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Engine running rich

what malfunctions cause a engines rich fuel mixture? smeone scanned my 96 buick lasabre with a hand held and told me my engine was running rich but o2 sesor was good. they mentioned emissions problem but didnt give me any codes. i have smelled the old rotten egg smell lately from the exhaust. sometimes the car really slugs going uphill when reaching about 40 mph.but if i really mash the acceleratorit will pick up and go. what things could be causing my rich engine run? is the list endless?

A worn out fuel injector. A dirty fuel injector. Really bad spark plugs that aren’t firing properly. Incomplete sentences.

No, it’s not endless. Dirty air filter. Dirty MAF (Mass Air Flow) sensor). Dirty throttle bore and throttle plate. Erroneous idle air control (iac) valve operation. Fuel pressure regulator set too high. Engine coolant temperature (ect) sensor reading too cold. Thermostat stuck open. Radiator cooling fans not shutting off.
What to do: Put in clean air filter. Use an MAF spray cleaner, and a Throttle Body spray cleaner (which also, cleans the iac valve). Check the fuel pressure. If it’s high, adjust or replace the fuel pressure regulator. If the engine is running cold, replace the thermostat. Or, if the radiator fan is staying on, replace the fan relay or ect sensor.
A fuel injector cleaner to the gasoline may help sticking, dirty, fuel injectors.

There’s not much info to go on so I suggest getting AutoZone, Checkers, etc. to scan the vehicle, give you the codes, and post them for discussion. They will do this for you free.

A clogged catalytic converter can cause a rich running condition along with loss of power so that could be considered.
It’s easily tested with a vacuum gauge.

There could also be underlying reasons for the converter problem if it exists. Leaking fuel pressure regulator, faulty ignition compontents, etc, etc.
One small problem often causes many big problems.

First of all, take the car to an actual shop that has a reliable, professional diagnostic computer and not a hand held computer that is prone to storing old codes and is only as reliable as the batteries that are in it to power it. The rotten egg smell has very little to do with the lack of power…unless the catalytic converter is plugged up, but then you would have very little exhaust coming out of the tailpipe.
Ignition componenets and spark plugs play a big part in power development. Which part of the ignition is faulty can be easily found out with a professional computer. I’d replace the plugs and then have the car diagnosed professionaly. But, in actuality I would be looking at a total rebuild because of the year of the car.

The “rotten egg” smell indicates a fuel mixture ratio that is incorrect.This will cause engine performance issues.