Misfire on all cylinders

[petflunky]

Hi
I have an 05 Aveo that has a problem. Specifically, it misfires on all cylinders. This is because the engine is dumping fuel into all the cylinders, because it thinks the engine is cold. This is what I know from the mechanic working on it. 1. It has spark to all cylinders. 2. The cooling sensor on the back of the block is good. He checked it. I hooked up one of those computer things and it said that it was reading a coolant temp of -70 degrees, signaling something wrong with the sensor. Well it's not the sensor. Next thing is to check the wiring from the sensor to the computer. Anybody have any ideas what else it could be?

Thanks!

[petrified.rabbit]

If the sensor is giving the wrong temperature, how do you know its good?

If it not the sensor, the misfire is probably plug wires.

Wait for it to be dark, or turn the lights out in the garage, start the car with the hood up. Mist some water out of a squirt bottle over the spark plug wires and watch for a light show. BE CAREFUL it is 40000+ volts. If your not comfortable with the test, spend the $15-25 on new wires and just put them on. Make sure not to mix them up (do one at a time, take on off, match up the length to a new on, and replace) make sure your hands are clean, and do the spark plugs as the same time.

[petflunky]

Hi
I think he said plug wires are ok. Thanks for the input, though. He's going to check the wiring back to the computer and make sure that stuff is all ok.

[petrified.rabbit]

Im not sure which temp sensor was tested, I'm not sure how he knows the spark plug wires are ok.

Im not even sure you know what code or codes you have. There is nothing, nothing on the engine that will make it dump fuel to the point of a misfire. Temperature sensor or otherwise. If you are dumping fuel, and continue to misfire, your cat will be toast.
The o2 sensor, air intake temp sensor, and the map sensor work together to get the right air/fuel mixture. The only things that will cause a misfire without setting other codes to point to the exact problem will be coil pack, plugs or wires. Typically if its a single cylinder misfire, p0301, p0302, p0302 or p0304 it a single cylinder issue, which is a fouled plug. If there is 3 codes, p0301, p0303 and p0300, or p0302, p0304 and p0300 its on side of the coil pack. If there is no codes but the p0300, or all five codes are present it is most likely the spark plug wires. If your mechanic pulled off a wire to test it, its probably now a broken wire.. I can almost never get every deep socket wire off an engine without stretching one of them..

The only thing that would allow the car to dump fuel would be a stuck injector. Odds of all the injectors dumping fuel is slim.. If you have a computer that read the temp, did it read the o2 sensor levels? is it running rich, i.e. dumping fuel? Is it idling high? any signs of too much gas other than a misfire?

since you have a live data computer to hook up to read the temp sensor, What are the codes?

[petflunky]

Hi I'm not sure which codes the computer showed. What he did was hook up the new cooling sensor and it made no difference. His thinking is since the sensor is reading that the engine is cold, it wants to run richer, putting too much fuel into the engine, regardless of the temp. Which (if I remember correctly) would cause the misfire because of too much fuel, plus engine heat.

I don't know if he read the o2 sensor levels. I will ask
It is not idling high.
Too much gas, yes. There was some gas in the oil.
When I see him, I will ask him which codes showed up.
Currently, he is going to check the wiring back toe the ecm to see if the sensor is getting the correct voltage, or the correct signal is being sent back to the ecm (i forget which)
Thanks!
Another edit. "dumping" might be a be strong of a word. Constantly running rich would be more appropriate.

[xintersecty]

Sounds like you need to get your hands on the codes and understand them. Honestly playing in-between us and your mechanic is not helpful without good information. If you have a smart phone load up Torque and buy a ODBII to bluetooth convertor. Get the codes out and put them up here. You need to put your hands on the information don't trust your mechanic and be a skeptic

[petflunky]

Ok, so the car got fixed.
1. Spark was good
2 Timing was good
3. Compression good
4. Cooling sensor problem, I'm not sure yet. Forgot to ask earlier, waiting on answer from him. EDIT: Got in touch with the mechanic. His little computer thing was reading wrong. He hooked up another one and gave different readings. So this is ok as well.
5. Injectors, good.
6. Decided to take the fuel rail off to look at the top end.

Last year, the timing belt broke. Even though I had it replaced, it broke with only 35k on it. Naturally, it took the head with it. So, I had the head rebuilt, and everything reassembled. The car ran fine.

Now, here is what the problem was. When he started poking around on the top end, seveal of the camshaft caps worked loose! He retorqued them, and now the engine is fine. His theory is this was allowing play, which wasn't opening the valves all the way, creating a incorrect air fuel mixture. My son is getting ready to take the car for a spin, so we shall see...

Thanks for the help everyone!