As title - I think there is an issue with fuel temperature and mixture leaning when the tank is below 1/4 of a tank.
I have ruled out MAT based heatsoak (the problem doesn't ever happen with a full tank), so this leaves fuel temperature.
I can monitor and fix this with an "anytrim" if I understand things properly. Has anyone used one?
That is very interesting. Do a test - have a 5 gallon fuel jug handy, wait for the car to lean out, and then slam in 5 more gallons and see what happens.
I did almost that test. I waited as long as I dared and went to the fuel station... Problem went away on leaving.
I haven't seen an OEM car need this feature before. I wonder if your pump/regulator are not working as well with the higher temperature fuel?
I know for sure the Rover T series N/A and Turbo engines used fuel temp compensation, and likely others in the range too.
How the fuel temperature issue is solved in OE applications with dead-end fuel rails?
Quote from: GintsK on July 25, 2010, 06:26:27 AM
How the fuel temperature issue is solved in OE applications with dead-end fuel rails?
Meaning getting rid of the hot fuel or how the ecu compensates?
All non return systems have voltage control to the fuel pump so the pressure can be varied accordingly.
Maybe they also have temp sensors to change how the pulsewidth and or fuel pump voltage changes.
Quote from: paul_f on July 24, 2010, 03:45:05 AM
I haven't seen an OEM car need this feature before. I wonder if your pump/regulator are not working as well with the higher temperature fuel?
You haven't ever looked at a v8 Range Rover or TVR then. The Lucas ECU had a fuel temperature sensor. It works in precisely the same way as MAT correction.
Lucas had, yes.
But for example Mercedes V6 has not. They also used fuel pump directly from 12V. and FPR (fixed) is builted in fuel filter next to the fuel tank.
Quote from: dnb on July 25, 2010, 07:59:28 AM
You haven't ever looked at a v8 Range Rover or TVR then. The Lucas ECU had a fuel temperature sensor. It works in precisely the same way as MAT correction.
Nope never looked at anything Lucas based. I wonder how Bosch systems handled this though as they would surely have the same problem?
Its particularly of interest to me as my tank is right next to my engine, so the fuel will get very warm
Quote from: dnb on July 23, 2010, 03:16:55 PM
I did almost that test. I waited as long as I dared and went to the fuel station... Problem went away on leaving.
That is an interesting find. How much leaner did it go?
It's one of those things that tuners get blamed for, haha. Especially with high flow fuel pumps running flat-out all the time.
Just before I filled up,the car was undrivable. It railed the lambda at 1.25 when it should have been 1.05.
044 pump and low fuel level is not a good thing!
Where is the pump located? In the fuel tank?
Lately we have been using external surge tanks to keep the OEM pump intact, which has its advantages.
External pump on the chassis rail just under the tank. There's no room for much else unfortunately.
I don't think it's surge as such since it happens at constant velocity.
If heat comes from high-flow pumping I suggest to run it trough resistor at low loads.
what is your base pressure?
I saw similar problem with 7bar pressure. When fuel is cold, pressure is 8+bar, but with hot 7bar.
bosch 044
What I call a "surge tank" is called a "swirl pot" over on your side of the pond. It's an external tank that allows the use of the OEM fuel pump/tank, but still supplies the "big" fuel pump with a consistent supply of fuel.