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92 deville poor mpg o2 sensor E44

7999 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

1 - 6 of 20 Posts
Try cleaning the TB and if the 2 EGR tubes down in it are all carboned closed, rod them out to open them up. A inoperative EGR will hurt gas mileage.
A leaky FPR WILL cause lower fuel mileage as it is sucking unmetered fuel into the engine. It sounds like all you need is a length of vacuum hose if I am understanding you correctly. You can buy that by the foot at any parts store.
Here is why, if the exhaust headers are not seal properly there will be unmetered air going inside the exhaust.
The exhaust is under pressure. If there is a leak air cannot enter, much like a leak in a garden hose. Unmetered air can only enter via an intake (vacuum) leak.
Does not sound logical to me. I've seen (and burnt my finger) on an exhaust manifold gasket leak. Believe me, there was no vacuum there drawing in fresh air. There was down right positive pressure and a lot of it.
1 - 6 of 20 Posts
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