need help emmisions
 

I have a 1983 E-350 ecololine with a 460 engine. I brought it to the smog shop and they told me it needs, carb and egr valve. We did that. Then we go back and now 200.00 more dollars they tell me I need a air by pass valve which I just put one in prior to going. So, it can't be that. I tried trading out a distributor and it didn't make a difference. New check valve. New injection pump is new. Had the heads redone so I know its not rubber seals or valves. New timing chain and no slack. Could their be any sensors or vaccum cylinodes? Any info would help.
We are trying to find what part to fix next.
thanks
Fred