Other than the diagnostic fault codes, there's no good way to diagnose this over a computer, but you have to share in the responsibility for your frustration. When you go to a doctor and you don't like the diagnosis, you run to a second one. He has to start all over with testing, then if you're not satisfied, you run to a third one. Do you feel you're being scammed by those doctors?
Mechanics are held to much higher standards than doctors. We put more value on the health of our cars than on our health. You didn't provide any information about your visit to the first mechanic other than to say one thing has been ruled out as the cause of the problem. You know that mechanic knows a lot more than that about your car, but you cut off the diagnosis and went to a second shop. The second mechanic came up with a diagnosis, but there's no indication you had the repairs done, so why are you blaming the mechanic? All you said is you took the car, continued to drive it that way, and somehow apparently expected it to be okay.
Next, you said it drove okay for three weeks, but that is wide open to interpretation. I can put up with a lot and I can nurse a car a long way when it isn't running properly, but whether that is considered "okay", depends on the person. We need specific details and observations to get a feel for what you're experiencing. I suspect you may think your engine is running "okay", as in "good enough" to keep you from having to walk, but it's not running like it is supposed to. If that is correct, three weeks is enough time for a totally different problem to develop, or the original one could have gotten worse.
Based on the information you did provide, I can give you some educated guesses as to what's happening, but these are just examples of the types of things that we consider when forming a plan of diagnosis. First of all, you got a fault code for one oxygen sensor's signal voltage being shorted to the 12 volt supply that runs its internal heater. That can be caused by an internal short inside the sensor, but it is very uncommon. The sensor itself will be responsible for that code perhaps one out of a hundred times. It's the last thing we would suspect. Now you have a second code for the oxygen sensor after the catalytic converter. Again, the chances of the sensor being the cause of the code is very remote.
The major glaring clue here is to have fault codes for two different sensors for the same thing, that are both uncommon. Now, more than ever, the mechanic should be looking for the most likely cause, and that is a problem with the wiring harness going to both sensors. These fault codes can be set by a break in the common ground wire both sensors share, or by that harness falling down onto hot exhaust parts, then the insulation melts and the wires touch each other.
I should point out too that oxygen sensors have very little effect on how an engine runs. Once they get up to operating temperature after a minute or two, the Engine Computer will modify fuel metering only plus or minus about ten percent based on the front sensor's readings. That's enough to affect emissions and fuel mileage, but you won't notice much running trouble. Ideally, the right thing to do is to reinstall the old sensors once it was determined they didn't solve the problem, but that isn't always feasible. Electrical parts usually can't be returned, and the labor to put the old ones back in might be more than the cost of the parts. Sometimes the mechanic will discover something that is going to cause a problem in the near future and will leave those parts in, depending on whether he has your best interest or your wallet at heart.
Again, I'm guessing here, but how can your engine run worse with new, known-good oxygen sensors? I can think of two possibilities. One is the Engine Computer had "given up" on using their readings to adjust fuel metering and it injected approximate values, based on other sensor readings and operating conditions, to run on. That's one of the things Engine Computers do when they know they can't believe or rely on a certain sensor's signal. With the new sensors, the computer could be getting enough of a signal to consider it a correct signal, and try to use that information. Any other defect in the circuit would now be included in the fuel calculations and would result in worse engine performance. This is where new parts can actually make a problem worse.
The other possibility goes back to my comment about a melted wiring harness. Disconnecting the old sensors would have disturbed and repositioned the harness, so now there could be more, less, or different wires touching or grounded.
The fault code for the fuel gauge refers to something that has no effect on engine performance, but it CAN be a clue if the cause is related to the first problem. I wouldn't worry about that at this time. There's always the possibility the cause could be inadvertently repaired by repairing the cause of the first problem, namely, a wiring harness issue.
I'm scratching my head about the fuel pump. There has to be some other information or reason the mechanic suggested replacing that. GM fuel pumps typically fail while they're running, leaving you stranded on the highway. Chrysler pumps almost always fail by failing to start up, leaving you stranded in your driveway. They rarely fail while you're driving. Next, some GM engines will not start or run if the fuel pressure is as little as two pounds low from the normal 50 pounds. I chased an intermittent problem in my '88 Grand Caravan daily driver for a year and a half, and since I had a fuel pressure gauge attached all that time, I can tell you my engine runs fine with as little as 20 pounds. Again, 50 is normal. It doesn't sputter until it drops to 15 psi. What did your mechanic see that pointed to needing a fuel pump? The engine did run so the pump had to be working. If the pressure was low and causing all this trouble, the new one would have solved it right away. We're missing some details here.
The way you described the next series of events suggests the engine ran fine for a few minutes. If that is correct, of course the mechanic would have thought he solved the problem, so you can't fault him for that. What needs to be done is to leave the car with one mechanic and let him test-drive it, possibly overnight or the next day, to be sure it is solved. I can share some history that may shed some light on things to check. Thank you for listing the engine size. A lot of people with engine running problems don't do that. Your comment,
"now it wants turn off if I even give a little bit of gas to actually drive past 10mph it backfires even more"
is a very useful observation. To continue with,
"it seems as though it is flooding with gas", is not because that's open to interpretation and can be misleading.
Here are some things to consider. First of all, if you have the single overhead cam engine, there has been a common problem where the dowel pin between the camshaft and its sprocket shears off, then the sprocket turns very slightly on the camshaft. That makes valve timing late. You won't notice that in the engine performance, but since the camshaft position sensor is smartly placed on the other end of the camshaft, (on the driver's side of the cylinder head), the Engine Computer will detect that tiny change and set a diagnostic fault code " cam and crank sync". You don't have that code so we can ignore this problem. I'll finish the story for information purposes. To set that code, the camshaft has to turn on the sprocket the equivalent of the timing belt being off by one tooth. If it turns the equivalent of two teeth, the computer will shut the engine down to protect it. This is an "interference" engine, and if the timing belt is off by three teeth, open valves will be hit and bent by the pistons. That's why the computer shuts the engine down before it gets that bad because that's a very expensive repair.
The issue here is when you're in the middle of one and two teeth off, the computer may still try to run the engine, or it may start to shut it down. The clue is one ignition coil won't fire its two cylinders, but the other one will. You'll be lucky to get to ten miles per hour on just two cylinders.
The next thing to consider is the pickup screen in the gas tank. If you get to 200,000 miles, chances are you're going to experience a screen that collapses or gets plugged. At 260,000 miles on my van, I just put in my second new screen a few months ago. The classic symptoms are the engine will start and run fine for perhaps 15 miles, then it will act like it's running out of gas. With fuel injected engines, they will run great at highway speed, and want to stall when the most fuel is being pumped, ... Which is during coasting. Once the engine stalls, it will typically start and run fine again for up to five miles after it is allowed to sit for a few minutes.
When replacing the fuel pump, some mechanics opt for the complete assembly. They're more expensive but take a lot less time to replace. They think they're providing the best quality product and the most reliable repair. Some mechanics disassemble your pump housing and install just a new pump and motor. They think they're saving you money because the parts cost a lot less, but it takes more labor time and dollars to do it that way.
When replacing the complete assembly, it comes with a new pickup screen attached already, so if that was the cause of the problem, it's fixed now. Replacement pumps that need to be installed into the housing may come with a new screen that has to be replaced separately, or it may not. Those screens can be visually checked for being plugged with mud, but not for collapsing and blocking fuel flow after a few minutes of operation. Much of what you described, as far as engine performance, leads to that screen collapsing, and a new fuel pump by itself won't solve that. What will is that $12.00 screen. This can be found by driving the car with a fuel pressure gauge connected so the pressure can be observed when the problem occurs.
If the cause of the problem is more elusive, or if there's something I'm missing, seriously consider leaving the car with one shop until it is solved. You can expect to be charged for their time, but when they have the opportunity to drive the car and evaluate its performance, they also have the time to remove parts that didn't fix it. A fuel pump can be put in stock for the next person who needs one. They won't want to do that with uncommon parts they're unlikely to sell soon because they would get too much money tied up in inventory. Some shops are also willing to remove new sensors, but only after they are sure the problem is fixed and those sensors didn't contribute to it. The problem here is sensors usually can't be returned, even by repair shops, because the mechanic could have accidentally damaged one, AND, most shops will consider it a used part now. They know you don't want to pay for a new part and get a used one.
Also consider that a plugged catalytic converter will cause an inability to accelerate and back-firing through the intake. That is rarely intermittent though and will act up right away. The fastest clue to that is you'll hear a steady hiss from the tail pipe instead of the normal "putt putt" sound.
Wednesday, September 24th, 2014 AT 9:53 PM