Failed emissions with high NO

[oreke]

Hello All,

Here's a chronological summary of my smog fail problem:

• Failed smog test with following results:
  RPM 1723
  CO2 14.5%
  O2 0.4%
  HC 10 ppm (max 95)
  CO 0.01% (max 0.58)
  NO 1620 ppm (max 795)
  
  RPM 2902
  CO2 14.7%
  O2 0.0%
  HC 3 ppm (max 77)
  CO 0.01% (max 0.44)
  NO 1096 ppm (max 676)
  
• Read a lot of forum posts: high NO, low CO usually means running lean
• Checked for vacuum leaks (pressurize the intake to 10psi and soap water method)

  • Intake J-boot had a tear -> new J-boot
  • AOS seals were leaking -> New AOS o-rings
  • Consequently -> new intake manifold gaskets
  • replaced almost all small vacuum lines with silicone lines
  • put in new hose clamps for a few bigger hoses

• Checked the spark plugs - tan/white'ish indicating lean mixture, replaced spark plugs
• Replaced air filter
• Noted that AFM bolt cover was drilled, indicating previous adjustment -> I didn't make any changes
• Got another smog check, failed similarly:
  RPM 1760
  CO2 14.5%
  O2 0.3%
  HC 10 ppm (max 95)
  CO 0.01% (max 0.58)
  NO 1449 ppm (max 795)
  
  RPM 2866
  CO2 14.7%
  O2 0.0%
  HC 2 ppm (max 77)
  CO 0.00% (max 0.44)
  NO 1076 ppm (max 676)
  
• Checked for more vacuum leaks

  • Bottom of oil dipstick tube -> put in new o-ring
  • One of the fuel injectors (turns out I damaged some of the old o-rings when putting the rail back together last time) -> replaced injector o-rings, spacers, caps.
  • Can't find any more leaks.

• While resealing injectors, broke a pintle, ordered a GB rebuilt one.
• Cleaned, backflushed, replaced basket filter, and flow tested old injectors. Compared flow rate to the rebuilt one. Close enough.
• Tested O2 sensor - Didn't get very conclusive results. Probably have to replace it. Didn't replace it yet because if I'm still running lean, I don't want to damage the new O2 sensor. Have a new one (Bosch universal 15735)
• Replaced fuel filter since I had the system depressurized anyway.
• Tested DME temp sensor -> Results look good
• Verified FQS setting was at stock

Things still to do:[LIST][*]Test O2 sensor again[*]Install new O2 sensor and see if I need to adjust the AFM air bypass bolt based on the O2 sensor voltage[*]Maybe check the fuel pressure, but I don't have the right adapter, and I doubt there is an issue with fuel pressure, because the car starts, idles, and runs fine.

I would really appreciate any suggestions. I already had quite a bit of help in a previous thread here:

vacuum leak question

I just wanted to start a new thread because that one started as a very specific question, which now expanded.

Thanks,
oreke

[Cocacolakidd]

Mystery on mysteries -

A couple of thoughts -

1.) A missing or improperly adjusted idle speed set-screw on the throttle body.

2.) ICV leaking air - allowing unwanted air into system...

[oreke]

Remembered one more thing. I measured the vacuum at idle by teeing into the fuel damper vacuum input. Got 16 in Hg. But the needle was rattling a small amount between 15-16. I read in some post that a rattling needle indicates burnt valves. I hope that's not the case.

Also, maybe I should go to a smog shop and pay for a NO check with a gas analyzer. I have fixed a couple of small leaks after my last smog check and reconditioned the fuel injectors (although they seemed to be in decent shape to begin with). I just didn't feel like the fixes would be good enough the get a significant reduction in NO.

Another thing I've been looking into is to find a way to measure my air fuel mix ratio. But as far as I can gather, I would need to buy a wideband O2 sensor, a controller, and a gauge. Those kits seem to run around $200. I'm not really planning on doing any tuning, so I wouldn't have an ongoing use for the setup. I just want it as a diagnostic tool and to adjust my AFM bypass bolt. I guess I'm going to have to settle for looking at the voltage output of the narrowband O2 sensor to get close enough, unless there is another way.

Thanks,
oreke

[oreke]

So, I did a compression test and got 185, 180, 185, and 190psi on the cylinders, which seems decent.

Then I tested my O2 sensor again, having made some cables this week to keep the heating wires connected. I couldn't get the O2 sensor to respond well, so I replaced it with the Bosch 15735. The old O2 sensor tip was completely covered in white stuff. Didn't seem like it should be working at all.




When I measured the voltage on the new O2 sensor, it was really low, some mV the whole time. So I went to adjust the AFM bypass screw (after changing the o-ring). I found it really hard to get a stable voltage less than around 750mV. Any time I unscrewed the bolt some more, the voltage would move around a lot, or if I tightened it a bit it would settle to something around 750mV. I don't know if that's normal. In F.R. Wilk's web site CO Level, he says that it should be adjusted to 500mV for the proper setting. Maybe I need to try using a big capacitor to try and stabilize it. Has anyone succesfully done this (adjust the AFM bolt and get 0.5V from the O2 sensor)?

I'm also going to try talking to the smog guy to see if we can attach the gas analyzer and tweak the AFM bypass bolt to optimize the CO level.

oreke

[Califred944]

Had a similar high NOX issure, turned out to be the test tube from the engine compartment to the exhaust pipe. Most have been broken off and should be pluged. I found the nut was there but open and let air into exhaust. You can weld the nut closed or install a ball bearing to fill the hole.

To check, go under the car and try to stick a piece of wire through the nut.

I finall found this was open and when fixed the smog test PASSED.

[oreke]

Califred944, do you mean the nut right next to the O2 sensor on the exhaust pipe?

[oreke]

I finally passed today. I figured I'll post the rest of what I did in order.

• After changing the O2 sensor, I made some cables from a PC power supply because the pins fit perfectly onto the O2 sensor plug pins. Adjusted the AFM bypass bolt as best as I could.
• I had another test and failed again:
  RPM 1758
  CO2 14.5%
  O2 0.4%
  HC 8 ppm (max 95)
  CO 0.00% (max 0.58)
  NO 1289 ppm (max 795)
  
  RPM 2883
  CO2 14.7%
  O2 0.1%
  HC 3 ppm (max 77)
  CO 0.01% (max 0.44)
  NO 770 ppm (max 676)
  
  Better than before but not good enough
  
  
• I never did find a shop with a gas analyzer to adjust the AFM bypass bolt. The places I talked to only had smog machines that would do a whole test, and no stand alone gas analyzers.
• I plugged the hole in the exhaust pipe next to the O2 sensor as Califred944 suggested. The one that normally houses the CO test pipe. I used a steel ball and the existing bolt there.
• I got this weird intermittent stalling and starting problem all of a sudden and went off trying to debug that. The car would just completely cut off all of a sudden, or have a hard time starting on a few occasions.
  • I replaced the DME relay, but I still had the issue
  • I measured the fuel pressure, which seemed fine
  • I replaced the DME temp sensor
  • I tested the AFM on the car as described in Clark's Garage or FRWilk's site, I forget which.
  • I cleaned the terminals on the ignition coil, and tested the resistance of the cable to the distributor, which seemed fine.
  • I sprayed some electrical parts cleaner on some gnd connections and the reference and speed sensor connections. Tested the resistance of reference and speed sensor plugs.

The last few days have been without stalls.
Today, good news: I finally passed smog. Bad news: I stalled after the smog check and had a hard time starting. Removed the DME relay and plugged it back in, and the car started up fine. Maybe something to do with the connectors in the fuse box being loose, or the wire from the fuse box to the fuel pump or DME.

Anyway, smog results:

RPM 1774
CO2 14.5%
O2 0.1%
HC 71 ppm (max 95)
CO 0.26% (max 0.58)
NO 272 ppm (max 795)

RPM 2838
CO2 14.3%
O2 0.0%
HC 48 ppm (max 77)
CO 0.23% (max 0.44)
NO 522 ppm (max 676)

As seen above, HC and CO went up quite a lot but NO came down.

[John_AZ]

oreke,

Compliments to you on the detail of your posts.

I'm curious to know what state your from. In AZ the 2nd test is free and you repay the $27.50 for the 3rd.

You should at least clean the relay board connections and make sure the wires are not brittle, burnt or loose behind the panel.

Glad you passed.

John

[oreke]

John,

I'm in Southern CA. The station I went to has the second test for $5 if you fail the first. But the third is full price $46 + $8.25 for the certificate. The fourth, again, is $5.

One caveat, you have to retest within a month to get the $5 retest price. I had to pay nearly full price today because it's been more than a month since my 3rd test. They gave me a $10 discount, though, which was nice.

I will take a look at the wires and connections for the DME relay this weekend. This intermittent stalling is pretty scary. I'm trying to avoid freeways and long distances.

Thanks, some of your posts on this forum were pretty helpful in debugging this smog issue.

oreke

[v2rocket_aka944]

I just got mine done - I failed the first time for high NOx, I swapped DMEs with the new one set to run rich and it didn't solve it.

The cat needed replacing.

After replacing the cat (back to original DME) the numbers went from about 730 NOx to 8. Yep, eight.

I am in Riverside.

[oreke]

Originally Posted by oreke

• I got this weird intermittent stalling and starting problem all of a sudden and went off trying to debug that. The car would just completely cut off all of a sudden, or have a hard time starting on a few occasions.
  • I replaced the DME relay, but I still had the issue
  • I measured the fuel pressure, which seemed fine
  • I replaced the DME temp sensor
  • I tested the AFM on the car as described in Clark's Garage or FRWilk's site, I forget which.
  • I cleaned the terminals on the ignition coil, and tested the resistance of the cable to the distributor, which seemed fine.
  • I sprayed some electrical parts cleaner on some gnd connections and the reference and speed sensor connections. Tested the resistance of reference and speed sensor plugs.

Just to follow up on this intermittent stalling issue I mentioned along the way:

I didn't get any more stalling but I had a lot of non-start issues since the post above. I've been trying to debug it for a while now.

A couple of weeks ago, I narrowed it down to a no-spark-to-the-distributor issue. Checked the coil, wires, ref and pos sensors, etc. Finally, I took out the DME and re-soldered the big honking transistor with the heatsink at one edge of the board. (See: DME Repaired w/pics - Rennlist Discussion Forums )

No non-start in the last week. Crossing my fingers that it'll stay that way.

oreke