I have a 99 24 valve and I put a 4.5 inch lift on it and am running 35 inch tires. I figured the fuel mileage would drop so I put an open element high flow air filter on it and put 4 inch flow through exhaust on, replaced the fuel filter and thought it would do the trick. Before the intake and exhaust upgrades I was getting 14 mpg, after the upgrades im getting 9 mpg and its still dropping, rapidly. Is my lift pump bad or is somthing else wrong, other than that its the best truck Ive ever owned.

 

When you added the bigger tires did u change the speedometer. Mines off by 10% with 305's and it was factory set with 245's, that could be where your losing the milage. Hope thats it: )

 

We need truck specifics Auto/manual, gear ratio. Did you do the lift, tires and other upgrades all at once?

 

This is simple!

Your tires are going farther than the engine thinks you are BECAUSE
your speedo is lying to the angine.


get it?

59

 

59 ford that makes sence (except)he said his mileage was still droping so he has another problem also.

 

Maybe , Maybe not , the fuel milage computer displays the average , So , with the speedo lying to the computer , it may think the truck is only getting 7 MPG , when in fact he is still getting 14 (Those numbers are just examples). Since it is an average , the milage will not instantly go to the current MPG , the average will slowly drop continuously until eventually it will level off at 8 (again , ficticious number) even though it displays 8 , that is NOT the actual milage. If you go to the dealer they can recalibrate the PCM for the new tire size with the DRB scan tool.
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I would hand calculate the fuel milage after figuring in the difference in tire sizes (for me, My truck reads roughly 10% low with my tires), and see if it is really as low as the overhead says it is.

If there is indeed a problem , start with the simple things , look hard for fuel leaks, change the filter, check air filter , etc , and go from there.

 

I agree with these guys, you are probably getting ok fuel milage still but your computer is gonna tell you otherwise due to the oversize tires. I have a 7 inch lift and 37 inch tires with 3:73 gears on my 03 cummins and my computer reads that I dont get very good milage but due to the cold air intake, 4 inch exhaust and leaving my chip on a low setting and driving it half *** responsibly I get can 1000km (621miles) to a 128 litre (34 gallon) tank of fuel on the highway. Going 120 km/hr (75mph) my tach is only at 1800rpm but then again I do have a 6 spd standard.
You could get your computer calibrated for it but I wouldnt worry too much about it.

 

Thanks

I talked to some of the guys at the local cummins dealer and they were hell bent on the problem being the lift pump so I think im going to tackle that as well as a possability.
It totally skipped my mind about the tire recalibration. Ill get that done. Im sure it doesnt help that the warmest its been is 6 below here for a while. Im going to put a digital monitor on and hopefully avoid any future troubles. Any suggestions on a good monitor?