7.5mpg help please!!
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4wd Low
Joined: Aug 2023
Posts: 11
Likes: 0
From: Eastern Long Island
7.5mpg help please!!
Alright so im on going on 3 months of getting a consistent 7.5mpg and im at my wits end
1990 f150 xlt lariat reg cab long bed 4x4 aod 302 and 3.55s on 31s 175k miles
ive replaced the following over the course of the last few months fuel pumps, distributor, icm, map senaor and ect sensor, coil, plugs wires cap rotor, manifold gaskets, O2 sensor, egr and evp and the egr vac solenoid. Iac and tps. Thermostat. My cats are also fine. Also intake gaskets and injectors. Also did a replacement ecm and it ran terrible so i did the capacitor replacement on the oem ecm and it smoothed out nicely. i am sure im forgetting things but I’ve basically shot the entire parts cannon at her. . I have no vacuum leaks and no codes at all. I checked with my scanner. Its bone stock besides a muffler. Both fuel tanks work and have no cross flow issues. Starts up fine runs fine. Has good power. But im lucky if i get 8mpg. I drive it like a grandpa. And I’ve noticed i can beat on it or drive light and get the same mileage. Im at the end of my rope with it. Any help is much appreciated
1990 f150 xlt lariat reg cab long bed 4x4 aod 302 and 3.55s on 31s 175k miles
ive replaced the following over the course of the last few months fuel pumps, distributor, icm, map senaor and ect sensor, coil, plugs wires cap rotor, manifold gaskets, O2 sensor, egr and evp and the egr vac solenoid. Iac and tps. Thermostat. My cats are also fine. Also intake gaskets and injectors. Also did a replacement ecm and it ran terrible so i did the capacitor replacement on the oem ecm and it smoothed out nicely. i am sure im forgetting things but I’ve basically shot the entire parts cannon at her. . I have no vacuum leaks and no codes at all. I checked with my scanner. Its bone stock besides a muffler. Both fuel tanks work and have no cross flow issues. Starts up fine runs fine. Has good power. But im lucky if i get 8mpg. I drive it like a grandpa. And I’ve noticed i can beat on it or drive light and get the same mileage. Im at the end of my rope with it. Any help is much appreciated
Hotshot
Joined: Jun 2015
Posts: 12,763
Likes: 2,420
Throwing your wallet at it is a ridiculous way to fix a problem. Was there any testing of those parts before you replaced them? You have now introduced multiple variables into the equation. If you didn’t use Motorcraft sensors, who knows if those new parts are any good?
Did you ever check the fuel pressure regulator to see if the diaphragm is broken? That will draw unmetered fuel into the intake manifold.
Did you ever check the fuel pressure regulator to see if the diaphragm is broken? That will draw unmetered fuel into the intake manifold.
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4wd Low
Joined: Aug 2023
Posts: 11
Likes: 0
From: Eastern Long Island
I replaced everything with motorcraft parts. The reason for all the parts is the truck sat for about ten years and mostly everything was not working well. I replaced the fpr when i replaced the fuel tanks and pumps. Most the parts i replaced cause i had them new in boxes. Ive had a few of these over the years but this one is by far the worst with fuel which is frustrating because its the cleanest one ive owned. My last one i retired around 275k miles due to frame rot and that one averaged 13-14mpg
Hotshot
Joined: Jun 2015
Posts: 12,763
Likes: 2,420
Does it hold fuel pressure ie checked for bad injectors? What do you mean by “no codes?” Are you getting the system pass 11 or 111 or are you not getting anything at all? I get 14-15mpg with that combination on my F-150 and Bronco.
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4wd Low
Joined: Aug 2023
Posts: 11
Likes: 0
From: Eastern Long Island
It holds fuel pressure fine. The injectors are all new as well. And sorry i should have clarified. I get the code 11 and if i forget ill get the code for the power steering switch and wot during the test. I never had one that was this brutal on fuel. It is my first auto but i know they do at least 11-12 city. If i go on a highway drive itll get around 10
Lead Driver
Joined: Sep 2002
Posts: 9,476
Likes: 2,009
From: North Texas
What is the actual idle vacuum? Back probe the O2 for voltage. Pull plugs and see if one hole different or all same.
Something is commanding excess fueling. TPS perhaps?
How are you calculating 7.5mpg? Ever verified speedo with a GPS?
Something is commanding excess fueling. TPS perhaps?
How are you calculating 7.5mpg? Ever verified speedo with a GPS?
Thread Starter
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4wd Low
Joined: Aug 2023
Posts: 11
Likes: 0
From: Eastern Long Island
What is the actual idle vacuum? Ill have to check again
Back probe the O2 for voltage. I haven’t done that but i changed it cause i had a code for it once.
. Pull plugs and see if one hole different or all same. They all look the same.
Something is commanding excess fueling. TPS perhaps?
I haven’t looked into that.
How are you calculating 7.5mpg? Ever verified speedo with a GPS?
Back probe the O2 for voltage. I haven’t done that but i changed it cause i had a code for it once.
. Pull plugs and see if one hole different or all same. They all look the same.
Something is commanding excess fueling. TPS perhaps?
I haven’t looked into that.
How are you calculating 7.5mpg? Ever verified speedo with a GPS?
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I see that you replaced the capacitors on the board.
I would start with checking the major sensors output to the computer. They can be providing faulty info and the computer will never know so long as the data is within the realm of possible.
Never hurts the verify base timing and that it is advancing as it should.
I would start with checking the major sensors output to the computer. They can be providing faulty info and the computer will never know so long as the data is within the realm of possible.
Never hurts the verify base timing and that it is advancing as it should.
Thread Starter
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4wd Low
Joined: Aug 2023
Posts: 11
Likes: 0
From: Eastern Long Island
its been on a few highway drives but only averaged about 10mpg
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4wd Low
Joined: Aug 2023
Posts: 11
Likes: 0
From: Eastern Long Island
no actually thats the only thing not stock. When i got the truck it was gutless and this mileage issue and long stort short the cats were literally melted inside so i gutted them and it ran wayyy better. But it still has the same mpg as it did.
Thread Starter
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4wd Low
Joined: Aug 2023
Posts: 11
Likes: 0
From: Eastern Long Island
I see that you replaced the capacitors on the board.
I would start with checking the major sensors output to the computer. They can be providing faulty info and the computer will never know so long as the data is within the realm of possible.
Never hurts the verify base timing and that it is advancing as it should.
I would start with checking the major sensors output to the computer. They can be providing faulty info and the computer will never know so long as the data is within the realm of possible.
Never hurts the verify base timing and that it is advancing as it should.
im going to look into that. I recently looked into the tos and it was beyond out of the recommended specs. A new tps fixed that but didn’t fix the mileage. I do have a second computer i may try
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