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Fuel Pressure drop when e85 put into gas tank

Old 11-03-18, 08:31 PM
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Fuel Pressure drop when e85 put into gas tank

Hi guys, this seems weird and hope you can help. My FD has been running perfectly on pump 98 gasoline for the past year.

Finally got around to organising a tune on e85 and so got my gas tank low, and then added some e85. My Adaptronic Modular was showing an ethanol content of e43, so decided to drive it around more to empty the tank and fill up again to get the ratio up to e85. It drove perfectly for 2 hours just cruising around. I put a few more litres in the tank and ratio went up to e48. Figured ill just empty my jerry can of e85 into it the next day before the tune and it should be close to e85.

Next morning I try to start it, and it won't idle, keeps dying. I noticed the base fuel pressure had dropped from the 40psi it had been at for the past year, to only 34 psi. And when the engine was trying to idle the fuel pressure was in the 20s.

I changed nothing other than the fuel. I checked the speedflow fuel filter, exact same psi with and without filter in place. Pump is a walbro 460, hardwired to 12v constant. FPR is a Turbosmart FPR2000. Injectors are oem 850s in primary and Bosch 2200 secondaries. FP sensor is TI. GM flex sensor. Fuel lines are raceworks ethanol rated rubber lines. Intank hose is an Earl's submersible hose. All these parts are about 5000kms/1year old.

Now today, I drained the ethanol out of the tank, put pump 98 gas back in, and the base fuel pressure has automatically gone back up to 40psi and the car drives perfectly again...

Does anyone have any idea what is going on? Why would ethanol be making my fuel pressure drop?

Thanks in advance.

Last edited by mikey13b; 11-04-18 at 08:47 AM.
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Old 11-05-18, 04:24 AM
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That is very odd, you would possibly expect ethanol to drag dirt through the filters but if it goes back to normal on pump I would only imagine that happening if your fuel pump was very finely PMW mapped and the extra volume demand on ethanol mean you needed high pump duty.
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Old 11-07-18, 06:17 PM
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It's very weird. The pressure actually seems correlated to the amount of ethanol in the mix.
As I added more pump fuel and the ratio went from e48 to e20 for example, the pressure increased a few psi. Then I added more pump fuel and the ratio went to e10 and the pressure went up another couple of psi, and now at about e4 the pressure is back up to 40 psi... What could be causing this?
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Old 11-11-18, 04:02 AM
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Are you reading pressure from the electronic sensor or an analog gauge on the regulator?
Was the ecu set up with custom compensations or the baseflex fuel compensation?
It is unlikely a mechanical problem with the pump/reg, especially if it goes back to normal with regular fuel.

Are you running idle air bypass control?
Are the injector dead times correct for the primary injectors?

The only thing i can think of is a combination of fixed idle air and possibly a touch more electrical load with poor dead time compensation resulting in more manifold vacuum from the evaporation of the ethanol pulling more manifold vacuum and pushing to different cells in the fuel table/ignition table which aren't tuned well enough. Or the pressure sensor is being effected by the ethanol and skewing the fuel model, but I imagine it should all be alcohol compatible?

Last edited by Slides; 11-11-18 at 04:08 AM.
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Old 11-11-18, 08:07 PM
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Thanks for your reply Slides. Yes I agree I don't feel it can be a mechanical problem, and suspected maybe the ecu is doing something especially seeing the pressure changes specifically in proportion to ethanol content, but didn't know how it could affect the base pressure with the engine off...

The fuel pressure is being read from an electric TI sensor connected to the port on the FPR. This should be ethanol resistant.
Regarding the compensation in the ECU I am not sure how it is setup. I did not change anything and my tuner only tuned it on pump 98 previously so I don't think he would have touched any settings related to ethanol yet. I'll have to have a search where to find this setting.

I am not sure about the idle air bypass control. I'll have to have a search.
I selected the 850cc primary injectors from the adaptronic drop down selection, should this already include the correct dead times?
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Old 11-12-18, 06:33 AM
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If you are running fd secondaries as primary injectors, yes.

other thought was if there is a blanket +5/10 degrees ignition timing or something weird with ethanol it will pull more vacuum at idle too.
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Old 11-21-18, 06:38 AM
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Well it seems the Haltech TI sensor was faulty. I hooked up a mechanical gauge and it read 40psi base pressure with e50 in the tank, whereas the sensor was reading 31psi.
Have now connected up a bosch sensor and getting 40psi base pressure also.
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Old 11-21-18, 10:44 PM
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So it was just flooding the car due to faulty reading? Runs ok now?
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Old 11-26-18, 07:58 PM
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Yes it must have been. Car is running amazing now.
I think I may have a leaking injector though as car keeps flooding when I leave it overnight...
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Old 11-27-18, 12:18 AM
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Leaking housing to manifold coolant crossover O-rings can show hard starting, does it smell like fuel?
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Old 11-28-18, 01:47 AM
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I didnt notice any smell. But the only way to get it to fire at all is to spray wd40 in the inlet manifold and then crank it with WOT. So that would mean its flooded wouldnt it?
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Old 11-28-18, 03:10 AM
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If its flooding the exhaust should stink or blow a bit of a cloud of fuel when it does kick otherwise i would be looking for water consumption or poor compression if it was starting ok before.
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