MPG Problems
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MPG Problems
Have an 86 F150 302 FI. Running 33's with a 4 spd and my MPG is brutal! 8.5 to be exact.
So one thing that comes to mind is my rear tank leaks so I just dont use it. However do I have to rig anything so as to not lose fuel? Will the return lines just pump it out and leak out the back tank? I'm not totally clear how the fuel system works in this truck.
Also I'm wondering if its my EGR valve, last resort however. My timing chain apparently needs to be done as well.
Would the fact that my air pump is disconnected affect my fuel consumption?
Thanks!
So one thing that comes to mind is my rear tank leaks so I just dont use it. However do I have to rig anything so as to not lose fuel? Will the return lines just pump it out and leak out the back tank? I'm not totally clear how the fuel system works in this truck.
Also I'm wondering if its my EGR valve, last resort however. My timing chain apparently needs to be done as well.
Would the fact that my air pump is disconnected affect my fuel consumption?
Thanks!
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From: Connecticut
Fuel tank selector valve will only feed and return to one tank. Unless the hoses have been hooked up improperly, then it will feed off one tank and return to the other. If eliminating the tank is your goal you can take 2 pieces of tubing and hose clamps to couple the lines from the good tank to the supply and retun side going to the front of the truck. This eliminates the tank and the fuel switch entirely. Then take a couple short pieces of rubber fule line with a plug and cap off the ends of the selector valve, so where as you will be able to reconnect later when you choose to replace the rear tank and not have to replace the selector valve as well due to dirt inside.
Bad egr valve would contribute to poor gas milage as does low oil or colant.
With the air pump diconnected it sounds like someone was trying to eliminate the emissions.
Bad egr valve would contribute to poor gas milage as does low oil or colant.
With the air pump diconnected it sounds like someone was trying to eliminate the emissions.
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Ok I'm stumped.
Got the EGR tested and it works just fine. Havent taken the selector switch out just yet but I doubt that's the problem.
What else could be making that engine suck fuel so bad?
Timing has been checked, needs a new chain.
Has new air filter.
Plugs are in good shape as well as rotor.
New Fuel filter.
I am running 33" TSL super swampers, they will hurt fuel economy but this much? I'm getting close to 8 mpg.
Help!
Got the EGR tested and it works just fine. Havent taken the selector switch out just yet but I doubt that's the problem.
What else could be making that engine suck fuel so bad?
Timing has been checked, needs a new chain.
Has new air filter.
Plugs are in good shape as well as rotor.
New Fuel filter.
I am running 33" TSL super swampers, they will hurt fuel economy but this much? I'm getting close to 8 mpg.
Help!
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Tires size shouldn't effect it that much. But it really depends on how you drive it, where you drive it and gearing.. If you arn't easy on the throttle, it will hurt it, and it you do alot of city driving, it won't be as high as highway driving. Start, stop, start, stop... I have a 351, I run 35's with 3.50 gears. I generally get about 12 mpg. I got 12 mpg before I put the lift and tires on too, so it actually didn't hurt me at all. Yes this is actual mileage, with corrected speedo.
Have you always gotten 8 mpg, or did this just start?
Have you always gotten 8 mpg, or did this just start?
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The truck is new to me, so as far as historical gas mileage goes its tough to say.
As far as shifting, my tranny is a 4 spd but has the granny first, so its essentially a 3 speed.
I generally shift just below 3000, otherwise its a real slug. I had a 3L V6 toyota before and it seemed to have way more pep, it had 33's too.
Maybe my engine is tired. Possible? It doesnt burn oil, it does leak a bit but not enough to really show on the stick.
As far as shifting, my tranny is a 4 spd but has the granny first, so its essentially a 3 speed.
I generally shift just below 3000, otherwise its a real slug. I had a 3L V6 toyota before and it seemed to have way more pep, it had 33's too.
Maybe my engine is tired. Possible? It doesnt burn oil, it does leak a bit but not enough to really show on the stick.
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I don't know. You can do a compression test to see if the rings are bad or if something else is messed up. I did a compression test on mine and the compression is around 100 psi... Which is low. And I have alot of blowby as well. If your not burning oil, I don't think your engine can be too bad. Which rear end do you have? And what gears? How about a bad o2 sensor or dirty injectors?
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On the rear axle, there may be a metal tag on it. There will be some numbers, one should say something like 3.5 or 3.73. ect. Also on the door jam, it should say stuff about the codes. If you post those somebody should be able to decode them.
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Yeah. H6 is same as mine. According to my book that's the same from 81-87. That shouldn't get you 8 mpg. I'd look into the o2 sensor. I am not really familiar with how the fuel injection was setup in 86. Do you have any codes or check engine light. My 85 has no computerized stuff whatsoever, so i'm basically no help when it comes to that.
Lead Driver
Joined: Dec 2002
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From: Kuna ID
I had an 83 F-100 with a 300/4spd, I could go 250 miles on a tank of gas. After I lifted it with 33's, I could only go 150 miles. I think it had real tall gears though, something like 3:08. The 460 I have now, gets 8mpg when I am hauling my trailer.
I not real keen on EFI, but could something like a dirty O2 sensor or clogged injectors be contributing to this problem. Whens the last time the truck had a real good tune up?
I not real keen on EFI, but could something like a dirty O2 sensor or clogged injectors be contributing to this problem. Whens the last time the truck had a real good tune up?
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Tough to say when it had a real good tuneup. Its new to me and I brought it back to life. However I checked everything over and the plugs looked good as well as the cap and rotor.
Injectors could be hammered, however expensive to replace.
The 02 sensor is an idea for sure. I'll check into that.
As far as the vacuum/pressure test I'll have to check that out.
I'm getting about 150 miles off the front tank. (19 gal)
Injectors could be hammered, however expensive to replace.
The 02 sensor is an idea for sure. I'll check into that.
As far as the vacuum/pressure test I'll have to check that out.
I'm getting about 150 miles off the front tank. (19 gal)
Junior User
Joined: Dec 2002
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From: Clovis, NM
My 86 F250 351w,carb, 33 inch street killers and 4.10 gears gets 8 mpg and that is after I fixed the leaking gas tank and I baby it around town but when I get on it I can watch the gas tank needle drop!! my 88 bronco 351w fuel injection with 33 inch swampers 3.55 gears got 10 mpg
Last edited by 88bronco351; Jun 24, 2006 at 07:08 PM.