My current fuel trims - idle, 2000rpm, 3000rpm all no load

[Fless]

Again, I've forgotten: is your engine a flex fuel engine? (What's the 8th digit of your VIN?)

If so, and IIRC, there will be a physical alcohol sensor on the driver's side frame rail. Later years dropped the physical sensor and calculate it with an algorithm. (There was an updated alcohol calibration for later models but that's not your issue unless it's FF w/o a physical sensor.)

 

[Scottydoggs]

I expect the O2 voltage to swing back and forth across zero (~14.7 or whatever it is going for). The controller must be also swinging the injector timing - I would expect to see the wideband also swing but it might look like a ripple and not 0.1-0.7-0.1 back and forth.

the faster he voltage swings 0-9 the better. injectors are done via the cam and crank sensors, o2's just monitor the fueling.

a wb should show 14.7 at idle and in a stock truck if you floor it it will stay at 14.7 for 60 seconds then drop as it richens up the fuel tables. got one in my tahoe for sh its and giggles and i tuned it some.

 

[Burban22]

Here’s a thread on my fuel trims. My 03 burb 5.3 LM7 (non flex fuel) likes to take away fuel aka negative long term fuel trims.

Helpful YouTube videos on page 1. My fuel trims at various rpm page 2.

I’ve gotten 16 - 17 mpg driving 65 mph on a 200 mile trip. So I’m calling it good even though my burb still has -5 - -10% LTFT especially at idle but less under load or higher rpm.

Long term and short term fuel trims intake leak, low idle, improving fuel mileage. Mpg

From some YouTube videos, I’ve educated myself on monitoring short term long-term fuel trims to diagnose intake, leaks, or bad oxygen sensors. I recently replaced all four oxygen sensors new spark plugs new wires suburban runs very good but fuel mileage isn’t the best 14-16 on the highway at...

www.tahoeyukonforum.com

 

[2006Tahoe2WD]

Again, I've forgotten: is your engine a flex fuel engine? (What's the 8th digit of your VIN?)

If so, and IIRC, there will be a physical alcohol sensor on the driver's side frame rail. Later years dropped the physical sensor and calculate it with an algorithm. (There was an updated alcohol calibration for later models but that's not your issue unless it's FF w/o a physical sensor.)

"T" I think it is not a flex fuel.
I did an interesting experiment today. Unplugged the purge valve and drove on the highway. The highway LTFTs went way down. Of course the CEL came on when I started it the second time. So it seems the air coming in the purge valve is not necessarily expected in the base map. Maybe too much air is coming in the purge route.

 

[Fless]

I assume that you have no evap codes, pending or active. When was the purge valve replaced?

Spitballing a bit here... think about the canister -- if it's saturated, maybe it's not clearing out completely and more fuel vapor than is expected is being pulled into the intake.

 

[2006Tahoe2WD]

I assume that you have no evap codes, pending or active. When was the purge valve replaced?

Spitballing a bit here... think about the canister -- if it's saturated, maybe it's not clearing out completely and more fuel vapor than is expected is being pulled into the intake.

Well, I have an evap code now because I drove with the purge valve unplugged. The purge valve was just replaced as part of resolving my original set of codes and CEL.
As mentioned unplugging the purge valve made a big change. Your rig looks in pretty good shape and low miles. I wonder what LTFTs you are getting on the highway. Since you have a Flex engine things might be much different to deal with high levels of methanol or no methanol. I also notice that bank 1 is usually calling for 2-3% more fuel than bank 2. In some cases they are the same.
The question of if the base map assumes some amount of methanol is still open. Also, how does the additional fumes/air coming in from the evap system play into things.

 

[Mudsport96]

Sorry for the late reply. I'm thinking you have some poor flowing/ clogged injectors. So the +9 etc. numbers is the ecm trying to make up for lack of flow. I know the T engines are not flex fuel, but I would run your tank down to about 1/4 and top off with e85. Just drive it easy and you won't have any issues other that crap mpg. But the extra ethanol should clean the injectors some. After that tank, reset your trims if necessary and drive and check trims again.
If you don't have any vacuum leak and it is still trying add fuel then it is initially not getting the commanded fuel at baseline.

I can check later tonight on an 06 tune, but I am 90 percent sure that all gen 3 ecms are setup for a base of 10% ethanol. I mean, I know of one station within 30 miles of me that is non-ethanol 87 fuel. And with the epa push for wanting e15 to be the new normal, why would the be programmed for less than the current base of e10.

 

[2006Tahoe2WD]

Sorry for the late reply. I'm thinking you have some poor flowing/ clogged injectors. So the +9 etc. numbers is the ecm trying to make up for lack of flow. I know the T engines are not flex fuel, but I would run your tank down to about 1/4 and top off with e85. Just drive it easy and you won't have any issues other that crap mpg. But the extra ethanol should clean the injectors some. After that tank, reset your trims if necessary and drive and check trims again.
If you don't have any vacuum leak and it is still trying add fuel then it is initially not getting the commanded fuel at baseline.

I can check later tonight on an 06 tune, but I am 90 percent sure that all gen 3 ecms are setup for a base of 10% ethanol. I mean, I know of one station within 30 miles of me that is non-ethanol 87 fuel. And with the epa push for wanting e15 to be the new normal, why would the be programmed for less than the current base of e10.

I was thinking along the same lines. However, in 2006 or a bit earlier the methanol was not mandatory. But it is a good question - Was the base map assuming 10%. I don't know where I would buy E85 around here. I'll have to google it and see.

 

[Fless]

Your STFTs are fine. Running E85 in a non-flex engine is going to cause lean codes. Your non-flex injectors are not going to be able to flow enough to make up for the E85. You might get by with a mix of E85 and gas to make, say, E30, but you'll be watching those STFTs go up.

As suggested before, run E0 (non-ethanol or ethanol-free) if you can find it and, if you think the injectors are not flowing as they should, use a good fuel system cleaner like BG44K, Techron, etc. for a few tankfuls. Others will have more suggestions on good cleaners. But I'm not convinced that's the cause of your slightly high LTFTs.

Get a scanner on it to see what the system thinks the current alcohol content is, just to verify. We're working in the dark here.

 

[Mudsport96]

Your STFTs are fine. Running E85 in a non-flex engine is going to cause lean codes. Your non-flex injectors are not going to be able to flow enough to make up for the E85. You might get by with a mix of E85 and gas to make, say, E30, but you'll be watching those STFTs go up.

He will be fine to mix a 1/4 tank of regular to 3/4 tank e85. Yes the trim will max out, but that is the point. To full duty cycle the injectors and run the most ethanol through them as possible because it is a very good cleaner. I ha e done it in my nonflex Silverado and yes it will guzzle the fuel, just light cruising will not blow it up.

As suggested before, run E0 (non-ethanol or ethanol-free) if you can find it and, if you think the injectors are not flowing as they should, use a good fuel system cleaner like BG44K, Techron, etc. for a few tankfuls. Others will have more suggestions on good cleaners. But I'm not convinced that's the cause of your slightly high LTFTs.

E0 while great in a vehicle that can use it, will typically cost more per gallon. And not fix his issue.

Get a scanner on it to see what the system thinks the current alcohol content is, just to verify. We're working in the dark here.

A scanner will not help determine the ethanol content. It will only show lean or rich.

1. It is an 06 if his name is a clue, therefore it wouldn't have a flex sensor as GM went to a " Virtual Flex" Strategy in late 05 where the ECM calculated ethanol content by Maf and O2 sensor variables.( Basically it guessed at what was in the tank, whelich ended up problematic) So a leaky intake gasket or failing O2 sensor could think you are running e15 to e85 even if you had regular in the tank.

2. He said it It was not flex, so it doesn't even have that algorithm to look at to assume ethanol content. It is just looking to get to 14.7:1 afr with regular 87 octane.

3. Only the flex fuel capable vehicles have a default percentage and that is 38.5 percent ethanol. This again is not present in the non-flex programming.


Other things that can cause trims to be off, incoming air temp sensor, coolant sensor, maf and map sensors. These all are in the calculation so even if they aren't off enough to set a code, they can tweak the air fuel to a point.