Using a scanner and fuel rate...

[DennisG01]

Is there a way to see exactly how much fuel (instantaneously) the truck is using. Say something like "x" amount over "y" amount of time? And can this be done while the truck is moving? I'm wondering if I can check how much fuel is being used and possibly compare it to a GM spec or other vehicles.

[gmctd]

Tech-II, and others, indicate the fuel rate as called for by the PCM for a given set of input values from APP, ECT, MAP and RPM.

If the Inj Pump has been modified for increased fuel rate, that increase will be effected from bottom end to top end.

PCM will not know this and will call for the programmed rate indicated from those sensors.

Only at idle will indicated fuel rate reflect the increased output from the IP, as PCM controls idle speed by comparing inertial differences in Optical Sensor output, cylinder to cylinder, then altering the fuel rate to compensate.

(Which reason is why one particular modification results in poor idle with increased APP sensitivity)

Example: if fuel rate is 8-9mm at 675rpm idle, tweaked IP will show 6-7mm at 675rpm.

One garage is offering a tweaked IP and re-programmed PCM to match.

So, you would need a flow indicator in the fuel line between the filter and the IP, for comparison to the 'scanned' rate.

[ 02-15-2006, 09:08 AM: Message edited by: gmctd ]

[DennisG01]

So if I understand you correctly: A Tech II will tell me what the computer is ASKING for, but will not necessarily tell me how much fuel is ACTUALLY going through the pump? In which case, as you stated, the only way to truly know how much fuel is being used is to add another gauge. Did I get that right?

[gmctd]

Correct

[rjwest]

I think all the gm vehicles that have the
fuel used/range/instant MPG etc. use computer
commanded fuel to do the calculations..
and not actual fuel flow
My buick always shows a MPG ( approx 1-2 ) better
than actual

For the truck, I get a fuel flow reading on my Car code scanner/laptop, and a calculated Instant mpg. my truck is close to stock and readings look as expected, but I am sure it is not precise...

I am GUESSING it does it by using the IP cmd time.
As GMCTD states, any mods would probably upset the
readings accuracy..

[ronniejoe]

To get the actual fuel flow to the engine, one would need to measure the flow to the pump and the flow back to the tank, then subtract the two.

[gmctd]

True - particularly since housing pressure is adjusted via the by-pass regulator, and some schools of thought indicate that increased housing pressure is necessary for increased fuel rate.

A differential pressure gage and senders, surplus from aircraft, would be handy.

For precise accuracy.

[DaveNY]

similar marine application is Flow Scan and is very accurate-fuel burned-fuel remaining-and GPH being consumed at present time. A little $$$pricey at around 5-600.00

[DA BIG ONE]

Originally posted by gmctd:
True - particularly since housing pressure is adjusted via the by-pass regulator, and some schools of thought indicate that increased housing pressure is necessary for increased fuel rate.

A differential pressure gage and senders, surplus from aircraft, would be handy.

For precise accuracy. Any idea where to source the gauge, senders and adapters?

[gmctd]

I'd try a web search - aircraft\marine\military surplus sites.