Hi all, it's been a while. My truck finally hit 100K this past weekend and was wanting to know what maintenance needs to be completed? I am also getting only 12 MPG pulling a 1700 pound Polaris with a windshield on a 14 foot single axel trailer. I would think I should be getting at least 15 MPG. Any ideas of where I can start to look for issues? Thanks.

 

16' box trailer with laminate flooring and pex tubing in it. 19 out loaded, 21 back unloaded. 600 mile round trip at 50 -70mph.

 

There are a ton of variables you didn't mention….

Speed of travel?
Gearing of truck?
Tire size?
Weight of trailer?
Elevation?
Lots of start and stop travel?
Lots of hills?
2wd or 4x4?
Health of the trans as you list a new valve body "on the way here" in your signature.

I can load and drive my truck where it gets 12MPG, I can load and drive it where it gets 21 MPG.
It make a HUGE difference in HOW you use it.

Hope that helps.

 

Well said.....

 

Thanks for the responses, I guess I should have mentioned the questions you asked. Below are the answers.

Speed of travel? 65 - 70
Gearing of truck? 3.55
Tire size? Stock
Weight of trailer? About 3000lbs loaded
Elevation? Very near sea level
Lots of start and stop travel? Mostly highway, slow down through some towns, and one town is a little stop and go. 90 miles one way.
Lots of hills? No, pretty flat land, south Texas.
2wd or 4x4? 2wd
Health of the trans as you list a new valve body "on the way here" in your signature. Transmission seems good, the valve body was installed a few years back, I just never updated my Signature.

 

12MPG seems low for that set up and usage.

It could be a simple as a cut lower boot loosing boost.
The boots like to rub on the inside of the fender and get a cut in them over the years.
You loose the power so slowly as the cut opens up slowly you never notice it, but when you work the truck without the boost the MPG suffer.
It could be loosing boost at other locations as well.
Do you have a boost gauge?

 

I do have a boost gauge, pulling at 65 or so it boots around 13-14 psi. At 70 it is usually boosting 16-17 psi. Both while pulling the setup I have described. Thanks for the advise, I have one thing to start looking at.

 

Thats definitely not the mileage you should be seeing with a load like that. Is the VP original/factory? Whats your running fuel pressures?

 

Running fuel pressure is about 5 psi towing, keep in mind I have the in tank solution provided by Dodge under warranty. From the research I have read that PSI is fine with the volume the in tank solution is suppose to be providing. I hope I don't start a war with that last statement.

 

No war from me.....but thats NOT enough fuel pressure to the VP. Even though this was the Dodge/Cummins/Bosch fix for the inadequate OEM Carter lift pump which failed repeatedly, the in-tank pump proved equally as horrible. And yes, there are plenty of people who run low fuel pressure and stock lift pumps but that still doesnt mean its good for the VP.

Because what happens is if this is the original factory VP the low fuel pressure causes excessive heat build up while the VP is running and this heat is detrimental to the PSG (computer). Also because of low fuel supply you get reduced lubrication which wears on the internal components like the rotor and timing piston. These problems became exaggerated too at the introduction of ULSD in 2007. Even though it still works, these fuel systems weren't designed to be run on that fuel. Therefor the wear and tear eventually affects the timing piston/sleeve and rotor/distributor which results in loss of power and loss of fuel mileage.

That said, over the years the VP has been greatly upgraded with better components and new computer which combats the fuel pressure and lubrication issue better. This by no means is reason to run low fuel pressure either as the only variable keeping the VP cool and lubricated is the "excess" fuel which passes through it.

So, am I saying this is your low fuel mileage problem.....? No, not really but I'm saying that it "could" be if you still have the original factory VP. There's other things which can affect fuel mileage, like a dirty IAT or MAP sensor. Especially if the truck has an exhaust brake.

 

No Exhaust brake. The VP44 was replaced under warranty, so not sure if it is an upgraded solution when they put in the in tank pump. How can I check if my VP 44 is starting to slowly die on me? Thanks.

 

Sadly no, the warrantied VP's were merely another factory spec VP sitting on the OEM stock shelf. The only VP's which saw any upgrades were the aftermarket ones. Even at that, you have to make sure you get a VP from the right source otherwise you can still get one with an old computer.

Also, there is no way to tell if the VP is showing signs of wear except for increasing the fuel pressure/volume. Again.....what happens is over time is the low fuel pressure causes the timing piston to wear as the low pressure side of the VP is forced to provide itself with enough volume to run the engine. So in turn the timing piston looses the ability to reach proper fuel timing without that necessary pressure from the fuel pump and mileage/power is slowly reduced. By installing a fuel pump which is now capable of higher pressures and volume the timing piston regains optimal timing and fuel mileage and power is regained. But.....understand that even though this sounds like a good thing, if this happens after installing a quality fuel pump, the VP may not last long.

 

Thanks for the information. Another thought I just had was about a possible boost leak, if that was the case would it be possible to build up enough boost pulling a hill (Texas Hill Country this past summer) to open the waste gate? I saw my boost gauge hit 21 PSI then immediately go to 20 and stay there while loosing speed. Again, same setup pulling the little trailer with the Polaris.

 

You very well could have a boost leak since you have an EZ and those boost figures are about stock. But.....since you have an HY turbo, have you "J" hooked the wastegate? If not then dont look for a boost leak until you get a "J" hook on the wastegate and see what the boost goes up too. Boost should get up to around 25-28 psi with that EZ. Its not going to help the fuel mileage much, if any, but you should be building more boost than 21 psi which will help with EGT's while towing.

 

are you getting a lot of black smoke?
if you are..
think intake leak, boost boots, intercooler and so on
also think cracked exhaust manifold..might be dumping too much air
and not making boost soon enough..

also you might consider larger injectors, if you haven't already..I like my 75hp injectors..

off the wall thought..how's your IAT sensor?

-dkenny