cutting off injection going downhill was [Vwdiesel] Why gasss cars mpg sucks

[dieseltdi at verizon.net]

The injection amount commanded by the ECU may drop to 0 but that  
doesn't mean injection stops.  If the TDI actually cut off the fuel  
to the engine as you went down hill, it would have to know when to  
"restart" the engine.  How would it know when to do that?  I spent 6  
hours in my car yesterday going up and down hills in East Texas and  
Louisiana.  The engine never stops running even if I let off the  
pedal.  It simply returns to idle status, meaning only enough fuel  
being injected to keep the car idling.  The ECU injection quantity as  
I see it is a demand ABOVE AND BEYOND what is needed to keep the  
engine running, not the total amount of the fuel injected.  In other  
words, there is some base amount - X that is injected all the time,  
but when the ECU senses a signal from the pedal, injection quantity  
goes up.  Let up on the pedal, injection quantity goes down.  There  
is simply no practical way for these engines to literally shut off  
when going down hill.  Just my two sense worth but as I said, I spent  
6 hours in my car yesterday thinking about this and trying to  
logically justify the concept.  It simply cannot work.  Hayden

On May 15, 2005, at 6:22 AM, Val Christian wrote:

>>> A couple of things...first, the TDI DOES shut off all injection
>>> in a coast operation.  I've observed that, and verified it as
>>> correct behavior for the TDI.
>>>
>>>
>>>
>>
>>   So when you top over a hill, (and keep going of course)  the TDI
>> engine actually shuts off?  Seems like something DOT wouldn't
>> approve of regardless of ramifications or not.  Seems like a
>> freewheeling (ala E-mode) would save even more fuel.  If that's
>> the intent.
>>     Loren
>>
>
> When you top a hill, and start down, coasting, the injection level
> commanded by the ECU can drop to zero.  It's a function of power  
> commanded.
> Taking your foot off the pedal, it will drop to zero.  Depending upon
> the hill, not moving your foot may cause some fuel to be commanded
> to be injected.  But simply stated, yes, fuel can (and often does)
> drop to zero.  It's not freewheeling, per say, because the entire
> engine (altenator, compressor, power steering, pistons and valvetrain)
> keep turning.  So when the available power exceeds those, you get a
> free ride.
>
> Val
>
>
>
> _______________________________________________
> Vwdiesel mailing list
> Vwdiesel at vwfans.com
> http://www.audifans.com/mailman/listinfo/vwdiesel
>

TX AND US DISTRIBUTOR FOR DIESELPOWER TUNING BOXES.  GO TO  
www.dieseltuning.com, LOOK AT THE INFORMATION AND THEN EMAIL ME TO  
MAKE YOUR PURCHASE.  MORE POWER, MORE TORQUE, GUARANTEED!!!!

Visit my website at:  http://mysite.verizon.net/resosxp8/mydieselpages/
Proud owner of:
2004 Passat TDI GLS, 2.0l, 8 valve, 134 HP, 247 lb/ft of torque, Blue  
Graphite, Anthracite leather interior, ABS, ESP.
1998 Jetta TDI (Wetterauer Chipset, 2 1/2" exhaust, K&N Filter, 119K+  
miles, and running biodiesel)
1981 Rabbit Pickup ( with a freshly rebuilt turbo engine, 10K+ on  
engine now), burns biodiesel and a WVO system is in the works.
One, yet to be finished, Caddy trailer (the back end of the truck  
that gave its life to my Rabbit Pickup).
And many, many, many VWs; from a 1946 Beetle (11 Beetles total), to  
Vans (5 - 3 splitties, 2 bay window), Rabbits (3), Karmen Ghia (1),  
Jettas (5), Passat (1), Dasher (1), New Beetle (1), and Rabbit  
Pickups (3) most now gone but not forgotten.