[Eric]

I just went down to the TEST ONLY station for my Smog check and failed because the NOx was too high so now I am a GROSS POLLUTER.

Here are my numbers:

Timing = 12* (spec is 10*)

15 mph (1710 rpm)
CO2 - 13.8%
O2 - 0.9%
HC - 129ppm (127max / 314gp)
CO - 0.84% (0.78max / 2.08gp)
NO - 2601ppm (1031max / 1822gp) Gross polluter!!!!

25 mph (2629 rpm)
CO2 - 14.8%
O2 - 0.5%
HC - 56ppm (108max / 264gp)
CO - 0.46% (0.99max / 2.29gp)
NO - 721ppm (891max / 1622gp)

Downey headers, 10K miles on new motor with rebuilt heads, 100K on all other parts.

Everything that I have read points to the EGR system. I pulled the engine codes and came up with error code 71.

Error Code 71:
EGR gas temp sensor signal (THG) is below "A" after driving for 240 seconds in EGR operation range. "A" is THA + 30*C for California spec and THA is the air temp sensor in the air flow meter.

So, I was inspecting the EGR circuit and I noticed that I could not get high vacuum when I put manifold vacuum on port R of the vacuum modulator while at 3500 rpm. I believe this is a problem with the VSV???

What controls the VSV to turn on and off?

Any help is appreciated and I will add more info as I have time to check each circuit of the system.

 

[4CrawlR]

ECU controls the VSV, make sure the vacuum ports feeding the VSV are not clogged, very common for them to get plugged where they leave the intake. Turn the timing back, when I failed (high NOx/22RE) at 5 BTDC, I retimed the engine back to about 1-2 BTDC for the retest. Also filled up with 91 octane and cleaned/ported out the EGR ports on the LC header on my 22RE as well as cleaning out the EGR valve and plumbing with a gun cleaning kit. Dropped my NOx from 2200 down to about 880.

 

[Eric]

All passages are clear.

I noticed that when the engine is cold the EGR VSV is energized which disables the vacuum modulator and vents any vacuum to atmosphere.

When the engine is up to operating temperature, the VSV is still energized and prevents the EGR from ever getting vacuum.

I checked coolent temp sensor and the air temp sensor and both of them pass. It looks like someting in the ECU may not be working correctly.

Anyone have any suggestions?

 

[4CrawlR]

On my '85, there are no VSVs for the EGR system, it is all passively controlled. I suppose you might try unplugging the VSV connector so that it is off for the smog test, assuming they don't check to that level of detail. Probably need to go through the EGR troubleshooting steps in a Factory Service Manual to find out why that VSV is on and how to get it to turn off. Maybe resetting the ECU might clear it.

 

[Eric]

I have been through the FSM many times and all the tests work fine......I guess that means something may need to be checked at the dealer with the ECU

Just for the heck of it, I called the dealer......Reman ECU = $980!!!!!!!!!!!

 

[4CrawlR]

Junkyard for a used ECU: http://www.car-part.com/

Sounds like it could be a wiring problem, too. Usually the VSVs are wired to +12V on one side and then the ECU grounds the other side to turn them on. Maybe the wire to that VSV has shorted to ground, thus it is always on. Or it may be plumbed wrong.

 

[Eric]

Yes, the VSV has +12V and the ECU switches to GND. The problem is that the ECU is always at GND at the VSV pin. I removed the harness from the ECU and checked continuity to GND and there was no short.

Thanks for help so far.

Can anyone with a 91 PU see if their EGR VSV is ON when the engine is cold and off when the engine is hot? All you need to do is turn the key to ON when cold and unplug the EGR VSV (has a green connector and is closest to the front of the engine compartment). See if it clicks.

Do the same thing with the engine hot and it should NOT click.

Thanks.

 

[4CrawlR]

Sounds like you found the cause of the problem then. Either a new or used ECU or pull the plug for the test or even wire a switch to the ground side and then flip the switch (and VSV) off for the smog test.

 

[wizard_Drd]

Sounds like you found the cause of the problem then. Either a new or used ECU or pull the plug for the test or even wire a switch to the ground side and then flip the switch (and VSV) off for the smog test.

If you unplug the or turn the VSV off for the test, you will get a surging idle that the SMOG referee won't like. That was my problem with a TBI 350 where the EGR would not turn off. Now that you are tagged a gross polluter, you have to do the referee bit.

A dirty way to fix it would be to add a circuit to selectivily turn off the VSV. If it is an automatic, then you can tap the VSV ground into the P/N switch so that when you are in P/N the VSV is on disabled the EGR. If it is a manual, then you can grab a tach with a RPM trip point to a relay to turn off the VSV after say 1200 rpm's. Another method would be to get a digital vacuum gauge with a trip point and set it to turn off the VSV after a certain vacuum reading. Whatever yours is at idle.

 

[4CrawlR]

Not sure how the V6 EGR is set up, but on my 22RE, the intake vacuum alone does not open the EGR. Rather it feeds to the EGR modulator, on mine switched by a bi-metal VSV (BVSV) that opens to pass vacuum when the engine warms up. Vacuum signals off the throttle body and feedback pressure from the exhaust manifold all get mixed up in the modulator and that turns the EGR valve itself on and off.

 

[Eric]

Mine is similar, but the ECU controls the EGR VSV instead of having the engine coolant control BVSV on your engine. So, I unpluged the VSV wire from the ECU so it would always turn on the EGR VSV and allow the EGR circuit to work like norma.

I still failed, but I dropped my NOx by 1000 at 15 mph and I need to drop it by another 500!!!!

Here are my numbers test 2:

Timing = 12* (spec is 10*)

15 mph (1720 rpm)
CO2 - 13.7%
O2 - 0.9%
HC - 136ppm (127max) FAIL
CO - 0.77% (0.78max) Close to fail
NO - 1550ppm (1031max) FAIL

25 mph (2719 rpm)
CO2 - 14.7%
O2 - 0.2%
HC - 43ppm (108max)
CO - 0.19% (0.99max)
NO - 261ppm (891max)


It seems to me that 1700 RPM is not enough to turn open the EGR circuit. When I test for vacuum on the EGR line, it seems like I need about 2000 rpm before I notice a vacuum signal.


I wonder if I can set the timing back to 10*, put some 31" tires on (probably adds 100 rpm) and change the O2 sensor and CAT.


The CO2 and O2 seem a little off at the 15 mph test compared to the 25 mph test.

 

[4CrawlR]

I used a new cat and O2 sensor for my test. Wonder if they can use a different gear for the test, I had around 1800 @ 15 (4.88s/worn 33s). And retard the timing more, I dropped mine from 5 BTDC (spec) to about 1 BTDC for my retest.

 

[Eric]

I wonder if the throttle plate is not opening EGR port at 1700 rpm. Maybe I can lower my idle which would let in less air(??) and require my throttle plate to open more for 1700 rpm??????? Is that how the idle screw and rpm work? Less air = less rpm?

I asked if they could use 1st gear and they said NO, it has to be second gear.

 

[2THEMTS]

I had a 90 3.0. Mine was a gross polluter for NOX also. Mine was passing the 25mph test but failed the 15mph test. It had downey headers and full downey exhaust. It also had 31" MTRs and stock timing. I tried changing the VSV and it didn't help at all. I found out that the EGR is opened by exhaust back pressure. The back pressure creates the vacuum that opens the valve. I tried plugging different vacuum lines to see if I could get it to pass. I had to create so much vacuum to open the EGR that it almost stalled the motor. I ended up having to put a stock muffler and change my free flow cat for a stock one to get it to pass. After changing both parts it passed by about 200 points. The mechanic that I had do the work said that toyota changed the EGR for the 3.4 to be controlled by the cams to fix the problem. Apparently it happens to a lot of people since they changed the smog test here in CA. I also didn't go to a referee station because I was told that if you are a gross polluter you can go to a smog only shop. You just can't go to regular shop.

 

[4CrawlR]

I made up a little restrictor plate for my exhaust. Sheet of 16 oz. copper cut to fit the header flange, perforated the pipe opening about 50% and bolts right in along with the header flange gasket. I think it helps boost the exhaust gas backpressure a bit to force more back into the EGR.

 

[Eric]

Hmmmmm, restricting the exhaust, I like that. Do you have a pic? What size were the holes you put in the sheet? I think I have some copper sheet at home too.

I have Downey headers, stock cat & O2 (100,000 miles), Borla exhaust.

I put a vacuum gauge on my enging while I was driving to work today.

TB EGR port - vacuum ranged from 4 to 15 depending on crusing speed and rpm.
Accel/decel showed 0 vacuum which was good.

TB port R - the vacuum gauge bounced and never showed vacuum. Almost like there was pressure instead of vacuum??????

EGR valve - vacuum seemed to be around 3 around 2K to 3K rpm

It just seems like the EGR can't open enough below 2K.

Anyway, I just went to PNP and got a vacuum modulator off an 88 Camery to replace the one I took from my 92 4Runner to see if it has a lighter spring in it???

Last night I set the timing back to 10* (TE1 and E1 jumpered) and 8* (without) and adjusted the idle from 1100 to 800. I also cleaned up the contacts on the dist cap since there was some arcing on them. I need to replace them.

Thanks for keeping this thread going.

 

[Grim Reaper]

I think your problem may be O2 sensor related. It would explain why the VSV is staying energized. There are a LOT of complaints on not being able to pass smog with RE motors and headers.

The fix is usually a heated O2 sensor. If the O2 is below range The ECM may assume it has not reached operating temp even though the water temp says it has. In such a case it may stay in a open loop mode till the O2 indicates and reasonable value that it can sample. As such it will run with out EGR as it does when cold....it will also run rich instead of lean.

 

[insp79]

I have the 3.0 V-6 in a '92 4Runner with Downey headers.
The last inspection, I was having trouble passing for High NOX.
Changed EGR Modulator, and bypassed the solenoid.
Still didn't pass.
Changed the O2 sensor, and passed no problem.
Perform the test on the O2 sensor throught the diagnostic connector.

 

[Toyoda]

If the motor was running rich wouldn't it lower the NOx?

I think I read that you could pour some rubbing alchy in the gas to lower the NOx. It won't fix the motor problem but it might get you through smog.

 

[4CrawlR]

High-tech restricter plate:

Holes are maybe 1/4", basically drilled wherever I could fit a hole.