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It's a 97 Bonneville SSEi with 150,000 miles

The emissions test is done while at idle as well at around 1400 rpm, on a dyno and with the tailpipe sensors in both tailpipes. It barely passed in the curb idle test but not the ASM =2525 test which is done at around 1400 rpm,

These were the readings

ASM2525 Test

HC ppm - Limit 55 - Reading 69 ......FAIL
Co% - Limit 0.31 - Reading 0.41....FAIL
NO ppm - Limit 408 - Reading 1245 ..FAIL

This is what I've done to prepare for the test.

Changed engine oil and filter two weeks ago.
Changed air filter today.
Use high octane fuel
Change plugs (NGK tr 55) plugs 7 months ago.
Cleaned exhaust tips of excess carbon build-up
Check that there were no codes stored
Ran car on highway for 10 minutes before test
Coolant was at 195 degree as seen via scan gauge


Two years ago I changed the complete exhaust including a high flow cat, new Belden wires and tune up, along with oil change and filter and cleaned EGR Valve and it tested as follows with a pass.:

ASM2525 Test

HC ppm - Limit 55 - Reading 17
Co% - Limit 0.31 - Reading 0.05
NO ppm - Limit 408 - Reading 368

Any ideas?

I had a friend fail Ohio's emmissions check on his '94 Grand Am. Seemed the culprit of the failing value (I think it was NO gases) was a failed cat. His car ran for crap for about 2 years and he neglected to do anything to fix it. Well, replacing the cat to pass emmissions check also fixed his performance problem.

Now, you mention you switched out your cat and now have a high flow one on.... Strange that two years ago things were fine and now they aren't.... Part of me wants to blame the cat, but in all honesty, I am outside my pay grade on this one...

Sorry...

Maymybonneliveforevr wrote:Two years ago I changed the complete exhaust including a high flow cat

Who made this cat?

I replaced my rattly factory cat with a "high flow" aftermarket from the local exhaust shop in February 2010. I had my emissions done in August (at another shop) and while HC and CO numbers were fine, I just BARELY passed the NOx numbers with results similar to your test two years ago. Conversation with the tech goes:

"Have you replaced the cat?"
"Yeah, earlier this year, February"
"Dealer or aftermarket?"
"Aftermarket."
"There's your problem"

Apparently these cheaper aftermarket cats don't really last longer than a year (which is surprise surprise - the warranty period). It wouldn't surprise me if mine is toast again. And even if its not, the NOx numbers are going to be higher than stock. Do bear in mind that I do have the rockers installed, but I was told that this generally won't affect too much if the MAF and fueling can account for it (which they do).

Personally I would have tried to go for a longer drive before taking it in for the test, and make sure the car isn't sitting long before being tested - I wound up bombing up the 400 to Bradford and back down again.

The cat was replaced with the Magnaflow high flow cat since it failed the test 2 years ago. After installing the new cat and whole new exhaust it passed.

I've only had 2 vehicle fail an emissions test. Both times I asked the inspector what was probably the cause and both times they told me. I did the repairs they thought caused the failure and had a pass both times.

So now the question is, did you ask the inspector what they thought might be the cause? - BC

When I was told the test failed I asked the tech if you could give me advice on what to look for and he told me to ask the attendant at the front desk. I did and he just gave me pamphlets and told me various possible causes which the internet could have told me. This location only does test and not repairs but there sucess rate is good which is why I have been going there for 15 years. Everytime I do the emissions test I ask fellow customers and only one so far told me he failed.

What kind of mileage are you getting?
How new/old is the O2 sensor?
Have you put Seafoam through the intake lately?

EDIT: And Jerry is right, you need to get the exhaust piping hot just before the test.

Maymybonneliveforevr wrote:When I was told the test failed I asked the tech if you could give me advice on what to look for and he told me to ask the attendant at the front desk. I did and he just gave me pamphlets and told me various possible causes which the internet could have told me. This location only does test and not repairs but there sucess rate is good which is why I have been going there for 15 years. Everytime I do the emissions test I ask fellow customers and only one so far told me he failed.

The testing place I use does only tests too. I am guessing that there were no error codes. Yes, two of the previous members are, I believe correct, get the tail pipe hot. As far off as the print out sez you are, my guess is that one or both the PCV valve and EGR valve need to be cleaned or replaced. Now, I am not a mechanic, but when the two vehicles I had failed, I did both - PCV & EGR and they passed. That doesn't mean that is what is wrong with yours. There are ways to test those two. The PCV is cheap and probably better to replace. The EGR is another story. I wouldn't replace it unless I had no other choice. Clean it and test it. - Good luck, I hope that what ever it is that it's inexpensive and easy to fix. - BC

repinS wrote:[Personally I would have tried to go for a longer drive before taking it in for the test, and make sure the car isn't sitting long before being tested - I wound up bombing up the 400 to Bradford and back down again.

I'll keep that in mind Jerry, are going to replace your high flow cat before your next emissions test?

dpcookson wrote:What kind of mileage are you getting?
How new/old is the O2 sensor?
Have you put Seafoam through the intake lately?

Appromitely 20 mpg city/highway at best.
A/C delco O2 sensor is 2.5 years old.
Seafoam was used 1 year ago.

1oldman wrote:I am guessing that there were no error codes. My guess is that one or both the PCV valve and EGR valve need to be cleaned or replaced. There are ways to test those two. Clean it and test it.

Nope no error codes, EGR valve was cleaned 20k ago, but I guess I can clean it again and the pcv passed the shake.....shake test.

Those are some high readings.

I have had a magnaflow high flow cat on my car with a flowmaster and its passed with really low numbers for almost 4+ plus years now.

How is the car idling when just in park, lumpy or smooth?

Check your 02 sensor that could be an issue, MAF sensor on top of the motor could be shot and causing a bad reading to the pcm,

Is the airfilter clean?

Just some thoughts, I have a buddy here that does the etests I can get him to check out the posted numbers and see what he thinks,

Same here... had a magnaflow high flow on my 92 SSEi, and even after beating the crap out of the car, the ECheck readings came back cleaner than a Honda Civic.

Car idles fine, air cleaner was changed same day as the test, and again no codes stored so I figured all other sensors were operating within parameters.

Try running some Amsoil PI or 2 bottles of Chevron Techron Concentrate, Gumout Regane, or Redline SI-1 through a tank if you have the time.

HC high is nothing more than unburnt fuel exiting the exhaust. - plugs, wires, coils
then check for vacuum leaks, make sure the pcv valve has an o-ring in it.

Maymybonneliveforevr wrote:Car idles fine, air cleaner was changed same day as the test, and again no codes stored so I figured all other sensors were operating within parameters.

=> Tripscarcare95

Those are some high readings.

I have had a magnaflow high flow cat on my car with a flowmaster and its passed with really low numbers for almost 4+ plus years now.

How is the car idling when just in park, lumpy or smooth?

Check your 02 sensor that could be an issue, MAF sensor on top of the motor could be shot and causing a bad reading to the pcm,

Is the airfilter clean?

Just some thoughts, I have a buddy here that does the etests I can get him to check out the posted numbers and see what he thinks,



=> i<3bonbons

HC high is nothing more than unburnt fuel exiting the exhaust. - plugs, wires, coils
then check for vacuum leaks, make sure the pcv valve has an o-ring in it.





Do the easy things first.
Make sure you have no vacuum leaks and all the vacuum lines are new of recently new.
Check and make sure the PCV valve is installed properly (“O“ ring too).
Check the plugs. See if they “tell” you anything.
Also, the EGR could be causing a problem. Check it again.
If you check these things and find noting, the next thing would probably check the O2 sensor. They can be defective and not necessarily throw a code.
I also use a product that I think works better for me than Seafoam. Greased Lightning concentrated Fuel System Treatment (Part Number GL-4000 www.greasedlightning.com). I put a bottle of it in the 92 and I was shocked at the noticeable difference it made.

Nothing like lots of advice. Lol! I just hope it’s all good and you get it fixed soon. - BC

tripscarcare95 wrote: Check your 02 sensor that could be an issue, MAF sensor on top of the motor could be shot and causing a bad reading to the pcm,

Ditto on the MAF sensor. I'd look at that first I think. Your NOx are through the roof! High NOx are caused by high combustion temperatures. Now, your thermostat is keeping the coolant at 195 as it should, but the combustion temperature is still high enough to make the NOx. NOx can be made by excess air or insufficient EGR gases. Take your MAF sensor and give it a really good cleaning. I've found from experience that MAF sensor cleaner is not aggressive enough so I've followed the lead of other certified technicians I've talked to and used carb cleaner on the MAF wires. This has corrected any MAF issues I've ever had with my cars.

After doing this, I'd make sure that the EGR valve can stall or almost stall the engine. Do this by applying a small vacuum to the EGR valve to introduce EGR gases artifially into the combustion chamber. If your idle drops, your EGR is working properly. If there is no change in idle, you either have a blockage in the EGR system, or the EGR is not opening.

After doing all this, disconnect the battery for 30 minutes. Then drive around for a few days under different conditions, then check the readiness monitors with your scantool. If they check as ready, you should pass.

One technician said that old coolant can cause emission failures. I guess old coolant may not be able to absorb heat as well as fresh coolant. Also check plug wires.

One more thing,

If your air mixture is so high (caused by dirty MAF), you won't have an ideal mixture for burning fuel. You will get a "lean miss" which happens when you have so much air the fuel doesn't ignite properly. These unburned gases raise your HC.

An update:

It cost me about $270.00 but I got a temporary pass for one year. In the meantime I have to figure out why why the readings are so high so that I can pass next year.

Thanks for all the suggestions.