Motiv flex fuel erratic ethanol content under WOT

jakeg

Specialist
Apr 29, 2020
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Hey guys,

just wanted to share my love for this forum, great community.

Anyway, so I decided to dyno my car, and the car felt like it had power fluctuations like crazy. On the dyno log (dynojet) the boost begins around 16, drops to 11 psi and fluctuates. Dyno log down below. We recently had time to trouble shoot, and it seems that the ethanol content is all over the place. We replaced the sensor and did a full write and it didn't help. I've read throughout the forums and checked the pins. ( all I could find )

What could be causing this?

Log:


Thanks!
 

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langsbr

Captain
Apr 5, 2017
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Double check your grounds to the ECA. Mine was doing that and the ground wasn't as good as it needed to be.

Also, you can embed your datalog natively here.

 
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jakeg

Specialist
Apr 29, 2020
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I tried cleaning the ground for the flex fuel module and it still did it after i logged again.
 

Milan

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Dec 24, 2016
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Is your sensor in the return line? If that line doesn’t have constant flow it will get air in it and mess up the reading.
 

jakeg

Specialist
Apr 29, 2020
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Is your sensor in the return line? If that line doesn’t have constant flow it will get air in it and mess up the reading.

I bought the precision raceworks kit, im pretty sure its not on the return. Ill double check though.
 

jakeg

Specialist
Apr 29, 2020
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Solved: Turned out to be the 12V reference line. I switched it to another 12v line and it cleared right up.

I'm assuming that the spikes were due to my PR coils. The reference wire would have more voltage running through it during WOT, so it would cause the output to spike.
 
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Threetirtyfive

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Jan 9, 2019
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False.
There is no lpfp return. Even on big power builds.
Especially true for an ethanol sensor that is on the lpfp feed.
 

Milan

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False.
There is no lpfp return. Even on big power builds.
Especially true for an ethanol sensor that is on the lpfp feed.

No, there is always a return. It might not always be up front but there is always a return.

Anyone with an external FPR, which used to be all of us when this forum started has a return line up front.
 
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Threetirtyfive

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? No the (non oem) pressure regulator, such as on an eth or meth tank clearly wouldn't be where he's mounting the ethanol analyser as that would be 100 ethanol and completely pointless. The LPFP feed, which is off the low pressure fuel pump does not ever have a return line. Feeling stupid?
 

langsbr

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Avoiding the pissing match, I think @Milan went a bit hard on @Threetirtyfive here. COULD someone have a return line added with an external regulator? Sure. Would you expect it on a sub 500WHP dyno? Not likely. Perhaps @jakeg has it and we just aren't aware but I wouldn't expect it.

I have to admit I was in the same boat as @Threetirtyfive and a bit dumbfounded by the mention of the sensor being in the return line, because I've seen numerous 600+, and even 700+ setups without a return line.

@Milan, can you elaborate on what your definition of "big power" is that would require a return fuel system?
 
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Threetirtyfive

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I wouldn't expect a return on a 6 or 700 bhp setup, a hobbs activated secondary lpfp doesn't need it, PI doesn't need it, Milan is trying to be clever for the 1 car that has an arbitrary return line. Unnecessary and completely irrelevant for this post about an ethanol content analyser.
 
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fmorelli

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There is a return. It's built inside the HPFP, which has a low and high side pressure chamber.

Filippo
 
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