Fuel Mileage dropping fast
#1
Fuel Mileage dropping fast
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.
#2
Registered User
Join Date: Nov 2006
Location: South Eastern Ohio
Posts: 145
Likes: 0
Received 0 Likes
on
0 Posts
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: )
#6
Registered User
Join Date: Jun 2004
Location: SunnyVale Trailer Park
Posts: 1,668
Likes: 0
Received 0 Likes
on
0 Posts
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.
\
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.
#7
Registered User
Join Date: Dec 2006
Location: Airdrie, Alberta
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
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.
You could get your computer calibrated for it but I wouldnt worry too much about it.
Trending Topics
#8
thanks
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?
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?
Thread
Thread Starter
Forum
Replies
Last Post
EdmontonCanada
3rd Gen High Performance and Accessories (5.9L Only)
37
12-09-2009 03:18 AM
PThree
3rd Gen Engine and Drivetrain -> 2003-2007
6
05-02-2005 11:46 PM