Hello,

I have had this 82 22R pickup for several years, and this year it failed emissions, three times over the last two weeks.

NOx are undercontrol, and CO passes, but Hydrocarbons are above spec and it seems to be coming during the decel phase of driving.

I have checked the plugs, polished the electrodes on Cap, changed the oil, checked the tire pressure, modified the amount of 'squirt' in the accelertor pump circuit, put timing to spec, and slightly restricted the EGR tube in an attempt to get more oxygen to into the engine rather than inert gas.

The manual says that there should be a Throttle Positioner: which is a vacuum diaphragm and arm operated device that is supposed to keep the thottle plate from completely closing at high rpm causing high vacuum that sucks in too much rich fuel.

I believe this also can act as the AC idle kick up circuit on some models.

Although on the throttle plate rod there is a place for the Throttle Positioner to go, there is no throttle positioner.

However, what is more perplexing is that there is also no evidence of the associated vacuum switches and tube that would control such a device.

It is 5% off on Hydrocarbons pass = 6.0 actual = 6.3

Anyone with any experience of this or advice on how best to get the HCs down?

by the way, the engine runs strong, has good enough compression, I live in Denver (high altitude).

Regards