim

timothy47129

idk if this will help or not but I know proper egr operation egr valve will be closed at idle and under a hard load and at full throttle.nox is caused by high combustion temp.which could be egr since it introduces exhaust gas to cool the combustion or a lean mixture will cause high nox which could be caused by a better flowing exhaust,but i would thing the ecm would compensate.Have you taken off your egr valve and cleaned the carbon off it and out of the egr passage?

scope103

If your question is "Is the manual correct?", I have to say that I don't know, but I would be really surprised if it were not. If your EGR VSV is switching after the engine reaches operating temp, that both sounds like a problem, and it sounds like it would cause a high NOx condition.

The VSV signal comes from the ECM, not straight from a temperature sensor, so tracking it down may be a little difficult. My best guess is a loose wire somewhere, that is making and breaking a connection with vibration. Since you've got the test light set up, I'd start by looking at the VSV signal back at the ECM http://www.ncttora.com/fsm/1990-1995...e/troubles.pdf (another source I have suggests it is on C22; you may have to actually ohm out the wire to make sure you've got the right one). If that one is stable, you've found your loose stretch of wire. If that one is also switching, I'd look for an intermittent connection to a temperature sensor, probably THW.

Let us know what you come up with.

jgrant721

scope103,

Yes, I had already checked the wiring of the EGR VSV all the way back to the ECU. I even opened the ECU and checked the circuit continuity back to the CPU chip. I am quite sure it is not a loose wire because I have been driving for a few days with the test light and the VSV operation is very consistent. Almost certain the VSV is actively being controlled by the ECU.

- Closed at idle
- Open under highway cruising and light to medium acceleration
- Closed under any more than medium acceleration.
- Closed under deceleration

These results actually sort of make sense for the EGR function.

If the A/F mix is a bit lean side (cruising and light acceleration) the combustion temp will tend to be high and EGR should be operating.

On the other hand, if the A/F mix is richer (idle, higher acceleration) the extra gas will keep the temp down a bit and the EGR should not be required.

This does contradict the #3 scenario in the manual however so I'm not sure which is right.

Thoughts?

Jim

timothy47129

The egr function u described sounds right on to me

scope103

Interesting. It sounds like the VSV is duplicating the designed effect of the throttle valve. (except for the no-EGR during heavy acceleration). But www.autoshop101.com / technical articles / Exhaust Gas Recirculation is consistent with your observations.

Which means, I guess, that the manual alone is an over-simplification.

Thanks to you for your careful observations.

jgrant721

Thanks for the feedback guys especially for the reference to www.autoshop101.com; what a great resource, now properly bookmarked!

In reading the EGR article I saw that the section "ECM Controlled VSV" exactly describe the operation I observed, so I agree, either the manual didn't keep up with the ECM software development or it's just been simplified.

Unfortunately this puts me back to square one in my search for the culprit in my generally degraded smog test results. I can't get why simply changing to a higher flowing exhaust system while retaining all the original smog gear would result in such a significant increase in smog readings.

Still looking for answers!

Jim

scope103

If you haven't already figured it out, I don't have all the answers. (At least, all the right answers.)

During my head gasket replacement, I examined my plenum (upper intake manifold) and found it alarmingly full of "crud." So bad, that once I cleaned it out the idle-ups (A/C, power steering) started working. If you have enough crud in the plenum, the ability of the EGR to inject combustion gases (exhaust) into the plenum could be really reduced. I think the EGR temperature probe is designed to catch the situation where no gas is making it to the plenum, but there will be a point where the performance is degraded but you're not getting a code.

The other, less obvious option is that your cat is not working well enough. The cat has only a small effect on NOx, but you've got elevated HC too.

Good luck, and if you find something new, let us all know.

timothy47129

Have u ever checked for proper fuel pressure or ever had ur injectors cleaned but if it. Was running that lean I would think there would be drivability problems

jgrant721

Thanks for the additional comments.

I am pretty sure the A/F mixture is OK. I have an O2 sensor meter that I built to check O2 sensor operation. Its just a small circuit that turns a ten segment LED display into a 0.0 - 1.0 volt meter. I stuck in in the shell of an old iPod for fun!

Once the engine is up to temp it shows exactly what the manual requires, swinging back and forth between 0.1 - 0.9 volts, 7 times in 10 seconds @2500 RPM. I think that indicates that the feedback loop on the A/F mixture is working.

I am beginning to think the same as you scope103, that maybe the cat is underperforming. I did have some trouble with "sensor safe" sealant when I did the work on the exhaust system. The O2 sensor mounting flange on the Thorley headers was not flat causing an air leak. I used some sensor safe sealant to repair it and went through 2 O2 sensors before realizing that the silicon in the sealant was the problem. I ground down the flange, replaced the sensor and had no O2 sensor problems after that.

I'm starting to think this same sealant may have caused a degradation of the Magnaflow cat as well. The reading I've done indicates this is possible but that it may burn off when the cat gets hot. With no way that I know of to test just the cat I may have to bite the bullet and throw in a new one.

I will post results if I get that far.

scope103

Ah, if you were in California you would be testing your cat every time you drove ...

California trucks have a second O2 sensor located downstream of the cat. If the second sensor is swinging 0v to 1v in time with the first sensor, then the cat is not doing anything, and the ECM throws a code.

I wouldn't mention this to (almost) anyone else, but if you went so far as to make your own Oxygen Sensor Meter, you might be into something like this. The downside is that you need another O2 sensor (and your extras are probably long-gone with the trash) and a way to mount it. Probably not worth it compared to the cost of just replacing the cat.

Still, before you replace the cat, at least put your hand on the EGR pipe into the plenum. I'm told it should be "warm, not hot." If it's cold, your EGR is not successfully injecting anything into the plenum (possibly due to crud), even though the valve, modulator, vsv and ECM are all working. You have very high NOx, and your HC isn't that high. While the cat may be the cause, I'm still suspicious of the EGR system.

PS LM3914?

jgrant721

scope103,

I actually thought about doing exactly what you describe and hesitated for the same reason: a lot of work to avoid changing the cat!

I have gone thru the EGR tests in the Service Manual and when, with the engine at idle, I apply vacuum directly to the EGR valve, the engine stalls immediately. Unless I am missing something I think this verifies basic EGR operation? I will do the "warmth test" though.

What is so frustrating is that when I look at the smog test results for my other car that is close to the same age and mileage, with very similar engine management technology ('90 Porsche 911), the results are very similar to the 4Runner's "Before" numbers in my original post. There is no reason the Toyota should have jumped so high other than whatever happened when I did the exhaust system work.

I will continue to investigate.

PS: Yes it's an LM3914 based circuit. Pretty much the one described here.

timothy47129

I know you can get a weld on universal magnaflow for 60 bucks at o'reillys.I put one on my 99 Ranger and it works great.

Punchy

ERG modulator could be bad.

Did you do the suck on the EGR valve hose test and stall the engine?

I found that Autos have the hardest time getting around this with incorrect gearing and tire size since it throws off the shift points and keeps the engine under a heavyer load which keep the EGR from opening up at cruise points.

Run a vacuum hose from the EGR valve connection into your cab and hook a vacuum gauge.
1.Shows good activation vacuum then bad or plugged EGR valve.
2.Shows bad activation then hook it before the green VSV and test if there is vacuum lvl changes, If not then its the EGR modulator or plugged P and E ports in the throttle body.
Its fairly easy to trace this way.
Also check that there are no airleaks in any of the hoses that connect to the upper intake and pre throttlebody.


Since I got my 92 V6 auto pick up I also found out that the wrong gearing and oversize tires throw off the shift points and keeps the engine under a load which keeps the EGR from opening.
On my manual 92 V6 4R I closed off the EGR manifold entry point except for a 1/8 hole to fool the EGR temp sensor and never had a NOX problem because the shift points are manual control.

jgrant721

Well I spoke to the people at Magnaflow about sending in the cat for warranty exchange and they said OK. The down side is, if they test the cat and find it OK they will just send it back and I will no further ahead in finding my emissions problem.

The other thing I asked them was if they thought the size of the cat (engine displacement rating) could be a factor in the poor emissions performance (the cat I have installed is actually sized for a 6.2L displacement engine in a 6000lb vehicle). The answer I got was "yes it could very likely be a factor" (although no specific documentation could be provided to back up that claim). I have been looking for some evidence to support that possibility (too big a cat may not get hot enough to work efficiently) but so far nothing solid.

Anyway, I pulled the cat this afternoon and I hope to get it on its way back to Magnaflow tomorrow, so within a couple of weeks I should have some more information.

jgrant721

So I got a warranty replacement Cat from Magnaflow. Put it on the truck and after a long highway drive went straight to the test station. HC and CO were much lower (close to results before the exhaust work) the NOx was lower but still a fail. It looks like the cat I removed might have been a bit contaminated by the "sensor-safe" silicone sealant I had used on the O2 sensor flange. Unfortunately I still haven't completely solved the NOx problem.

The most interesting thing I learned from the test was that the EGR system is not actually operating under the test conditions! I had a test light hooked up to the EGR VSV so I could see it go on and off. Even though it does activate the EGR while driving during highway cruising and light acceleration/engine load, there is not enough load during the 25mph test to cause the ECU to switch off the EGR VSV and allow the EGR to operate.

I got in touch with a senior tech at the Provincial Vehicle Testing Department and explained my situation. He was very helpful and we had quite a long conversation on the technical details. He offered some info and suggestions:

- He said that in their experience less than 25% of the NOx reduction was done by the EGR and about 75% was done by a properly operating cat.

-When I told him the brand of cat on the car he suggested that "certain aftermarket cats" they had tested did not have nearly enough catalyst in them to reduce NOx effectively and that the mostly likely cause of the high NOx was an under-performing cat. He said of the cats they had tested, the Walker CalCats were one of the best performers.

- He did suggest as a quick fix I could try rigging the EGR VSV so the EGR would always be active (controlled by the EGR vacuum modulator) and this might reduce the NOx enough to get me a pass.

- Also suggested that I do a complete check for any exhaust leaks ahead of the cat as this could lead to higher NOx

I told him I was wondering if the lower back-pressure in the aftermarket header/cat/muffler setup is somehow causing changes to the ECU input sensors leading to incorrect control of the EGR? He agreed that it could certainly be a factor if the ECU was somehow misinterpreting the engine operating conditions and was not switching on the EGR at the right times.

So the saga continues. I am now thinking it is likely a combination of under-performing cat and improper ECU control of the EGR, perhaps due to lower exhaust back-pressure.

Will post any new results.

Jim

j2the-e

I see you've tested the egr and you've tested the vsv. did you check to see that you are actually getting vacuum to the valve using a vacuum gauge? Those little metal vacuum pipes notoriously rot away on the inside and get plugged. The egr modulators also fail regularly.

jgrant721

Yes, I checked all the pipes and hoses and hooked up a gauge to confirm vacuum on the EGR hose. I think the big problem is that under control of the ECU, the EGR VSV is shutting off the EGR system during the emissions test. Still don't know why exactly that is or how I might resolve the problem (see previous post for more info).

Jim

j2the-e

If the vsv is being shut off by the ecu, you likely have a bad coolant temp sensor. Your egr vsv should remain on when the coolant temp is above 126 degrees F. The egr flow itself is controlled by the modulator

jgrant721

Yeah, because the temp sensor is key to EGR operation it was one of the first things I checked when I started working on this problem. Before the truck warms up the ECU keeps the EGR disabled completely via the VSV. Once warmed up (above 52 degC) the ECU will switch the state of the VSV based on other sensor inputs and when it thinks it should, it will allow the EGR to operate under control of the EGR Modulator. The ECU/VSV will still switch the EGR system on and off at different engine loads depending on things like throttle position, air flow, RPM etc, but as I said, the EGR is switched off by the VSV at the load presented by the 25mph emission test so it is not helping my test results at all!.

Jim