Failed Emissions test.. Couple of ?'s

[Hucker]

I brought my (new to me) 1992 Golf in for an emissions test today. Up here in the great white north you need to pass emissions before you can plate a car. Now I passed everything except the NO ppm part. I'm assumimg this has something to do with nitrogen? I have no idea. Anyhow here are the numbers...


------------LIMIT-----READING----RESULT
NO ppm 633---------1059----------FAIL


Everything else on the car passed with flying colours, I just wanna figure out what part could be causing this reading? Maybe the cat? EGR? I honestly don't know, I bet Rich could figure this out in about 3 seconds :) Any help would be appreciated, so I can fix this thing and get it on the road!!!

 

[jmics19067]

oxides of nitrogen happen I believe from combustion temps to high. not sure of the science but look for a vacuum leak ,too advanced spark timing , the egr, O2 sensor.

I am unfamiliar with vw's but if you can collect the codes off the computer it can help you narrow down the problem. If you have multiple codes youhave to try and play the chicken or the egg routine and figure out which sensor failed throwing off the others that are trying to compensate. Time to get out the ohm meter and check parameters.
If the are no codes then it is probably a basic<non electronic> mechanical problem ,vacuum leak, egr, distributor timing off <if possible>.
How does the car run? rough at idle and smooths out with throttle, manifold vacuum? runs good except at lower midrange rpm ported vacuum? egr?
How are the co and hydro carbon tests?

 

[Rich Rohrich]

You guys pretty much narrowed it down NOX is related to combustion temps and EGR is used to help control those temps. You can sometimes cheat the test a bit by running a cooler thermostat and getting the test done when the engine isn't at PEAK temps. But the more logical approach is to pull the EGR valve and verify it's operation, verify it has a clean passage to the exhaust feed, and verify that the valve is being signaled at the proper time.

 

[MikeT]

Don't know if this is totally true or not, but the service manager at a Pep Boys I used to work at once told me that on an older car with worn rings, that if you changed the oil right before the emmissions test, the car would do better. He said this was because the old oil in the pad had absorbed a lot of gas due to the blowby. The gas in the oil then makes the mix in the combustion chamber richer and gives you higher emmissions.

I don't know if this was true or not, but he said he used the oil change techniqie before with good results. Doesn't "fix" the problem, just band-aids it.

 

[jmics19067]

that may be true for high CO and hydro carbons. Situation where rings sealing plays a apart in the gas air mixture or crankcase oil not burning clean enough. High NOX is from too aggresive of a burn.

 

[a454elk]

Here's your personalized plate you can use now, "CANT PASS":) Sorry.