Emmisions test help please
10-11-2007, 08:01 AM
#1
Pro
Thread Starter
Emmisions test help please
Hi guys, been awhile. Vettes running great with no problems however two years ago I had an emmisions test and just squeaked by on NOX.
I just had another one done. The tech said the car came up extremely clean but I did fail NOX by just a touch. I can post the numbers here.
We both talked and he said its probably something simple like the EGR valve. I'd appreciate anyones thoughts on all this. The car is bone stock ,the motor only has about 25000 miles on it and it runs really good. We took it for a great boot before and heated up the cats really good before the test.
The tech guy was actually kinda shocked at the other numbers because they were so good.
I just had another one done. The tech said the car came up extremely clean but I did fail NOX by just a touch. I can post the numbers here.
We both talked and he said its probably something simple like the EGR valve. I'd appreciate anyones thoughts on all this. The car is bone stock ,the motor only has about 25000 miles on it and it runs really good. We took it for a great boot before and heated up the cats really good before the test.
The tech guy was actually kinda shocked at the other numbers because they were so good.
10-11-2007, 08:22 AM
#2
Pro
Thread Starter
These are the etest numbers rpm 2098
Hc ppm limit 57 reading 0
co% limit 0.32 reading 0
NO ppm limit 421 reading 459
curb idle test rpm 645
Hc ppm limit 200 reading 4
co% limit 1.0 reading .08
NO ppm n/a
gas cap pressure test- passed.
Hc ppm limit 57 reading 0
co% limit 0.32 reading 0
NO ppm limit 421 reading 459
curb idle test rpm 645
Hc ppm limit 200 reading 4
co% limit 1.0 reading .08
NO ppm n/a
gas cap pressure test- passed.
10-11-2007, 08:28 AM
#3
Your profile is not filled out, you will get more help if you let us know what year car you have.
In general it is not all that surprising that you fail NOX with the other readings shown. Unless you are running so lean that it misfires a low CO reading can raise NOX.
The EGR suggestion is a good one, also check the ignition timing if yours is adjustable. High NOX is normally caused by high combustion chamber temperatures, lean fuel mix, lack of EGR or a combination of these, good luck.
In general it is not all that surprising that you fail NOX with the other readings shown. Unless you are running so lean that it misfires a low CO reading can raise NOX.
The EGR suggestion is a good one, also check the ignition timing if yours is adjustable. High NOX is normally caused by high combustion chamber temperatures, lean fuel mix, lack of EGR or a combination of these, good luck.
10-11-2007, 08:35 AM
#4
Pro
Thread Starter
sorry, the car is a stock 92 LT1. As I said before, the engine is GM new with less than 25000 miles on it. I'm going to take it back next week and I want to be well informed before I do.
As a side note, the cars runs really great with no misses. Been driving it a lot this summer with no issues at all.
As a side note, the cars runs really great with no misses. Been driving it a lot this summer with no issues at all.
10-11-2007, 09:15 AM
#5
Your LT1 has no provision for timing adjustment so if you have no evidence of high engine temperature or SES light illumination I would concentrate on verifying the EGR functions properly. Since you indicate the car runs well, it seems logical to rule out low fuel pressure or restricted injectors.
If you have a vacuum pump, apply 10 to 15" inches to the EGR vacuum port with the engine off, the stem should move.
If it does you may have a restricted exhaust passage due to carbon buildup that prevents the exhaust from entering the intake when commanded by the ECM.
This scenario could be the most likely since history indicates a gradual increase in NOX until it exceeded the limit, hope that helps.
If you have a vacuum pump, apply 10 to 15" inches to the EGR vacuum port with the engine off, the stem should move.
If it does you may have a restricted exhaust passage due to carbon buildup that prevents the exhaust from entering the intake when commanded by the ECM.
This scenario could be the most likely since history indicates a gradual increase in NOX until it exceeded the limit, hope that helps.
10-11-2007, 01:11 PM
#8
Le Mans Master
On my 92 when I applied vaccum to the EGR I could hear it leaking!
Also check the EGR selenoid, I replaced mine at the same time as the EGR just for drill, it can be checked but its cheap enough to just replace.
I vaccum tested the new one before I put it on and it worked smooth and held vaccum.
Also check the EGR selenoid, I replaced mine at the same time as the EGR just for drill, it can be checked but its cheap enough to just replace.
I vaccum tested the new one before I put it on and it worked smooth and held vaccum.
10-12-2007, 06:54 AM
#9
Burning Brakes
Run the thing low on gas, say 1/4 tank, then add a quart or two of dry gas (isopropyl alcohol). Buy it as Fuel line antifreeze in pint bottles. (Methanol would work too but it's harder to find, unless you happen to play with alcohol fueled race cars..).
With a decent percentage of alcohol in the fuel like that it'll sail through the tests - you (and the tech) will be amazed at the difference in readings.
The alcohol won't hurt anything in the system either - even at that high a concentration. It'll run fine - maybe even better than "normal", depending on how knock sensitive it is with the fuel you regularly use.
With a decent percentage of alcohol in the fuel like that it'll sail through the tests - you (and the tech) will be amazed at the difference in readings.
The alcohol won't hurt anything in the system either - even at that high a concentration. It'll run fine - maybe even better than "normal", depending on how knock sensitive it is with the fuel you regularly use.