The synthetic oil shouldn't have had a negative effect. I'm fighting
this same demon right now, albeit without a dealer (past warranty).
I guess my first question for you is, what does this flash do? I'm not
fond of the PCM being reprogrammed without knowing what's being done.
Have you checked your tire pressures? Has your O2 sensor been checked?
Is the end of your tailpipe covered in soot? Are you carrying several
hundred pounds of Steigermud cemented to the undercarriage? Have you
checked your brakes to make sure they aren't sticking (front or read)
and keeping slight contact with the drums/rotors?
Jeff Durling wrote:
> I am hoping that some of you can give me some input as to where to start
> looking at this problem. I am getting poor gas mileage. To start off I
> have a '01 4x2 QC with the 4.7 and an auto. I also have an LSD and
> 4-wheel ABS just to get all the info out there.
>
> This problem has been going on for over a year when it had 9k on it. I
> now have 26k. I used to get 14 to 15mpg around town and 20 to 21mpg on
> the highway cruising at 75mph. I now get 11 mpg and 12mpg if I'm lucky
> and 18 to 19 mpg on the highway at the same speeds. To make this
> interesting this all started in the period of a week. I went to the
> dealer for a minor problem and while there they flashed my computer with
> an update. The next weekend (couple of days later) I changed my oil to
> synthetic. The mileage drop maybe started happening when I left the
> dealer or after the oil change not really sure but it was all under one
> tank of gas.
>
> I have since had it to the dealer several times and they have flashed my
> computer every time along with new updates but to no avail. I have
> changed my spark plugs, air filter, and cleaned the TB several times but
> to no avail either. I did find when I changed my spark plugs that the
> tube that runs from the PCV valve to the rear of the intake behind the
> throttle body was not attached back there. I put it back on but it fits
> so loose that it comes back off if you just touch it. Could this be a
> problem? Could the PCV valve be a problem which btw the only place I can
> get one for the 4.7 is the dealer.
>
> The engine seems to run fine other than the pinging I have got ever
> since that flash they did. I tried new plugs which helped but not
> entirely. The only other thing I can think of is maybe the synthetic oil
> isn't compatible. Not sure what to do but any suggestions and thoughts
> would be helpful.
>
> Jeff Durling
> Systems Administrator
> (954) 741-9742
> jdurling@wdci-telecom.com
> www.wdci-telecom.com
>
>
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