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Discussion Starter · #1 ·
Hello everybody.

I'm really not used to writing on forums. But since I have exhausted all my solutions, I turn to you today. For a few years now, I have had a problem with my volt that no one has been able to fix. Here is the problem. When the car runs on gasoline, consumption is high. About 7 to 8 liters per 100 km. on the highway at 100 km / h (30 to 33 MPG at 63 mph). On mountainous journeys, with the mountain mode activated and the battery balanced, the engine lacks power and consumption is disastrous. For comparison, when I made the same trip with my old 2006 Mazda Tribute, it consumed the same as my Volt now. And the volt should do better since it regenerates on the way down.

With the help of a mechanic friend, we checked the engine and here it is: The compression on the 4 cylinders is about 160 psi when cold. The air filter is good. The spark plugs have about 20 engine hours and are covered with carbonaceous soot. Does not consume oil or coolant. The sensors are good. When the engine is idling, it seems to have little hesitation. Nothing major but enough to feel them in the car. The car never released any code or "check engine" for its and I checked with my diagnostic software.

Then, I checked on the way and with my OBDII and my software the O2 sensors downstream and upstream and it is there that I am lost. I know from the spark plugs and the symptoms that the mixture is rich. The downstream oxygen sensors read approximately 0.75V to 0.8V when the engine is hot and at constant demand. This tells me once again that the engine is running rich. On the other hand, and this is really what troubles me, is that the upstream sensor oscillates between 0.1V and 0.8V (without ever exceeding 0.8V). While it should go up to 0.9V in its peaks. This therefore means that the probe returns a lean mixture signal. So I deduced that the probe was defective. I replaced it and the new probe reads exactly the same. A lean mixture. Note that the old probe was covered with carbonaceous soot. How come the engine runs so rich and the upstream probe returns a lean mixture?

Finally I would like to clarify this: The autonomy on the battery is within the standards (about 50 km during winter and 65 km during summer) and therefore it excludes the brakes or any other friction in the kinematics.

I'm starting to lose hope and even consider getting out of my car and going back to a regular gas car. Indeed, hybrid technology does not seem to be mastered by mechanics and say anything.

Please help me.
 

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Your Volt was rated at 37mpg. You are driving faster than the EPA test loop, in cold weather, using winter gas. You are still getting 33mpg. There is probably nothing wrong with your car. Drive it at 90KM/h, and I bet that you will get real close to the rated 37mpg.
 

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You have done much investigation already, so good for you. Sad to know this forum is the last place you're looking for an answer. For most of us here, its the first place for help. Could be the Gen II EGR issue but will need to know your model year, mileage etc...
 

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Discussion Starter · #4 ·
Your Volt was rated at 37mpg. You are driving faster than the EPA test loop, in cold weather, using winter gas. You are still getting 33mpg. There is probably nothing wrong with your car. Drive it at 90KM/h, and I bet that you will get real close to the rated 37mpg.
Hello, note the excessive carbon deposits on the spark plugs and on the oxygen sensor. Also, the car does not do better in the summer. The engine does run a rich mixture. This is not the point. If I don't correct the problem, it will eventually clog the catalyst.
 

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Discussion Starter · #5 ·
You have done much investigation already, so good for you. Sad to know this forum is the last place you're looking for an answer. For most of us here, its the first place for help. Could be the Gen II EGR issue but will need to know your model year, mileage etc...
Hello thank you. The car is a 2014 Chevrolet Volt with 138,000 km (86,250 miles). The gasoline engine about 35,000 km (22,000 miles)
 

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Discussion Starter · #6 ·
Also, consumption in the city is disgusting. approximately 10 l / 100 km (23 mpg). When the engine is in wide revs (in town) its efficiency is very low. Do we agree that a hybrid such as the volt is supposed to be particularly efficient in the city?
 

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One thing to keep in mind when analyzing your 2014 Volt engine performance is that the Gen 1 Volts are propelled 100% of the time by the larger electric motor MGB. When the battery is depleted, or when you switch into Hold Mode, the engine is clutched to the smaller motor MGA and cranks it as a generator to fuel MGB. The gas engine was designed to function as a generator operating within a narrow range of parameters, which allows it to obtain maximum advantage of the benefits of using premium gas (er... you are using premium gas, right?). The question is, is the rich/lean mixture, etc., appropriate in terms of this engine’s function? The more efficiently the generator consumes fuel when creating gas-generated electricity, the further you can drive on generator output during the time it takes the engine to burn one gallon of gas, i.e., the better your "gas mileage."

The Gen 1 Volt is propelled by generator output when the range is extended, and "borrows" from the extended range battery buffer when a power demand exceeds generator capability (e.g., you floor the accelerator to pass someone). Mountain Mode should be activated at least 15-20 minutes before you reach the uphill part of a trip that has high power demand driving conditions. This temporarily increases the "switch to gas" state of charge point to keep another ~4 bars of power in the buffer to be "borrowed and replaced" when needed if generator output is insufficient to meet the motor’s power needs. If you don’t switch to MM before you are already in the high power demand driving conditions with a depleted battery, the engine will run harder and use more gas to keep fueling the motor while also trying to put those ~4 bars of power into the depleted battery.

Under steady demand driving conditions when the range is being extended, the engine/generator combo may also be clutched to the drivetrain to increase efficiency by enabling the speed of MGB to be reduced and the engine off/on cycles to be smoothed out. This configuration allows engine torque to contribute to the propulsion torque while cranking the generator. The Gen 1 Volt system is not engineered to provide propulsion using only engine torque.

I’ve been driving my 2012 Volt for 8.5+ years, and by my estimate the generator is capable of creating ~90 kWh of "as needed" gas-generated electricity on a full tank of premium gas. IOW, my Electric Miles range on a full charge is about the same as the Gas range while burning 1 gallon of gas in the generator (or, full charge Electric km range = Gas km range while burning ~3.8 liters of gas?? If you get 7-8 liters/100 km when using gas, that’s ~50 km/3.8 liters, and you say you get about 50 km per full charge in winter, so isn’t that about where it should be?).

At lower speeds and stop and start city driving conditions, generator output capability may exceed motor power needs. Cycling the generator engine off and on to reduce gas consumption is not particularly efficient.
 

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Also, consumption in the city is disgusting. approximately 10 l / 100 km (23 mpg). When the engine is in wide revs (in town) its efficiency is very low. Do we agree that a hybrid such as the volt is supposed to be particularly efficient in the city?
Generally for efficiently you drive electric in the city and on gas on the highway (if you are beyond battery capacity). I've only did one calculation on mileage. I did a little CS mode then some MM mode to charge up battery from 20 to 40% and continued in MM up the Malahat (steep mountain grade) followed by some up and down, then completed the journey on electric when I was close enough to home. Did the calculation when I got home based on fuel use and mileage on fuel. Worked out to 53 mpg (imp). or 44 mpg (US). That was a tough test for mileage.

You shouldn't have carbon fouling. Assuming your plugs aren't too cold (correct range), you have a problem. O2 sensors are for fine tuning injection, not setting it. Some early BMWs with Bosch L-jetronic didn't even have O2 sensors (my TR7 with same Bosch L jetronic does). Could be sensor problem, Air mass meter, ECU, any sensor connection (particularly temp sensors) and so on. I would think on todays engines you would get a code. Something a GM mechanic should be able to diagnose.
 

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only thing i can think of that would affect fuel without flipping a code is your map sensor
55573248
 

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Possibility #1 - Improper installation

Caution: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor.

Possibility #2 - It works right

Sensor voltage range 50mV-900mV.

This parameter indicates the heated oxygen sensor (HO2S) sensor 1 or 2, output voltage as measured by the control module. The scan tool will display a higher value during a rich condition, and a lower value during a lean condition. (450mV is ideal).

Possibility #3 - Check Long term fuel trim (Might want to reset all data after sensor change)

The scan tool range is -99 to +99 %. This parameter indicates the Long Term fuel trim correction as commanded by the ECM. A change made to the fuel delivery will be indicated by the Long and Short Term values. The Short Term values change rapidly in response to the HO2S signal voltages. These changes fine tune the engine fueling. The Long Term values change in response to the changes in the Short Term. The Long Term makes coarse adjustments to the fueling in order to recenter and restore control to the Short Term. The Short Term and the Long Term can be monitored with a scan tool. A positive fuel trim value indicates that the ECM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition.

Possibility #4 - Did you run relearn?

This function is used to trigger the reset of the learned resistances for the oxygen sensor heaters following a replacement. The learned resistances are reset to a calibration used to prevent overheating of the sensors until more accurate resistances may be learned following an extended engine OFF time.

HO2S Test - This device control is used to trigger a service bay procedure to execute the oxygen sensor response test following a sensor replacement in service. This procedure is required to set the oxygen sensor inspection and maintenance ready flag.


Anyway, if the sensors have issues they should throw up errors DTC P0030, P0036, P0053, P0054, P0135, or P0141


Check the piston ring seals for stuck condition & oil leakage to cylinder.
 

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can you post pics of the spark plugs and maybe the O2 sensors.
 

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Check the piston ring seals for stuck condition & oil leakage to cylinder.
yup,he needs to do a leak down test on the cylinders,this will tell where the cylinder is losing the combustion process.
 

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Here are some off-the-wall ideas:

I believe that this engine was designed to run with almost a wide open throttle plate with rpm controlled by the fuel injector operation. If, for some reason, the throttle plate is stuck so that it is not in the wide open position, the rich condition might result. I would look at the throttle plate and physically move it to check for ease of movement. Also, motor that rotates the throttle plate may not be working.

Another potential cause might be the Mass Air Flow (MAF) sensor. Off hand I don't know how to check this. I did clean one once. Oily soot on the wire sensor needed to be removed. There probably are YouTube videos to guide you.

Good luck.
 

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Discussion Starter · #14 ·
Hello everyone, firstly, I would like to thank you for your detailed and prompt answers. Here is some clarification, When replacing the oxygen probe, I used a copper based oxygen probe compound on the thread of the new probe. I have taken special care not to touch or contaminate the sensitive part of the probe.

This photo shows the spark plugs covered in carbon soot. Note that these spark plugs have approximately 20 engine hours.
171791


This one mounts the old oxygen sensor, also covered with carbon soot.
171792


Finally, here are the data from the oxygen sensors collected by my diagnostic device during a 20 km trip on the highway at 105 km / h with an engine at temperature. If necessary I have other data collected. We see that the upstream probe returns a peak signal of around 0.8V and the downstream probe which returns around 0.75V.
171790


As several mentioned, I will re-inspect the MAF sensor and the throttle actuator.
 

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Everything in your photos look 100% normal. Those plugs look brand new.

If there is problem with a sensor or an engine control, you will have a code, and the check engine light will illuminate.

I'm sticking with exactly what I wrote in post #2.

BTW, this is carbon-fouled spark plug:

 

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Discussion Starter · #16 ·
Everything in your photos look 100% normal. Those plugs look brand new.

If there is problem with a sensor or an engine control, you will have a code, and the check engine light will illuminate.

I'm sticking with exactly what I wrote in post #2.

BTW, this is carbon-fouled spark plug:

Hello JayOldSchool, If you're right, then the volt is really a poorly made car. I can't believe this car is doing 10 L / 100 km in the city and 7 to 8 L / 100 km on the highway when a civic, a corolla or a sentra do much better and without hybridization. At first the car had no problem and its performance has nothing to do with it. I can feel the difference.



Otherwise, how do you explain the values of the oxygen sensors (a balanced mixture, the sensors should indicate 0.45v approximately, mine indicates 0.75v), the lack of power in the mountains, the hesitation in idle speed. Don't get me wrong, I use the mountain mode very well, when I plan to make my trip, I activate it when leaving home and the battery is balanced well before the first climb. This summer in August we were in Toronto, a trip of about 2000 km for us the car consumed about 160 liters.

A gasoline engine, whether it is a mated to a generator or to a transmission does not change the physics. For efficient performance there must be an exact mixture of gasoline and air. Too lean, and the engine will generate too much heat which can damage the engine, sensors and emissions system. While a mixture that is too rich and you clog the engine with carbon deposits and eventually you clog the catalyst. This car should do about as much in the city as it does on the highway.

And precisely, if in addition you have to put premium in this car and it consumes 7-8 L per 100 km, it will literally cost me less to go there with my diesel truck.
 

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My 2012 delivers 5.4 l/100 km on gas only. You're analytical skills are good, maybe open to interpretation, but very thorough. Don't give up on this, theres gotta be something out of sorts that is not throwing a code. Is there a fuel leak perhaps skewing you consumption results?
 

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Definitely something wrong with the engine. You should get 6-7l/100km on highway and 3-4l/100km in city.

Out of curiousity... Have you checked / replaced the engine air filter?
 

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check the air tubes after the MAF for cracks and make sure all the clamps are tight.just had a 5.3l w/ a loose clamp causing a random misfire and lean condition.
 

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It was -20 on my drive to work today in Ottawa. Short drive of less than 10km. My L/100km when I got here was 6.6. This is just ERDTT. Sound familiar?
 
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