5.7LImport

Kinda in a pickle right now.

I took my car to get inspected so I can get rid of my bright green 2003 sticker and it managed to fail emissions.

Its a 91 300zx... but they actually typed up 5.7L as the engine size. So I think they're running me on newer Corvette emissions.

It passed all the emissions test with flying colors except the "Nox(ppm)" test. For high speed rpm.. my car was 951 (751 is standard) and at low speeds my car was 1213 (829 is standard).

Specs on my setup:

- 1998 LS1... stock
- EGR bypass w/ newer LS1 passenger manifold
- Dual catalytic converters - X-pipe - dual mufflers

I do have an exhaust leak on my driver side header if that might be effecting it. EGR wasnt deleted from my PCM, but I dont think that matters since they had the sniffer on my car taking the measurements.

So what could be wrong here? Is it a matter of getting EGR put back on? Or will that not cover the margin I'm failing by?

Any help would be awesome... I want to get my car on the road... legally!

-Vann

Speartech

iTrader: (14)

The main function of EGR is to reduce NOX, so I would say "Yes", no EGR is why you failed the test.

5.7LImport

well... Ive been talking with MTI and they've pretty much said the EGR wont effect it... besides, newer LS1s dont even have EGR.

My engine is running extremely lean though and I think that has a lot to do with it. I just need to get some diagnostics done to check what codes I'm throwing.

I'm taking it to them tomorrow to get it checked out... lets hope it's an easy fix!

-Vann

crainholio

iTrader: (2)

I don't have cam specs handy, but I'm inclined to think the '01+ engines which don't have EGR accomodate that via cam design.

I believe this was the case w/ the LT4 cam back in the LT1 days...it had enough overlap to negate the requirement for external EGR.

Other causes of NOx emission increase are usually:
-leanness in the air:fuel mix
-excessively-hot chambers
-failed cat converter(s)

The cat converter piece is pretty typical...the reaction that breaks NOx molecues happens on the first brick of the cat...this part takes the damage if you're running pig rich and overheat the cat.

Speartech

iTrader: (14)

Well I've got news for you and MTI; it does affect it! The newer engines eliminated it thru different cam specs and calibration changes. The main purpose for EGR is to reduce NOX. It wasn't on there for decoration!

You may be able to tune around your problem and get it to pass, but to say EGR doesn't affect it is completely false.

5.7LImport

Ok cool, thanks for clearing that up! I didnt know the newer LS1's had different cams to accomodate for the EGR.

I know it's not the cats.. theyre new and the car has never run rich so I know they arent damaged.

I need to get my car tuned to get the air/fuel back to a correct ratio.

I still need to get my codes read.. so hopefully that'll tell me something and these issues can get resolved.

-Vann

crainholio

iTrader: (2)

Sounds like a great excuse for a cam swap!

If you're running the PCM in closed loop mode, it wasn't likely a tuning issue that failed you. With a stock engine, it's not likely your fueling is so wrong the PCM can't trim it out in closed loop.

You say you're running lean...what indications are you getting and under what conditions?

chevy42083

You could try this approach, although I'm not sure what all it entails.

In our area, most 96+ vehicles don't get the sniffer. They get a diagnostic check to look for codes, and to make sure the computer is working correctly. If they are trying to pass you as the LS1 emmissions, then they should only be checking the computer, not the sniffer. But then again, you are throwing codes, so that'd have to be fixed.

Just trying to give you another approach. Hope you can figure it all out.

John B

iTrader: (10)

Something doesn't sound right here!

Try my easy fix! Get your fuel down to about 4 to 5 gallons and then add 2 gallons of de-natured alcohol. You can buy this at any Lowe's or Home Depot for $10/gallon. I passed my very lumpy cam thru the sniffer with this additive

5.7LImport

Ok.. from what I know.. the PCM is running is open-loop mode constantly right now since I dont have my thermo installed... I could be wrong, but I do know that in open-loop I'll have ratio issues at low rpm. I'm going to redo my cooling system this evening so I'll eliminate that as a possibility.

Honestly, I'm not sure of whether it's running rich or lean since my gauges could be off or my 02 sensors could be bad. My AF gauge touches the rich part about 1/1000 times. Here are my other test results... do these tell you anything about how the engine is running?

HC(ppm) - High RPM - Standard 108, Current 39; Low RPM - Standard 112, Current 32

CO(%) - High RPM - Standard 0.60, Current 0.11; Low RPM - Standard 0.62, Current 0.04

C02(%) - High RPM - 14.3, Low RPM - 14.4

02(%) - High RPM - 0.0, Low RPM - 0.0

Nox(ppm) - High RPM - Standard 751, Current 951; Low RPM - Standard 829, Current 1213

Dilution - High RPM - Standard >6.0, Current 14.41; Low RPM - Standard >6.0, Current 14.44

Pretty odd numbers from looking at it even though I don't know much about emissions. I do know that C02 % should be around 14.5 if I remember correctly... 02 should be around 2 I think.. and mine shows 0. Is this a mixture problem or bad 02 sensors?

Thanks for the help guys.

-Vann

5.7LImport

Someone else just told me that! I'll have to go run my gas tank down tonight and try that!

My PCM is throwing codes... MTI is going to check em for me tomorrow. I know one is being thrown for no EGR and I didnt have the PCM flashed to accomodate that. Oh well.. I'll be happy if I just get that damn amber light to stop shining in my face!

-Vann

Oscar Will

You are right about temperatures, if the system is fooled into thinking its cold or actually is running too cold, your mixture is going to be all messed up. I've seen plenty of these things fail Calif. smog tests due to cold thermostats or IAT readings too low. The OEM calibrations really watch that cold operation to avoid "drivability" complaints and our very strict emissions standards here in Calif..

crainholio

iTrader: (2)

Not sure how you got it together w/ no thermostat but evidently it's possible. I'd definitely not operate an aluminum block/heads for long without controlling the coolant temp. Factory 195degF stat is working fine for me, 5 open-track events this season plus a few thousand street miles.

As for the emission data, it's tough to make a single frame of info useful. Kind of like looking at a picture of a car on the highway and figuring out how fast it was going. And in the case of your smog data, even tougher because it was sampled downstream of the cats.

I'd get a thermstat on it, fix or delete as appropriate the powertrain error codes you're getting, drive it for an hour or so to let the PCM run thru a complete cycle, then take it back for emission testing. Should pass easily.

-Kevin

5.7LImport

Added 1 gallon of the unatured alcohol to my 8 gallons of gas that were in the tank and passed with flying colors!

Of course.. that was only a temporary fix so I could get my sticker... I'm going to go get diagnostics done and then fix my cooling system tonight.

I'm just happy I dont have a bright green 03 sticker on my windshield anymore!

-Vann

John B

iTrader: (10)

Hell, maybe I should be charging for such good advice!!! Congrats!