Tahoe Flexfuel Problem

[Habnixzuverliern]

Hi

i have a Problem with my Tahoe 07 5.3, the alcohol calculation is always wrong, it Ends up at 15 to 17%, but the gas here in Germany has only 5%, so i dont know why and i hope someone can help me, with some ideas. I reset the calculation a few times, but it is still wrong.

cheers

[txab]

Here's what I can offer at this point. Read through the entire thread.

 

How are you re-setting the calculation?

 

 

http://www.gm-trucks.com/forums/topic/78169-e-85-refueling-events/

[MikeNH]

I think by 2007 GM was not using a sensor to determine ethanol content in fuel but rather it adjusts timing to calculate ethanol content. GM released a bulletin at some point in the past advising to fill up with at least 7 US gallons (about 26.5) liters to ensure this process takes place properly.

 

 

I also found this, though the minimum fuel fill amount is different than what I recall reading previously:

 

Subject:SES Light due to DTCs P0172 and/or P0175 - Check Fuel Alcohol Value

Models:2010 Cadillac Escalade
2009-2010 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe
2009-2010 GMC Savana, Sierra, Yukon
with V8 Engine RPO Code L20, L77, L94, L9H, LC9, LH9, LMF, or LMG

This PI was superseded to include additional suggestions outlined in Steps 1 and 4. Step 4 was added as a way to prevent this concern since a service calibration will not be released to address this issue if it is a result of the ethanol learn taking place during a cold start. Please discard PIP4792.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
<A href="#ss1-2542215">Condition/Concern:

On rare occasions, some customers may experience a hard start cold, brief rough running on cold start, black exhaust color, and/or SES light. If a SES light is experienced, DTCs P0172 and/or P0175 may be stored.
If driveability symptoms are experienced, they will generally diminish within 1 minute of start up. This may be the result of an inaccurate fuel alcohol value calculated by the ECM. This can be confirmed by displaying the ECM calculated alcohol % on the scan tool and comparing it to the known alcohol content of the fuel as determined by the J44175 fuel composition tester. If the engine is still warming up or running lean during the fuel alcohol learn process, the ECM may interpret it as high alcohol content in the fuel, causing the calculated fuel alcohol value to inaccurately increase. This may cause the engine to misfuel, which may eventually lead to the concern above.
<A href="#ss2-2542215">Recommendation/Instructions:

If SI diagnosis does not isolate the cause of this concern, follow the Fuel Composition Diagnosis in SI.
If the concern is repaired by resetting the fuel alcohol value and resetting the fuel trims as outlined in the Fuel Composition Diagnosis, perform the following suggestions to determine why the inaccurate fuel alcohol value was present before releasing the vehicle:

1. Determine if the customer has used E85 fuel. If they have, advise them that it is best not to alternate repeatedly between regular gasoline and E85. If they do switch fuels, it is recommended that they add as much fuel as possible -- do not add less than 11 L (three gallons) when refueling. They should also drive the vehicle immediately after refueling for at least 7 miles (11 KM) to allow the vehicle to adapt to the change in ethanol concentration. This is outlined in their owner's manual as well
2. Inspect all vacuum hoses, the complete air intake system, the dipstick seal, the oil fill cap/tube seal, the PCV system, and the valve covers for any vacuum/air leaks. If any leaks are found, repair as necessary and re-evaluate the concern.
3. Inspect the air filter, air intake, and MAF sensor to ensure that they are all OEM with no sign of debris (leaves, pine needles) or casting flashing, which could cause this due to a skewed MAF sensor input. Clean or replace as necessary and re-evaluate the concern.
4. Determine if the customer has a habit of filling the fuel tank before the engine has reached operating temperature or immediately parking it for a long period of time after they have filled the fuel tank. If they do, the alcohol learn process could be occurring during engine warm up, which may eventually cause the calculated fuel alcohol value to inaccurately increase.

Here are some examples of filling habits that may cause the alcohol learn process to occur during engine warm up:

• Cold starting the engine, driving directly to a nearby gas station, filling the fuel tank, and cold starting the engine again.

• Filling the fuel tank while at operating temperature, driving to a nearby location, parking long enough for the engine to cool down, and cold starting the engine..

If these filling habits are contributing to this, the concern may be prevented by filling the fuel tank with the engine at operating temperature and driving at least 7 miles (11 KM) before parking the vehicle.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

I think by 2007 GM was not using a sensor to determine ethanol content in fuel but rather it adjusts timing to calculate ethanol content. GM released a bulletin at some point in the past advising to fill up with at least 7 US gallons (about 26.5) liters to ensure this process takes place properly.

[Habnixzuverliern]

i reset the calculation with a tech2 and the calculation is correct for e85 but not for e5.

 

while reading, there came 1 question in my mind, why it is important that the tank is empty? i mean if i have 10% gas with 5% Ethanol in the tank, if i reset the calculation bevor i fill up the tank, why there is a Problem?

 

is there a common vacume Problem that i can check? oh befor i forgot, i have a chip tunig, but i have this Problem with or without the chiptunig and i have a open k&N air filter, this was installed by the pre owner.

[MikeNH]

I don't think that the tank needs to be empty or close to it- the electronic control system just needs there to be a sufficient change in fuel level before it will conduct the alcohol learn process. I think the most important thing to follow from the bulletin would be to make sure you are filling up according to the instructions above. If you consistently are using E5 fuel then it should be no problem. I will generally run E85 most of the year aside from when I make the long drive from Michigan to New Hampshire to visit my parents and then again once it gets cold because the reduced fuel efficiency of E85 combined with winter driving conditions would result in extremely low fuel economy. But once I have run a few tanks of fuel after switching, I no longer worry and can easily buy fuel at one of the stations that are less than a mile from my home.

 

I suspect that either the tuning or the intake may be causing a lean condition. What sort of chip tuning has been done to the truck? If it is a programmer that allows you to restore a stock configuration I would try this to see if the problem goes away. As for the K&N filter, there should be at least one vacuum hose connected to that from the valve cover I think, so that would be a good place to start.

[Habnixzuverliern]

Good Morning,

 

so it is definitly not the chip Tuning, i restored the stock Image, but this changed nothing. i also checked the vacuum hose, but i cant find anything.

My Car has 180tkm maybe it is a Problem with the oxigen sensors, but the sensor results looks good.

 

cheers

[ariunboldmk]

Have you solved the problem yet?