CA Smog Nightmare: Please Help! - Chevy Impala SS Forum
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post #1 of 14 (permalink) Old 11-29-2016, 10:48 PM Thread Starter
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CA Smog Nightmare: Please Help!

Hello,

I've been lurking on the forum now for about 6 months as I restore my '95 SS. The information here has been completely spot on and amazing in helping me get this beast back on the road. Try as I might searching myself, I can't really figure out how to attack the following problem:

My car passed the emissions portion of the smog test with CARB-illegal long tube headers. Due to the fact that these headers had no provision for the AIR pump (not deleted, but just venting to atmosphere) it failed the visual inspection.

I went and searched out the CARB-legal headers, and after much wresting (and a ton of money) they have been installed. I also completely replaced the EVAP canister, purge valve, and all of the accompanying hoses. Fully re-welded the exhaust including brand spanking new cats (now with ~100 miles on them). Now the car won't pass emissions due to NOx. All of the other emissions readings for CO2, 02, HC, and C0 pass with flying colors. The only bad one is NOx. And I'm talking a ton of NOx.

With the "illegal" setup, we were looking at:

MAX: AVE: MEAS:
15mph: 677 267 0
25mph: 680 248 15

With the "legal" setup, we are looking at:

MAX: AVE: MEAS:
15mph: 677 267 635
25mph: 680 248 1114

It's almost as if the EGR is not working whatsoever. But I can almost stall the car by manipulating it by hand, making me think it's operational. I have no CEL.

I did hook the car up to Freescan to see I there were any DTCs, and the only one I got was a CODE 18 (relating to the injector circuit). Coolant temperature looks great according to Freescan as well.

I'm not an expert at what the 02 sensor data should be say, but I know it's supposed to bounce around, which it is doing. It's not flattening out under load or anything like that.

I just blasted a can of Seafoam through the brake booster hose out of desperation today, but other than that I'm stumped. Any ideas out there?

- A guy who just wants to drive his damn car!

- Why do we do this to ourselves?
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post #2 of 14 (permalink) Old 11-30-2016, 10:35 AM
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High Nox can result from a few things. Generally due to high combustion chamber temps

Some things to check:

1. lean condition. Check fuel pressure to see if it is low (lean)
2. bad EGR (yours is new?)
3. Bad CAT (you have new CATS so they should be good)
4. Carbon build up on pistons (the seafoam may help)
5. vacuum leaks
6. exhaust leak pre-02 (this will cause the PCM to dump fuel). Confirm your new headers are well sealed pre CAT

\'96 BBB 383/T-56
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post #3 of 14 (permalink) Old 11-30-2016, 11:11 AM Thread Starter
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1. lean condition. Check fuel pressure to see if it is low (lean)

Brand new fuel pump, but maybe a problem with the regulator? Maybe something with that Code 18?

2. bad EGR (yours is new?)

Definitely not new, but the car is running perfectly. Shockingly well. Usually if the EGR goes the car runs like a pig, right?

3. Bad CAT (you have new CATS so they should be good)

I'll be super upset if these are bad, haha. Possible, but not likely.

4. Carbon build up on pistons (the seafoam may help)

Maybe something gummed up in the manifold itself?

5. vacuum leaks

Again, car is running smooth as eggs. Probably not a big enough leak to spike NOX the way it is.

6. exhaust leak pre-02 (this will cause the PCM to dump fuel). Confirm your new headers are well sealed pre CAT

What's a good way to smoke test the seal from the header to the head and from the header to the cat? The hot sensor is on the header right before it meets the cat.

- Why do we do this to ourselves?
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post #4 of 14 (permalink) Old 11-30-2016, 02:23 PM
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The EGR diaphragm can leak or the tip of it is so gunked up with carbon build up it won't seal. If the age of the EGR is questionable you should consider replacing it as a malfunctioning one does contribute to high NOX

The only way to confirm fuel pressure is good is with a guage. Sometimes local auto part stores have a "loan-a-tool" where you can get one. IMHO I would have one in the toolbox.

IDK the detail in doing a smoke test so Google it.

A cheap vacuum gauge would show "something" is wrong if the needle bounces around at idle or reads low vacuum=leak somewhere

Check header to CAT connection to confirm no leak and bolts are tight

next time you go for the smog check drive the car for about 1/2 hr on Fwy and don't shut it off when you get to the smog shop. You want those CATS nice & hot

02's should be AC Delco ONLY

I have never used anything like Seafoam. Watched a few B & A videos on youtube and the results were mixed.

I have used "throttle body" cleaner (spray can) to clean the inside of the intake manifold. I change the oil after driving for a few hundred miles after as all that crud eventually makes its way down to the oil pan.

ALWAYS have fresh oil in the motor before smog test

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post #5 of 14 (permalink) Old 11-30-2016, 03:03 PM Thread Starter
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Thanks for the advice. I just ordered a new Delco EGR valve and solenoid just for good measure. I'll give a good squirt to TB cleaner (though I've heard this is bad for 02 sensors?). I don't know if the O2 sensors on the car are Delco or not. I'll definitely have to change the oil after these treatments. I'm about to toss some gas treatment in as well. I'll do all of the above and report back.

- Why do we do this to ourselves?
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post #6 of 14 (permalink) Old 11-30-2016, 04:36 PM
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Quote:
Originally Posted by spacedock510 View Post
Thanks for the advice. I just ordered a new Delco EGR valve and solenoid just for good measure. I'll give a good squirt to TB cleaner (though I've heard this is bad for 02 sensors?). I don't know if the O2 sensors on the car are Delco or not. I'll definitely have to change the oil after these treatments. I'm about to toss some gas treatment in as well. I'll do all of the above and report back.
the EGR on these of this design used for decades is not very good. so with normal miles on it every year these need replacing every 10 years.

I have had my 96 IMP 21 yrs . I am now on the 3rd EGR. the EGR on my vehicles failed due to the valve not fully closing . what happened with this issue which did cause me to do lots of testing, I found that the EGR did not fully close all the time. since no emissions on this vehicle up here and no codes on the last one I put in... 1st EGR was the 400 code, on the 2nd valve being so intermittent it would cause the engine to backfire/pop thru the intake on a cold start , but not all the time ..

cleaning the TB with TB cleaner with the engine off using a tooth brush. keep TB plates open allow time to dry out before starting .. I would also remove the IAC and clean out that passageway. do not move the IAC valve on it ..

if the EGR is stuck open the spark plugs should be checked/replaced after you replace the EGR.

with higher exhaust pressures this can pop up ... with a small EGR leak ,,,.
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post #7 of 14 (permalink) Old 12-01-2016, 12:14 PM Thread Starter
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For anybody interested, I found a really cool writeup on how EGR and cats work. It's pretty durn scientific. I think my problem lies somewhere in page 10 and up:

http://www.lbcc.edu/attc/documents/B...ng-methods.pdf

The new headers may have changed my backpressure, the EGR valve could be bad, and I also have that Code 18 meaning I could have something going on with the injectors too. I'm waiting on my EGR valve and solenoid from partsgeek.com right now. I'm hoping that just fixes it otherwise there is a deep and terrible rabbit hole to climb down.

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post #8 of 14 (permalink) Old 12-01-2016, 12:31 PM
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Quote:
Originally Posted by spacedock510 View Post
Thanks for the advice. I just ordered a new Delco EGR valve and solenoid just for good measure. I'll give a good squirt to TB cleaner (though I've heard this is bad for 02 sensors?). I don't know if the O2 sensors on the car are Delco or not. I'll definitely have to change the oil after these treatments. I'm about to toss some gas treatment in as well. I'll do all of the above and report back.

good move on the Delco EGR. However, which EGR did you order...Stock or the 1 from a F-Body? There is info out there that talks about using the EGR from a F-Body Car with Manual trans. This is known to be a better EGR for our cars than the B-Body EGR.

================================================== =============


'95 Caprice SS conversion - Bonny Buckets - 96 Column, Shifter and Console - 3.73 Gear and Herter tune - Z/28 Cluster - Blazer OH Console - Green/Pink bushings - Chromed Impala Wheels - Eibach Springs and Bilstein Shocks - Corvette Engine Dress - the list goes on and still more to do...it never ends.
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post #9 of 14 (permalink) Old 12-01-2016, 12:38 PM Thread Starter
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I probably just got the stock part. I wasn't aware the F-Body ones were even different!

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post #10 of 14 (permalink) Old 12-01-2016, 01:21 PM
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Taken from the Qalo'ss Handbook.....


EXHAUST






EGR Valve Replacement








One of the common repairs to the B-body LT1. It will cause hesitation, stumble, and hurt


gas mileage. Itís an easy fix but a little pricey and annoying.


Get a new one or get the 6-speed EGR valve from the F-Body LT1. They tend to last longer


and are the same price anyway. So buy it. Go ahead and get the solenoid as well, theyíre not that


much and itís good to replace it while youíre back there.


1. The valve and solenoid are located on the back of the


engine on the driverís side. The valve looks like the one to


the right.


2. It is held on by two bolts and connecting by hoses to the


solenoid. The solenoid is connected by bracket to the engine


that is secured a bolt.


3. Be sure to make note of how the hoses are connected while removing it.


4. Remove the old gasket from the valve and engine, and replace it with the new one and install in


the reverse order.


EGR Campaign Letter:




If you have a 1996 with less than 100,000 miles on it and fewer than 10 years old, you may be


eligible for a free replacement. Read the campaign letter at this link:


http://www.impalaclub.com/naisso/egr.pdf

================================================== =============


'95 Caprice SS conversion - Bonny Buckets - 96 Column, Shifter and Console - 3.73 Gear and Herter tune - Z/28 Cluster - Blazer OH Console - Green/Pink bushings - Chromed Impala Wheels - Eibach Springs and Bilstein Shocks - Corvette Engine Dress - the list goes on and still more to do...it never ends.
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