Ethanol percentage flex fuel

[gooffeyguy]

@swathdiver had an issue finding the FPDM on his a couple years back I believe. It wasn't were it was supposed to be

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[swathdiver]

@swathdiver had an issue finding the FPDM on his a couple years back I believe. It wasn't were it was supposed to be

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That was the solid state relay for the trailer brake controller. I have no idea where the fuel pump computer is though! LOL

 

[iamdub]

OK, here is another twist. I decided there was enough confusion when looking up part numbers for my FPCM, that I decided to drop my spare and get exact part number on my FPCM. Guess what, no FPCM on my truck that I can find. Whatever my truck is doing to manage fuel pressure, it seems very different than previous and later model years. I went and looked to see if maybe they carried the pressure regulator over from earlier model year, didn't see anything. Frankly, it is starting to piss me off.

I thought the FPCM is in front of the tank, mounted to the face of a cross member, kinda at a 45° angle.

 

[wsteele]

@swathdiver had an issue finding the FPDM on his a couple years back I believe. It wasn't were it was supposed to be

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I think they have moved around. There is enough evidence of that, that some of the better informed YouTube clips on the subject have a pretty long drawn out explanations of why some of the other modules in the area, ain't it.

Frankly, right now, it really seems like the FPCM team didn't have their shit together when the "cut off" date was there for spec zero for NNBS. So the overall powertrain design team went to plan B and used a hybrid approach, using the fuel pump from previous years and some code in the PCM which seems to tell the pump when to rev up. In the end, the "Virtual Ethanol" coders were likely left in the lurch with not enough actual sensor inputs to accurately deduce what the Ethanol percentage was, so like the good troopers big company coders are, they faked it, at least and until they had some more hard data their algo's could rely on to be more robust. Seems by 2008, they were just a little shy still.

But then, I find the 2015 and on, FF engines have a Flex Fuel Sensor, so it seems, as miserly as GM is about putting hardware back in, maybe they just realized the team lobbying for "we can do it in code" maybe were smoking a little too much of the Ganga.

Sorry to be so cynical.

 

[gooffeyguy]

That was the solid state relay for the trailer brake controller. I have no idea where the fuel pump computer is though! LOL

Oops, my bad....lol

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[wsteele]

I thought the FPCM is in front of the tank, mounted to the face of a cross member, kinda at a 45° angle.

In all the videos I have seen, they have them back behind the rear axle, very near the spare lift crane. But I will skoot under tomorrow and look. In any case, if it is there, it aint actually a FPCM, at least, as later models see them.

 

[wsteele]

I thought the FPCM is in front of the tank, mounted to the face of a cross member, kinda at a 45° angle.

Great place for it, just across from the BM, unfortunately, like all my other explorations, just another dry hole.



I think there likely is a hint in that they used the 2006 fuel pump in the 2007. I think the pre-2007 models used a different fuel pressure management strategy as it pertains to the pump. I need to read more about the NBS gen to see if I can figure out what that system looked like.

 

[iamdub]

In all the videos I have seen, they have them back behind the rear axle, very near the spare lift crane. But I will skoot under tomorrow and look. In any case, if it is there, it aint actually a FPCM, at least, as later models see them.

I thought in the back was on the trucks and the SUVs had them in front of the tank. I know when I had my tank down recently, I saw a computer-looking thing that had "FSCM" (or was it "FPCM"?) whit lots of other numbers on a white label.

 

[wsteele]

I thought in the back was on the trucks and the SUVs had them in front of the tank. I know when I had my tank down recently, I saw a computer-looking thing that had "FSCM" (or was it "FPCM"?) whit lots of other numbers on a white label.

I think it could well be there, at least for a few model years. I know for a fact (thanks to Ken), that the 2008 models have them, so if you saw your's there, almost for sure it was there. Mine, I am convinced doesn't have one. At least, tonight, that is what I believe.

 

[iamdub]

I think it could well be there, at least for a few model years. I know for a fact (thanks to Ken), that the 2008 models have them, so if you saw your's there, almost for sure it was there. Mine, I am convinced doesn't have one. At least, tonight, that is what I believe.

Gotta love them first year problems.

 

[wsteele]

Gotta love them first year problems.

Yeah, one more thing for my "important things I learned in my life" pamphlet.

Never buy the first model year of a generation and maybe stay away from the last (as they might be changing the trucks network tech so your expensive scan tool may not work, and in the end some teams will be ahead of schedule and you will get their first bad ideas... and all of it won't be well documented).

I think I have figured some of it out. The 2006 (maybe back a few years as well), had the fuel pressure regulator in the fuel pump module. That is why they used the 2006 pump. My truck doesn't have a FPCM, it just uses the regulator in the pump assembly. I think that is why I get the 60 psi at idle. I will try and capture some under load runs somehow with my new gauge (when it gets here) and an old POV camera I think I have somewhere, but I suspect my pump is fine.

I just think the code for the 2007 "Virtual Sensor" didn't have enough real sensor input and they faked it as best they could. There is a calibration that addresses Ethanol calculations (I have it), but in the end, it just isn't good enough to capture all the possible variations of tolerances in an old truck starting to show a few grey hairs.

 

[wsteele]

Doing a little more research into the FPCM status of 2007 model years.

While it appears the Tahoe, Suburban and Yukon(s) of the 2007 model years don't have a FPCM (also called in some texts FPDM, FSCM) and use the 2006 fuel pump with its built in pressure regulator, for the sake of someone with a Silverado 1500 (non Classic) stumbling into this thread, it appears the (non Classic) Silverado 1500's did have a FPCM and use the same fuel pressure management scheme as later 2008 and on Tahoe's, Sub's, etc.

 

[wsteele]

So I responded to James' thread (@swathdiver) on his measuring the real ethanol content, versus his calculated content on his trucks. I really appreciate the effort James in getting that measurement. It confirms what others have experienced that many trucks can figure out the Ethanol content quite accurately.

As I posted on one of my responses to that thread, in recent fill-ups, according to my shop manual, I am squeaking under the wire of "normal" at 15% different in real versus calculated (real 6% vs 19% calculated), as long as the truck is running fine otherwise (which it is).

I had one outstanding item I was going to try and test for this thread, which was fuel pressure. As it turns out, literally while I was typing my response to James' thread, the Amazon guy delivered my Actron fuel pressure gauge. I was surprised it was a pretty nice looking piece, great instructions, etc. Amazing when I consider the $25 price tag.

I had a chance to run the same test I ran with the Napa AP loaner gauge, using the shop manual procedure Key on, Engine off and came in at 53 psi, a couple psi lower than the Napa gauge, but close enough for government work. So according to my shop manual, my FP is fine. I then started it up and it too registered exactly 60 psi idling, at 2000 rpm and 4000 rpm, so exactly the same result as the loaner gauge.

I know that everyone who has a model year that has a FPCM, can see their commanded vs running pressure and report 43.5 psi as nominal at idle, as I have found out my 2007 doesn't have a FPCM, so not only can I not see running FP on my Tech 2, it appears the FP management is exactly the same as 2005 and 2006 Tahoes and Yukons, with the pressure regulator in the FP assembly (versus on the drivers side of the engine and using intake vacuum as a reference in pre-2005's).

I have seen a few other YouTube videos of people doing fuel pressure debug on a 2007 Tahoe/Yukon and when things are right, they all report the Key On, Engine off pressure I see (and the shop manual calls out) and running pressures of 60 PSI, so my basic assumption is again, my fuel pump is fine.

The only thing left I have that the shop manual calls out, and only if my calculated Ethanol percentage is greater than 15% above my actual percentage, is to drop the tank and clean my whole fuel system.

That is a lot of work for something that is not affecting the running of my truck other than rich cold starts and those only when I don't reset the Ethanol content to 3% with my Tech 2 after fill up. So my plan right now is to just keep using E10, resetting the Ethanol content to 3% with my Tech 2 after fill ups and just try and love the old gal with all her imperfections.

A beaten man.

 

[kbuskill]

Got new Delphi Pump installed today. Ran the truck extremely low on fuel to make it easier, very uncommon for me as I usually fill up when it hits 1/4 tank.

So far so good. I fueled up afterwards and it calculated the Ethanol percentage at 3.1% after driving it for a while.

I am curious what it shows after the next cold start.

I will keep you posted.

 

[wsteele]

Got new Delphi Pump installed today. Ran the truck extremely low on fuel to make it easier, very uncommon for me as I usually fill up when it hits 1/4 tank.

So far so good. I fueled up afterwards and it calculated the Ethanol percentage at 3.1% after driving it for a while.

I am curious what it shows after the next cold start.

I will keep you posted.

Sounds promising already.

I have it worked out how to snake the hose through the hood opening so I can see the fuel pressures under load while driving. I will see if there is any change in pressure under load, but honestly, based on all the revving I did while sitting in the garage, with the pressure not moving at all, I am pretty sure it will sit pretty constantly at 60 PSI.

I suspect on my model year with the integrated pressure regulator in the pump, the pump runs continuously while the engine is running and any excess fuel not needed to keep pressure at 60 on the rail is dumped right back into the tank. On my model year, I don't believe there is a fuel pressure sensor at all, as there is no intelligent FPCM and PCM doesn't manage the pump/pressure other than making sure it is running (I think).

 

[kbuskill]

Sounds promising already.

I have it worked out how to snake the hose through the hood opening so I can see the fuel pressures under load while driving. I will see if there is any change in pressure under load, but honestly, based on all the revving I did while sitting in the garage, with the pressure not moving at all, I am pretty sure it will sit pretty constantly at 60 PSI.

I suspect on my model year with the integrated pressure regulator in the pump, the pump runs continuously while the engine is running and any excess fuel not needed to keep pressure at 60 on the rail is dumped right back into the tank. On my model year, I don't believe there is a fuel pressure sensor at all, as there is no intelligent FPCM and PCM doesn't manage the pump/pressure other than making sure it is running (I think).

If there is a fuel pressure sensor it will be just in front of the tank on the metal fuel feed line, at least that is where mine is.

 

[wsteele]

If there is a fuel pressure sensor it will be just in front of the tank on the metal fuel feed line, at least that is where mine is.

Unfortunately, no sensor. Which I guess is not all that bad, given it wouldn't have anything to be connected to anyway... What a gyp!

The good news is RockAuto will sell me both a FPCM and a Fuel Pressure Sensor...

 

[kbuskill]

Ethanol percentage today still rock solid at 3.1% after sitting all night. I have checked it multiple times today after the truck has sat for several hours and it hasn't changed any.

Not definitive proof as of yet but I will keep an eye on it for several more fill ups and see what happens.

 

[wsteele]

Ethanol percentage today still rock solid at 3.1% after sitting all night. I have checked it multiple times today after the truck has sat for several hours and it hasn't changed any.

Not definitive proof as of yet but I will keep an eye on it for several more fill ups and see what happens.

Pretty good news. I have never had mine "get it right" occasionally, or even once for that matter, since I first noticed it being off so if it did it right just once, I would consider it almost for sure a fix.

Just for the record, restoring AFM from the Diablo Predator didn't change anything on mine. I disabled it at about 3/4 a tank and drove it until it needed a fill. I had also reset it to 3% with the Tech 2 and like always it stayed at 3% for the rest of the tank. I filled it this morning with 0% Ethanol and after about 20 miles it is showing 18% Ethanol. I will check it again on tomorrow's cold start, but I am pretty sure (as I expected), the Diablo Predator disabling AFM didn't change anything. I will again disable AFM with the Diablo Predator after cold start confirmation tomorrow.

I still have some full power fuel pressure tests to do using the analog gauge duct taped to the windscreen (sure hope that safety on the hood holds ). I will be surprised if I see anything other than a rock steady 60 psi during full on power runs. It really looks like the pressure regulator in the tank is just an overpressure bypass. Given I have no FPCM or fuel pressure sensor, I don't think the PCM can do anything about managing pressures on the rail.

 

[kbuskill]

Pretty good news. I have never had mine "get it right" occasionally, or even once for that matter, since I first noticed it being off so if it did it right just once, I would consider it almost for sure a fix.

Just for the record, restoring AFM from the Diablo Predator didn't change anything on mine. I disabled it at about 3/4 a tank and drove it until it needed a fill. I had also reset it to 3% with the Tech 2 and like always it stayed at 3% for the rest of the tank. I filled it this morning with 0% Ethanol and after about 20 miles it is showing 18% Ethanol. I will check it again on tomorrow's cold start, but I am pretty sure (as I expected), the Diablo Predator disabling AFM didn't change anything. I will again disable AFM with the Diablo Predator after cold start confirmation tomorrow.

I still have some full power fuel pressure tests to do using the analog gauge duct taped to the windscreen (sure hope that safety on the hood holds ). I will be surprised if I see anything other than a rock steady 60 psi during full on power runs. It really looks like the pressure regulator in the tank is just an overpressure bypass. Given I have no FPCM or fuel pressure sensor, I don't think the PCM can do anything about managing pressures on the rail.

For me, without actually testing the ethanol content of the fuel I purchased, I am just happy to see anything under 10% ethanol content since that is what I am purchasing.

It would definitely be more accurate if I bought one of those ethanol test kits and actually checked the fuel but I don't really care that much as long as it continues to calculate at something under 10%.

I will continue to post my calculated ethanol percentage over the next several fill ups so we can see if this was the actual fix.