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Hi everyone! I recently purchased a 95 suburban 1500 5.7 and Im trying to get it to roll through emissions but my idle is still a bit too rich. The limit in our state (NJ) is 220 on low idle HC’s. To make a long story short, It originally blew a 520 for low idle hydrocarbons -high idle passed with flying colors. I Have it down to a 277 but thats still not enough to pass. The truck did have a miss but i was able to fix that. I have replaced plugs/cap/rotor, egr valve, egr vac switch, new vac lines, idle air control valve, and put the “correct” thermostat in it (195). The timing was also 8 degrees advanced- so i bumped it back to 0 which is factory spec. I am running premium fuel, there are no vac leaks, and no codes. The truck is running awesome, just not awesome enough to pass emissions. My next replacement will be the o2 sensor even though it is showing good on the scanner- I have seen some be “lazy” in the past.
Some friends have suggested a fuel additive called “guaranteed to pass” – I think its made by CRC. I’ve seen other things out there like seafoam and marvels, etc..Has anyone tried this stuff? does it work? I would rather fix it the old fashioned way / the right way, but im running out of my 45 day failed inspection time limit.
Thanks!
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It could be the cat like stated, retard the timing a little bit more for the test and it should pass, then advance it back up afterwards. That’s what I’d do.
+1 on r e t arding the timing a little bit. However, that’s just a temp fix like you said to pass inspection. Anyway, the higher hc emmisions is usually caused by a lean misfire, not under rich conditions. in any case, I would change the o2 se
Quoted From EndSupremacy:
+1 on r e t arding the timing a little bit. However, that’s just a temp fix like you said to pass inspection. Anyway, the higher hc emmisions is usually caused by a lean misfire, not under rich conditions. in any case, I would change the o2 sensors. I don’t believe it to be the cat converter. It really is tough to say what the problem is, being that you did the EGR valves and you don’t have any vacuume leaks. I would check to make sure everything is installed properly and re-check to see if there is a vacuume leak. You did everything right, so my guess is that you missed something, and that something is causing your hc’s to sky-rocket. Change your o2’s. If that doesn’t work, than I’m just as stumped as you. Maybe these guys are right and it’s just the cat converter. Try replacing that along with the o2’s. Good luck though. Keep us posted.
Throwing those parts at it would be a waste if it’s not the problem.
Don’t forget the fuel system either. Verify the fuel pressure is within spec. That engine shouldn’t need premium, but I do see that you advanced the timing. Lower octane should help with engine at factory timing.
HC can also be oil too. I’m not sure what oil you are running, but a thicker weight can help reduce oil consumption slightly. If you are running a 5W30 throw in a 10W40. Maybe even a 20W50 just to get it to pass, then put a more suitable winter oil back in.
Excessive HC emissions can be down to serverly lean running condition as already stated but also can be down to rich fuel ratio’s.
+1 on checking for fuel pressure at idle, along with vacuum leaks, PCV system and any defecive or worn out ignition components.
It’s not the cat, the cat is responsible for keeping NOx emmissions down NOT HC people, any HC that the cat deals with is purely a secondary occurance because it’s hot enough to burn them as they pass through but it’s purpose is not to keep HC down. Leave the timing alone too since you have it at factory spec. One thing to be sure of is that the truck is warmed up when you take the test, if it sits for a while before they run the test the computer will make it a little rich in order to keep the engine running in cold weather and given your location I’m guessing things are getting chilly this time of year. Aside from making sure the engine is fully warmed up when they do the test I would also be looking for vacuum leaks especially around the intake gasket as we all know GM intake gaskets are famous for leaks, intake leaks will drive the mix rich BTW.
Lastly a little bit of ‘dry gas’ will help you pass as it has a high alcohol content and as a result will burn cleaner that straight gas.
Good luck and keep us posted on what you find and if you pass.
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