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92 deville poor mpg o2 sensor E44

7997 Views 19 Replies 6 Participants Last post by  Ranger
Hi guys,

i have a 1992 sedan deville 4.9L with about 250,000 miles on the clock. i have nearly finished restoring it as it was due for the scrap heap. Anyway the exhaust had like 9 holes running down it so i replaced the entire exhaust including catalytic converter and silincer and the O2 sensor as well.

Now it runs like a dream but the MPG is down to 10MPG from 15MPG that is just crazy. the DTC that comes up is E44 O2 sensor running lean. i do maninly highway miles and if you turn on cruise control the mpg meter goes slight erractic then the code comes up.

just so you know i have changed the following in the last 2 years:

spark plugs, ISC motor, genrator, Vbelt, idler, battery, HT leads, airfilter, water pump all are AC Delco

many thanks

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what i think could be causing your problem is a leak maybe around the exhaust. Here is why, if the exhaust headers are not seal properly there will be unmetered air going inside the exhaust. The O2 picks up this lean condition due to the leak. The 02 sensor sends a signal to the computer to richen up the mixture to bring back the air/fuel mixture to 14.7 which is the ideal mixture for the safe of the catalytic converter. That's why maybe your MPG is not good because the ECM(obd 1)computer is energizing your fuel injectors more than it should to bring that mixture to proper mix. What you can do is, check LTFT(long term fuel trim) to see if it's with in normal ranges. If it is between 128 to 138 that's consider normal. But if it is above 138, you got a problem. This number means the computer has richen the mixture due to the lean mixture or leaking air. You can also check the ON TIME of the fuel injectors. Or what i do is, get a propane can and start spraying around the exhaust headers or vacuum lines. If you hear the engine RPM increase a bit, you found the leak. Do this while monitoring the 02 sensor voltage. I hope this helps you identify your problem and get your MPG to proper levels.
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I forgot something, it's really important to fix this problem because RICH mixtures(high CO)are the #1 causes of catalytic converters to go dead. here is why, the cat is trying to oxidize(add air)the rich mix for lower emissions. too much CO the hotter the cat gets, causes could melt the inside. ur looking at a brand new cat. expensive by the way.... that's it. bye
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