California smog expert please advise

[brave sir robin]

I have been using Supertech knockoff Lucas fuel system cleaner for the last week. Come to think of it I have been using a double strength dose.........


I took apart the EGR system and it was free of any crud. The valve moves freely and holds vacuum....no leaks. I did notice that the brake booster vacuum hose was not fully seated on the booster and that MAY have caused a leak I guess.

Does anyone here know what would cause the NOX levels to be cut in half at the higher speed test? Should it not go up considering the limit is higher n all...... What does this signify?

 

[i_hate_autofraud]

"Does anyone here know what would cause the NOX levels to be cut in half at the higher speed test? Should it not go up considering the limit is higher n all...... What does this signify?"


I don't have a 95 Nissan Pathfinder, but if there's a carb, then it can do 15mph on the dyno partially thru the idle circuit of the carb that's not super good at precise settings to get low NOX. It's always been hard for carbs to meet California smog limits.

If it's fuel injection and a California model, then the smog requirements would go lean for the low HC, and a half dead cat won't clean out the NOX created.

KEY ISSUE: An overly hot lean mixture and the combustion chamber design forces nitrogen in the air charge to react when it's just over the tipping point. If you could tweek it leaner, the HC would rise too with a lean miss where some of the fuel in the cylinder does not get burned before the flame front burns dies.

In carbed engines I'd go rich by a bit, NOX drops and HC drops to, however to rich and CO and HC rocket up. You're balanced on a knife edge!

Up here the gov introduced smog testing at the tail pipe in 1999 (OBDII plug in check now) I was determined to do it all myself to avoid repair rip offs and I might learn something! So I've done a lot, once once did I get a shop repair from a pal who gave me a few tips that I've used since.

Once a car fails here via the OBDII smog systems check, then I'll be back doing repairs on the 09 Impala but I wanna nail it myself.
The tricks I posted earlier I ran by a GM tech guy who agreed the EGR mod on the 98 Lumina was cool. BUT with a computer based check you can rig the data to hide a defect that was circumvented as I did, so I do miss that!

 

[PandaBear]

Originally Posted By: brave sir robin
Does anyone here know what would cause the NOX levels to be cut in half at the higher speed test? Should it not go up considering the limit is higher n all...... What does this signify?


I have seen it on my car before and an old upstream O2 sensor was the problem. Replacing it with another unit of the same brand, reset the ECU and then run it for a while fixed it.

Usually the typical aging would not make you fail by doubling the limit. You have something out of whack in the system for sure. Hopefully it is not a CAT as that would be very expensive even for DIY. Try all the typical low hanging fruit first, like O2, plugs, cap and rotor, oil change, 91 gas, adjust timing to the lower limit allowed, fixing all the vacuum leak, etc.

One of my friend saw this on his car and bring it to a mechanic, and he found a crack in the intake manifold being the culprit. So, if you can't figure it out, a mechanic with the right skill and tool is worth the money.

 

[PandaBear]

Originally Posted By: brave sir robin
a few months ago I replaced the timing belt cuz....old (the belt was immaculate btw) replaced water pump and fan clutch. Spark plugs and rotor a year and maybe 1k miles ago (just cuz).


Don't forget to double check if you have accidentally skipped a teeth or two in the timing belt alignment. I've seen friend's car fail smog because the the belt stretched and skipped a tooth (he was way overdue on replacement).