Fuel Economy on Information Center way off

Has anyone had a problem with the Drivers Information Center Average Fuel Economy being way off? Has anyone found a cause.

I use to see high 16 mpg on the DIC all the time when I was getting low 15 mpg consistantly calculating by miles driven vs gallons pumped. Lately, the DIC is telling me I'm getting 19+ all the way up to 23 mpg when I'm actually averaging 14.5 to 15 mpg. I have to say something is not as it use to be. I've been wondering about injectors but the balance rates have been off ever since I purchased the truck 70K ago and have not changed much.

With a couple other threads saying 4+ will cause smoke, my truck never smokes and the balance rates on some cylinders are in excess of 4. The only issue I had was a surging and a new fuel pressure regulator fixed that right after I purchased the truck.

I do have some EGR codes that I have not fixed. P0401, P0404, P1404 P2365 I think is the last one. EGR Open, Closed, Insufficient Flow, and a I think it is a Turbo Vane Position Sensor Code but it has more to do with the electrics. I am also thinking the EGR and EGR cooler are plugged with carbon and if it has gotten far enough in the exhaust, maybe it is restricting the turbo vanes from moving correctly which I guess could be causing my fuel economy reduction. I can't imagine it is playing a part in the DIC Average Fuel Economy calculation. Other thoughts?

I just checked the balance rates tonight and here is where they are. I did not drive it to get it good and hot.

ECT 91F ECT 91F ECT 120F
Park In Gear In Gear
#1 -1.7 -2.0 -1.5
#2 0.3 -0.2 0.2
#3 4.6 5.1 4.9
#4 0.2 -0.1 0.3
#5 4.2 4.0 5.3
#6 -3.9 -3.6 -3.5
#7 0.6 0.8 0.3
#8 -3.9 -4.1 -5.8

I'm sure many will tell me that I need the injectors replaced but I can't believe this. I have no smoke, the truck starts and runs great. Maybe a set of injectors would be good but the cost, it will have to wait.

Feedback is welcome. Once I can put this truck down for a week or two, I'll dig into it to find out what is going on but right now, it is getting me to and from work. Not exactly an econobox but a little cheaper than buying another car.

Thanks
Steve

Personally, I'd work to solve the codes first, then worry about fuel economy/DIC. Like you, I'd leave the injectors for another time. ;)

Jim

The DIC calculates mileage based on miles traveled and fuel scheduled by the ECM. If the injectors are delivering fuel at a different rate than normal (I think the balance rate is an indicator of this) then the calculations will be off.

Like Jim said, get the codes fixed first, but, next time you fill up zero the fuel used counter and see if it agrees with your subsequent fill up or not. If it's off the mileage calculation will be off too.

I'm going to go after the EGR codes and when I'm there, I'll check out the turbo for the P2563 code. I'm still thinking it all has something to do with carbon buildup and am hoping it doesn't cost a bunch of cash to get it cleaned up and back on the road with no codes.

The DIC gallons used has always been off which was causing the MPG average to be off about 2 mpg. Most of the time, I'd pump 26-27 gallons in when the DIC would tell me I used 23-24 so maybe the injectors could definently have had something to do with it all along.

My wonder is what are others seeing with the DIC calculations gallons used and average MPG with old vs new injectors?

Are you using any electronic power modification? If so, they will cause the actual/DIC mileage to disagree.

Truck is totally stock.
I don't think it has been its entire life though. There is an EGT sensor bung in the down pipe from the turbo. I know the ECM had been recalibrated to Stock prior to purchasing the truck. The previous owner was chasing a surge from around 80K until they traded it at 138K. They were driving the truck about 10K a month. Figured from the build date to when they traded it. Unfortunately the dealers they were using never picked up on the fuel pressure sensor as being the cause of the problem. I'm sure if they were able to get the truck fixed, they would have put many more miles on it.

I didn't have a chance to get to the truck this weekend and at the moment, it really is a back burner project since it still runs and I now have a spare car back on the road.

I'll keep you all posted on this one if I can ever get time to work on it.

My DIC has consistantly been HIGH by about 5% (example...it reads 20 mpg when the math says I got 19mpg) for the entire time I've had my 2003. My friend's DOGED (oops, did I mix up some letters??) is about 10% high!!

The best explanation I've been given is that the DIC uses 'fuel scheduled' (like mentioned earlier in this post) and was 'calibrated' using different (better?) fuel than is typically available in the real world, so the 'scheduled fuel' is not the same as the 'real' amount delivered (it's less than 'real') thus the error in mpg.

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