well my 1990 bronco rebuilt 302 w/ one newer cat and new o2 sensor failed the "test only' smog. here are my results:

15 mph:
HC max:115 gp avg:302 meas: 90 - passed
CO max:0.63 gp avg:1.93 meas:2.79 - failed
NO max: 986 gp avg:1758 meas:395 - passed

25 mph:
HC max: 95 gp avg:252 meas:145 - passed
CO max:0.82 gp avg:2.12 meas:4.01 - failed
NO max:846 gp avg:1558 meas:309 - passed

Tech advise:
too rich on load, unburnt fuel. check MAP

I'm thinking of getting the second cat and inspecting the vacuum hose from the MAP. Can anyone offer some other advise? on what else I can do?

thanks, tHeCoS

 

I would highly doubt the two cat theory. I only have one cat on my 88 302 and our hc ppm limit at idle is 220 and I passed with a 9. Our co% at idle is 1.20 and I passed with 0.00. Ya, nothing, and that is with one cat. There are a number of things that can make it run rich. Is the engine light on? If so, check the codes. Sometimes, even when the engine light is not on it will still give codes. Many people on here swear by that sea foam stuff. It is a type of engine flush, you could try that.

 

ya. I here the same about seafoam. I'll give it a try. Even though I cleaned throughly the upper intakes while installing the rebuilt engine.

no, the engine light isn't on and no codes.

 

i did it!! passed the smog test....ya!~ In the past I always got it hooked up to the diagnostic machine at a shop, if it didn't pass(cost $85). But this time with a little research and by learning the curves of the sensors. I managed to find out it was my cat. But before a replaced it I already had lucas oil fuel injector cleaner inside the tank and for the extra bonus used SEAFOAM through the intakes along with basic maintainence (oil, plugs) then replaced the cat ...then went straight to the smog station (test only).

here are my numbers: (HUGE difference!)

15 mph:
HC max:115 gp avg:51 meas: 26 - passed
CO max:0.63 gp avg:0.12 meas:0.00 - passed
NO max: 986 gp avg:301 meas:453 - passed

25 mph:
HC max: 95 gp avg:37 meas:11 - passed
CO max:0.82 gp avg:0.09 meas:0.00 - passed
NO max:846 gp avg:241 meas:394 - passed