As the title says my truck failed its emissions test on nearly everything.
Results as follow;
Idle 900 rpm
Co .53 limit .5%

high idle 2600 rpm
oxygen 1.056 limit .97 to 1.03%
Co .53 limit .3%
Hc 30ppm limit 200ppm (passed something)
Any ideas what would cause such high emissions, it has the cat.
Thanks

 

Year truck? Miles? Engine?



How old are the O2 sensors? Do they do these tests with the engine warmed up?

 

1994
112000 miles
318ci
Yes the truck was warm, had drove it about 20 miles to test center.
Oxygen sensor has about 6000 miles done, (nsk) i think
The truck is stock expect for the performance pcm.
I think I posted this in the wrong section!

 

you are not that far over the limit in the categories where you are over


first thing you start with is tune up parts, air filter, spark plugs... also did you do both O2 sensors ?

 

Its not that much over but still too high.
At the moment there is about 4000 miles on the present set of plugs (champion),air filter is good. My truck has just the pre cat oxy sensor. I going to put in a bottle of fuel additive and hope that helps. I keep my truck fully serviced and it gets anything it needs especially if it might help the gas miles. Thanks for suggestions so far.

 

Plenum fixed?

 

strange, auto zone has listing for both upstream and downstream sensors for 94.. go figure..

 

Replace cat with decent quality unit (eg. magnaflow)

 

Yes I done the plenum mod a few years ago.
The auto stores are not always correct
I think your spot on the money about the cat, I will get a new one, (the present cat is a walker if I remember rightly). Would summit or jegs be my best option?
Thanks

 

you can do the cat and it will probably get you past inspection but from experience i can tell you when the cat is actually bad your numbers will be greatly higher.. again you are barely just over the limit and they obviously do a tailpipe test to get the readings like they do here in my home state of new jersey on older vehicles..


long story short when we would have readings this low that just went over the limit it was usually because they had carboned up from not being blown out ( having a full throttle run ) in a while, hadn't been tuned up or had a dirty air filter ( which you have done already ) or because we were stuck sitting in the inspection line for an hour or better..


if you haven't taken in on the highway and mashed the pedal to the floor in a while I would do that or find a deserted road where you can mash it to the floor from a rolling 15 mph and hold it there for about a 1/4 mile, this was usually all it took to get rid of the carbon build up and then the vehicle would pass with flying colors