ILive4This

I own a 2013 Suburban 2WD, 5.3, Automatic, LT, 285,xxx miles.

I found I had a problem by accident last year. I run E85 all the time $1.59/gal (Unl $2.39). I stopped at a local gas station and put a couple of gallons of unleaded (87) to get me to a station with E85. After about a mile the engine lost power, started backfiring thru the intake. The engine would not idle. Engine rpms would not go over 1,000. Engine light comes on. Engine has no power to move the truck. I put in 10 gals of E85 and after a few mins it started to run fine. I thought it might have been a fluke. After a few tanks of E85 I let the low fuel light come on and put in 5 gallons of UNL at a station that also had E85. The same thing happened. The code from Onstar are emission codes. P0171, P 0174, P015B.

Over the past year I have replaced the following:

(2) AC Delco 213-4229 GM OEM Heated Oxygen Sensor,

(2) AC Delco 213-3866 GM OEM Heated Oxygen Sensor.

(1) MAP Sensor

(8) Spark Plugs and wires

ACDelco 22963841 GM OEM Vapor Canister

ACDelco 19257603 GM OEM Evaporative Emissions Canister Vent Valve Solenoid Jumper Wiring Harness

ACDelco 23481275 GM OEM Vapor Canister Vent Valve

After all this, I can still replicate the problem. According to the local dealer, parts store and internet there is no E85 (Alcohol sensor). Now the dealer wants to reflash the ECM.

I will add a few weeks I tried this. I only put in 5 gals of E85 in the tank instead of 10 gals. The engine started to run better but not normally. After about 10 miles the engine lost power, started backfiring thru the intake. would not idle. The engine rpms would not go over 1,000. Engine light comes on. Engine has no power to move the truck. I put in the other 5 gals of E85 and it started to run correctly. After half of a tank the engine light goes off. The codes from Onstar are emission codes. P0171, P 0174, P015B.

Today I plugged in a FIXD OBD2 Code Reader (live gauges mode) and noticed the following with a ½ tank of fuel: Ethanol Fuel 69.0%, Fuel Tank Pressure Sensor 16,xxx Pa, Evap Purge (Command) 100%.



While driving the Evap Purge (Command) cycles between 0 – 100%. The Fuel Tank Pressure Sensor reads around 14,xxx - 16,xxx Pa. With the engine running I took off the gas cap and the reading never dropped below 14,000 Pa. Should it have dropped to 0 PA?



I did notice the Fuel Tank Pressure Sensor reading 4-10 a few times immediately after a fill-up. Possibility fuel hitting the sensor.

Should I replace the ACDelco 13502903 GM OEM Fuel Tank Pressure Sensor and ACDelco 20893611 GM OEM Fuel Tank Pressure Sensor Cover?


Any ideas?

a55bruce

I think what you've found is the computer doesn't know the correct gas/ethanol ratio when you're adding small amounts of regular gas to an almost empty tank of E85. You have to add enough fuel for the computer to know when to recalculates the ratio of the fuel in your tank. The computer calculates the ethanol ratio by monitoring the oxygen sensors and adjusting the timing, injectors, air/fuel ratio, etc. It can take several miles of driving for the calculation to finish. If the computer doesn't you've changed the fuel ratio, you'll have a very bad running engine.

tech2

E85 compatible vehicles no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle calculates the alcohol content of the fuel through measured adjustments.

The ethanol calculation occurs with the engine running after a refueling event has been detected via a measured change in the fuel level sender output. The virtual flex fuel sensor (V-FFS) algorithm temporarily closes the canister purge valve for a few seconds and monitors information from the closed loop fuel trim system to calculate the ethanol content. This logic executes several times until the ethanol calculation is deemed to be stable. This may take several minutes under low fuel flow conditions such as idle, or a shorter time during higher fuel flow, off-idle conditions.

Air-fuel ratios and the corresponding ethanol percentage are updated following each purge-off sequence. The fuel alcohol content percentage value can be read on a scan tool.

When an E85 compatible vehicle is built, an ECM or PCM replaced, or if the learned alcohol content has been reset with a scan tool the fuel system will need to contain ASTM gasoline with 10 percent or less ethanol content.

A minimum of 11 liters (3 gallons) must be put in the tank in order for the vehicle to recognize a re-fueling event. It is not necessary to turn the ignition OFF in order to have the re-fueling event recognized, however local safety regulations should be followed.

After the re-fueling event, the system registers the amount of fuel that was added, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines if the fuel added was either ASTM Gasoline or ASTM E85. Based on that determination, the system adjusts to the expected alcohol mix in the fuel tank, and then the fuel trim and O2 sensor activity fine tunes the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or E85 to gasoline, can result in driveability symptoms due to the inability of the system to adjust for fuel composition by not attaining closed loop operation.
Switching Between Gasoline and E85No special precautions need to be taken when switching back and forth between gasoline and E85 other than re-fueling events must be 11 liters (3 gallons) or greater, and the vehicle must remain in closed loop long enough, usually by the time the engine has maintained full operating temperature, to calculate the composition of the new blend in the tank.

tech2

0 pa reading...no.. pressure at sea level is 101 000Pa. measure the ftp cap open psi with the engine off. even with the cap off the purge during idle may be strong enough to skew the reading. depending on your altitude it will vary. i switch the unit on the scan tool to read inches of h20....it reads 0 at cap off and engine off...negative during purge and positive under pressure.