Hey so I got an ELM scanner and ran forscan today. I have no CEL on but I came up with a P1000 PCM trouble code. I drove around for a while and logged some data, not sure on the best way to share it on here. Basically I'm trying to figure out why I have lousy fuel mileage and I'm thinking maybe my temp sensor isn't working. It says I have no fault but it could be stuck open and causing the truck to run in cold mode?

I also noticed a pretty big difference on my longterm fuel trim from bank one to bank two. Bank one was typically twice the value of bank one. I'm guessing these should be close to equal?

Anyways any thoughts and advice on what I should be looking at/for would be much appreciated.

Thanks
JB

 

62 reads & no replies, so I'll see if I can get things started. Good idea to have come by the ELM scantool for your poor mpg trouble shoot.
Set up the dashboard to display & record IAT, ECT, MAF, O2 sensors #1 for both cyl banks, long & short term fuel trim for both cyl banks, drive it & see if it finds anything out of normal.
If the O2 sensors have 75K or more miles on them, they belong on, or at the top of your suspect list, as their voltage switching range & speed get slow & lazy with age, sorta like me & that can cause the computer to corrupt fuel trim & turn in poor mpg.
If you've been running an oiled foam, or cotton gauze air filter, or have an ill fitting air filter, or improperly buttoned up filter air box, or an opening in the intake air tube, it can cause the MAF sensor to get dirty & corrupt its PID output to the computer about true air flow into the engine & that'll mess up fuel trim & affect mpg.
Dirty fuel injectors can affect mpg, as their spray pattern fuel droplets get course, we won't get a good spray pattern or a complete fuel burn & that'll cause a drop in mpg.
A dirty sticking open PCV valve, its loose rubber fittings, or dry rotted/cracked rubber tubing, can cause what amounts to an unmonitored vacuum leak, as its down stream of & not monitored by the MAF sensor, thus can corrupt fuel trim, but usually for both cyl banks.

Seeing as how you seem to have an unbalance of fuel trim in one cyl bank, concentrate for now on things that'll mess with fuel trim on that one bank, like the #1/upstream O2 sensor, or a vacuum leak, or leaky fuel injector. A plug read on the suspect cyl bank can give an idea whats going on inside each cyl & one with carbon fouled plugs, would suggest a fuel injector problem, like being dirty & having a runny nose.
Some beginning fuel trim trouble shooting thoughts for consideration, let us know what you find.

 

Some scan tools will tell you when the engine is in closed-loop mode. If it's closed loop, then at least the ECT sensor is reading something warmer than ambient. Also, if the sensor is reading a low enough but still valid temperature, OD (and maybe TCC lockup, I can't remember exactly) will be inhibited, assuming you have an automatic. Have you noticed a change in transmission behavior?

Are you thinking the thermostat is stuck open? I consider them maintenance items and change them every 2-3 years when I drain/fill the cooling system. Believe it or not, I've had one fail in less than 2 years and I use what I consider to be a decent brand (Stant). I've had OEM fail in 5 years. It's easy enough to change while I have the system drained and the cost is insignificant. Might be a good time to change yours if it's been a while.

 

Yea I'm thinking that it's possible but forscan reads there is no fault with my ECT status and reads between 52-56 deg C. So it's probably more likely an O2 Sensor issue?

Should my oxygen sensor voltages be the same on both banks or will they be different to each other due to being at different stages of combustion?
I also just noticed that my O2S_TEST notes an error, but O2S11F and O2S21F read no fault.
Long term fuel trim 1 is consistently above -20% and LONGFT2 is consistently below -10%.

Some other information to help, my PCV valve is brand new (replaced last week), my air filter is clean (it's not oiled), I've inspected my vac lines and they are all in good condition and I didn't notice anything loose or out of place. Truck is standard so that eliminates the OD inhibition.

I will pull my plugs tomorrow if I have time but I think I'm leaning toward O2 sensors.

 

Good idea to pull the plugs for a read, as they can provide info on how combustion in each cyl is doing. A plug with heavy dry carbon deposits suggests a fuel injector problem, wet oily carbon deposits suggests a problem with valve stem seals, or a ring problem, maybe piston ring land deposits, causing them to stick, worn rings, wrong viscosity or service grade oil, oil fuel dilution, ect, so a plug read on each cyl in a bank is really important input on how that cyl bank is doing.

Seeing as how we only have two upstream O2 sensors, one for each cyl bank, we are just seeing the average of all cyls on that bank, one cyl may be running lean, while another is running rich, but a plug read will tattle on how all cyls in a bank are doing. Now if we had O2 sensors for each cyl, all we'd have to do is look at the fuel trim numbers for a particular cyl to know how it was doing!!!!
Anyway if all things are equal & running ok, fuel trim for both cyl banks should be closely matched. Here is some good general TSB input *01-9-7***DRIVEABILITY - HO2S (HEATED OXYGEN SENSOR), CATALYST, AND FUEL SYSTEM MONITORS - SERVICE TIPS - OBD II VEHICLES ONLY
Let us know how the plug read goes.
BTW, how many miles on these O2 sensors????
EDIT: Here is a fuel trim mini-tutorial. http://www.aa1car.com/library/what_is_fuel_trim.htm

 

How long had the engine been running when you took the above posted ECT temperature reading???? 52-56 C = about 126-133 F!!!! So if the engine was fully warmed up when you took that reading, the ECT sensor is lying to the computer about true engine temp & it won't know to go into closed loop operation, so the fuel trim will remain richer than it should & that'll sure mess with mpg.