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1984 Toyota Pickup. 2.4 L EGR valve question; failed smog check for high NOx.

Hello. My question is about Nox. I have a set of carb approved (D-462-1) headers on my truck. I used a vacuum gauge teed off my EGR valve so I could watch the vacuum going to my EGR valve while driving. I understand that a part of the triggering process of the EGR is exhaust back pressure. I believe the headers produce little or no back pressure by design. I see no vacuum to the EGR until just before 3000 RPM, and then it is "slight vacuum" 4-5 in Hg. My truck never reaches this RPM during the ASM test, hence my EGR is not functioning during the test. As expected my Nox numbers are too high. I installed a new cat (under California's new cat law) and a new quality O2 sensor. It helped, but still my Nox numbers are too high. I don't want to lose all the improvements the headers did for this truck, ie: improved performance and better fuel mileage and greatly improved over all drivability. The hard spot in the gas pedal (where opening the secondary venturi begins) would produce 62-63 MPH with the stock exhaust, with the headers and everything being equal, it will bury the 85 MPH speedometer. They make a tremendous difference. In my research I have read that 1985 Toyota pick ups (1 yr newer) get their EGR triggered by the speedometer cable. I cannot find out how this is done, and assume a sensor of some type is used. I also cannot find out if this is the only difference in the EGR system, when compared to mine or if there too many difference's to adapt it at all. I believe 1985 was the only year Toyota did this. This is also the time period when some 84's had FI and some Carbs. 1985 also, some had FI some Carbs. Mine has a production date of July 1984 and has what is commonly known as an early 22 R Block. I seem to be stuck in between a rock and a hard place by not being able to find out if I can use an 85 speedo set up on my 84 to get this issue resolved. If it will work, a quick trip to the referee for certification would be in order. Any thoughts about this?L S
Answer:

We can tell you the referee will not allow 1985 emission components on your 1984 truck, with that said, if you do in fact believe it is the header causing low back pressure we can only suggest you install the original header on your truck for the smog inspection and than revert to the aftermarket. posted by SmogTips Support

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