View Full Version : Failed emisions test

02-24-08, 10:08 PM
I have a 1986 Fleetwood with 5.0 that has been garaged for 4 years, drained gas. It has new battery,gas,plugs,air filter and oil change. it failed emisions test on the Nitrious Oxide part of the test. Any thoughts on this?

02-26-08, 09:13 PM
You didn't fail Nitrous Oxide test. No such test. There is a test for N0X, oxides of nitrogen, which is a byproduct of too high combustion chamber temperatures. NOx causes acid rain. Nitrous Oxide is a GOOD thing for power!

So what to do? Easy one. You may or may not like the answer, but it IS the problem with 307's. There is these EGR jet extensions that sit under the carb. They are very common to get plugged up with carbon. They cause part throttle pinging, and most people end up running premium to either mask it or thinking the car needs it. It is designed for 87 octane runs excellent with it.

To test: (we should ALWAYS test first), start engine (cold is safest, you can get burned if it is hot, so be careful, gloves are hard to use for this), and either squeeze the EGR valve underneath and the engine SHOULD stall. If not, the EGR passages are blocked. EGR valves aren't often the problem, the passages are. If you have a handheld vacuum pump, that works, but you need to rev engine to see if EGR valve opens and that can't happen without backpressure as the valve is a positive backpressure type, but then you can check the EGR flow. So it isn't ideal. Depressing the valve manually is best.

To fix: Remove carb from engine (not as hard as you would think), and run a drill bit down the tubes. Do NOT remove them, the risk of dropping them in or if the intake is soft there (when old they WILL soften!) and you may end up with a unusable intake. I honestly found mine ok and put in brass plugs with 3/8" holes drilled in them to boost intake flow.... I don't recommend unless you are nutty as I am.... Install carb with new gasket, if good shape, I always stack gaskets to improve heat rejection.... Too hot carbs causes issues...

You can try to use a welding rod down the carb to try to punch through, but honestly the time you waste and risk to hurt the ventrurii's is very high. Carb is easy to pull. Remember, 10 ft/lbs mounting torque!!!! 10! Retorque every 6 months! Rarely done....

02-27-08, 03:13 PM
Will a seafoam treatment clean those passages? I had some part throttle pinging on my 86brougham lately, I just slowly poured about a half a can of seafoam thru the carb while it was running, then I flooded it till it stalled. did some other work on the car while it sat for 3 hours and started it up to let the smoke clear for a few minutes.. I havn't driven it yet , but the idle is remarkably smooth now, not the slightest hint of vibration or shaking I had before..


02-27-08, 04:14 PM
Maybe, I would pour it down and get it directly into the tubes. It might help. Probably repeated applications.

It isn't too hard to pull carb honestly, 1in wrench, 5/8" line wrench, 1/2" socket and 6in extension, stuff like that. Not too bad really. I can do it in probably 15 min or less. And I haven't done one in YEARS.

Try the seafoam. Can't hurt, it will help the engine anyway. I would use the Deep Creep and spray directly into the tubes (get a small hose and direct it in use light and small 1/8" vacuum hose or something you will see them) Deep Creep is aerosol version of SeaFoam. Spray at night and let sit in the jets. Might just do it.

4.9L and 4.5L Cadillac's would benefit a lot here too.

02-27-08, 07:19 PM
My 5.0L (soon to be 5.7L Olds) failed twice. Check your O2 sensor. Or better yet, check the throttle position sensor on your carburetor. Your gas might be running too rich. My mechanic fixed mine with a computer and it ran fine. Not to mention I had it freshly rebuilt. Plus, I passed emissions right afterwards. Couldn't hurt.

02-28-08, 01:13 PM
Oxides of Nitrogen are more common seen with lean mixtures and/or high timing, or lack of EGR flow. I did some detailed posts on emissions failures in the past, don't recall if I put much on NOx failures.

But. For a NOx fail only, all other emissions ok:

Idle Fail: Base Ignition timing too high, compression too high (Seafoam or X66P will help here)

Cruise Fail (and not idle fail): EGR flow insufficient (backpressure of exhaust changed (note these have POSITIVE backpressure EGR valves, so it is EXPECTING backpressure to some degree, if you have done headers and high flow exhaust you probably need a 70's ported non BP EGR valve, which is what I did with mine when I did a cat back), EGR passages blocked up (real common on 307's), EGR Valve bad, vacuum control to EGR bad (the little black box on driver's side valve cover), vacuum routing changed and not correct, EGR on these cars connects to the old distributor vacuum port on the Q-Jet (driver's side, middle/low (in body), ensure it has vacuum just off idle.

Idle/Cruise Fail: Timing, carb buildup (Seafoam/X66P treatment needed), engine modified with higher compression, cam overadvanced.