smog issues 77kammback

[E.Groscup]

Hello everybody, I am new here with a recently purchased 77 kammback. I am having a real problem getting this thing to run properly to get it to pass Ca. smog. It will not run just off idle with the egr valve connected. It pings, misses badly and surges. If I disconnect it, the miss goes away, it smoothes out, but the pinging does not. Ign timing is correct at 2b, and the cam timing looks right. Thinking that it might be lean, I just opened up the carb and replaced the power valve assy., float needle and seat, accelerator pump diaphragm, and bowl gasket. I can't find a vacuum leak. It still will not tolerate any egr. Any thoughts? Thanks, Erik

[cjbiagi]

Are you sure that the valve is connected to the correct (ported vacuum) source? Here's a good explanation of how egr should work. http://www.asashop.org/autoinc/dec97/egr.htm

[ColinOpseth]

Have you checked the air passages that run to the EGR? Sometimes they plug completely with carbon.

[mldeolde]

my experience with smog motors from GM from 1974 - 1979 is that they always seem to run very crappy when they are adjusted to meet smog regs here in California. i've had some that would barely get out of their own way when the "emisssions tech"
got it to where it would pass tail pipe test. then again i had a 1974 914 2.0 porsche with webbers that originally was fuel injected and would actually pass emissions tests but fail the equipement portion ,for obvious reasons. after my recent expierience with my 74 Nova i just can't wait to see what kind of gyrations the state puts me threw when this beast goes back on the streets.75 406 sbc Monza IMSA

[cjbiagi]

You have to look at the whole egr system to evaluate it. For instance, the EGR valve is connected to a ported vacuum source so theoretically it should have no effect at idle since it is not, or should not, be receiving any vacuum to open it. Some of these are controoled by temp sensors, delay timers etc., plus the mentioned buildup that can occur in the valve or passage that cna keep it open.

[PeerStalkHawk]

Erik, the pinging with and without the egr valve hooked up seems like it is staying closed for some reason like the other guys mention. The distributor(vaccum) advance usually has more timing added to it to work with the egr. If it is closed(egr) instead, of opening under light load/part throttle driving, it is not diluting the fuel mixture with the extra exhaust gas to stop the pinging. It could be plugged, the actual valve could be leaking, or it could be stuck. Also check all the vaccum lines and carb mounting area for any leaks to as it can also cause a similar problem or add to it. The vaccum lines like to crack right by the ends of the nipples from the combination of engine shake and heat. Hopefully nothing is stuck or blocked in the carb too. If the lines are routed correct and in good shape you should be able to trace your problem easier. Hope it helps some....Dean.

[E.Groscup]

Thanks for all of the info, the egr is plumbed to ported vacuum through a tvs and the passages are clear enough that if I operate it manually at idle it will stall. It is the off idle to about half throttle that is the problem. I think that it may still be a bit lean and will try to follow that up. Posibly the wrong egr valve opening too far? Does anybody have a factory vac. diagram out there? This is a 49 state low altitude w/auto wagon. I am working off of a Motors manual diagram. I have run across discrepencies before. Thanks for all of your replies, Erik