Ethanol percentage flex fuel

[gooffeyguy]

It is the KOKO reading. It does allow for some bleed down after KO, but not much. I am out, but will look it up when I get home. If it was in the cloud, I could look it up now, but the cloud is for rich people.

What's this cloud? I don't use any clouds I don't think, lol

Buying one of these rigs brand new is rich!

Poor people can't afford to drive a big gas guzzling SUV? lol

I'm not rich
but I'm not poor

 

[gooffeyguy]

I thought he said he couldn’t?

Post #136

https://www.tahoeyukonforum.com/threads/ethanol-percentage-flex-fuel.126426/page-14#post-1577590

 

[kbuskill]

Reading my shop manual on the subject, it says 50-60psi, so if you are getting 43.5 that definitely is a problem and would call out a pump replacement.

If you happen to be using the Tech 2, could you take note of which menu and section you are at when you are reading the fuel pressure and post it back up? I looked and looked and couldn't find it anywhere. I suspect the 2007 model year doesn't communicate between the PCM and any fuel pressure sensor (maybe an internal sensor in the pump itself that the pump uses) as when I did the "all sensor" read on my dongle scanner, it lists 155 different sensor values, but fuel pressure isn't one of them. The shop manual calls out using a manual gauge on the fuel rail to test pressure, so again, I think the 2007 model year didn't get that ability, which is actually quite surprising giving how important fuel pressure is in an EFI engine.

Anyway, anxious to hear the results of the pump swap. I will check my pressure at the rail with a gauge here in the next day or so and will report the results.

That fuel pressure spec is for the Flex Fuel trucks??? I have always read that the FF trucks run 43.5 psi.

 

[wsteele]

Post #136

https://www.tahoeyukonforum.com/threads/ethanol-percentage-flex-fuel.126426/page-14#post-1577590

OK, I understand, in post 130 he was talking about a member's 2007 that he couldn't get to display FP by telling the Tech 2 it was a 2009. So it looks like FP (and perhaps the presence of a FP module) is model year dependent.

 

[wsteele]

That fuel pressure spec is for the Flex Fuel trucks??? I have always read that the FF trucks run 43.5 psi.

I am not at home where I can read it, but if I remember correctly, the manual parts I was looking at didn't segregate the FF from non-FF. It had sections on FF operations, but I can't recall any heading that were FF specific. What I do remember is the key on key off pressure test was to be performed with a convention gauge at the fuel rail and pressures were supposed to be between 50-60psi with a maximum bleed down of like 5 psi after key off, after like 5 minutes. But I don't have it in front of me, so can't quote chapter and verse.

 

[kbuskill]

OK, I understand, in post 130 he was talking about a member's 2007 that he couldn't get to display FP by telling the Tech 2 it was a 2009. So it looks like FP (and perhaps the presence of a FP module) is model year dependent.

I can verify that my Tech2 can see the fuel pump control module on my 2008 5.3l LMG VIN 0 flex fuel Suburban LTZ.

So I am guessing the 2007 doesn't have that option, which seems strange.

 

[wsteele]

I can verify that my Tech2 can see the fuel pump control module on my 2008 5.3l LMG VIN 0 flex fuel Suburban LTZ.

So I am guessing the 2007 doesn't have that option, which seems strange.

Yes, going through the same pages @gooffeyguy went through that he posted above, when I go to the Powertrain menu he has a Fuel Pump Control Module section. Mine doesn't have that option.

Frankly, I am not sure why I am so fixated on finding a fuel pressure sensor reading on the Tech 2, given the accuracy of my Ethanol calculation sensor, even if I could see it, it could be just as off as the Ethanol "sensor".

I have to spend some time looking for that analog gauge and seeing what it reads on the rail and comparing it to what the shop manual says is the right pressure.

 

[gooffeyguy]

Except the fuel pressure is an actual sensor and not a virtually calculated sensor

Sent from my SM-G930V using Tapatalk

 

[wsteele]

Except the fuel pressure is an actual sensor and not a virtually calculated sensor

Sent from my SM-G930V using Tapatalk

Right, my point is if the actual sensor (if I even have one that the PCM can read, seems unlikely at this point) is reading incorrectly, maybe that is why my Ethanol Virtual Sensor is incorrect. In the end, the only sure way to tell if the fuel pump is fine is to measure it the way the shop manual says to.

Given I have no engine hard starting, stutter, stumble, drivability issues, the pump is fine from a seat of the pants method of measurement. The only possible indication of a fuel pump or fuel pressure issue is the virtual Ethanol sensor calcs are way off and seemingly randomly so.

As I have said before at previous low points of this diagnosis, I suspect I may be looking at a combination of margin coding in the virtual sensor and tolerance stacking in the old gal.

 

[wsteele]

That fuel pressure spec is for the Flex Fuel trucks??? I have always read that the FF trucks run 43.5 psi.

What I was reading actually doesn't call out a pressure spec for engine running (at least the section I am looking at). In fact, I can't find a running pressure spec. It only says 50-60 psi for key on, then key off test. There is a pretty long and complex decision tree on leak down diagnosis, etc. In the end, if I am reading the decision tree correctly, if the on, then off pressure is above 60, replace the pump, if the on/off pressure is below 50 and none of the leak down tests are failed, then replace the pump. There is a section on low on/off pressure where they take you through dropping the tank and looking for clogged filters, strainers, feed line, etc. After all that. it seems to net down to replace the pump.