Failed Emissions in Houston, Tx..need help


May 28, 2001
Hi guys,
I have a 89 TTA
Stock exhaust, green stripe injectors (30lb)
I set the fp at 42-43 psi.
Using an emissions chip.
My 02's were showing around 200 mV
Block learn was about 137
integrator around 130.
I failed at 25 mph and 15 mph

At 25 mph
HC 152 std ppm, 157 ppm FAIL
CO% .97 std, .60 PASS
NOX 1082 std ppm, 2988 ppm FAIL
Dilution >6%, 14.7% PASS

At 15 mph

HC 157 std ppm, 154 ppm PASS
CO% .88 std, .48 PASS
NOX 1184 std ppm, 3134 ppm FAIL
Dilution >6%, 14.5% PASS

High NOX and I am real close on HC.
It has the stock cat on it car has 75K miles on it.

It has a power plate, but I drilled the hole for the EGR.
Any advise is appreciated. They mentioned something about the EGR valve...I will take it off and see if it is carboned up and test it with the mighty vac.

Should I put the stock chip in? instead of the emissions chip?
I'm gonna go with EGR on this one , put your finger under the valve and press up on the diaphram and see what it does, a properly working EGR should kill the car. I've noticed a lot of cars EGRs get blocked off by the intake manifold gasket (most you have to drill a hole in the intake gasket), has the car ever had the intake off or any work done otherwise? For the HCs drop the fuel pressure down to 38 or so line off. How warm was the car, cruise it around for 30 mins or so to make sure the cat it fully warmed. Make sure the dyno operator is keepin the car within its mph on the computer as well. Is the emmisions chip burned for the 30s? or stockers, i know its only a small difference but it could be running too fat if its burnt for stockers.
Thanks for the feedback. I will check out the EGR function.
I have only had the doghouse off to put the powerplate on, but I drilled the hole in the powerplate for the EGR function.

Intake has not been off the vehicle as far as I know. I have owned the car since 1996.
The EGR valve has been replaced though....before I got the car. Maybe it is carboned up.

I drove the car for about 15-20 minutes on the highway before they tested. They did the safety inspection first and that took some time.

I think I will put the stock chip back in also. I have been told that since my 02's are so low (lean) that it increased the combustion temps and that increases NOX.

Where are u located in Houston?
Spring, Tx
hey the low 02s(if it is lean) can create higher NOX numbers, but not to the point where a good functioning EGR setup can't keep the NOX under control(which i don't believe yours is). How active is the 02 sensor? BTW im in the southwest part of houston , in the meyerland/westbury area. If ya need any help with the car, shoot me an email or pm me. :)
I found the problem
with the EGR. The darn nipple is snapped off the EGR
solenoid. So no vacuum was going to the EGR valve.
Now I need to figure out how to mechanically fasten a
new nipple to the solenoid or find another one..
Doesn't look like there is much meat to work with or
depth. I took the solenoid and bottom
halves, but it did not reveal anything.

Any ideas?

On the HC's, I am just going to put the stock TTA chip
back in and tune the fp at idle for close to 128. Maybe my
emissions chip is a little wacky.

I also remembered I have the ATR check valve in there along
with a AC PCV. I will take the check valve out.

Thanks everyone and Happy New Year

The factory O2 works on a very narrow band. It tries to maintain the mixture between 14.5(rich)-14.9(lean). This creates O2 in the cat and subtracts O2 in the cat. During slightly rich mixtures, there is less (or no) O2 in the cat and the cat tries to shut oxidation down the reduction bed of the cat and reduce NOx. During slightly lean mixtures, O2 is stored in the sustrate material (beyond the reduction bed) and is released for oxidation (changes HC and CO to CO2 and H2O). So a good functiuoning O2 is necessary to promote proper three-way catalyst operation. When you replaced your EGR vavle, did you use a factory unit? Many aftermarket units were never tested in dyno emissions testing era. Therrefore, it's hard to tell how they will actually perform. From experience, I have noticed that aftermarket EGR valves tend to increase HC (too much flow) or increase NOx (too little flow). CA uses the same type of emissions testing in our enhanced areas, so these comments should fit for Texas. I have passed with a Reds93 and 33lbs injectors on my GN, so a factory chip or your current performance chip should be fine (so long as it is not an open loop chip). If you run an open loop chip on the street with a cat (and you're in allot of stop and go traffic), you take the chance of deteriorating the cat.
Thanks for the infor Gofast, but the EGR sensor was replaced before I got the car, but it appears to be aftermarket to me.

The nipple on the solenoid snapped off, so I was not getting any EGR function. I need to figure out if I can glue or drill and install a new nipple or get a new EGR solenoid.

I will look into getting a GM EGR valve if it does not pass with the EGR functioning and the stock chip.

The O2 sensor is pretty might have 5K miles on it at the most. I just ohmed the wires and replaced the plugs.
I have a nice update. If you never have disconnected your cat from your catback exhaust and decide to get your vehicle emission tested, please do it before you try the first time.
My cat was gutted also. Pretty hard to pass emissions with no cat and a broken EGR solenoid. I feel very foolish.
I have made so many changes to my GN since the last emissions test, I thought I would just check how the emissions are doing. I have temporarily (may be permanent) switched back to the 33# injectors (with REDS93), due to a possible excessive KR problem. Here are the results (includes new tranlator and LS1 MAF):

MPH, spec, HC meas., spec, CO meas. , spec, NOX meas,CO2, O2

So, it can still be done. Now that I too have corrected a EGR (sticking) problem, I will attempt to re-install the 009s and Testa chip. Additionally, the factory EGR valve is still available from GM
SuperTTA , at least you found the problems, have you tested it yet with the fixes? Anyways good luck
Haven't re-tested it yet....I have a newborn at home and the car is up on jack stands. I am trying to get the stock cat off intact, so I can put it back on down the road for originality ;)

I'll let you know.
I failed emissions again today for Nox being high. :(

Tuning(My block learn at idle is about 127-130), plus a new cat conv, and a JB welded nipple on the EGR solenoid and I went to retest. My EGR valve was replaced before I got the car.

My brother felt vacuum on the hose to the EGR after glueing the nipple back on (Had to put the rear wheels in the air and put it in drive), but I want to put a gauge on it this weekend. When I applied vacuum with a mighty vac to the EGR at idle, the engine stumbled. I still want to take the EGR off and check the passages. I might pick up an EGR gasket tonight and pull it off.

Stock chip, I ran the car down the road. Everything was nice and hot before testing.

I lowered the NOX from 3000 to 2000, but it needs to be around 1000 to pass. I passed HC though this time...yeah!

Hopefully it wasn't getting enough vacuum to the EGR, but if everything checks out OK, then my next recourse is to replace the EGR valve and/or the solenoid. I have another solenoid now.

I am trying to ask my TTA buddies to look at their original EGR to get the OEM number off of it. The number should start with a 1708xxxx or 1711xxxx.
Thanks in advance,
James "No pass go"
I have a new thing to ask. I hooked up a vacuum gage
to the output of the EGR solenoid and had turbolink up
and running.
They test my car at steady 15 mph and 25 mph.
I went out and drove at 25 mph steady and I noticed
that the computer was asking for 0% EGR at a steady 25
mph....there is no way I will pass NOX if this is the
If I give the car gas to put a load on it, then the
EGR duty % goes up and I get a max of 5 psi of vacuum.
I read somewhere on that some did the
same measurement and got the same 5 psi...might be OK, but GM manual says to put 10" vacuum to EGR to test operation.
Anyway, the question is "Do emission chips ask for EGR
most of the time off idle?" Or could I get a chip
burned that asks for EGR off idle.
I am going to get my bro to sit in the pass seat and
watch the pc and vac guage to confirm what I
saw...hard to drive and look at the windshield and pc
at the same time.
I might just pop in the emission chip and do the same
test....I need EGR operation to pass this test.
Finally success. I passed.
The darn TTA finally passed emissions....on the 4th
I was using normal fp(45psi) and the stock chip. I
put on a new cat since mine was gutted, a new EGR
solenoid and the check valve going to the solenoid.

Here is what I learned. If they do the 15 mph and 25
mph dyno tests, make sure they keep the trans in
second gear. My car goes into 3rd gear at around 23
mph and then the throttle is almost closed at 25 mph
and the computer doesn't ask for EGR function then.

Driving it normal (like home from work) and going straight to the
test place helps.
My car had to sit for 1/2 hr before the 1st try today
and it missed on HC at 15 and nox at 25 mph. Running
it the 2nd time today after it ran a bit after the
first test was the charm.
My nox numbers at the very first test were 3000, then
2000 on the second test and legal limit is 1000.
Today on the 2nd test my Nox #'s were only 175 and 62.
HC at 15 were 155/157 barely passing, but at 25 they
were 87/152, easy pass.
Also, I was using the maf translator and 3" impala
Might be easier to pass with a good known stock
maf. I also ran a bottle of that guaranteed to pass
stuff in the last tank of gas. Maybe that help clean
up the intake valves and chambers.
Now I look forward to going through all this crap 1
year from now I wish I could of put all
this time and money toward performance parts.

Thanks for all your help.

I'm beside myself, why it was so difficult for your vehicle to pass emissions. But I'm glad it finally did pass. As posted above, my car was just tested in drive. I don't know the requirements in TX, but in CA, the emissions test is performed in drive, not OD or 2nd. If the inspector was require to test in drive and the test was actually performed in OD, that may explain the excessive NOx numbers (as forced drive may differ from OD).