Flex Fuel sensor readings drop when in boost

[dreksnot]

Yes, running hard line. I still can imagine what's causing it. My ID1700 duty cycle is not even 50% and with triple pumps. It's -6AN supply line.

[mrimpala02]

Just thinking here. How is the status of your battery? Could it be possible that the draw of the pumps kicking on under boost is causing a potentially failing battery to cause some wierd electrical stuff? Any other strange observations? Alternator failing?

[eLeSthree]

When I was experiencing this. My values would fluctuate between 14 and 77%.

If your values are staying above 50%, and you know you’ve got good E, maybe just change the tune to run 100% of your added FF timing above 49% Alchohol.

[rgrmoreira13]

Originally Posted by dreksnot

Never noticed this before, but my FF sensor reading drops when I do a run down the strip. I have a Triple Fore pump setup and the FF sensor on the return line after the fuel regulator (no bypass line around the FF sensor). So, my question being, what's going on? Yes, my 2nd/3rd pumps are kicking on. Shortly afterwards, my FF sensor output reading goes from 65% to 41%. IDC happy at 43%, FP hanging fine at 78psi. The issue doesn't appear to show up with low boost, it gradually worsens as my boost goes higher.

Noob Question
But why was the Flex sensor installed on the return line instead of the feed line.
It could cause the inconsistent reading of E85

[dreksnot]

Originally Posted by mrimpala02

Just thinking here. How is the status of your battery? Could it be possible that the draw of the pumps kicking on under boost is causing a potentially failing battery to cause some wierd electrical stuff? Any other strange observations? Alternator failing?

Relatively new battery. Watching my Control Module Voltage in the logs doesn't show more than a half of volt drop when doing a run with the 2nd/3rd fuel pumps kicking on (like from 14.7 to 14.27), so I don't think that's it. Thanks for the suggestion.

[dreksnot]

Originally Posted by eLeSthree

When I was experiencing this. My values would fluctuate between 14 and 77%.

If your values are staying above 50%, and you know you’ve got good E, maybe just change the tune to run 100% of your added FF timing above 49% Alchohol.

The issue of my alcohol content falsely dropping is that I lose the higher spark add (benefit) from the FF table with the lower alcohol values. Sure, I can make some compensation or adjustments where it doesn't, but I'd like the FF table to add with respect to what actual alcohol I have in the tank (not something artificially low that I'm compensating for).

[dreksnot]

Originally Posted by rgrmoreira13

Noob Question
But why was the Flex sensor installed on the return line instead of the feed line.
It could cause the inconsistent reading of E85

Several arguments to support this:
1. The return line will have less flow thus less restriction through the "small" orifice through the sensor channel. That's why some install a bypass route around the sensor if installed in the supply line.
2. The alcohol content of the fuel flowing through the FF sensor is the same either in the supply or return.

In all actuality, I can't see that I'd have below some threshold of fuel flowing through the sensor even though it's in the return line - I have triple pumps.

[Greenhornet2]

Originally Posted by dreksnot

Several arguments to support this:
1. The return line will have less flow thus less restriction through the "small" orifice through the sensor channel. That's why some install a bypass route around the sensor if installed in the supply line.
2. The alcohol content of the fuel flowing through the FF sensor is the same either in the supply or return.

In all actuality, I can't see that I'd have below some threshold of fuel flowing through the sensor even though it's in the return line - I have triple pumps.

It has to be linked to the low fuel pressure, it probably wouldn't be happening if you had your command fuel pressure but with the pressure drop it's compounding the problem. Fix the fuel pressure and the FF sensor will probably then read correctly.

[Big Biscuits]

Originally Posted by dreksnot

Several arguments to support this:
1. The return line will have less flow thus less restriction through the "small" orifice through the sensor channel. That's why some install a bypass route around the sensor if installed in the supply line.
2. The alcohol content of the fuel flowing through the FF sensor is the same either in the supply or return.

In all actuality, I can't see that I'd have below some threshold of fuel flowing through the sensor even though it's in the return line - I have triple pumps.

This is why I find it hard to believe it’s flow being so close to the FPR. Is it facing the correct way? Mine had arrows for flow route.

[dreksnot]

Originally Posted by Greenhornet2

It has to be linked to the low fuel pressure, it probably wouldn't be happening if you had your command fuel pressure but with the pressure drop it's compounding the problem. Fix the fuel pressure and the FF sensor will probably then read correctly.

Now that I think about it, since my FF sensor is after the FPR (and my FP is boost reference), it could be a much lower FP after the regulator and in the FF sensor. Not sure how FP would affect the FF sensor reading though...?

[stevieturbo]

So you're having some other issues with fuel too ? Some are saying about low fuel pressure ?

With triple pumps, there is no way FP should not be behaving as it should

And you say hardline...so it's a hardline the entire length to the tank with no flexible connection anywhere ?

[Greenhornet2]

Originally Posted by dreksnot

Now that I think about it, since my FF sensor is after the FPR (and my FP is boost reference), it could be a much lower FP after the regulator and in the FF sensor. Not sure how FP would affect the FF sensor reading though...?

Where is the fuel pressure read from? Before the rail? If you have 29psi before the rail you have to be basically using all the fuel that's getting to the rail, essentially running out of fuel and there's no fuel in the return line to get a proper reading. Just a guess, i have no idea how your system is set up just thinking out loud.

[dreksnot]

Originally Posted by stevieturbo

So you're having some other issues with fuel too ? Some are saying about low fuel pressure ?

With triple pumps, there is no way FP should not be behaving as it should

And you say hardline...so it's a hardline the entire length to the tank with no flexible connection anywhere ?

NO FP issues! Not sure where that came up or from.

I'm using the original stock supply line as the return line for my setup. I'm not sure if it's entirely metal or what.

[RyangAsh]

Originally Posted by dreksnot

Now that I think about it, since my FF sensor is after the FPR (and my FP is boost reference), it could be a much lower FP after the regulator and in the FF sensor. Not sure how FP would affect the FF sensor reading though...?

It would affect it if the volume was so low in the return line air was crossing the sensor like I said earlier. Call Dave Steck, he will answer.