[george kujanski]

hey gang: having a cold start issue with the Tahoe...investigation seems to be fuel rich situation... Adding some air when starting helps out.
I have an innova 5610 OBD2 reader...shows Long term fuel trim at -25% and fuel compositon sensor at 65% Alky.

According to research, the fuel comp needs to be reset since there should be no more than 10%, causing fuel rich condition.

This OBD2 scanner has no rest function for the Fuel comp, at least not for a tahoe they (innova) say.

Any other way of doing it? pulling the connector on the sensor or battery?

George

[george kujanski]

Never mind

[dataway]

What was the solution?

[george kujanski]

I actually found the reset function, buried deep in the fuel system menu. Strange that the Innova tech guy said this model scanner didn't have it for the Tahoe.

In any case, after resetting it, the fuel alky comp went from 65% to 3% and the Long Term Fuel trim went from -28% to a more normal few percent.

I'lll check the cold start performance this morning. I wonder why the alky comp went that high in the first place, messing up the fuel trim.

BTW, disconnecting the battery did not reset it either.

George

[MatthewKlein]

Originally Posted by george kujanski

I actually found the reset function, buried deep in the fuel system menu. Strange that the Innova tech guy said this model scanner didn't have it for the Tahoe.

In any case, after resetting it, the fuel alky comp went from 65% to 3% and the Long Term Fuel trim went from -28% to a more normal few percent.

I'lll check the cold start performance this morning. I wonder why the alky comp went that high in the first place, messing up the fuel trim.

BTW, disconnecting the battery did not reset it either.

George

I see this from time to time. So far we have just reset the customers vehicle - Same thing you have done - And its been fine. We have yet to replace a fuel composition sensor.

[chevymad]

Just ran into this same issue with a ford explorer. It was a head scratcher at first, until I noticed the flex fuel reading. The service manual seemed to totally ignore the fact flex fuels were a possibility.

[george kujanski]

Normal cold start this morning. Interesting how a weird sensor reading could foul up normal operation. I only noticed the difference on a cold start, then did a youtube search for a P0175 error. I also did not get the error immediately either. I reset the power train error and did not get a MIL afterward, even while driving while Long Term Fuel Trim was out of whack.

george

[MatthewKlein]

Originally Posted by george kujanski

Normal cold start this morning. Interesting how a weird sensor reading could foul up normal operation. I only noticed the difference on a cold start, then did a youtube search for a P0175 error. I also did not get the error immediately either. I reset the power train error and did not get a MIL afterward, even while driving while Long Term Fuel Trim was out of whack.

george

Alcohol runs WAY richer than gasoline

So that alcohol % was flooding the engine. You might get slightly better mileage now.

[george kujanski]

Now that the problem as been corrected, I wonder how the sensor got messed up? Could a filling station's tanks get contaminated with the wrong fuel type, i.e. mixing !0% alky with E85?

George

[Ben M.]

Originally Posted by george kujanski

Now that the problem as been corrected, I wonder how the sensor got messed up? Could a filling station's tanks get contaminated with the wrong fuel type, i.e. mixing !0% alky with E85?

We have sensors for this sort of thing at work that randomly get "corrupted" data that feeds into whatever algorithm or machine loop and starts having problems. In almost all of those cases the sensor is just fine but something the code did got the values shifted and it isn't accurate anymore, hence the reset loop options in the computer. It's almost never the sensor either.

It could have had a water bubble, could have had a bad mix of gas, or where the alcohol had settled out of the gas because the car sat at a weird angle overnight, could have even had nothing wrong at all and the computer just went "derp" on you. We also have our logic controllers at work randomly "lose" their setpoints and control loop values on one particular brand of controller and to this day haven't been able to determine why it happens on a handful but not all or duplicate it consistently - and this is with multiple engineers working over years taking data. Sometimes things just don't work right for one reason or another and with these proprietary controllers you won't necessarily ever be able to figure out why.

[george kujanski]

Stuff like this is what I do....find causes of problems and then determine solutions, hence the curiosity.

George

[MatthewKlein]

Originally Posted by george kujanski

Now that the problem as been corrected, I wonder how the sensor got messed up? Could a filling station's tanks get contaminated with the wrong fuel type, i.e. mixing !0% alky with E85?

George

According to the classes I've attended:

The fuel system is somewhat slow to adjust. Meaning for the most part you wanna choose e85 or standard 10% and stick with it. Not alternate every other tank. Otherwise the system is always moving in one direction or the other.

[george kujanski]

Never used E85...i see no need.

George

[tom s]

I run E85 out here in CA.$2.99 against $5.00 87.Tom

[rod cole]

on the impala i worked on there was no actual sensor it was guessed by the ecm from inputs not a flex fuel sensor . Seems like it checked with car off pressure /temp rise guessing the reed pressure for e content