Failed Tennessee emissions test twice...Results below.

HC - 717PPM Limit: 220 PPM
CO - 13.17% Limit: 1.2%
CO2 - 5.9% Limit: n/a

I have done the following: New header pipe, new plugs, wires about one year old, Techron through the oil trap (changed oil twice), oil change before first test, sprayed throttle body cleaner in the throttle body - gently cleaned with a clean rag, sprayed MAF Cleaner on the MAF, full bottle of Lucas Fuel INjector cleaner and took a road trip (600 miles)

Possible culprits: O2 sensor (have not checked), throttle control (have not checked), temp sensor (have not checked), one broken manifold stud causing leak at start up, but it seemd to close one the engine warms fully, need to change airfilter, removed 'heater helper' hose.

I know she runs VERY rich because I can smell the fuel. Gas consumption is better than before the road trip (was 12mpg, now is closer to 16-18). No CEL, but service light comes on when I first start her up, but goes out. Slight stumble when she's cold, but a couple of revs and a cloud of smoke later she runs like a top.

Plan on going through the Hanes Manual Emissions chapter and FAQ recommendations this weekend. Any other advice or pointers would be greatly appreciated.

Loose Moose

FPR and O2 sensor sound like a good place to start. They both look original to the car. I can easily test both of these this weekend and get the parts. I'll update on what i find out. Thank you.

Loose Moose

I tested out the FPR and it is working like a dream. I wasn't able to get to my O2 sensor. I went to test the sensor the next weekend and something strange happened. I was running the car for a few minutes to warm everything up and check the diagnostics. After running pretty good, albeit running rich, for a about 10 minutes, the engine just died and will not restart.

I am going to replace the O2 sensor because its pretty elderly looking and diagnostics returned 113, 221 and 231. Would the O2 sensor not allow the car to start, maybe by allowing too much fuel to the plugs? It does almost sound like the engine is flooded. There is a strong fuel smell at the tail pipe while trying to start the car.

Could this be a problem with a completely blocked catalytic converter? Everytime I start the car I get a "poof" of carbon that leaves a dusting on the ground.

All help is much appreciated.

Loose Moose

High unburned hydrocarbons (HC) and high carbon monoxide (CO) both mean there is insufficient oxygen for proper combustion of the fuel. Ergo, the engine is running rich. The manifold stud isn't the source of your problem.

The two most likely culprits, IMO, are the oxygen sensor and the fuel pressure regulator. On a '93 Volvo if you still have the original O2 sensor and/or the original fuel pressure regulator ... replace them. Both are wear parts.

Fuel economy should be in the low to mid 20s.

Fix this ASAP. You run a very high probability of destroying the catalytic converter by running rich. You are also burning a lot of gas for no good reason.

For the O2 sensor, get one which is a direct fit, not one of the cheesy splice it in universal sensors.

I was able to pick up a fuel pressure regulator at our local Carquest auto parts store on a Sunday afternoon. It is the most common cause of rich running.

I would go after that broken stud on the manifold. ANY O2 that gets into the system after the AMM and before the Cat will raise your NOX.

The next thing to check is for any sort of vacuum leak. That will also raise your NOX.


Good Luck,

Paul