At a loss.......literally

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Wapiti7

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New Mexico
Ram Year
2003
Engine
5.9
Good morning everyone, looking for any advice possible. I have a 2003 dodge with a 5.9 Cummins. 375,000 miles, new injectors two years ago, and a new lift pump last summer. I live at higher elevation and going up over mountain passes the truck slows down to approximately 28 miles an hour and will not go any faster until I reach the top of the pass at which point it dies. So I throw it in neutral hit the key and it fires right up and off I go. On flat ground this never happens. I checked the turbo and it seems to be in good shape as well but I can't afford to just start throwing hundreds of dollars worth of random parts at the truck. Seems to be a fuel issue but not sure. Thank you for any input
 

06 Dodge

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Forest Grove, Oregon
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2022
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6.7L CTD
Good morning everyone, looking for any advice possible. I have a 2003 dodge with a 5.9 Cummins. 375,000 miles, new injectors two years ago, and a new lift pump last summer. I live at higher elevation and going up over mountain passes the truck slows down to approximately 28 miles an hour and will not go any faster until I reach the top of the pass at which point it dies. So I throw it in neutral hit the key and it fires right up and off I go. On flat ground this never happens. I checked the turbo and it seems to be in good shape as well but I can't afford to just start throwing hundreds of dollars worth of random parts at the truck. Seems to be a fuel issue but not sure. Thank you for any input
When was the last time you changed the fuel filter, I hope you using a good one like the 5 micron Baldwin PF 7977, also if you use B20 bio diesel when if at all have you treated your fuel tank for algae?
 

tron67j

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Maryland
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2018
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6.4 Hemi
Have you checked your fuel pressure, it should remain within a few points at level and at the peak. Are you running a filter like K&N? A good regular air filter is preferred. Also, maybe a bad MAP sensor?

Good luck
 
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Wapiti7

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New Mexico
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2003
Engine
5.9
The fuel filter gets changed with every oil change. I've been running a K&N since I bought the truck new in 03 and this is a new problem. I run fuel treatment with almost every fill up. Not familiar with the MAP sensor or it's function.
 

Choupique

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Dec 25, 2022
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Location
Louisiana
Ram Year
2018
Engine
Cummins
You need to measure fuel supply pressure and manifold pressure under load to really troubleshoot this.

Are you getting black smoke while holding the pedal down and losing speed?
 

CanuckRam1313

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If I'm not mistaken, the 5.9's have the VP44 injection pump.
These are known to cause issues from time to time with their diaphragms, etc.
Perhaps an injector is acting up?
 
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Wapiti7

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New Mexico
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2003
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5.9
If I'm not mistaken, the 5.9's have the VP44 injection pump.
These are known to cause issues from time to time with their diaphragms, etc.
Perhaps an injector is acting up?
I believe it does have a VP44 but it would seem like all of the injectors would be involved. It acts up like I described when it's under a load going up a steep grade or hammering down in 4 wheel drive in the snow.
 

Smokeybear01

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2005
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Cummins 5.9
No black smoke at all
My first thought was turbo because of the altitude, but if there is no black coal pouring out the pipe, then it's definitely not getting enough fuel. I would assume that you have a problem with power at all altitudes if it's not the turbo. Sorry I can't just tell you what it is. Good luck
 

Choupique

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2018
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Cummins
Sounds like a fuel problem to me. Rig up a way to read fuel pressure at the pump while mashed out up the mountain and check vs internet information. May be a clogged tank strainer, bad lift pump, anything else involving fuel delivery
 

Fjr vfr

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Hanover VA
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2008
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6.7 Cummins
Are you getting any codes? Plug in a code reader and check for fault codes
It sounds to me like the fuel over pressure check valve on the fuel rail
Some of them have a weak spring and release pressure under heavy loads
Another thought might be a weak lift pump in the fuel tank
 

Ram1958

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Carstairs AB
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Hemi 5.7
Pull the sending unit and check the pickup filter. Most likely clogged after all those years.
 

CaptCurt

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Waynesburg
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2009
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Hemi 5.7
Good morning everyone, looking for any advice possible. I have a 2003 dodge with a 5.9 Cummins. 375,000 miles, new injectors two years ago, and a new lift pump last summer. I live at higher elevation and going up over mountain passes the truck slows down to approximately 28 miles an hour and will not go any faster until I reach the top of the pass at which point it dies. So I throw it in neutral hit the key and it fires right up and off I go. On flat ground this never happens. I checked the turbo and it seems to be in good shape as well but I can't afford to just start throwing hundreds of dollars worth of random parts at the truck. Seems to be a fuel issue but not sure. Thank you for any input
I don't know if diesels have catalytic converters or not, but sounds like what my car did w/a gas engine. Could also be partially plugged mufflers.
 

Smokeybear01

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US-NW Coast
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2005
Engine
Cummins 5.9
There's a valve that resembles a Schrader tire valve on the back of the fuel filter housing. With the right fitting it takes less than 5 minutes to check your lift pump pressure. Dodge says you should have 5 PSI minimum. After market liftpumps are usually pushing 15-20 PSI. If it's low, your lift pump is failing or like Ram1958 said, the pickup filter is clogged. IF i'm not mistaken, your truck has the lift pump in the tank. If you're getting a low PSI reading you're looking at removing the bed or dropping the tank (it's part of the sending unit assembly) Either way it's a pain in the ****. Let us know when you get it figured out. There are other parts to the Cummins fuel system, but nothing else points to a loss of power like your describing. Good luck,
Quick edit here, I mistook your 2003 for a 2008 in which case you might have the fuel lift pump on the block or behind the fuel filter. Much much easier to remedy.
 
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