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Car Forum / GMC Cars / February 2006Emissions Question- modified 79 Trans Am
Hey everyone I recently found a good deal on a 1979 Pontiac Trans Am that has been modified quite a bit and I couldnt pass her up. Im having some trouble getting this car to pass emissions. Here is the list of known modifications: Holley 770 Street Avenger carburetor Edelbrock Performer Intake Lightweight pistons & rods Comp Cams xtreme energy cam & lifters Hooker Headers Flowmaster 30 series exhaust TCI transmission 3200 stall The 403 Olds engine has a fresh rebuild and has been bored out. I took her in for a smog test the other day and she failed miserably on the HC portion (500 max, read 3100!). I had the timing set the day before and it was running great- no obvious ignition problems. The car does idle very rough and Ive noticed it has a tendency to die when put in gear (esp when cold). Any idea on whats going wrong here? thanks, Greg You will never pass emissions with that carb/cam/intake, what made you think it would? First of all, the original emissions components that were are on the car, pcv, egr, cat are they still there? > Hey everyone I recently found a good deal on a 1979 Pontiac Trans Am > that has been modified quite a bit and I couldnt pass her up. Im having [quoted text clipped - 18 lines] > thanks, > Greg I know there is an EGR on there.. but as far as the cat and everything else this car is exempt from all that here in Nevada due to it's age. The only portion of the test the car did failed was the HC. When I took the car into the shop it was there for an oil change and they did the smog afterward. They did let the car sit for a few minutes before the smog test and I bet the electric choke didnt have time to open up fully. Like I said the car idles really rough and barely has enough vacuum to operate the brake boost but once it's cruising it runs really smooth. Im just wondering if anyone else has had any luck passing emissions tests with an engine that idles this rough. > I know there is an EGR on there.. but as far as the cat and everything > else this car is exempt from all that here in Nevada due to it's age. [quoted text clipped - 6 lines] > smooth. Im just wondering if anyone else has had any luck passing > emissions tests with an engine that idles this rough. I can guarantee it won't pass. The reason for the "rough" idle is that cam is high lift and duration. It is literally dumping raw fuel into the exhaust all the time. Won't matter if they ran the car for 3 hours and had it so hot you could cook on it. At idle it will still dump fuel into the engine. That is why it has the high stall converter in it, off idle that engine is a dog, it has to rev up before it produces any power. It is also the reason your power brakes are not working very well. The cam produces very little vacuum due the lift and duration. You >> MIGHT<< be able to help the lower end power and reduce SOME of the HC if you changed out the lifters to something like a Rhodes style rapid bleed lifter. Just be aware that they clatter some and may not do enough to help you. ugh...maybe she wasn't that great of a deal after all :( I took the TA to another smog station again today, the guy didn't want to even attempt to test it based on how irregular it idled. I told him it had an aftermarket cam but he's convinced there is an ignition problem and recommended some new spark plugs and/or wires. I pulled a spark plug out afterwards and it looked good with a little grey coating. I also checked the plug wires with a multitester and they showed normal resistance and found no leaks. I put a new distributor in last week and the timing seems like it's fine. Oh and I found the specs for the cam: Competition Cams 42-226-4 Olds Xtreme Energy Cam - #CAM 42-226-4 HYDRAULIC-Pro street/bracket race, good intake, headers, gear, 3200 stall. Intake/Exhaust Lift:554/558 Intake/Exhaust Dur:294/306 RPM Range:2800-6800 I can't believe this car can cruise so smooth with this wild of a cam! The guy must have done one hell of a rebuild job because not only does it run sweet but I'm getting pretty decent mileage.. better than a stock 403 TA I owned a couple of years ago. I'm still breaking in the engine but I can't wait to see what It'll do at the strip All these mods require a good set of am heads as the 403 were junk from a performance satnd point, what do you have, no matter what the cam is too big. This is not a 6800 rpm engine, more like a 5500 torquer motor, typical of Olds. > ugh...maybe she wasn't that great of a deal after all :( I took the > TA to another smog station again today, the guy didn't want to even [quoted text clipped - 18 lines] > stock 403 TA I owned a couple of years ago. I'm still breaking in the > engine but I can't wait to see what It'll do at the strip Yeah I forgot to mention the car does have aftermarket heads on there although I really dont know anything about them.. |
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