Festy runs rough after a exhaust flange gasket replaced

[DaleInTN]

I replaced the exhaust gasket (from the manifold to the exhaust pipe) and she is running rough. Any ideas? Do I need to set the idle? Also, is the new gasket supposed to smoke? Will it go away after a few miles? I've never replaced a gasket like this before so I'm not sure. Thanks.

[1chrisapple]

yea prolly smoke for bit bc the grease u got on it off of ur hANDS AND STUFF BUT IT SHOULDNTSMOKE ALOT

[Snail]

The part might have had preserving oil on it that would smoke quite a bit when first ran. It should stop after 5-10 minutes of running. If it now runs like crap either the ecu needs to relearn the now correct o2 sensor reading, your o2 sensor is bad, or your catalytic converter is bad. The leak would allow enough of the exhaust to escape before the cat that it would run fine before you fixed the leak.

[DaleInTN]

The PO did a cat delete, no smog in my county.... yet

I should have said that it is idling rough, she drives out fine!

[Snail]

Did you take anything else off the engine to do the repair?

[DaleInTN]

No

[Snail]

You have an odd problem for sure. Do you know if your fuel mileage changed any?

[DaleInTN]

Nope, filled up yesterday and checked mileage... 42.7. Which is in my average area. I'll drive it in a few hours and see if I still have the problem.

[Snail]

Let us know what happens

[DaleInTN]

Well, she starts right up and runs fine.... then its like she's only running on 3 cylinders and then she smooths out. What is going on? I had no issues until I replaced the gasket. The o2 sensor is right there, could it be bad and without a cataletic converter the "check engine" light not work? The light still isn't on. Ant thoughts?

[Snail]

You can test an o2 sensor to see if it is bad. Dou you have a service manual? I dont have mine handy right now, but it specifies the test procedure

[WmWatt]

Smoke could be exhaust gas leak at flange? Happened to me when mechanic installed wrong tail pipe.
Assume reduced back pressure from removing catalytic converter?
Also computer reads oxygen sensor to set air/fuel mixture.
My carbed '89 only has the one sensor before the converter but some
later cars have two sensors (Festiva? Aspire?), one after the converter, and compares
readings to see if the converter is working. Don't know what effect
al that has on engine performance.

[SiliconSoul]

Ohm check your sparkplug wires. If they are older, perhaps you bumped them a few times moving things around and caused some damage?

[DaleInTN]

Should the check engine light come on if the o2 sensor is unplugged? I unplugged it and the light still doesn't come on. I know the light works because it lights up when the ignition is turned on.

[Snail]

Not right away. You would have to wait until the car is warmed up and driving.