Ethanol percentage flex fuel

[Fless]

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

I know the FF psi spec for the NBS is a few psi lower than non-FF, but the FF pumps have more volume to feed the larger injectors. The specs are with KOEO (Key On, Engine Off).

Obviously there are further tests to determine if there is too much leak down, perhaps a leaky injector or the fuel pump leaks down when off.

 

[wsteele]

You say you want a pressure gauge?

Like always, lots of gauges found, not one fuel pressure gauge.



I am off to Napa to see if they have a rental.

 

[wsteele]

So I am thinking it probably isn't the fuel pump.

Key on engine not started.




Key on engine idling.

 

[swathdiver]

So I am thinking it probably isn't the fuel pump.

Key on engine not started.


View attachment 280365

Key on engine idling.

View attachment 280366

No take it out and womp on it and see what the pressure is.

As for the pressure, I don't claim to know everything, but I do know that the Gen IV 5.3s and 6.2s have a running pressure of 43.5 psi all the time. So being that yours is well over that idling, I would be suspicious that something might be wrong but would verify such with the shop manual specs first.

 

[wsteele]

No take it out and womp on it and see what the pressure is.

As for the pressure, I don't claim to know everything, but I do know that the Gen IV 5.3s and 6.2s have a running pressure of 43.5 psi all the time. So being that yours is well over that idling, I would be suspicious that something might be wrong but would verify such with the shop manual specs first.

I couldn’t find any reference to running pressures or testing pressures under load. Actually, the only reference I found was the key on engine off test, which lists 50-60 PSI as nominal, with leak down limits. Mine didn’t seem to drop more than about a 1 PSI in 5 minutes.

None of the above means it isn’t there, just that I couldn’t find it. Frankly the manual seems purposely written for someone to just follow rote without any judgement.

I did rev it up a few times but had to watch the gauge through the window. The pressure didn’t drop more than a few PSI at like 4K. But no load tests.

The hose wasn’t long enough to snake it up trough the hood opening, and the gauge was a free loaner with a $200 deposit, so no road tests were conducted.

 

[iamdub]

I couldn’t find any reference to running pressures or testing pressures under load. Actually, the only reference I found was the key on engine off test, which lists 50-60 PSI as nominal, with leak down limits. Mine didn’t seem to drop more than about a 1 PSI in 5 minutes.

None of the above means it isn’t there, just that I couldn’t find it. Frankly the manual seems purposely written for someone to just follow rote without any judgement.

I did rev it up a few times but had to watch the gauge through the window. The pressure didn’t drop more than a few PSI at like 4K. But no load tests.

The hose wasn’t long enough to snake it up trough the hood opening, and the gauge was a free loaner with a $200 deposit, so no road tests were conducted.

You can't verify the accuracy of the gauge, either.

 

[kbuskill]

I couldn’t find any reference to running pressures or testing pressures under load. Actually, the only reference I found was the key on engine off test, which lists 50-60 PSI as nominal, with leak down limits. Mine didn’t seem to drop more than about a 1 PSI in 5 minutes.

None of the above means it isn’t there, just that I couldn’t find it. Frankly the manual seems purposely written for someone to just follow rote without any judgement.

I did rev it up a few times but had to watch the gauge through the window. The pressure didn’t drop more than a few PSI at like 4K. But no load tests.

The hose wasn’t long enough to snake it up trough the hood opening, and the gauge was a free loaner with a $200 deposit, so no road tests were conducted.

Here are the pages from the factory service manual that I found to be relevant...

I hooked up the Tech2 tonight and I am more convinced that it is the fuel pump, at least in my case.

Following the service manual it states that KOEO should be between 50-60 psi and should remain steady for 5 mins. *Mine does not remain steady for 5 mins.

The service manual then states to check to see if it loses 5 psi in 1 minute. If it does, it says it is a leaking injector. If not replace fuel pump. *Mine does not lose 5 psi in 1 minute.

The manual then says to relieve the pressure down to 10 psi and verify that it doesn't lose more than 2 psi in 5 mins. *I did this and mine lost all 10 psi in 5 mins. It lost the first 2 psi within the first 1 1/2 minutes.

The only caveat I have in my testing is that I didn't verify these pressures with a physical pressure gauge hooked to the fuel rail. I just watched the pressures through the Tech2.

I know this may not be 100% accurate but I believe it is close enough for me.

As an FYI for @wsteele since you can't see your trucks FPCM with your Tech2.

The truck commands the desired fuel pressure to 58.5 psi with the key on and engine off.

The truck commands the desired fuel pressure to 43.5 psi when the truck is running. This includes while the truck is being driven, even under hard acceleration.

I watched mine today while driving and the fuel pump seems to be operating at the proper pressures while driving, only dropping a pound or two of pressure when first going WOT. The commanded fuel pump percentage of course varies with demand and during normal cruising my pump was sitting around 43% and upon hard acceleration would go up to around 70ish %. I don't know if that is considered normal or not since I don't have a baseline to compare it to.

Also my fuel pump short term trim is sitting at 1.00 and the fuel pump long term trim is sitting at 1.34... I don't have a clue what any of that means or how it would compare to a new pump but thought I would post the info in case someone else can interpret any of it.

Also @wsteele your engine idling PSI seems high as it should be 43.5 psi.

 

[wsteele]

You can't verify the accuracy of the gauge, either.

Right, but to assume the gauge is way off when it is displaying what the shop manual says is a nominal value for an engine with no faults, all the while the engine exhibits no problems that are listed as things that get you to check the fuel pump in the first place? Of course it might not be accurate, but Occam would tend to favor the opposite.

 

[iamdub]

Right, but to assume the gauge is way off when it is displaying what the shop manual says is a nominal value for an engine with no faults, all the while the engine exhibits no problems that are listed as things that get you to check the fuel pump in the first place? Of course it might not be accurate, but Occam would tend to favor the opposite.

I thought your engine was supposed to be running at 43.5psi. I can't keep track anymore. lol

 

[wsteele]

I thought your engine was supposed to be running at 43.5psi. I can't keep track anymore. lol

If you can’t keep track, I have no chance.

Everyone tells me my engine should be running at 43.5psi. I can’t find that in my shop manual (doesn’t mean it isn’t there), in fact, I can’t find it anywhere in GM documentation.

For whatever reason, the Tech 2 on my model year can’t see the Fuel Pump Control Module, so I can’t see values that module is determining is the desired pressure based on rpm, load, etc. , I can’t see even actual pressures at the rail with my Tech 2. For all I know, there might not be an intelligent fuel pump drive module in my model year and my pump might just be a single speed with a basic pressure relief valve on the return, if there even is a return, if not maybe just a relief valve at the pump, I have no idea.


All I know right now is the truck runs great and can’t figure out what percentage of Ethanol it has in the tank.

 

[swathdiver]

I watched mine today while driving and the fuel pump seems to be operating at the proper pressures while driving, only dropping a pound or two of pressure when first going WOT. The commanded fuel pump percentage of course varies with demand and during normal cruising my pump was sitting around 43% and upon hard acceleration would go up to around 70ish %. I don't know if that is considered normal or not since I don't have a baseline to compare it to.

Also my fuel pump short term trim is sitting at 1.00 and the fuel pump long term trim is sitting at 1.34... I don't have a clue what any of that means or how it would compare to a new pump but thought I would post the info in case someone else can interpret any of it.

My LT Fuel Trim had been creeping up over the years. At one point it was up to 1.54 but the other day was down to 1.4. I do not remember if there is a correlation between running gasoline and ethanol with those trims. My pump behaves the same underway as your observations.

 

[wsteele]

Here are the pages from the factory service manual that I found to be relevant...
View attachment 280389 View attachment 280390
View attachment 280391

I hooked up the Tech2 tonight and I am more convinced that it is the fuel pump, at least in my case.

Following the service manual it states that KOEO should be between 50-60 psi and should remain steady for 5 mins. *Mine does not remain steady for 5 mins.

The service manual then states to check to see if it loses 5 psi in 1 minute. If it does, it says it is a leaking injector. If not replace fuel pump. *Mine does not lose 5 psi in 1 minute.

The manual then says to relieve the pressure down to 10 psi and verify that it doesn't lose more than 2 psi in 5 mins. *I did this and mine lost all 10 psi in 5 mins. It lost the first 2 psi within the first 1 1/2 minutes.

The only caveat I have in my testing is that I didn't verify these pressures with a physical pressure gauge hooked to the fuel rail. I just watched the pressures through the Tech2.

I know this may not be 100% accurate but I believe it is close enough for me.

As an FYI for @wsteele since you can't see your trucks FPCM with your Tech2.

The truck commands the desired fuel pressure to 58.5 psi with the key on and engine off.

The truck commands the desired fuel pressure to 43.5 psi when the truck is running. This includes while the truck is being driven, even under hard acceleration.

I watched mine today while driving and the fuel pump seems to be operating at the proper pressures while driving, only dropping a pound or two of pressure when first going WOT. The commanded fuel pump percentage of course varies with demand and during normal cruising my pump was sitting around 43% and upon hard acceleration would go up to around 70ish %. I don't know if that is considered normal or not since I don't have a baseline to compare it to.

Also my fuel pump short term trim is sitting at 1.00 and the fuel pump long term trim is sitting at 1.34... I don't have a clue what any of that means or how it would compare to a new pump but thought I would post the info in case someone else can interpret any of it.

View attachment 280394

Also @wsteele your engine idling PSI seems high as it should be 43.5 psi.

The fact that my Tech 2 can’t see the “Fuel Pump Control Module”, leads me to believe the design between our two trucks may be different as it pertains to how fuel pressure is regulated.

I believe you when you and James and Chris say you think my pressure is running too high.

The only thing from GM on the subject that I have in front of me says my fuel pump is fine. I put that with a perfectly running engine and it is frankly a stretch for me to conclude my fuel pump is defective because my virtual Ethanol sensor can’t get the number right.

Not saying you guys are wrong, but my shop manual says my pump is fine.

 

[kbuskill]

The fact that my Tech 2 can’t see the “Fuel Pump Control Module”, leads me to believe the design between our two trucks may be different as it pertains to how fuel pressure is regulated.

I believe you when you and James and Chris say you think my pressure is running too high.

The only thing from GM on the subject that I have in front of me says my fuel pump is fine. I put that with a perfectly running engine and it is frankly a stretch for me to conclude my fuel pump is defective because my virtual Ethanol sensor can’t get the number right.

Not saying you guys are wrong, but my shop manual says my pump is fine.

I'm not saying your pump is definitely the problem either. Personally I am just glad that my testing shows, what appears to me, that there is an issue with my pump and that corresponds with my hunch and that article mentioned earlier in this thread.

If the new pump cures the miscalculations of my virtual ethanol sensor then I will be tickled pink. If it does not cure the miscalculations then at the very least I will have peace of mind knowing that I don't have to worry about my pump taking a crap on me at an inopportune time. 270k miles, assuming this is the original pump, is a lot of miles so I know having a new pump isn't going to hurt anything.

I will most certainly keep you posted, after the new pump, as to my E% readings.

 

[wsteele]

I'm not saying it isn't either. Personally I am just glad that my testing shows, what appears to me, that there is an issue with my pump and that corresponds with my hunch and that article mentioned earlier in this thread.

If the new pump cures the miscalculations of my virtual ethanol sensor then I will be tickled pink. If it does not cure the miscalculations then at the very least I will have peace of mind knowing that I don't have to worry about my pump taking a crap on me at an inopportune time. 270k miles, assuming this is the original pump, is a lot of miles so I know having a new pump isn't going to hurt anything.

I will most certainly keep you posted, after the new pump, as to my E% readings.

I had planned to replace my pump regardless of what the pressures read, if your replacement fixed the Ethanol calc errors.

If for no other reason than I would be waking up occasionally for months wondering if the pump was the culprit. If we end up changing pumps and your calc is fixed and mine not, at least we will have one more data point.

 

[wsteele]

I am also going to reverse the AFM delete with my Diablo Predator before my next fuel up. I hate running around with it on, especially so after having it off for a while, but I did first notice the rich cold starts pretty close to the time I did the Diablo AFM delete.

I can’t think of any reason why it might have affected the Ethanol calc, but I also have no idea how they turn the AFM off, so it is just one more point alley to run down.

It will be for only a few fill ups and I think I will do a reset of the percentage and the trims after I reverse it but before I refill again.

If I get a lifter collapse during that period, I will be so pissed, I will probably beat myself up for a month.

 

[wsteele]

Morning update.

As far as I can determine, there is no difference in the components of the fuel pressure control in the 2007 and later models. The Fuel Pump Control Module (Fuel Pump Drive Module) is there and is the same part number as later models. Obviously there are differences in how it is programmed as my Tech 2 can't even see it. I also noticed that the fuel pump for the FF 2007 is a different part number than the later models. I doubt I will be able to determine the differences in the fuel pumps and whether it does some fuel pressure regulation that is controlled by the FPCM in later model years.

Anyone reading this that has access to a 2009-2013 model year shop manual, I would be forever in your debt if you could look up the Fuel System Diagnostic procedure and see if it is different than the one posted by @kbuskill above. Specifically, if it includes using the Tech 2 to communicate with the Fuel Pressure Control Module. It would also be helpful if in that manual there is reference to fuel pressures while running, etc.

I did go ahead and order my own fuel pressure gauge and I will see if there is a way I can use it to do load tests for fuel pressures. Without the Tech 2 being able to talk to the FPCM, I have no way at this time to monitor fuel pressures while driving. Maybe the old duct tape the gauge to the windscreen will work for me.

Also, I will try and get into the SPS side of the Tech 2 and see if it can see the FPCM. I can't see how I could flash a new one with the Tech 2, if it can't see it, but obviously the dealerships have to be able to do that.

 

[kbuskill]

Morning update.

As far as I can determine, there is no difference in the components of the fuel pressure control in the 2007 and later models. The Fuel Pump Control Module (Fuel Pump Drive Module) is there and is the same part number as later models. Obviously there are differences in how it is programmed as my Tech 2 can't even see it. I also noticed that the fuel pump for the FF 2007 is a different part number than the later models. I doubt I will be able to determine the differences in the fuel pumps and whether it does some fuel pressure regulation that is controlled by the FPCM in later model years.

Anyone reading this that has access to a 2009-2013 model year shop manual, I would be forever in your debt if you could look up the Fuel System Diagnostic procedure and see if it is different than the one posted by @kbuskill above. Specifically, if it includes using the Tech 2 to communicate with the Fuel Pressure Control Module. It would also be helpful if in that manual there is reference to fuel pressures while running, etc.

I did go ahead and order my own fuel pressure gauge and I will see if there is a way I can use it to do load tests for fuel pressures. Without the Tech 2 being able to talk to the FPCM, I have no way at this time to monitor fuel pressures while driving. Maybe the old duct tape the gauge to the windscreen will work for me.

Also, I will try and get into the SPS side of the Tech 2 and see if it can see the FPCM. I can't see how I could flash a new one with the Tech 2, if it can't see it, but obviously the dealerships have to be able to do that.

Not to side track here too much, but I noticed when looking at RA that all of the FPCMs listed say they have to be programmed EXCEPT for the Dorman. It says it comes preprogrammed which I found interesting. Not sure exactly how that works but that is what it says.

 

[wsteele]

Not to side track here too much, but I noticed when looking at RA that all of the FPCMs listed say they have to be programmed EXCEPT for the Dorman. It says it comes preprogrammed which I found interesting. Not sure exactly how that works but that is what it says.

I hadn't looked at the RA beyond the fact that they only offered an SMP product, no OE, Dorman, etc. for the 2007 model year. Frankly, I don't know how Dorman can do it either as a place I found last night that will flash the different modules with the latest calibrations VIN specific says the FPCM needs to be flashed like any other intelligent module with VIN driven calibrations.

Going in a little deeper in the online suppliers, I was wrong about the FPCM being the same part, the FPCM aren't the same part numbers year to year, so I suspect there are changes in the hardware year to year.

I am going to give these guys I found a call and ask about the FPCM in my 2007, see if they flash those and why my Tech 2 can't see it. I suspect they probably have a high end Snap On like product that knows all, but it would be nice to understand why the Tech 2 can't talk to my FPCM and what differences in the fuel pressure regulation design exists year to year.

 

[wsteele]

I have done a little more digging and found on TIS2web, using my VIN and requesting SPS stuff, it returns a list of controllers for my truck. There is no FPCM listed on the controller list. I know I have a FPCM in my truck, but maybe it is being used in some dumb mode, being controlled completely by the ECM. The ECM has calibrations for fuel control and it looks like it does all the work in that respect. I understand why my Tech 2 can't see my FPCM as it doesn't exist as a "controller" in my model year. I wonder how much work it actually does or if it just supplies the connections for the various wiring harnesses? As far as it being "programmed" if replaced, I suspect there is no way to program it for things like VIN, as nothing in the system knows it is there as a controller.

 

[wsteele]

I PM'ed Ken @kbuskill and asked if he could get to TIS2web and see with his VIN if he had a FPCM that supported being programmed. He checked and he does in fact have a FPCM with a few calibrations.

This last bit confirms what I suspected when I first saw the Tech 2 couldn't see my FPCM. From a software standpoint my FPCM doesn't exist.

My conclusion is fuel pressures must be controlled exclusively by the ECU and the Fuel pump and the FPCM in the 2007 model year must just act as a kind of pass through device.

When my pressure gauge arrives, I will do my best to rig a way to see the pressures driving under load (as James recommended, I will womp on it) and see what my less intelligent than a 2009 model year truck does about the fuel pressures. I may end up using some kind of POV camera to record the pressure runs as I am pretty sure the hose isn't going to be long enough to reach up to the windscreen.

One thing that did strike me is if the pressures do stay in the 55-60 psi range, I can see how that might work to fool the Virtual Sensor software doing Ethanol content calcs, but the glitch there is it would be in the other direction than what I am seeing, causing it to report less Ethanol than was actually there and trying to lean things during open loop warn up operation.

All very strange. I will keep posting as I find stuff, but frankly, if a new pump doesn't fix Ken's Ethanol calc problem and turning AFM back on with the Diablo Predator doesn't help for me, I will be kind of dead in the water after that.