Flex Issue: E% content drops at high rpm
 

I have another possible gremlin. This time with flex fuel.

The car:
Turbocharged FA20
FIC 770 cc port injectors
Deatschwerks intank pump
MotoEast Flex Fuel kit on Port Line

The issue:

Looking at all my logs over the past 3 weeks of tuning, I have noticed the Econtent dips at high rpm. It usually starts dipping right at 4500-5500 and comes back up by 7500-8000. I have confirmed this dip by visually watching the ECA during a wot pull. Is this normal? Is this cause for concern.

I followed the install instructions to the letter for the motoeast kit and the ECA definitely works properly otherwise (ie. 91 octane shows E10 and E85 here shows E78-E82 on the display).

https://fbcdn-sphotos-c-a.akamaihd.n...77601813_o.jpg

The only thing that I can see that may correlate with this dip is PI duty % which starts ramping up at 4,000 rpm. Meaning that the dip only happens when fuel from the gas tank is sent through the PI lines (where the Flex sensor resides). Battery voltage is solid at 14V. Any ideas?



@moto-mike @ptuning

Thanks for the call today...I've seen fluctuations by 1-2 % depending on load, but never gave it much thought as it wouldn't affect fuel by more than a percent, and timing by less than .25 degree (at least with our mapping). But you definitely have a pattern there. Might be fuel pressure, or maybe just a factor of the higher flow your setup uses. Hopefully you'll get a chance to measure the readings so we can see.

Just to add some data points, my setup consists of this:

ID1000 injectors
Walbro 485 in-tank fuel pump
V-something Flexfuel kit hooked up to the front-most fuel line
Otherwise pretty much exactly the same setup as @sw20kosh

I was doing some logging last night and did NOT see this issue. My E% drops about 1% point the moment I go WOT and holds steady throughout the run.

DI line and stronger intank pump. Since there would be the same flow increase in this line vs. the PI line when going WOT, can we deduce that perhaps it is not flow but rather pressure differential that makes the sensor readings drop?

Also Mike confirmed that on a mid 300 whp car with the sensor hooked up to the PI lines, he does see a 1-3% fluctuation in E content.

Or it could be an electrical interference issue of reading the sensor.
How is the sensor read into the system?

It could be that at certain frequencies (RPMs) some other signal in the engine is at just the right frequency to mess with the sensor.

It uses the CPS input to the ECU if I am not mistaken.

The drop was most dramatic while doing pulls on the dynojet (5% drop). On the street it is more like 1-3% drop. Why would that be? The RPM pickup wires maybe?

Sounds reasonable. The pickup wire could be increasing the crosstalk.

It might sound crazy, but cover the flexfuel sensor wires with aluminum foil as far as you can on the harness.
See if that makes a difference.
If it works, you can make a nicer looking fix later.

Tried the foil...Didn't work.

Strange, mine acts opposite. I may need some more time to observe this, but I get 2-3% fluctuation going higher during WOT runs. I've been on e85 less than a week.

It could still be an electromagnetic interference issue. The foil was to try to block radiated emissions.
There would still be conducted emissions.
Trying to block that would require adding components (caps, ferrite beads) and is a little more intrusive.

Do you also have your sensor on the PI high pressure rail like sw20kosh?

The Haltec tech site says it is best to put the sensor on the low pressure return line:

http://www.haltech.com/flex-fuel-sensor-explained/

Maybe they have a voltage offset as pressure varies?

Coud be due to slight voltage changes. The alternator is controlled via ecu its likely the ecu limits alternator output when going wot to limit hp loss this may cause change in supply volts to ethanol sensor and if it does not have good voltage regulation built in may cause the slight variation your seeing. Also run direct ground to sensor if not done already.

I have mine connected to the fuel line closest to the firewall as per moto east instructions.

the only time i noticed mine dropping was after priming, key on (car not running). pressure was leaking past the dw in tank pump because it came unseated slightly. i never repaired it to test again, replaced with a 485 in tank pump