CA Emission test failure - '93 Buick Roadmaster Wagon

Hi there ! - looking for some advice on my Buick Roadmaster 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

NOX values are low in both tests (max allowed at 15 mph - 472, measured 100 -- max allowed at 25 mph - 471, measured 107) .

15 mph HC max allowed-71, measured 76.... CO max allowed- .31, measured .29
25 mph HC max allowed-30, measured 63.... CO max allowed- .29, measured .24

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

put a new aftermarket cat on it,.


Nick
worked for me with a 91 tbi car,.

Not the EGR.

Personally, I would do cap/rotor/plugs and test again. Also, go into the diagnostics on the HVAC head and check the coolant temps when driving to make sure the thermostat is working correctly.

speedrace54 wrote:

Hi there ! - looking for some advice on my Buick Roadmaster 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

NOX values are low in both tests (max allowed at 15 mph - 472, measured 100 -- max allowed at 25 mph - 471, measured 107) .

15 mph HC max allowed-71, measured 76.... CO max allowed- .31, measured .29
25 mph HC max allowed-30, measured 63.... CO max allowed- .29, measured .24

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

I have a 93 and passed but barely 2 yrs ago. I expect much the same. I test mine at my mechanic vs a smog shop. Not that a mechanic can 'cheat' you through, but they will be more likely to take those little steps to get you through.

If your trying the drive-by-smog make sure the car is hot or up to temp when you get there, a cold engine doesn't run clean.

New Air Filter matters, car breaths better, runs better.



No idea if running a higher octane fuel will help or hurt, but I'm due in a month, so have been putting varioius additives in the tank to try to clean it up but run it out before the test (in case they work against me)

Post when you pass. I'm interested in how you fair since I'm soon to be in the same boat.


JRoss

You don't show whether your 'check engine light' is on or not.
The O2 sensor is not a lifetime device. I would start by changing that.
If that doesn't do it, then maybe take Nick's advice.
I can't remember, was the Catalytic converter invented for NOX emissions?

I'd try the O2 sensor, if it ain't that, Summit has CA legal cats that are not too pricey.

-Rich

Mike,

I would also make sure that you drive the wagon for a good drive before going to the test lane..
Look into doing a SEAFOAM treatment.. How has the fuel mileage been has it changed lately.

When my 92 wagon got up in miles I had a new cat put on it, it started getting poor gas mileage.
I had 162000 miles on it when I had the new cat put on as the original one was plugged up...

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