Engine overheat -> excessive fuel consumption?
William Liao
Got a question regarding how D-Jetronic injection system works. I just
topped up the fuel tank in my '73 164E (with D-Jetronic fuel injection).
I've been driving with my heater on full blast coz my 164's engine overheats
at idle and I want to know if the overheating is contributing to the
excessive fuel consumption, so I've had the heater on at all times since the
last time I filled up the fuel tank. Today when I filled it up again, I
found out that I've done 198.5 miles after burning 51 litres....with the
heater off it usually does around 180 miles for about 50 litres. Before I
jump to any conclusions, I want to know if there is a relationship between
engine overheating and excessive fuel consumption for the D-Jetronic, or if
the better fuel consumption is purely a coincidence. I didn't have the
engine re-tuned at all during this "trial". I know with later fuel
injection systems such as LH2.4 it'll automatically adjust amount of fuel
for the engine temperature...but dunno if the D-Jetronic is that "smart".
Anyway if anyone knows the answer please drop me a reply...thanks!
Will
'90 744GL
'73 164E
Mike F
Yes, D-Jetronic is that smart. On the 4 cylinder engines, the
temperature sensor was mounted in the side of the head beside the
auxiliary air valve, not sure where it is in yours. There is also a
sensor for intake air temperature, this adjusts the mixture slightly.
(Actually a hotter engine would get less fuel, so it looks like a
coincidence.)
--
Mike F.
Thornhill (near Toronto), Ont.
Change cant to ca and remove parentheses to email me directly.
William Liao
"Mike F" <"mikef2316()"@attcanada.cant> wrote in message
news:3B8260EA...@attcanada.cant...
> (Actually a hotter engine would get less fuel, so it looks like a
> coincidence.)
Really? Hmm...I didn't know that...
In most piston-engine aircraft, the mixture is adjustable by the pilot from
the cockpit. We were taught that in the event of an engine overheat, the
immediate reaction is to shove the mixture to full-rich setting. By doing
so you increase the fuel consumption and possibly reduce power, depending
what altitude (air density) you're at...but this is the most effective way
to cool an overheating engine, as you're effectively putting more fuel in
the cylinders.
I assumed that fuel injection system on cars would be designed to do the
same...
Robert Dietz
detected or excessive coolant temp is detected. Both conditionms will pop
the MIL on.
In 73 running enrichment was controlled through manifold pressure and
throttle position. Disconnectiong the ambient air pressure sensor will
effect slight enrichment. Adding resistance up to 1000 ohms in series with
the coolant temperature sensor will make effective changes. With the fuel
pressure set to 31.5 psi instead of the 28-30 psi range you will gain
further enrichment. Doing a good motor-vac service will significantly
improve the injector performance and help decarbonize the backside of the
intake valves.
Bob
"William Liao" <fox...@innocent.com> wrote in message
news:KUtg7.138999$Xr6.7...@news-server.bigpond.net.au...
Mike F
>
> On your 90 model the injection goes full rich when excessive pinging is
> detected or excessive coolant temp is detected. Both conditionms will pop
> the MIL on.
>
> In 73 running enrichment was controlled through manifold pressure and
> throttle position. Disconnectiong the ambient air pressure sensor will
> effect slight enrichment. Adding resistance up to 1000 ohms in series with
> the coolant temperature sensor will make effective changes. With the fuel
> pressure set to 31.5 psi instead of the 28-30 psi range you will gain
> further enrichment. Doing a good motor-vac service will significantly
> improve the injector performance and help decarbonize the backside of the
> intake valves.
>
> Bob
Right. You have to remember the computer on the '73 is analog. It's
fairly complicated to make analog circuits do fancy things like lean the
mixture as the engine warms, then start richening it again as it gets
too hot. (i.e. changing the direction of the slope of the response to
sensor input at a certain point.)
Phillip Garside
I do not know if this Input will help but here goes.
I have a 740 with LH Jetronic.
To govern the mixture settings it goes *at idle* as follows:
Air Mas Meter Flow PLUS Throttle Body Swich PLUS Engine Temp Sensor PLUS O2
Sensor in exhaust EQUELLS The leanest running it can do.
Basically. I personally think that William might be well advantaged by
testing the Throttle Position Swich. 2 Moded Full open and Full Closed.
Air Mass Meter *if present* They can fail as happend to me and car not
realise it was failed.
Engine Temp Sensor, If that is *dead* the computer lookes at it as a Cold
engine. Were talking -30 below 0 Degrees. So it will go rich. And evean
there is a remote possability that if the car has a Cold Start Injector that
is also open pouring fuel in to the engine *ouch*.
O2 Sensor in exhaust system. If that has failed and is sending a LEAN MIX
signal back to the Computer it would also cause the Injector Pulse with to
increase because the car thinks its running to lean and there fore its
subject to Knock and other dramas :(.
I hope I have not confused you all. I have had a LOT of fun with Fuel
Injection systems in Holdens Fords Volvo's and VL Commodores (Nissan Engine
and Managment System)
They all work on the same Basic prinsible. Some have more sensors some have
less.
Some have bells and whistles they dont evean need. Just because it "Looks
Good"
Check out all the Sensors, See if there all A Okay, If so have a look at the
Ignition timing and Fuel Pressure.
Also dont forget. Volvo Computer swiches the EARTH on its engine. So look
for a injector that has shorted to engine or some metal somewhere. That will
hold it open. If the Cold Start Injector is open that would be causing the
car to over heat and possable flood. Have a look at the spark Plugs see if
there Black or Gray. Gray is GOOD. Black is BAD.
Black means the car is being flooded.
Finally. Leaks in the Manafold (Intake). Vacume Leaks. Air intake Leaks.
Cracked pipes anywhere at all.
Blocked Cooling system. EG: Thermostat. Or build up of CRAP because somone
did not use a good Coolant and DISTILLED water in radiator.
Unlike in a Air Craft, If they start to over heat richen them up and they
cool off. Cars are not Air Cooled. There Liquid Cooled. And if the Car is
over heating evean richning up the mixture wont help if the Friction from
expansion is to high.
What cought my eye is. Its only overheating at Idle.
Wich to me tells me Either Throttle Swich fail, Injector Fail/Engine Flood
or Cooling system fail.
But Air flow will assist in the cooling of a car's engine.
I hope that was usefull after all my blabbering. Sorry to put u through it
all.
Lastly. If the Car has a Eletric Thermo Fan. And its over heating it shuld
click in !! If not. BRIDGE the Thermostat and get it working ASAP!!. It will
make a Diff.
Rgds,Phill
Mike F <"mikef2316()"@attcanada.cant> wrote in message
news:3B83A797...@attcanada.cant...