Hi there ! - looking for some advice on my Buick wagon. Below are the smog test values. It failed on HC (both low & high speed) and CO passed, but was near the max allowed on the low and high speed test (measured .29 and .24 ). NOX values are low in both tests. 15 mph HC max allowed-71, measured 76 CO max allowed .31, measured .63 Okay, I have replaced the MAP sensor, TPS, Alternator (was overcharging), Battery, the Idle Air Control Valve, Ignition control module, fuel pump, external fuel filter, and fuel level sensor assembly. A cross reference chart of the three measurement types, their values, and possible cause or recommended action indicates "Rich AFR (Air-fuel ratio), air injection). The 5.7 V-8 has 160K miles on it. The plug wires and cap are fine, and I just changed the oil before this smog check. It runs/idles great -- with no misfires or surging. Anyone out there have any idea's of where to look? -- for instance, is there a sensor that could be causing the rich fuel mixture? I thought this was a fixed (non user adjustable) ---The O2 sensor only results in High CO, low HC from what I've been told, so I ruled that out. And a bad CAT results in high values across the board. But maybe one of you has direct experience with this engine of the 1993 vintage with the throttle body injection, and can give me some advice. Thanks in advance, Mike
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If your getting a bunch of unburned fuel out the tail pipe, high and low speed, It more than likely is the ignition system. Make sure it's all good.... relatively new, good condition, good parts. Ign. coils do were out, and produce lower voltages over time. Base timing set properly? I stick with AC Delco for this stuff. A good test for Ignition parts is to get a spray bottle, fill it with water and add some table salt (so it tastes like salt water). Spray down the plugs, plug wires, coil, cap.... If it's so-so, the salt water will revile it. Don't forget to rinse it all off with fresh water. Other possible stuff: Air pump is working correctly? Poor maintenance by PO, worn rings giving you excessive blow by? Try not to over think things, keep it simple. Good Luck, Mike
Definately what 200OZ says. Keep it simple. 1. Determine condition. Do a compression test. If you have one or two low cylinders that would need to be corrected. 2. A failed O2 sensor may certainly cause a rich condition. It sounds counter intuitive but a rich condition will result in low NOX. A lean condition results in high NOX. If rich (which it is) then depending how long it's been that way the CATs could certainly be at least coated with carbon and not functioning well. Over the long term they will melt down. 3. At 160,000 miles I would hope the O2 sensors are not original. Also they'll be coated with carbon too. Non-heated O2 sensors begin losing efficiency around 80,000 miles. You can test them with a meter but you can't test the reactive time with a meter. I'd replace them first. My 2 cents is replace both O2 sensors. If the engine has anything other than a smooth idle also do a compression check dry first and if you find a low cylinder then do a wet test on that or any other low cylinder. The hard part is the engine really needs to be warmed up first so you'll be working around hot manifolds. The wet test is putting in through the spark plug hole about a teaspoon full of oil then retest. If the pressure reads higher on the wet test the rings may be bad. If not it indicates valves not seating. You may need new cats too but DO NOT replace them before you correct the rich condition or you'll just be wasting your money. I also wanted to add that one or more fuel injectors could be leaky too. Those buggers are expensive. Not sure how to test but if you have a leaky injector you may have a carboned spark plug or more and look wet. It's much more difficult to troubleshoot on an OBD I system like what you have. An OBD II system will tell you rich or lean with codes and on later systems with coil on plug it will tell you which cylinder. Not so on yours. Good luck. If the engine mechanicals are good then generally the fix is simple once you identify the problem. Try not to throw money at it. And by the way O2 sensors can cause high HC too because when failed the computer goes in to a mode which causes more fuel to be delivered so that the engine doesn't run lean. Lean results in overheating, holes in aluminum pistons and burnt valves. As I said before lean would result in high NOX so you are definately not lean.
What those guys said and replace the O2 sensor. They get old and don't work as well but won't fail or set a code. Also any exhaust leak before O2 sensor will be an issue. If you have a laptop get TunerPro and a cable and you can record data from your car and learn to tune yourself.
I know I'm a little late on this post, but I have the 1992 version of the same car with the same 350 engine and same mileage. For a while when cold, I had an exhaust leak coming from the AIR injection pipe at the diverter valve where the connection had rotted in two. Got a new pipe only to realize the tubes were welded into the exhaust manifold as they were original. So i went with plan B. Got a new diverter valve from the GM dealer then went to Lowes and got a brass plumbing adapter to fit the diverter valve on one side and a barb fitting on the other to fit into the original AIR pipe. I pressed the fitting into the AIR pipe then soldered the fitting to the pipe to seal it up. So far after a year, it's still holding. One more thing- if the battery is over 3-4 years old, change it. My '97 Sonoma ran fine with no codes but at the time for inspection, kept giving "vehicle not ready" meaning the readiness code would not set. Problem was not voltage but amperage and a new Interstate battery solved the problem.
The most likely culprits for High HC and High CO with low NOX are (from cheapest to most expensive) a bad or too cold thermostat, a bad O2 sensor, an ignition fault. Your car uses a cheap 1 wire non-heated sensor. If there is any doubt as to it's age or condition, just replace it. They are generally under $30.00 or so for your car. If there is any doubt as to the condition of the plugs, wires, cap, rotor, etc. replace them. Check the ignition coil for resistance values. If out of spec, replace it. Whatever you do though, don't just throw parts at it. Try to methodically work your way through the problem. If it's not hesitating/missing under load or stumbling at idle, it's more than likely not ignition related. I'd start with the thermostat. Make sure the engine reaches operating temperature quickly. If not, replace it and re-test. Also, just for prevention, if the age of the O2 Sensor is in question just replace it because it is cheap and can make a huge difference.