Only getting 5 MPG, excessive fuel consumption

That much fuel usage is most likely due to faulty injectors that are just dumping too much fuel. We should do two things even though you tested the injectors. First check the fuel pressure because high pressure can cause this as well.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Next is to monitor the live o2 sensor data with a scan tool. You should have an OBD II vehicle which means most scan tools (not code readers) should be able to do this. We can either monitor the short term fuel trims or o2 sensor voltage so that we can see that it is in fact running rich. If the o2 sensors are not showing a rich condition then that could be the issue.

Is there any smoke coming from the exhaust?

https://www.2carpros.com/articles/engine-black-smoke

Black smoke shows a rich condition. Let's start with this and go from there.

If you are getting real poor fuel mileage, we would expect the o2 sensors to show the exhaust is very rich. If the o2 sensors are not showing the exhaust as rich then they are not operating and giving the PCM correct information so it just keeps dumping more fuel. We can get to that after the fuel pressure checks out.

Good thought. I didn't think of a vacuum leak. We would have gotten there but that is pretty easy to check.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If the o2 sensors are new, let's assume they are ok. If you want to go ahead and pull a plug you can however, if you are getting that poor of fuel mileage, we can assume it is at this point.

Okay, here are the basics:

O2 voltage and stft is measuring the same basic thing. The o2 sensor is measuring the amount of oxygen in the exhaust which we can determine air/fuel ratio based on that. It does not measure fuel. We just know that there is fuel and oxygen in the exhaust so if there is more o2 then there is less fuel. When there is less o2 then we know that is because there is more fuel.

So here is where people get confused when looking at the +/- number of the fuel trims. Keep in mind this is a measurement of o2 in the exhaust and nothing else. So if the number is negative, that means there is less o2 in the exhaust then desired. You want the number switch around 0. It will never just be zero because the exhaust is always changing and the PCM is constantly adjusting it. So that is why we want it going negative a couple points, and then it adjusts and goes positive. Then negative and it keeps switching back and forth from negative to positive.

So if a negative number is less o2 that would be considered a rich exhaust. This means a positive number has a larger amount of o2 in it then desired. This would be considered a lean exhaust.

Take a look at the attachment that illustrates this.

As for the voltage, that is just a different way of looking at the same thing. The lower the voltage, the more lean the mixture. The higher the voltage the more rich the mixture.

Let me know what questions you have. Thanks

As for the coils, your secondary side should be around 5-8 K ohms. I am sure that is what your meter was reading but I just want to make sure that is clear in case others read this in the future. So that means 5,000-8,000 ohms. The primary side should be less then 1 ohm. So they appear to be working. If you meter is dropping to 0 and not showing an open circuit then that is probably just the meter as it gives you an average of what you are trying to read so that it is not bouncing all around so it is not uncommon for it to tell you 0 on something like this. Also, the fact that the engine runs well tells us they are operating.

However, this appears to be conflicting information. The reason is, if you are getting that poor of fuel mileage, I would expect you to smell fuel in the exhaust and in the engine compartment. Plus the o2 sensors should be showing very negative fuel trims or the voltages should be below.2 volts. What were the numbers when it was running?

Also, I never asked, how did you calculate the fuel economy?

Okay. That would make more sense. Let's address the misfire issues and then retest the fuel mileage. Misfires are horrible on economy. So let's not worry about the fuel trims or voltages at this point. Let's change out the plugs and if you can get pictures of them so we can see the condition and we can go from there.

Sounds great. Let us know what turns up. Thanks for keeping us updated.

What was the vehicle doing when you took these numbers? Did you find anything with the vacuum leak that you mentioned above?

Basically these numbers are not out of line. The numbers should be bouncing back and forth from positive to negative. This shows they are going rich then lean as the PCM makes adjustments.

The only one that is concerning is the Bank 1 sensor 2 that holds steady at.75 volts. This means the sensor is seeing low oxygen content after the converter. Which would mean it has a rich condition after the converter. This means either the sensor is faulty or the bank is really rich, or the converter has failed.

Swap the down stream o2 sensors and see if the bank 2 sensor 2 then reads the same.75. If it does, change the sensor.

Okay. If you found a bolt missing then we may still have a leak as once there is a leak the gasket (depending on what type) will fail at that spot and it will not seal.

Let's use this guide for the vacuum check and do the method of spraying the engine with a combustible fluid so that we can listen to the RPM. If there is a leak the RPM will raise when it pulls in the liquid.

Or put a vacuum gauge on it and get a video of the gauge when running the engine.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge