temperature vs injectors

[fezz57]

i have a feeling that the physical temperature of the injectors alters the flow rate.

i only say this as ve tuning seems to vary after the engine has been running for a while

has anyone had this experience?

[5.7ute]

With the dead head fuel systems we have, I think you will find it is the temperature of the fuel not the injector which is altering your wideband AFR.
Also if you fill your tank with fuel after getting your Bens to converge watch what happens. That is why I get the whole car up to temp before doing any VE tuning.

[Chuck L.]

Yep. I can check the sp gr on the bench flow fluid at various temps. It changes. I see no reason it would not be the same with gas.

[swingtan]

As above, I don't think the temp of the injectors themselves will make that big a difference. However, going through the theory of it all...

• A "hot" injector will mean that the windings in the coil that operate the injector are also hot.
• Normal copper wire has a positive temperature coefficient of resistance, IE. resistance goes up as the wire gets hot.
• If the coil increases in resistance, then the amount of current flowing through the coil reduces.
• Less current through the coil (injector) means it opens slower, but closes in the roughly the same amount of time.

So if the injectors temp alone was to be altering the fueling, it should be leaning out as the injector gets hotter.

But, here's something to mess that up. Because the needle valve in the injector is made of metal, the orifice will ( in theory ) expand as it heats up. This will make the orifice bigger, allowing more fuel to pass through. This may match or exceed the reduction caused by the higher resistance of the coil...

The "real world" finding would probably show that the changes during normal running would be very minor and not really make that big a difference. This is probably due to the fuel and the intake air keeping the intake manifold and injectors within a fairly small range of normal operating temps.

What does make a difference is IAT correction and charge temp blending. These can have a big effect on the overall fueling calibration and will help to keep measured AFR's very close to the commanded values.

Simon.

[fezz57]

After some thorough research, my afr is roughly 13.0 upon start-up, and after about half an hour of driving, they are spot on.

maybe it the larger injectors, it seem to be spot on WOT hot or cold.

as it is a non-return system, will be running a return system through the rails soon, has anyone had good results with doing this?

Cheers

[nevinsb]

Sorry no one answered your post from before. Are you referring to on your vehicle in particular or just in general? Most people run from the pump, through the injector rail, then back to the FPR and the tank. I actually ended up running my truck with the injectors after the FPR, so the fuel doesn't flow through them. It wouldn't have cleared the distributor otherwise. I had to bleed the injector rails, but other than that, I couldn't tell a difference.

[joecar]

fezz, are you running SD...?

[fezz57]

SD, yes, sure am.

my car has a returnless system

havent as yet set it up, but keen on running the return through the rail system.


will post results.

cheers