I have a 92 Aerostar with a 3.0. It failed emissions test because of high NOx. Hc and CO were well under required numbers. This van has 120,000 miles on it and runs perfect. The only problem it has is there is a slight delayed 2-3 shift at times. The emission test runs at 24-28 MPH. Any suggestions on how to get the NOx down? Need help--no license allowed now.

 

Check your EGR system. Make sure the vacuum lines are good, open the valve by hand with the engine running and it should kill the motor. Also get it up to about 15-1800rpms and see if it opens up. If that's all ok then pull the valve and make sure the passages are clear.

 

Good advice on checking the EGR system. It's job is to reduce NOx by reducing combustion chamber temperatures.

Other things that can cause higher temps and hence NOx include a lean condition (vacuum leak, clogged fuel filter/injectors, etc.), deficient cooling system, carbon buildup (increased compression), and those kinds of things.

P. S. Welcome to FTE!

 

Does the '92 use an EGR valve? If so, where is it located? Thanks for the quick replies and help already.

 

Now that you mention it, I don't think your '92 has an EGR valve...

 

You're right. I just looked in my book and they show the 3.0 didn't have one. I thought that only the 4.0 was like that. Now I'm at a loss. Other things that will cause high NOX would be a lean condition or high combustion temps. If you could post your numbers, it might help. (all of them) Does it "ping" at all? With your milage, you may want to run some "top-end cleaner" thru it.

You got me wondering now. I'll keep thinking.

 

EGR was my first thought too, but then I didn't see it in the usual place. My test numbers were as follows: HC--68.7 PPM, CO--.46%, NOx--2100.7, CO2--14.55%, but CO2 is not a test requirement. The only time it gets any ping at all is with one particular brand of gas, which I quit buying.

As far as lean mixture--try this out. When climbing a long hill or under wide open throttle, I've noticed the heating--air controls switch into default as if they have lost vacuum, but I don't see or here a leak. Maybe something is mis-routed?? Thanks again.

I'm going to check the MAF filaments also.

 

Sorry to say this but, I feel that you may need professional help with this one. I talked to one of the guys at work last night and he says that the Nox is reduced by the design of the heads. He said you should have 2 spout connectors, one for timing and one is for knock or nox (not sure which) but he says it should have an octane bar. He said it could be that the engine is running hot or your cat is bad. I think you will need to find someone that has a "5-gas" that can take a look at it.

Lean conditions cause high NOX levels but, I don't see that in your numbers. .46 CO seems a little high to me for something that new. Your CO2 is mostly a "diagnostic" value. It lets you know how well the mixture is burnt? 14 is really good. I don't see too many much over 12.5. Anyways...by looking at your numbers, my best guess would be that your cat is dead. But that is all I can give you from here is a guess. Sorry.

 

This Aerostar finally passed the emissions test on the third try. I tried just cleaning the air intake, replacing the air filter, ran injector clean through, topped of with higher octane gas, and found a tiny, occasional vac leak in a/c vent line. It improved 10%, but not enough to pass. Their certified emmisions shop wanted $80 to test and $215 to replace cat if it tested bad. Cat was only thing left to affect NOx so I did it myself for $150. It passed on the 3rd try. Thanks for you help!

 

Glad to hear you got it thru. What were your final numbers like?