Gas Mileage..... :(

[biddy_91]

Hey everyone. Its been awhile since I last posted but I am having a problem. For the longest time I had a bad vacuum leak so my car had a bad idle and gas mileage problem. Well I fixed the egr valve which was stuck open and I also found a line that was completely broken in half. I performed a smoke test on the car and that seemed to be the only issues with vacuum that I could see. My main question is, what could be making my mileage as bad as it is. I don't drive the car hard, I have never had an issue getting around 17 in city and 23-25 on highway. Now, even after new spark plugs, cap and rotor, seafoamed the intake, fixed vacuum lines and egr valve, 02 sensors and then basic general maintenance, what else could it be???? I haven't unplugged the battery yet to reset the computer because the check engine like quit coming on so I figured it was ok. Any suggestions on what I should do??? Oh, I forgot to say what mileage I am getting.....11 in city and no better than 18 on highway but only going 70 plus. If I go 55-65 I only get around 15-16 mpg.

[GTvert90]

Hows the ignition? Plugs cap rotor wires?

Run a KOEO KOER and cylinder balance test LUK

On OBD-1 you can have codes that don't turn on the check engine light.

[biddy_91]

Ok thanks. I do have a scan tool for my car at my college so I will look into that and see what it says.

[Whtstang]

Have you tried cleaning the injectors? When was the timing last checked?

[biddy_91]

I have ran seafoam and a lot of other injector cleaner through my gas and I seafoam my upper intake every other oil change so clear the carbon. I havent had the timing checked. I will look into that also.

[biddy_91]

ok so today I ran a KOER test and I got the same codes as last time. 012, 021, 041, 091 which are low idle, ego lean, system lean, and I can't remember what the 021 was. I think it had to do with the thermostat. I talked to a professor of mine he thinks that it could be a vacuum switch going to the air pump so we disconnected the line going to the main smog pump tube. The line we took off plugged in directly under the air intake hose on the smog pump line. When we ran the test after that the lean codes were gone and 094 and 044 came up instead which were thermo codes once again. This makes me think back to a thread I read that had to do with a TAD and TAB switch that directs the vacuum system. Any suggestions???

[Whtstang]

KOER self test code 21- ECT out of self-test range.
This could be at the root of the problem. This sensor gives the ECA important info about engine operating conditions & affects A/F ratio, spark timing, idle control & emissions. Start by checking the wiring & connector to the sensor. Make sure the wiring doesn't have worn insulation & that the connector is clean & secure.

More info:
http://fordfuelinjection.com/?p=28

Did you run the KOEO part of the Quick Test? Any codes there will should be addressed first. Without this part of the test you may not be getting a complete picture.

[shemp]

Originally Posted by Whtstang

More info:
http://fordfuelinjection.com/?p=28

Wow! Great site. thanks!

[Whtstang]

Gotta love the Information Hiway!

[biddy_91]

I read some other threads that were posted with some of the same symptoms that I was having. I read that a bad TAB and TAD switch could also be the root of the problem. I still haven't checked the timing because I don't have the tools here at my house. I went ahead and purchased the TAB and TAD switches for the car and installed them. Here is whats going on. After installation of the two switches, I ran a scan tool on the car to see if the same lean codes were being thrown. All of the codes that were present before were gone and the only code that my car had thrown was a low idle which i believe was 012. I drove the car around afterwards and did notice that my mileage got a lot better than 11 in city and 13 city and highway mix. After a 100 mile trip that I took the car on, I averaged 17 almost 18 mpg. On the way back from the trip, I only did 15 mpg going slowing and driving very easy. Now the car is getting the same mileage or even worse than before. Car runs smooth, extremely strong, and isn't really showing any signs of issue until you see the mileage. Well yesterday I was driving the car and my check engine light flashed at me for the first time in a few months. I thought that was taken care of but I guess now. I will run the tool again on the car. Till then, anymore suggestions for me?

[Andrew jerald]

This is the reason i have a nissan altima 29 city 34 highway...My mustang gets about 9 or 10mpg on 112 octane.

[m80j]

Codes 44 and 94 are normal codes to have with your smog pump bypassed.Code 21 just means coolant temp out of specified range.This does not mean the sensor.If there is a problem with the sensor or the sensors voltage the code 21 will be followed by code 51 or a 98 or both.You will get the code 21 if your car is not up to operating temp when the test is performed.So if your running a cool thermostat 160 for example this will increase the likelihood of this code showing up.With a 160 your car may never reach operating temp and the computer always thinks the car is cold and as a result will stay in an open loop all the time.That means way more fuel resulting in poor mileage but if your at a low altitude it also means more power.I run mine in an open loop purposely just for the extra pony's.Try a warmer thermostat and see if that helps.I think ford recommends a 180.As far as the code 12 goes have you tried to up the idle screw?If so this can cause a mileage prob too because when you turn that screw you're also changing your TPS voltage and to much of that can be bad.

[Whtstang]

Code 21 is telling you that the ECT sensor readings are out of spec for the Quick test. Granted it could mean that the coolant level is too low or that the coolant is not up to normal operating range. But if the engine is not operating under these conditions, it would indicate that there is a problem with either the sensor or it's circuit. You do not have to have the code 51, 61 or 98 present for the ECT to be bad. Test the sensor as per the link I gave above if in doubt.

[biddy_91]

I will go ahead and check the sensor then for the 021 code. After I replaced all of those parts, I went ahead and changed the TAB and TAD and the codes went away on my next test. I drove the car 100 miles and got 17 mpg. Drove back the same 100 miles and got 15. Then I filled up in city and drove the whole week in city and only got 133 miles on the tank before I "HAD" to fill up. I will perform the KOER test again and make sure the car is warm when I do it. It prompts that about the temp at the beginning of the test so I am sure that my car has always been warm when I do it because I run it for 3 min at 2 grand. Im just wondering what it could be now that I thought I had everything fixed and the mileage jumped up that much and just dropped.

haha about the nissan maxima for city.....thats a great idea. I am a poor college student that works at sears auto center for my college job. I can't afford another car let alone save for one with this gas mileage. haha

[Whtstang]

Running the engine at 2000 RPM for 3 min will heat up the O2 sensors but may not be enough to open the stat. The engine coolant has to be moving past the sensor tip before it will get an accurate reading of the state of the engine. I would either use the temp gauge to determine if the engine is up to normal operating range and/or make sure the upper radiator hose is hot & pressurized.