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mpg question?

1451 Views 25 Replies 10 Participants Last post by  vms
alright im new to diesels and don't know much about them but my 99 single cab 4x4 is stock except a 4" straight pipe exhaust and im only getting an average of 12.5 mpg. i know something isn't right. it should get better right? i drive everyday to college and this is killing my wallet.
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· ILLINOIS NORTHERN VP
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alright im new to diesels and don't know much about them but my 99 single cab 4x4 is stock except a 4" straight pipe exhaust and im only getting an average of 12.5 mpg. i know something isn't right. it should get better right? i drive everyday to college and this is killing my wallet.
First off welcome to Cummins Forum!
Nick
 

· Future Fly Boy!
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gears? tire size? type of tires? driving habbits? auto/manual? all of those take a toll on your mpg...things like a really dirty air filter, fluids that havent been changed in a while can also make your mileage drop...id start first with an aftermarket lift pump, make sure your vp is kept happy...
 

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Discussion Starter · #8 ·
the tires aren't very big, its an automatic, and i just recently replaced all fluids and filters, i dont drive hard at all. i haven't yet hand calculated it but i know its not getting very good... u can pretty much watch the gas gauge drop. about how much do lift pumps run?
 

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The price of a lift pump can be mild to wild. It all depends on your plans for the truck. If you’re going to do major mods go with a fass or an airdog. If you’re like me and don’t plan huge power. Go with something cheaper like a raptor or like I did and get a holly. Most of the guys hate the holly’s but their cheaper then a stock lift which is good for a budget guy like me.
 

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Any codes? I had the clock spring go out and I was getting 13mpg tops because it's related to the APPS and things went nuts. Also, it could be the APPS. There is lots of reading to do here.
 

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the tires aren't very big, its an automatic, and i just recently replaced all fluids and filters, i dont drive hard at all. i haven't yet hand calculated it but i know its not getting very good... u can pretty much watch the gas gauge drop. about how much do lift pumps run?
that might be part of your problem right there. try hand calculating it and report back. :thumbsup:

a fass or airdog will run ya $400-$500.
 

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Cycle to key to 'on' three times. This will read out any codes on the PCM and it will show P1693 if there are codes on the ECM. You will need a scanner to retrieve those.
 

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Discussion Starter · #14 ·
my friend wanted me to ask about a truck he is wanting to buy. its an 01 4x4 dodge cummins ext cab. the guy replaced the lift pump but he said the he let it go so long that it cost him 2400 to fix everything...could this damage the engine?
 

· Rescue Tower
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my friend wanted me to ask about a truck he is wanting to buy. its an 01 4x4 dodge cummins ext cab. the guy replaced the lift pump but he said the he let it go so long that it cost him 2400 to fix everything...could this damage the engine?
First welcome to the forum. Second, get familiar with searching. Your subject is covered in massive detail all over the internet, and this forum.

Summary: Factory lift pump doesn't feed adequate fuel to the injection pump (VP-44). IP's cost 900-1300 depending where you purchase from. Labor is extra if you can't / wont install it yourself. Minimum lift pump is a raptor. It comes with larger lines and can support mods. Holly is absolutely not recommended for this application and will wind up costing you additional pumps and probably an IP down the road. Install a fuel pressure gauge and maintain greater than 10 psi at all times. Now go read up on this subject.
 

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I got 25mpg on my truck when it was stock with the stock lift. That’s on a 2wd but my point is you don’t need a giant lift pump like a fass or air dog on a stock truck. Those pumps are made for trucks making big hp and are not necessary on a stock truck. I would upgrade to a bigger lift, but I don’t think it’s the root of your problem. Have you changed the fuel filter? I change mine twice a year. I just don’t want you to think a massive lift pump will solve your mpg problems.
Remember guys it sounds like a stock truck. You don’t need a fass or air dog pump on a stock truck.
 

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my friend wanted me to ask about a truck he is wanting to buy. its an 01 4x4 dodge cummins ext cab. the guy replaced the lift pump but he said the he let it go so long that it cost him 2400 to fix everything...could this damage the engine?
just ruined the VP from lack of fuel psi. should have no long term damage on the engine if replaced with a good vp and lift pump:thumbsup:
 

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Then maybe some of you that have more money than you know what to do with can buy fass or air dog fuel pumps for everyone. Not everyone can afford one of those pumps. I’ve never had trouble with Holly but then again I’m not after insane hp ether.
 

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I agree with vms. Having a bigger/better pump will not necessarily fix your mpg issues. Going down to 10mpg is not going to be solely from the lift pump. It could partly be because of this, but not the only reason. On the other hand, you need to get a better pump to keep that VP happy. If not, you'll be writing checks out for about $1,000 or so for a new one. Like said before, they need at least 10psi of fuel for lubrication. I keep mine at about 18-19 psi driving. It drops down to about 14 at WOT.
 
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