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flex fuel base fuel pressure issues

Practical Standalone Tuning

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Hi all,

I have a 2jzgte with elite 2500 with FPR 1200. I recently conducted datalogged runs with E81 and E30 to check if fuel supply was good and found some weird things.

E30 Datalog run:

I notice that on E30 the base fuel pressure during idling (with vacuum hose still attached) was only 30psi.

Is this normal as I thought minimum base fuel pressure should be 40-43psi regardless of ethanol content??

When i compared the expected fuel pressure vs actual fuel pressure curves, the actual fuel curve follows the exact shape of the expected (during transient and WOT) but was lower by 4psi (transposed downwards by 4psi) at all points.

E81 datalog run:

Fuel expected vs fuel actual was on point, fuel actual was even marginally higher than fuel expected, fuel pressure off boost (ie idling) was around 40psi.


Fuel pressure on E80 seemed to be fine (no major deviations during WOT), however on E30 the Fuel pressure was consistently 4psi below expected. What could be causing this - is it a setting within the ECU? would changes in ethanol content change the base fuel pressure settings???

Looking forward to your reply/feedback



Hi Clint this is not something i have heard of before i also look forward to hearing from others in case I'm wrong but base fuel pressure should be base fuel pressure the type of fuel should not alter what the fuel pressure reg is reading unless other things affecting it like voltage to the fuel pumps of faulty fuel pumps

watching in interest

The base figure o 30psi, is that to atmosphere or fuel rail to manifold differential? 30 psi to atmosphere while pulling idle vacuum is reasonable.

I think I do recall seeing a thread somewhere where an electric pressure sensor read differently with different ethanol content.

Are all those readings to atmosphere or differential or a mix? If they are to atmosphere especially if ignition timing varies with ethanol content it will change idle vacuum (as will evaporative cooling effects) and hence rail pressure to atmosphere.

Ross, neither had I.

Michael, I rather suspect you have partially called it - any changes that change the pressure (absolute) in the manifold will change the fuel pressure if it's referenced to it. However, I'd expect that to be primarily at idle, i would have expected it to have come back into line as they started to reduce vacuum and come onto boost?

Clint, you can check that if you look at the MAP values when running the two fuels? As Ross pointed out, there may be some characteristic change with the regulator and/or pressure sensor that is known to be affected by the fuel - what are you actually using?

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