Failed CO emissionss--high NOx

[kerrye]

Yep, that's me. 80 is maroon. We live on W. Irvington. I've ordered the EGR, should be here in a couple of days. Dealer didn't have one.
My 80 has been throwing the EGR code as long as I've had it. Always passed emissions until this year. So like 3 or 4 tests since they're required every 2 years I think. I'd just pull the fuse prior to the test and the check engine light would go off long enough for the test. Although nowadays I think it's still possible to pass emissions with a check engine light. Mine's OBDI.

 

[LFD2037]

Ahhhh, OBD I. Disregard my prior comment then. They don't even do emissions for OBD I here. With any OBD II I've had, and had any check engine light or one just for EGR, I've failed even if vehicle seemed to run perfect.

 

[blkprj80]

OBD1? I guess PinHead was right then.
Wish more folks would list their year in their signature... It only takes a minute.

 

[kerrye]

EGR valve arrived today. Took me about an hour to install it. I didn't have a socket to fit the studs so I removed and installed it without removing the studs. Had to pry it off with a screwdriver but installation wasn't bad. Unplugged the temp sensor and removed it from the EGR after I got the EGR off the engine. I'll get it to the emissions testing station in the next few days and see if it reduces the NOx emissions. It'll also be interesting to see if the new EGR resolves the check engine light code 71 problem.

 

[Timpanogos Slim]

worst case scenario some people have had to drill out the egr port inthe throttle body

 

[kerrye]

Port looked clean when I had the EGR off.

 

[ToothDr]

I hope your new egr will get your nox levels low enough to pass colo emissions. I was in a similar spot last month. I ended up replacing very old o2 sensors and the cats as well. My 93 cruiser now has nox numbers lower than my 2007 audi.

 

[kerrye]

OK, still some issues. Check engine light is still coming on. With the new EGR, if I pull a vacuum on the passenger side nipple of the egr with the engine running, the engine does not stumble. However, if I pinch off the vacuum hose on the driver's side nipple and pull a vacuum, the engine will stall. (This didn't happen with the old EGR). This tells me the EGR diaphragm is good and it can operate. But something is still not correct, because it should stumble with vacuum on the passenger side nipple from what I've read.
Any suggestions as to what to try next? I replaced the vacuum modulator (thing attached to the EGR on passenger side) a couple of years ago.

 

[scoop]

I fraught this for years and it was the ports in the intake. Remove the TB and make sure it is clean all the way. I have not had another problem in 4 years.

 

[kerrye]

That may be an issue but my EGR is not behaving the way it should according to the test shown in the YouTube video. The new valve won't hold vacuum or cause the engine to stumble without me pinching the driver's side vacuum line from the EGR that goes down to the intake plenum. Maybe my Mity Vac is not producing enough vacuum to make it operate and cause the engine to stumble but other people have written that that happens just by sucking on the passenger side nipple. So it seems to me that the driver's side nipple/hose which goes to the intake plenum is open to atmosphere stopping the build up of vacuum. Should it be doing that?

Here's the Youtube test:

http://www.youtube.com/watch?v=CsZV5YbWOQ0

Nothing happens when I do the first test. Engine stalls when I pinch off the hose as in the second test.

 

[Pin_Head]

If it stalls when you put a vacuum on the actuator, you can be pretty sure that the passage in the intake is clear. Do you still have the same code? The FSM has a great trouble shooting guide.

 

[kerrye]

If it stalls when you put a vacuum on the actuator, you can be pretty sure that the passage in the intake is clear. Do you still have the same code? The FSM has a great trouble shooting guide.

Yes it will stall if I pull the vacuum on passenger side nipple while pinching off the vacuum hose on the driver's side going to the intake plenum.

So yes, I agree this shows the EGR is working and the passage clear. But I still have a check engine light. (I need to confirm that light is still a code 71. But it's coming on under the same conditions it always has with Code 71) So something else has to be malfunctioning I think. I'm thinking it must be the VSV, the modulator or the temp sensor.

But I'm confused as to why the truck in the you tube video stumbled on the first test and mine doesn't. I can't pull any vacuum on the EGR without pinching the hose going to the plenum.

 

[ToyotaDon]

The nipple on the driver side goes through the intake and attaches to another hose which goes to the VSV (Vacuum Switching Valve). The VSV is another common failure, and it's important because the computer commands it open or closed based on engine temp, load, etc. It's hard to get to under the plenum, though some have used a substitute valve in a work around.

HTH

 

[kerrye]

At idles, should the VSV be venting to atmosphere which is what it appears to be doing? Seems like it should be since there is no demand for the EGR at idle as I understand it. So if that's true, then I'm confused by the YouTube test video which appears to show that side of the system holding vacuum at idle.

 

[Pin_Head]

It depends on if it is at operating temperature. Download the '96 FSM and do the diagnostic tests. It is close enough. Just disregard the OBDII specific comments.

 

[kerrye]

Thanks. I just tested my relatively new modulator to confirm it's working correctly. It is. So at this point the only two possiblities seem to be the temp sensor or the VSV. Unless there's a bad vacuum hose but all my hoses seem to be in very good condition. I'll read that pdf and see if I can figure out what it should be doing in the conditions I am testing.

 

[Pin_Head]

That pdf is only 1 out of 15 that you need to be reading.

 

[kerrye]

I read the pdf. As I read it, with the engine warmed up and at idle, the VSV should be open to atmosphere so EGR does not open. So my tests so far indicate the VSV is operating correctly but it means the YouTube test shows a faulty VSV because he was able to open the EGR by pulling a vacuum on the passenger side EGR nipple without pinching off the other line to the VSV which should have been open to atmosphere at idle to stop the EGR from opening. So if I 'T' a vacuum gauge into the line between the modulator and the EGR passenger side nipple I should see vacuum at cruising speed when the EGR should be operating. If I don't see that, it means either the VSV is bad or the temp sensor is bad and isn't indicating the engine is warmed up.

 

[kerrye]

That pdf is only 1 out of 15 that you need to be reading.

I got another pdf from another thread with testing procedures. It's a 1996 EGR inspection procedures pdf. It includes tests for the operation of the VSV and the modulator. Modulator passed those tests. So with a new EGR and proven modulator I think I've narrowed it down to either the VSV or temp sensor.

 

[Pin_Head]

By pinching off the hose that the VSV vents, it allows vacuum to build in the EGR and stalls the engine. You need to rule out the temp sender, vsv, ECU and the wires and hoses in between. This is 5-15 pages of stuff.