olskool720 Posted September 24, 2019 Report Share Posted September 24, 2019 (edited) My 86' 720 ST king cab failed smogged on the last test....25mph emissions. My mechanic worked on some vacuum lines. Then, the 720 failed again, so I've used my one free re-test. The testing site suggested the EGR valve. Anyone have any ideas??? Just one test I need to pass ARGH. I should add that I'm not much of an engine guy, so if you suggest something, it'll be for me to pass along to my mechanic, thanks : ) Edited September 24, 2019 by olskool720 updated 1 Quote Link to comment
Stoffregen Motorsports Posted September 24, 2019 Report Share Posted September 24, 2019 Did it pass the visual inspection? Why did it fail? NOx too high is common for older mid 80's vehicles and a lot of times , simply replacing the cat does the trick. 2 Quote Link to comment
olskool720 Posted September 24, 2019 Author Report Share Posted September 24, 2019 Yes, the CO was too high on the final test at 25mph at 1700rpm. It passed every test including visual. By "cat" do you mean the catalytic converter? The guy at the test shop stated that this wasn't the issue : \ 1 Quote Link to comment
Stoffregen Motorsports Posted September 24, 2019 Report Share Posted September 24, 2019 It may not be THE issue, but replacing the cat (yes, catalytic converter) is sometimes a quick and easy trick to get them to pass. Ask him if he thinks a new cat will get it to pass. 1 Quote Link to comment
olskool720 Posted September 24, 2019 Author Report Share Posted September 24, 2019 Thanks for the idea 2 Quote Link to comment
john510 Posted September 24, 2019 Report Share Posted September 24, 2019 Never buy into what the smog guy tells you.I just had my '85 Toyota pickup fail.He says it's running rich.It gets 27 MPG and is properly tuned with new parts so i'm thinking bullshit.I replaced the catalytic converter and what do you know ? almost zero emissions. 2 Quote Link to comment
olskool720 Posted September 25, 2019 Author Report Share Posted September 25, 2019 Good advice thanks 2 Quote Link to comment
olskool720 Posted September 27, 2019 Author Report Share Posted September 27, 2019 Finally passed. No cat needed. Whew, good for another 2 years. 1 Quote Link to comment
720_Jeff Posted September 27, 2019 Report Share Posted September 27, 2019 So, olskool, what did the trick, so we know what is a possible fix for the future? 2 Quote Link to comment
olskool720 Posted September 27, 2019 Author Report Share Posted September 27, 2019 [coming from a non-engine guy..aka me] So my mechanic replaced two hoses and cleaned out some other hoses and did some adjustments on the air filter holder. That was about it. 1 Quote Link to comment
blackbomber Posted October 4, 2019 Report Share Posted October 4, 2019 I have had my 84 since new. still has original carb.. have to test it every 2 years. Heres what I do.. I advance timing a little. make sure you mark original spot so you can put it back. Use a clean rag and , while you rev motor by hand .put rag over carb and make it suck air, rev it preety high. This kind of cleans out carb or carbon deposits I guess. then I put about one can of iso heet to half of a tank of gas. I think I used two bottles one year. burns cleaner. Then pray you get a guy who knows how to drive a stick shift at the emission place. most those guys never seen or heard of a carb. I have the original catalytic on my truck.. 1 Quote Link to comment
john510 Posted October 4, 2019 Report Share Posted October 4, 2019 7 hours ago, blackbomber said: I have had my 84 since new. still has original carb.. have to test it every 2 years. Heres what I do.. I advance timing a little. make sure you mark original spot so you can put it back. Use a clean rag and , while you rev motor by hand .put rag over carb and make it suck air, rev it preety high. This kind of cleans out carb or carbon deposits I guess. then I put about one can of iso heet to half of a tank of gas. I think I used two bottles one year. burns cleaner. Then pray you get a guy who knows how to drive a stick shift at the emission place. most those guys never seen or heard of a carb. I have the original catalytic on my truck.. Advancing the timing makes it more likely to fail. 1 Quote Link to comment
olskool720 Posted October 4, 2019 Author Report Share Posted October 4, 2019 Mine passed and that's good enough for me. I'll deal with it again in September 2021 LOL 1 Quote Link to comment
datzenmike Posted October 4, 2019 Report Share Posted October 4, 2019 9 hours ago, blackbomber said: I have had my 84 since new. still has original carb.. have to test it every 2 years. Heres what I do.. I advance timing a little. make sure you mark original spot so you can put it back. Use a clean rag and , while you rev motor by hand .put rag over carb and make it suck air, rev it preety high. This kind of cleans out carb or carbon deposits I guess. then I put about one can of iso heet to half of a tank of gas. I think I used two bottles one year. burns cleaner. Then pray you get a guy who knows how to drive a stick shift at the emission place. most those guys never seen or heard of a carb. I have the original catalytic on my truck.. Heet is (more or less) just alcohol and as most gas is 10% ethanol it isn't going to do much. Make sure your engine is at peak temperature before the test and is in good tune. (it should be anyway) Fix ALL emissions devices as they fail. Check all hoses for cracks. Check the EGR tube for leaks that will let in any oxygen and make sure the EGR valve closes at idle... or even remove and wire brush it clean. The later 720 uses exhaust pulses and one way valves to draw fresh air into the exhaust manifold so the catalytic converted has oxygen to burn off any HCs. A new converter won't do much without air to burn with. Look for leaks on the pipe(s) to the air cleaner. Do an oil and filter change. 2 Quote Link to comment
olskool720 Posted October 4, 2019 Author Report Share Posted October 4, 2019 Thanks for the tips that I'll keep in mind for 2021!! 👊 1 Quote Link to comment
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