FAILED Smog Test_NO level too high? - need help

[Socal_dmc]

So I failed my Test-Only this morning and I've attached a copy of the printout. My CO2 and O2 levels were fine, but my NO levels were way too high.....around 2000 ppm when it should be around 400 ppm.

According to the smog guy, he said it was likely caused by the engine running too hot. It was a fairly warm day and the engine had been warm at the time of the test, but I've never noticed any unusually high temperature readings before. I checked my coolant level afterwards and while it was low, there was definately coolant in the system.

Can anyone weigh in on this and help me out? Thanks so much.


Matt

[jawn101]

So I failed my Test-Only this morning and I've attached a copy of the printout. My CO2 and O2 levels were fine, but my NO levels were way too high.....around 2000 ppm when it should be around 400 ppm.

According to the smog guy, he said it was likely caused by the engine running too hot. It was a fairly warm day and the engine had been warm at the time of the test, but I've never noticed any unusually high temperature readings before. I checked my coolant level afterwards and while it was low, there was definately coolant in the system.

Can anyone weigh in on this and help me out? Thanks so much.


Matt

Have you made sure your mixture is set right? How is your idle?

[Socal_dmc]

It idles smooth...just a little below 1000

[jawn101]

That's high. It should be 775 +/- 50 RPM. Your mixture probably needs to be adjusted. Many threads here on the forum about doing so (search for high idle)

Is your frequency valve buzzing?

How old is your O2 sensor?

[tiger38117]

It's the mixture. Set it with a dwell meter and you'll pass. Instructions are around here somewhere.

[jawn101]

Here's a good thread to read. There's a link to a great article that describes the process in detail on page 2.

http://dmctalk.org/showthread.php?4022-Co-Mixture-odd-dwell-readings

[vwdmc16]

your CO2 levels are a bit low ( should be in the high 13% or more), and you have more o2 in there than you should ( you want almost 0%) this indicates a possible exhaust leak which also contributes to higher nox. do you know if your exhaust is solid?

[DCUK Martin]

If the lambda system is working as it should, the mixture should be spot on, adjusting with a dwell meter is a good idea but you'll only be adjusting within the "window" the lambda system controls anyway.

One thing to check - when idling, pull the vacuum hose off the distributor. Is there vac there? There should be none at idle. This will cause an artificially high idle and hot running with an occasional misfire. I've seen this many times when the vac hoses are plumbed wrong or the throttle stops are poorly adjusted.

[tiger38117]

If the lambda system is working as it should, the mixture should be spot on, adjusting with a dwell meter is a good idea but you'll only be adjusting within the "window" the lambda system controls anyway.

One thing to check - when idling, pull the vacuum hose off the distributor. Is there vac there? There should be none at idle. This will cause an artificially high idle and hot running with an occasional misfire. I've seen this many times when the vac hoses are plumbed wrong or the throttle stops are poorly adjusted.

I respectfully disagree, 1905's mixture was FAR out of whack 2 years ago, running super rich. It was so far out of kilter that the frequency valve wouldn't even run. Once I reset the mixture with the dwell meter everything went back to "normal".

Oddly enough, even with the mixture out of whack, the car still ran/idled great. The exhaust smelling like gas was the only thing that caused me to take notice.

[DCUK Martin]

I respectfully disagree,

Then I was not clear enough and should have said "If the lambda system is working as it should and not running so rich that it's not running at all" ...

If he's producing too much NOx, then the engine is running lean, not rich. This is actually a very difficult region to get in to - if you dial the mixture down too lean that you fall out the bottom of the lambda window, then you're a whisker away from stalling and full throttle will induce a lean condition. Tuning with a dwell meter will get you back into the correct spot in the lambda window but it won't make any difference to your emissions unless you go too far and end up going off the top of the lambda window and run rich, where you'll see too much HC and CO.

[Bitsyncmaster]

Problem is, a lot of POs adjust the mixture to get a good idle. You get a better idle (no hunting) when the FV is not working by adjusting the mixture to far off. You only have about a 1/4 turn max for it to be to far rich or to far lean. My guess are most are adjusted rich because they idle better that way.

Never adjust the mixture by how good it idles.

[jawn101]

Never adjust the mixture by how good it idles.

Stellar advice. My idle was wacky when I got 2100. But it had just passed smog the day before. I eventually adjusted the mixture to compensate for the idle hunting when cold, not knowing what I was doing. Then I learned how to properly set it, and the measurements I took showed that I had totally screwed everything up. Pulling the mixture back into correct spec sent my idle a-hunting again when cold (although once everything is properly warmed up, it's smooth and perfect at 750) but eliminated the fuel smell.

[Bitsyncmaster]

Stellar advice. My idle was wacky when I got 2100. But it had just passed smog the day before. I eventually adjusted the mixture to compensate for the idle hunting when cold, not knowing what I was doing. Then I learned how to properly set it, and the measurements I took showed that I had totally screwed everything up. Pulling the mixture back into correct spec sent my idle a-hunting again when cold (although once everything is properly warmed up, it's smooth and perfect at 750) but eliminated the fuel smell.

I did the same thing when I first got my car.

[Alves]

I thought after a certain age cars didn't require emissions testing anymore, a sort of grandfathering in?

[DMC5180]

I thought after a certain age cars didn't require emissions testing anymore, a sort of grandfathering in?

It's California! You probably have to meet the emission standards that were imposed during the Year of manufacture. Starting about 1973 to present. I'm not quite sure how the rules apply Modified cars though.

[jawn101]

It's California! You probably have to meet the emission standards that were imposed during the Year of manufacture. Starting about 1973 to present. I'm not quite sure how the rules apply Modified cars though.

Anything newer than 1975 must still be smogged. Smog requirements vary from county to county. There is absolutely no modification to exhaust "systems" permitted. You can't even buy (that's right, BUY - let alone USE) an aftermarket cat here. California ARB certifies "systems" not "parts" so you must stay with 100% OE parts (or there is one certified aftermarket brand I am aware of that is available to replace OE cats) or you will fail the "visual inspection" portion of the test.

Draconian in the extreme.

[DMC5180]

I was close on the Year. So your telling me there are NO stage I exhausts on California Registered Deloreans. That would be hard to believe.

[Alves]

Oh man I'm glad I asked. I'm in massachusetts and so far where I live they don't seem to strict. With that being said I'm going to try and find the shadiest looking place when I get mine inspected.

[jawn101]

It actually looks like they've relaxed the rules on the aftermarket cats a bit since I've been here. Some references for posterity:

Smog requirements/FAQ
http://www.dmv.ca.gov/vr/smogfaq.htm

Rules governing aftermarket catalytic converters (the only part of the exhaust system allowed to be exempt from the anti-tampering laws, but still very tightly controlled)
http://www.arb.ca.gov/msprog/aftermktcat/aftermktcat.htm

On the plus side, you can modify your exhaust (mufflers) if you like, but there are strict dB levels you must comply with and you must still pass emissions, of course.
http://www.dmv.ca.gov/pubs/vctop/d12/vc27151.htm

[jawn101]

I was close on the Year. So your telling me there are NO stage I exhausts on California Registered Deloreans. That would be hard to believe.

To my knowledge that would have to be correct to be legal, unless the cats had recieved one of the aforementioned Executive Order waivers. I know I haven't seen one installed! There are counties here that don't require a smog inspection biannually, so if the car was inspected when it was first imported, registered in one of these counties, modified afterwards and never sold to a new owner who wasn't a parent, sibling, grandparent or child of the original owner (and didn't live in a county requiring biannual certification)... well, the state wouldn't know.

Edit: Checking the EO exemption database (https://ssl.arb.ca.gov/PartsSearchTool/CatalystSearchTool.aspx) I don't see any exemptions for the DeLorean...

[DMC5180]

California where everything Automotive is for "OFF ROAD USE ONLY" Or "Is Known to Cause Cancer only in the State of California" :evilgrin:

[jawn101]

California where everything Automotive is for "OFF ROAD USE ONLY" Or "Is Known to Cause Cancer only in the State of California" :evilgrin:

Preaching to the choir, man. I'm so tired of those Prop 65 (everything causes cancer) warnings on every single thing. Like literally everything. I was waiting for a taxi outside the airport not long ago and noticed one screened on the windows of the terminal.

This facility contains chemicals known to the state of California.... :banghead:

Anyway we've gone off OP's topic here. OP, have you had any luck investigating your mixture control system? Is the FV buzzing? Did you hook up your dwell meter and try to dial things in?