Water temp and MPG

[2TimingTom]

I never did resolve this issue. As you can see in the ScanGauge, the water temp is 195 (cycles between about 190-197, breaks 200 briefly in heavy stop-n-go). Temp need isn't quite in the middle. Here's a pic (finally):


I'm getting about 13 mpg (230 miles to a tank).

The real question is: because the temp gauge isn't reading "in the middle", is the computer getting wrong info and selecting a fuel table that's too rich (like the warm up cycle)? Or is my crappy mileage because it's wintertime, I'm geared with 4.56s, and I'm SAS'd? Lots of factors.

 

[Turdle]

If this is of any use-
During our trip to Colorado using the AC on I70 doing 70 mph the coolant temp reached over 225 degrees according to my scangauge, however the idiot needle stayed dead center.

Another thing that deserves mention.

My info center shows poor economy, but the actual mileage computed by gps distance traveled and gallons to fill, is higher.

I also noted my tank is not as needy as the fuel gauge says it is, and wonder if the sender float isn't sogged down and heavier that it should be. In other words it seems like the float might be dropping faster than it normally would. Full tank shows just over full, but 1/4 tank shown on gauge will only allow 11 gallons back in. What the fudge can this mean?


I am not sure if the message center economy is computed using the sender unit input, or, if it uses feedback from the fuel pump injector driver circuit. Either way mine is wrong.

 

[fastpakr]

I never did resolve this issue. As you can see in the ScanGauge, the water temp is 195 (cycles between about 190-197, breaks 200 briefly in heavy stop-n-go). Temp need isn't quite in the middle. I'm getting about 13 mpg (230 miles to a tank).

The real question is: because the temp gauge isn't reading "in the middle", is the computer getting wrong info and selecting a fuel table that's too rich (like the warm up cycle)? Or is my crappy mileage because it's wintertime, I'm geared with 4.56s, and I'm SAS'd? Lots of factors.

The temperature and gauge behavior you're describing doesn't sound abnormal to me. If there is a problem causing your low fuel economy (other than the temperature, gearing, etc that you mentioned) I don't think it has anything to do with the cooling system.

 

[Craigerz]

My info center shows poor economy, but the actual mileage computed by gps distance traveled and gallons to fill, is higher.

I also noted my tank is not as needy as the fuel gauge says it is, and wonder if the sender float isn't sogged down and heavier that it should be. In other words it seems like the float might be dropping faster than it normally would. Full tank shows just over full, but 1/4 tank shown on gauge will only allow 11 gallons back in. What the fudge can this mean?

My console showed even with the odometer even when I swapped to bigger tires. I put a new speedo gear in to re-calibrate the speedometer and the console still matches the odometer, which is now about right +/- 1 mph.

I just put a new fuel pump in and mine does the same thing also. I have learned to use the console as more of a judgment, the fuel gauge as a back up, but really I just watch the odometer. I really wanted to have all the neat little functions working like miles left per tank and fuel economy, just because its already there. Now they are somewhat trustworthy after I swapped the speedo gear out.

 

[koda2000]

Your water temp needs to be hot enough to enter "closed loop mode". That's roughly 190-195 degrees F.

When I first bought our 2000 Mountaineer 5.0 the temp gauge read near the "C" mark unless I let it idle for 15 mins. Even then it read maybe 1/4 way up max. It seemed to make good interior heat, but wasn't normal. My fuel economy sucked at around 13 MPG hwy. Eventually it set the CEL with a P0125 code. I replaced the t-stat and the gauge started reading approx mid way on the temp gauge (normal) it had fantastic heat and started getting around 20 MPG hwy, which matched my 2 other 5.0's over the same trip.

Apparently the PCM requires a coolant temp in excess of 167F to enter closed loop mode, otherwise it's like running with the choke on.

 

[2000StreetRod]

My Sport PCM goes to closed loop about 20 seconds after cold engine start. That's just long enough for the O2 sensor heaters to get hot enough to make the O2 sensors reliable. As I recall the 2nd generation PCM adjusts the AFR based on inlet air temperature (IAT), engine coolant temperature (ECT), time after engine start and load. The engine temperature gauge on the instrument cluster has a dedicated engine coolant temperature sender that has no effect on the PCM that has its own sensor. The 3rd generation has a cylinder head temperature sensor for the PCM and no ECT. The PCM relays cylinder head temperature info to the instrument cluster.

A defective engine coolant thermostat or an intentionally low temperature thermostat will significantly decrease fuel economy with the stock tune.

 

[2TimingTom]

My info center shows poor economy, but the actual mileage computed by gps distance traveled and gallons to fill, is higher.

My '97 is a bit of a ******* year. The ScanGauge can't read fuel usage on '97s. So no info center either.

I compute my MPGs the old fashioned way: I enter it into an app that does the math for me. I've tracked every tank I've ever pumped since about 2008. I've changed the speedo gear so my speedometer/odometer is reasonably accurate.

I was looking through my logs and my mileage does improve when not on the winter blended gas. And while I did get better mileage in the winter when I first got it, that was on stock gearing, stock tires, stock height.......

 

[2000StreetRod]

I remember reading that the PCM uses injector pulse width and engine speed to compute fuel consumption. If the injector size or the fuel pressure is changed from stock and the tune parameters are not changed accordingly then the computed fuel consumption will be inaccurate. The rear axle sensor drives the 4WABS which generates a vehicle speed signal for the PCM and the speedometer. I think the PCM uses the vehicle speed signal, axle ratio and tire size to compute vehicle speed. Changing the axle ratio or tire size from stock and not changing the corresponding parameters in the tune will result in vehicle speed and distance traveled errors.

If the odometer is accurate then using miles driven on the odometer and fuel added to refill the tank to compute fuel economy is an accurate method.

 

[Dono]

Hope this helps,
It shows (At least on my 2000 v8 strategy) how fast the pcm goes closed loop based on temp. Adaptive learning does not occur till temp is 150 degree's or more.

 

[Dono]

Here's a screen shot for adaptive learning.

 

[2000StreetRod]

Don, unless I'm mistaken, for your strategy if the start up ECT is 60 degrees or greater the delay to switch to closed loop is 16 seconds. Closed loop means that the PCM is controlling the AFR based on the O2 sensors. Look at one of your datalogs when closed loop is recorded for a cold engine start.

My understanding is adaptive learning is the process when the PCM computes and stores parameters for various engine conditions for future use for similar conditions. The stored parameters reduce PCM computation time and provides backup data when a sensor has failed.

 

[Dono]

Absolutely correct.
I thought I would include both so that the difference between closed loop, and adaptive learning would be seen.

To further simplify things, closed loop enforces changes made by adaptive learning while using data from the 02 sensors.

So, in my current Strategy, I never, ever want my truck running cooler than 150 degree's. If my thermostat can't get my truck to that temp, any auto learning will not take place.

To the op, what we are seeing is that the coolant temp is not the issue with your poor gas mileage.