bad fuel economy - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 8 (permalink) Old 11-05-2010, 03:26 AM Thread Starter
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bad fuel economy

hey all of a sudden my truck went from getting about 16 to 18 mpg to like 5.. it seemed to drop once the temps started to drop.. any ideas as to why this would happen? also if i am running a push button switch for my glows how long is the limit for them to be on? im getting ready to put some zd9's in it. thanks

86 F-250 4X4..7.3 non turbo from an 89.. E injectors and pump turned up.. 4 speed..3.55 gears.. new dual 4" exhaust by diamond eye-- with the muffler > for now!
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post #2 of 8 (permalink) Old 11-06-2010, 01:35 AM
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Are you sure you are calculating your MPG correctly? 5PMg ive never heard of something that low. Are any of your brakes dragging, you Emergency brake on? Glowplugs wouldnt cause any issues with MPG. For your push button question, 10 seconds is what you will want to hold them on.

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post #3 of 8 (permalink) Old 11-06-2010, 01:44 AM
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Winter fuel will cause a drop in fuel economy, but not by that much. Not to sound like a smart ***, but is the truck leaking fuel?

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post #4 of 8 (permalink) Old 11-06-2010, 04:54 PM
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At 5 MPG the smoke trail from the tailpipe, fuel in the oil or coolant or leaking onto the ground would be the things I look for.

How long to push the GP button depends on which GPs you have:

Spade (older) type GPs = 10 - 15 sec cold.

Bullet (newer "fast start") type GPs = NO MORE than 10s or you WILL fry them.

That assumes you have OEM "BERU", Motorcraft/International GPs, if you have aftermarket ones, well pray.

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post #5 of 8 (permalink) Old 11-07-2010, 02:02 PM
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Low power? Hard start? White or excessive black smoke? More engine rattle?

Possible causes-

Dragging brakes (even caused by worn ball joints)

Bad air filter

Low fuel pressure

retarded timing

air leaks in fuel system

fuel leak

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That assumes you have OEM "BERU", Motorcraft/International GPs, if you have aftermarket ones, well pray.
Well put.

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post #6 of 8 (permalink) Old 11-07-2010, 09:13 PM
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You also want to check the muffler, if a baffle breaks loose it will back up and block flow. Usually it will sound different, and when you put your hand over the tail pipe it will have an even flow and possibly even whistle.

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post #7 of 8 (permalink) Old 11-07-2010, 11:50 PM
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Boss blew his headgaskets out on his 5.7L Vortec when the cat took a dump. Plugged that pig right up.

"Some people are educated beyond their intelligence."

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post #8 of 8 (permalink) Old 11-28-2010, 07:55 PM Thread Starter
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thanks for the info, no its not leaking any fuel and i haven't noticed any fuel in the oil or coolant... im thinking that the e brake cables are bad and not letting it release the whole way... seems like it really sucks down the fuel on the highway not so much around town... gonna save some money and replace the brake cables asap.

86 F-250 4X4..7.3 non turbo from an 89.. E injectors and pump turned up.. 4 speed..3.55 gears.. new dual 4" exhaust by diamond eye-- with the muffler > for now!
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