Mpg problem

[02cammy]

Hello I own a 02 camaro 3.8L and I'm having a huge mpg problem, I'm getting about 11-13 mpg. I've gotten codes and changed parts for catalytic convertor, knock sensors, bank one o2 sensor, egr valve and solenoid. And I've fixed all ad my mpg is still bad. The only thing I can think of is a tune up but my idle isn't erratic I feel some shanking sometimes at idle but when it happens my r needle doesnt move at all.. Do u think that's all I need is a plug and wire change even though my idle is fine or do it anyhow?

[thcardoc]

Originally Posted by 02cammy

Hello I own a 02 camaro 3.8L and I'm having a huge mpg problem, I'm getting about 11-13 mpg. I've gotten codes and changed parts for catalytic convertor, knock sensors, bank one o2 sensor, egr valve and solenoid. And I've fixed all ad my mpg is still bad. The only thing I can think of is a tune up but my idle isn't erratic I feel some shanking sometimes at idle but when it happens my r needle doesnt move at all.. Do u think that's all I need is a plug and wire change even though my idle is fine or do it anyhow?

Do you drive in town the majority of the miles that you travel? Do you take it easy with the car, or drive it like it's a racecar? Those are the first few thoughts from there once we rule out a useage issue here is how to proceed.

Next time you drive this pay attention to how the car coasts, does it seem to slow quicker than you would expect as in possibly a dragging brake? Can you feel more heat from any of the wheels after driving this for a few minutes where you were able to travel a good distance with very little use of the brakes? While your at it, how are the tires wearing?

Attach a scan tool that is capable of storing O.E. (not just global OBDII) data. Get a second person to drive this as you collect some snap-shots under different driving conditions. One of the things that we want to see are the fuel trims, and if they are making much of a correction in one way or another. You should be able to monitor ignition timing advance and when cruising is the displayed advance 25-35 degrees? Does the scan data display engine pinging and the use of the timing retard? That "could be" an indication of a mechanical issue and the timing might be getting retarded falsely.

Go to the misfire data screen. Are there any current misfires ooccurring especially under cruise? What about the historical data? Has the computer been counting many misfires? If so, what cylinder(s)?

Have you tested the fuel that you have been using for alcohol content? The car will usually learn to run on the alcohol performance wise but it takes about 30% more alcohol by volume so your mileage appears to suffer. Testing for alcohol requires a small fuel sample to be taken and put in a graduated cylinder. Add water to achieve ten percent of the fuel sample and then stopper it and shake it for a minute and let it settle. The difference in the water line from ten percent that was originally water to what you end up with is alcohol, because the water will pull the alcohol from the fuel.

Now manual transmission or automatic? If automatic watch shift and torque convertor clutch data. Is the TCC engaging and limiting slip to well under 100rpm at highway speed cruise? Does the shift correction data indicate that the computer has to work the transmisison pressure control solenoid pretty hard to reduce slipping in any one or more gears?

OK that's a start, manual visual inspections would also include testing fuel pressure, and inspecting the fuel pressure regulator for leaks. That would be reflected in the fuel trims, high negative correction at idle that returns closer to "normal" with higher engine loads. You need to collect all of this data before you throw any more parts at this.

[02cammy]

Originally Posted by thcardoc

Do you drive in town the majority of the miles that you travel? Do you take it easy with the car, or drive it like it's a racecar? Those are the first few thoughts from there once we rule out a useage issue here is how to proceed.

Next time you drive this pay attention to how the car coasts, does it seem to slow quicker than you would expect as in possibly a dragging brake? Can you feel more heat from any of the wheels after driving this for a few minutes where you were able to travel a good distance with very little use of the brakes? While your at it, how are the tires wearing?

Attach a scan tool that is capable of storing O.E. (not just global OBDII) data. Get a second person to drive this as you collect some snap-shots under different driving conditions. One of the things that we want to see are the fuel trims, and if they are making much of a correction in one way or another. You should be able to monitor ignition timing advance and when cruising is the displayed advance 25-35 degrees? Does the scan data display engine pinging and the use of the timing retard? That "could be" an indication of a mechanical issue and the timing might be getting retarded falsely.

Go to the misfire data screen. Are there any current misfires ooccurring especially under cruise? What about the historical data? Has the computer been counting many misfires? If so, what cylinder(s)?

Have you tested the fuel that you have been using for alcohol content? The car will usually learn to run on the alcohol performance wise but it takes about 30% more alcohol by volume so your mileage appears to suffer. Testing for alcohol requires a small fuel sample to be taken and put in a graduated cylinder. Add water to achieve ten percent of the fuel sample and then stopper it and shake it for a minute and let it settle. The difference in the water line from ten percent that was originally water to what you end up with is alcohol, because the water will pull the alcohol from the fuel.

Now manual transmission or automatic? If automatic watch shift and torque convertor clutch data. Is the TCC engaging and limiting slip to well under 100rpm at highway speed cruise? Does the shift correction data indicate that the computer has to work the transmisison pressure control solenoid pretty hard to reduce slipping in any one or more gears?

OK that's a start, manual visual inspections would also include testing fuel pressure, and inspecting the fuel pressure regulator for leaks. That would be reflected in the fuel trims, high negative correction at idle that returns closer to "normal" with higher engine loads. You need to collect all of this data before you throw any more parts at this.

You said something about tire wear.. Is aligment a big mpg problem cause it does drift a bit

[thcardoc]

Originally Posted by 02cammy

You said something about tire wear.. Is aligment a big mpg problem cause it does drift a bit

It can certaintly have an impact. Now it can't be the only issue because your talking about 1/2 of the fuel mileage that I would expect you should be getting.
To kill your mileage that bad you'd be destroying tires in a couple weeks.

[carsandcycles]

Perhaps one or more of the engine sensor are preventing the engine from going into closed loop function; this would artificially enrich the engine (I'm guessing coolant temperature sensor as a likely candidate). Ensuing rich running engine could lead to the codes encounter by over stressing the catalytic converter, oxygen sensors, etc.

[02cammy]

Originally Posted by carsandcycles

Perhaps one or more of the engine sensor are preventing the engine from going into closed loop function; this would artificially enrich the engine (I'm guessing coolant temperature sensor as a likely candidate). Ensuing rich running engine could lead to the codes encounter by over stressing the catalytic converter, oxygen sensors, etc.

If it was the coolent temp sensor wouldn't the cel come on?

[carsandcycles]

Originally Posted by 02cammy

If it was the coolent temp sensor wouldn't the cel come on?

You would think so...............but something is wrong and the CEL's you already got and corrected didn't fix your problem. Just seemed to me that the car was running good (and mileage was poor) that you were running in a rich condition and something was keeping the car in open loop (warmup mode); just trying to 'shadetree' a solution. You can always take it to a dealer/mechanic as you are truly getting mileage (probably less than half of what you would expect).

[thcardoc]

Originally Posted by 02cammy

If it was the coolent temp sensor wouldn't the cel come on?

You would have more specific symptoms as well. That's why the diagnostics start with a good study of live data taken with a snapshot (or several) while your on the road. The CTS voltage and the PCM's interpretation of that voltage as the engines temperature is displayed in the data.

Code enabling criteria are also an important consideration. While it's unlikely that you have a coolant sensor issue, consider that if you did the problem has to be present for a set period of time and under other specific operating conditions (engine run time, engine load, comparison to other sensors etc.)

[02cammy]

Originally Posted by carsandcycles

Perhaps one or more of the engine sensor are preventing the engine from going into closed loop function; this would artificially enrich the engine (I'm guessing coolant temperature sensor as a likely candidate). Ensuing rich running engine could lead to the codes encounter by over stressing the catalytic converter, oxygen sensors, etc.

Could this have anything to do with my fan always running from the time I turn on the car to the time I turn it off.. Or is that normal for my year, make and model?