Failed CO emissionss--high NOx (1 Viewer)

[kerrye]

I've done some more reading and it appears that the VSV should only be open to atmosphere during cold warm up. After that it closed and allows vacuum to assert its effect on the EGR. So, since the emissions test is done warm, I think blocking off the VSV won't have any negative effect on an emissions test.

 

[kerrye]

Temp sensor hasn't arrived yet and despite the fact that I think my VSV is stuck open I had to do the emissions retest today since tomorrow was my 10 day window of grace and it was predicted to be a high of 4 degrees then. So I stuck a bb in the driver's side vacuum line from the EGR to the manifold, mimicking a closed VSV and took it down for the test. It passed. NOx has gone from 5.74 down to 3.56 grams per mile. Limit is 4.
So it was a bad EGR valve along with other things. If your VSV is bad and you need to pass emissions before you have a chance to replace it, you can do what I did and 'manually' close the valve in the meantime.

 

[Timpanogos Slim]

Glad to hear that you got this resolved.

. :Sent by pneumatic tubes

 

[kerrye]

Thanks to everyone for the help. I'll add more once the temp sensor arrives. I've also ordered a Dorman VSV to replace the original one. I couldn't find any online parts supplies with a listing for the OE VSV. It's be easier to install the Dorman anyway, since the failed one can be left in place.

 

[ToyotaDon]

Good to hear!

 

[TrickyT]

... It passed. NOx has gone from 5.74 down to 3.56 grams per mile. Limit is 4...

Excellent news!

 

[kerrye]

Just for the record, my new temp sensor arrived and I could only get a reading on the Ohmeter at the 2000k scale. It read around 500 at room temperature.

 

[kerrye]

I thought I'd conclude this thread with a picture of the installation of the Dorman 911-850 in place of the poorly located original VSV. Got the valve from Amazon for $26. Left the original VSV in place and actually ran the vent vacuum hose thru the original valve (it is open all the time) since it was easier to plug the vent line from the Dorman into the driver's side of the OE VSV rather than snaking it over and putting a coupling into the hose on the passenger side of the original VSV. I've never had the brace holding up the plenum that later models have so I just used a piece of flat stock aluminum to fabricate a bracket for the Dorman. Tested everything with a vacuum gauge and it's working nicely.

PS--I should add that I don't think my temp sensor was bad. Before switching in the new one and with the engine warm I did another resistance test on the 200k scale and it showed 35 which I think is within the acceptable range. So, either I screwed up on my first test and wasn't getting a good connection with the probes, or it's just working when warm, which is when it needs to work anyway. As a result, I haven't installed the new temp sensor yet. I'll drive it for a while and confirm I don't get a code 71. So far so good.

 

[TrickyT]

Nice solution. Certainly in a more accessible spot than the OEM VSV. I think the correct p/n for the Dorman is 911-850 though.

 

[kerrye]

Nice solution. Certainly in a more accessible spot than the OEM VSV. I think the correct p/n for the Dorman is 911-850 though.

Yep, thanks. Corrected it.

 

[wpns4l]

can you post a pic of what hose you put a bb in?

 

[kerrye]

It's the one that goes from the driver's side of the EGR down to the manifold (although it's important to be aware that the hose does not actually go into the manifold. It goes thru the manifold to the VSV) In this picture I have my vacuum gauge line T'd into the line so it doesn't look the way it normally does without that T in it.

 

[mercfan]

My own P0401 woes

I Kerrye - thx for the writeup. I've been following your thread and studying the diagrams that were posted in your thread because I have P0401 (Insufficient EGR gas flow) code on my '95.

Following your thread I did my own investigation as follows:

1) EGR: With the engine cold, I've hooked up MityVac to the passenger side nipple on the EGR valve. I too had to pinch the Driver side hose to pull the vacuum, so I've concluded that the ability to pull the vacuum means that at leat the EGR valve diaphragm works on mine.

2) VSV: I've lookup this thread and followed instructions there to test the VSV operation. It's open to the atmosphere by default, but when voltage was applied to the two wires (as suggested), VSV did close and my MityVac was able to pull vacuum - just like when I had pinched it before. Therefore, I THINK the VSV is working when cold. Someone suggested that it may work when cold and be open when engine warm/hot. So this test may not be conclusive yet.

3) Temp sensor - on mine, the first mearurements I took fooled me to believing that I have an open circuit, but after reading the posting from PinHead (thank you) I retested with a 200KOhm range and it measured 352K when cold - at least it's not open like I thought.

So at this point, I dont' have a conclusive evidence to pinpoint to anything specific. Could it still be a bad EGR valve even if the diaphram tests out ok?!

What else should I be checking? Thx.

 

[kerrye]

Could be the modulator. Take it off and pull a vacuum on the bottom nipple. It should hold vacuum. Then blow into the single nipple on top while blocking off the two other nipples with your fingers. Air should come out the top of the center thru the filter. If not, the modulator is bad.

You can T into the line at the EGR on either side and monitor the vacuum levels while driving by running a vacuum hose into the cabin thru the hole that is plugged with a plastic plug just below the master cylinder. You should see vacuum under the conditions which call for the EGR. If not, it's either the modulator, the VSV or a bad vacuum line. Sticking a BB in the line on the driver's side of the EGR will cut the VSV out of the system and allow you to check the modulator also. You should get vacuum under far more conditions with a BB in that line.