Perfusion

Interesting... That could be where my problem lies (past tense, I guess). I have LTs and RT cats - maybe it was my EGR not getting enough back pressure.

tdr1919

I agree, I could pay $100 bucks and get an inspection, but that would not cure my problem, a re-test is $27 here. I will continue to work on this problem until it is solved!

Jim McCombe

I am still fighting the high NOX issue on my 87 and just failed my 2nd attempt to get it passed. It had failed at both the 15 &25 mph tests but everything else was well within the limits.
I was advised to fill the fuel tank with the highest unleaded octane gas that I could find and go back in for the retest.
Luckily I work at Infineon Raceway and we carry 100 octane and $77.00 later I found myself back on the dyno on to find I was now good at the 25 mph test but failed the 15 mph test once again.
The engine is a 383 stroker using Edelbrock Performer heads that carry a California EO# on them making them legal for use. Compression is 9.5 to 1 and the Crane Cam also is legal for use. The Cat is new and the exhaust manifold system is the factory set up using a MagnaFlow cat back system.
The EGR valve was changed 2 years ago after failing the last test and that cured the problem at that time and both the new engine and EGR valve has less than 2,500 miles on them both.
As was mentioned earlier, high NOX is caused by high combustion temperatures usually as a result of either a faulty EGR valve or carbon build up of which both should not be my problem.
My only option now is to scan it and find out the exact cause of the problem and hope that I will be able to pass the next test as warmer weather is just about here and I want to do some ET Bracket racing with it this Summer.
Will post the results of my next emissions test and what was done to correct the problem provided it was corrected.

tdr1919

Jim, my 86 is also failing for NOx, although my scanner shows the EGR being activated, the solenoid and the valve are in question, I went and applied vacuum directlly to the EGR valve, and found it to be bad would not hold any vacuum at all.
I would take out a few minutes and test the EGR, it doesnt take much time and this could be the cause of your failing.

GKK

Be aware that aftermarket parts with a California EO# are given that number to certify that the part will not affect the original engines emissions output.

These CARB (California Air Resource Board) certified parts are not meant to be used Along with multiple other CARB certified parts. In otherwords Yes, these parts are o.k. to have installed on the engine but, You may still have to remove one or more of these certified parts and install the originals if your engine is failing emissions because these parts are not certified to be used together.

I was told this by a California emissions referee a few years ago.

JrRifleCoach

NO.....I said RETARD. Drop it back to 2-3 BTDC.

JrRifleCoach

Try this; Let your tank level drop to below a 1/4 and add a pint or so of denatured alcohol. This will drop the CO count since the alcohol burns SO clean.

tdr1919

Thanks for straightening me out! I always thought retarding was going the other way.

Tom

nitecruizer

Thank goodness I live in a place where there is no testing, I have had hot cams, different heads, different carb, the only thing the tech does is raise the hood and check to see if all the smog equipment is there. It is and 30 minutes after looking under the hood, passing inspection it's gone again. I feel for you guys, good luck with the test.


Cruizer

qwiketz

so if I have high 25 mph nox, then I can try higher octane gas or retard the timing 2-3*? I need to be at 720ish on the nox scale and I was about 1100 last time. I barely passed the 15 mph nox test. I think my 3.73 gears actually hurt my car on the 25 test because it turns more rpm than it should

Jim McCombe

Thanks for that bit of information and to all of you who have tried to help me resolve my NOX problems. The higher 100 Octane Sunoco helped but not to the point where it would pass so will try some of the other recommendations that you guys have made as well.
I will try it once again early next week to see if the 3rd time will be the charm and that I can get it to pass.

qwiketz

how much did the 100 octane drop your nox?

Desert1957

I have seen this on a few GM vehicles at Emission Inspection time.
What happens is the diaphram is bleeding off vacum because of a leak,
at certain rpm's and load it will actually flutter between partially open and closed. so its overall performance reduced.

Its sometimes hard to understand but the purpose of the "EGR" (Exhaust Gas Recirculation) is to redirect exhaust gas back through the intake , this heated gas is still cooler than the cylinder combustion temperature whick does two things. Reduces NOX's and can reduce spark knock.

Sorry for Rambling on

Desert

Jim McCombe

This was the results from the 1st Test on the NOX readings using 89 Octane
15 mph test: Max allowable: 778 Measured 998 Failed
25 mph test: Max Allowable: 717 Measured 747 Failed

2nd test results using Sunoco 100 Racing Octane unleaded
15 mph test: Max Allowable: 778 Measured 861 Failed
25 mph test: Max Allowable: 717 Measured 658 Passed

The 100 Octane at the 15 mph test reduced the numbers by 137 points but still received a failing grade
At the 25 mph test, it reduced the numbers by 89 points which was good enough to pass on the 717 limit.

All other readings were well within the legal limits and only the high NOX numbers were the problem.
I have a appointment tomorrow morning at a recognized state repair station to try to get the problem fixed. They get $180.00 just to do the diagnosis and this doesn't include the cost of any additional parts or labor parts.
If they can isolate the problem and repair it, I will then take it out onto the highway for a 30 minute ride to build some heat into the engine and the cat and head straight to the emissions test station for which I hope will be the final time.
I hope to have the results posted here once everything has been completed so for the time being, keeping my fingers crossed for a happy out come.

qwiketz

darn... I was 300 points too high on my 25... all others were good. I'm going to unpulley the blower to reduce the hp require to go 25 mph. The blower just drags on the motor at vacuum. I'll probably try your 100 octane solution too and if I have to retard the timing.

Jim McCombe

And The Nightmare Continues...

Once again the car failed the emissions test and this was at a state approved repair staion.
I was asked if I had replaced the chip with an after market type of which I haven't.
On the print out it stated that the probable cause could be the exhaust system. The report read "Found No back Pressure on Exhaust System, customer said all new exhaust was installed in January 07.
No back pressure keeps the EGR from opening causing high NOX and CO emissions.
He told me if he operates the EGR manually, the numbers all look good and it would pass.

I find this hard to believe, the Cat is a factory type and from the Cat back is a Magnaflow system. I'm at a loss...

Barbara_S

Interesting - I have a 91 that has yet to pass emissions and I bought it in November - but northeast weather prevents me from getting much done. I changed bad cats, failed again, and the car is at an emissions garage right now. HC and NOx both were too high. The new cats helped some but not enough to pass.
Their scan didn't point to the egr and they found 1 O2 sensor totally dead, and the other too rich. No codes thrown either which made me think of mentioning it to you. Today the sensors were replaced in my car and we have a snow storm so I don't know if it got on the dyno or not. Have you checked the O2 sensors out?

SunCr

Lot's of different problems popping up - Basically, design of everything built is to deliver a 14.7 to 1 mix and then cool down the burn with EGR. Change the mix and you end up with different results. With high HC's and high NOX, sounds like a lean misfire. Start with a scan to verify fuel delivery - BLM's somewhere between 122 and 132 wih 128 being right on. If the numbers are anything else (too rich/too lean), there's a bunch of easy things to look at to track it down. If fuel delivery is right and you can't pass HC or CO (and sometimes NOX), the CAT is shot or for those that use it, the air pump is broken. High NOX and everything else good means the combustion temps are too high. A functioning EGR will cure that - or Edelbrock is supposedly bringing back water injection (actually a 50/50 mix of water and alcohol) - for those with Blowers or other high performance mods.

SS409 425HP

The "found no back pressure on exhaust" would apply to a "Positive Back Pressure" type EGR valve. Your '87 has a "Negative Back Pressure" type EGR valve which is not as dependant on back pressure to function. The "N" type valve is opened by a combination of applied engine vacuum to the control valve and negative exhaust system pulses that happen as each exhaust valve closes.
Do a Google search on EGR valves and you will find lots of good info on the different types of valves and how each type functions.

Desert1957

once again check for ported vacum (with a Gauge) at the valve , if its good and the valve is staying wide open at speed , not half way or pulsing , Nox's should come down , are you sure you have checked proper operation of the valve and hoses? 99 times out of 100 with NOX's its a related valve problem.

Desert