open loop problems
 

I have a 1994 Thunderbird with a 4.9. At startup engine cold, The engine will stumble the exhaust stinks of rotten eggs, and run that way till it's warmed up, and then run fine. Any ideas?

RE: open loop problems
 

Try replacing the coolant temperature sensor, i've seen them go bad and not trigger the service engine soon light.

RE: open loop problems
 

Could it also be a problem with the oxygen sensor?

RE: open loop problems
 

Yes, somethimes the a heated O2 sensor will not warm up in time for closed loop. It causes the engine to stumble for a few minutes after going into closed loop until it is warmed up, then drives fine. So the car runs good at start up then after say, 2-5 min. it stumbles. It will not set the check engine light because it is within spec. just not working properly.

RE: open loop problems
 

hey yeah i have a 96 tbird v6, and my check engine light has been on. so i took it into my auto tech class to scan it with an obdII scanner. it read 2 codes, both of which an o2 sensor. these cars have 4 o2 sensors on them and they are not cheap. about 55$ a piece, plus im not sure which 2 are bad for sure. my gas mileage has STUNK. terribly. i was looking here and thought maybe a coolant temp sensor but it doesn't smell funny and it runs good in cold start. it has tried to stall out some times when i start it right away and put it in drive. my gas mileage has gone from around 17 or 18 mpg ( depending on how i drive that week ) to around 10 or 11 now. it sucks. do you guys have any ideas or should i just suck it up and buy 2 o2 sensors?

RE: open loop problems
 

Do you know which codes were present? There will be a different code for each sensor.

RE: open loop problems
 

i had same problem with 96 bird the two codes were lean mixture follow by rich mixture ended up replacing the y pipe and all 4 sensors because catlytic converters plug up and the car would not run after it heated up the two sensor before the converters are not heated and the two after are heated this problem to the mechnic two weeks to find and set me back 1500 the quick check is the back pressure if it is going higher than the converters a starting to plug because the engine is dumping raw fuel into them