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Sudden mileage drop


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We’re in a 2003 pulling a 28’ camper from OK to Breckinridge, CO down I-40 toward Amarillo. Fuel mileage had suddenly dropped to 8.5mpg. Air filter has been checked, new tires are on and truck was just aligned, fairly new fuel filter, valves were recently ran, oil level doesn’t seem to be rising, no noticeable smoke coming out of exhaust, truck isn’t overheating, possibly feels a little weak but still running well. Any suggestions on what the problem might be? Should we find a diesel mechanic or keep driving? Thanks for any help!

Edited by DownHomeDiesel
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Could use a little more information.  Approximate combined weight, mph traveling, rear axle ratio, tire size, method of calculation. etc.

 

A couple of factors that can lower fuel mileage.

 

    * headwinds

    * elevation change - Pocola - OK 500 feet, Amarillo TX -3,600 feet

 

- John

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Hey John! This is partially in comparison to a previous trip in the same truck pulling the same camper on the same road at the same speed with lower temps and less headwind this trip than last. We don’t have approx weight of the 5th wheel camper, but truck is 2500 automatic 4WD 3:73 ratio. It has 220,000 miles and we’re on 265/70/17 tires. We calculated mileage based on GPS miles from one fuel station to the next and how many gallons to fill up at the pump, which is how we’ve calculated on previous trips. 

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Good information - but, more questions.

 

*  Are you the original owner of the truck? 

*  Are the injectors still original? 

*  Are you using a tuner?  

*  You said "Same road at the same speed", but you didn't say what the speed was.

*  Is your transmission an automatic or a six speed manual?

 

From your information given so far, I would just keep driving and continue to monitor fluid levels and and gauges.  Also, stop occasionally to check tire, brake, and wheel bearing temperature on both vehicles.

 

- John

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Not original owners and not sure on injectors. No tuner or part upgrades except steering components.  We just put T-steering and new mopar steering box upgrade on it Wednesday night before having it aligned.

sorry, 70mph.  It is my dad’s truck so I’m not as familiar with it as I’d like to be.  He “feels” it doesn’t have the power it should. 
Automatic trans.

I’ve been watching the oil level for a rise.  I can’t smell diesel but it is windy.  We are now headed north towards I-25.  MPG’s seem to be holding steady.

I’ve been thinking weak or leaky injector? 
Thanks again for helping.

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This is where an infared thermometer shines. Could possibly be a brake dragging. You could put your hand on each wheel at every stop and see if they're about the same temp, but a cheap (harbor freight) infared thermometer works best. You say 8.5 mpg, but you don't say what it was last time. One mpg on two different trips, even though same route and conditions isn't unusual. Could very well be an injector starting to die. Like was said, keep driving and watching. If it gets worse, you may have to find a mechanic, but for now I'd just continue on.

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I've got to ask how many miles on the truck? Then ive got to askhave you ever replaced injectors? Injectors are only good for 100k to 150kmiles and should be replaced.

 

Reading back now I would say there is a injector(s) that are most likely leaky and/or not spraying good.

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We did make it to Breckinridge but power did seem to dwindle a bit more and when I put it in park it high revved for about 10 seconds this time.  Backing in the camper there seemed to be a stutter of some sort.  Not knowing the total age of injectors I’ve suggested they get their minds ready to buy new and install before the ride home.  
We are shopping online but does anyone have a suggestion for a place not too terribly far where we could take the injectors and have them tested and buy new if needed. And/or suggestions on a good mechanic?  We don’t have a big arsenal of tools with us. 
 

I noticed the 5th nut back on the fuel line coming off the rail is wet.  I’m wondering if we could be leaking fuel and/or air there and causing the symptoms also.

 

thanks again for all the help.

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On 7/1/2022 at 6:09 PM, Mopar1973Man said:

I've got to ask how many miles on the truck? Then ive got to askhave you ever replaced injectors? Injectors are only good for 100k to 150kmiles and should be replaced.

 

Reading back now I would say there is a injector(s) that are most likely leaky and/or not spraying good.

A little more than 220,000 on the truck.  Previous owners didn’t mention any injector changes. 
 

We had to move it across the parking lot.  I could have swore I heard a pingy rattle sound coming from the engine area.  We are still looking for a local mechanic.

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@DownHomeDiesel, I highly recommend calling High Country Auto Specialist in Silverthorne.  Ask for Curt - he is the owner.  He is a reputable guy.  He has the proper test equipment and knowledge to diagnose your problem.  The address is 150 13Th St #1, Silverthorne, CO.  Phone 970-513+9148.  

 

- John

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1 hour ago, DownHomeDiesel said:

A little more than 220,000 on the truck.  Previous owners didn’t mention any injector changes. 
 

We had to move it across the parking lot.  I could have swore I heard a pingy rattle sound coming from the engine area.  We are still looking for a local mechanic.

Injectors are shot. Injectors need to be changed ever 100k to 150k miles other than that engine damage might occur.

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19 hours ago, DownHomeDiesel said:

I noticed the 5th nut back on the fuel line coming off the rail is wet.  I’m wondering if we could be leaking fuel and/or air there and causing the symptoms also.

I would fix that before doing anything else.

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Doesn't help either with a weeping line. Still in all 220k on injectors I would pull all 6 injectors and crossover tubes and replace all 6 crossover tubes, o-rings and injectors. I highly suggest getting +50 HP injectors from @dieselautopower and then I know all 6 are flow matched and tested. This will resolve all this issue.

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The crossover tubes don’t need replaced unless there is a problem. 
 

Unless the OP want to install an adjustable boost elbow, as well as boost and EGT gauges then I would likely not run +50’s on a stock CR
 

Is the motor a Cali, SO, or HO motor? What trans? 

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  • 2 weeks later...
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Thor when I did the injectors I did what 6 random injectors that were not not pop tested and flow matched so when I ordered them I picked the +50HP injectors from @dieselautopower and did the crossover tubes because after 180k miles the crossover tubes are wore out internally. Ive seen several photos of crossover tubes after 150k miles that wore out from high pressure and fine particules pushed through. I chose the +50HP because they are the smallest injectors i could get flow matched. I even drove to @dieselautopower and pick the parts up in person. As for running no EGT issues, small 2 MPG gain over the 170k injectors i pulled out.

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On 7/14/2022 at 5:57 PM, Mopar1973Man said:

Thor when I did the injectors I did what 6 random injectors that were not not pop tested and flow matched so when I ordered them I picked the +50HP injectors from @dieselautopower and did the crossover tubes because after 180k miles the crossover tubes are wore out internally. Ive seen several photos of crossover tubes after 150k miles that wore out from high pressure and fine particules pushed through. I chose the +50HP because they are the smallest injectors i could get flow matched. I even drove to @dieselautopower and pick the parts up in person. As for running no EGT issues, small 2 MPG gain over the 170k injectors i pulled out.

 

 

Hoping we don't have to wait for this set of injectors to wear out before we visit again!  It was great to meet you in person!

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2 hours ago, dieselautopower said:

Hoping we don't have to wait for this set of injectors to wear out before we visit again!  It was great to meet you in person!

 

Not a problem you'll most likely get to see me on the trip to Pigeon Forge TN. I've got to pass through Utah. 

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