[V8] Poor fuel economy

[urq]

... this is one of the benefits of ProDiag (whatever they call it now) or
VAG-COM ... you can see the temperature reported at the ECU.  One of my cars
gets better fuel economy than the other ... I'm starting to suspect the MAF.
One of these weekend I will swap the parts between the cars to see if it
makes a difference.

One other possibility, especially if the weather is cold at the same time
... if the thermostat is stuck open the engine can be cold while its
running.  This happened on my 5kCSQA driving home from Sacramento one of
those rare nights where the temp was below freezing.  The engine was so cold
that the heater wasn't working and the windows fogged up.  I had to
physically cover some of the radiator to get the temperature up to drive
home ... 

Steve B
San Jose, CA (USA)

-----Original Message-----

If the ecu temp sensor is bad it could be telling the ecu the engine is
colder than it is and causing the ecu to feed more gas to the engine.  In
addition this could lead to fouled plugs and damage OXS and cats.



> -----Original Message-----
> 
> Breather hoses:
>    I find it hard to believe that they would loose me 2 or 3mpg?
>   (of course, I've never tried pulling one off and driving 
> around for a week!  :)
> 
> distributor caps and rotors:
> These were replaced (twice actually) about 6 years ago when 
> the incorrectly installed steering arms smashed them.  But I 
> guess they could be deteriorating. The Hall sensor plug on 
> the passenger side distributor has broken off and is taped in 
> place right now.
> 
> ECU temp sensor on rear of passenger side cylinder head:
> Is the theory here that the engine isn't allowed to get warm enough?
> 
> fuel filter:
> I haven't changed this in 70K miles. But how is it going to 
> give bad mileage? If it's clogged I'll use less, won't I?  :)  hee hee
> 
> air filter:  is new
> tire pressures:  new tires, all good
> junk in the trunk:   trunk empty
> 
> 
> ---- Ed Kellock <ekellock at gmail.com> wrote: 
> > -breather hoses
> > -distributor caps and rotors
> > -ecu temp sensor on rear of passenger side cylinder head 
> -fuel filter
> > -air filter
> > -tire pressures
> > -junk in the trunk
> > 
> > > -----Original Message-----
> > > 
> > > 
> > > I realize that when I come to sell my car I will have to post
> > > with a pseudonym as everyone will know what a horrendous 
> > > catalogue of complaints my 200K mile car has!  Anyway . . . 
> > > I'm currently only getting about 14mpg around town and 17mpg 
> > > on a longer run. The computer reads about 1 mpg better but I 
> > > know it's lying from filling up and checking odometer 
> > > readings. The car also has an uneven vibration that is 
> > > noticeable when stationary at idle. The Oxygen sensor is 
> > > about a year old and the plugs are even newer. The car seems 
> > > to accelerate OK, but then again, I doubt I would notice the 
> > > difference between 190bhp and 245bhp if it happened slowly 
> > > over time. Any obvious quick checks I can make?
> > > 
> > > Mark.