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HWeaver184
HWeaver184, Dodge Mechanic
Category: Dodge
Satisfied Customers: 220
Experience:  ASE certified all 9 fields, specialize in diesel, trans, drivability. With chrysler 4yrs
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5.9 have lag or flat spot..push..accelorator..it shifts down .runs

Resolved Question:

resently purchased 2002dodge with 5.9 have lag or flat spot at intermediate speed. push on accelorator and nothing happens until it shifts down .runs well otherwise .highway mpg 16 ,is this normal, hoped to do better,any suggestions?
Submitted: 7 years ago.
Category: Dodge
Expert:  HWeaver184 replied 7 years ago.
5.9 liter gas engines are naturally gas hogs.... there isnt much you can do for that but add a programmer, air intake and maybe a different exhaust system. When you say nothing happens until it down shifts, do you mean you can full throttle it and it just wont down shift? Alot of these trucks will get to a certain speed and it will catch the transmission where its going just fast enough that it will stay in the present gear, but is going too fast to where it will not downshift to keep it from overreving the engine. The only thing you can do is adjust your kick down cable to the transmission and this may help you, but if you are describing what i think you are, this is just a characteristic of a transmission. If you could, please ellaborate on the problem a little more
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Customer: replied 7 years ago.

5.9 DIESEL engine lag in overdrive at speeds below 60mph , sorry i didnt specify DIESEL. 16mpg normal ? 305/16 tires 3.55 gears

Expert:  HWeaver184 replied 7 years ago.
well on a diesel, yes you will have turbo lag on it when it is in lock up . BUT you should have more gas mileage than that. If this truck has over 100K miles or even over 50 thousand miles, i would replace your lift pump on the truck. If this lift pump goes out, you will be buying a 1500 dollar injection pump shortly after. Also when these lift pumps goes out you will see some power and gas mileag losses. I would go to oreillys and get a high flow block mounted lift pump and install it. You should be able to see a big increase in gas mileage after that install. Unfortunately depending what the previous owner did, that injection pump is really only good for 100K miles
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Customer: replied 7 years ago.

HWeaver184 i did not get to change lift pump yet,in the last 3 days when I started my truck I could not go over 20 mph ,had no throttle response even when I held it to the floor. After about a half mile the engine took off like normal. Is this another sign my lift pump is bad. Customer/p>

Expert:  HWeaver184 replied 7 years ago.
Definitely a sign of a lift pump failure. I can guarantee if you let the truck sit for a minute or two when you know its doing it, it will clear. Be careful though, it may be also having the injection pump go down too. If that lift pump has no flow anymore and the injection pump is pulling enough vaccum to suck the fuel from the tank through your lift pump, then you may be looking at changing your injection pump. We will cross that bridge when we get there though. If you change that lift pump and your able to get it running ok after the lift pump, you should be ok. Keep in mind though, best rule of thumb is to change your lift pump every 40 to 50 thousand miles and injection pumps last about 100,000 miles.
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