PLEASE help me! VNL670 with an ISX CM2350 4.4 MPG!

[VNL670]

(07-06-2018 )smorgan87 Wrote:  That oil coming out an injector would have me real nervous. I might would wanna run a compression test.

It was actually an O'ring that goes around the fuel quail (I think that's what they are called).

[ammjay61]

So, did this story end up having a happy ending? Were the overhead settings the culprit, did your mileage come up?
Sometimes these threads are like books from the library where someone the out the last two or three pages.
Hope you ended up deciding what the issue was.

[walterk]

(06-26-2018 )Rawze Wrote:  Just for reference there hammerhead, on a 2350 with egr still active, a couple psi higher than a demandated truck if it is using a lot of egr gas.


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What is the rear ratio of the truck? What is the mileage? - I did not see it mentioned.

Like hammerhead has said,.. has anyone verified that the truck has the correct program in it based on the engine ser#?. I.E.> Make sure someone did not "up the hp".

* Has anyone bothered to look at the decomp tube and verify it is not partially clogged? Reference: http://rawze.com/forums/showthread.php?t...07#pid1807

* Has anyone bothered to see if the Doser injector behind the turbo is leaking fuel?

* Has anyone bothered to pressurize the CAC and check it for leaks? -- How about pressurizing the entire engine between the intake filter and the back of the turbo and checking it for leaks as well?

* Does the truck have an after-market CAC unit on it? - Many brands of after-market CAC uints are very restrictive and cause fuel mileage losses.

* Does it have an after-market EGR cooler on it? -- Same thing, they can rob you of fuel mileage and in fact many have even caused engine damage due to excessive egr temps.

* Anyone bothered to pressurize the fuel tanks and check the lines for leaks?

* Does it pass a leak-down test? Reference: https://youtu.be/eH9GRkeozTM

* Anyone bother to flow-test or even inspect the the SCR unit for clogging?

* Anyone bothered to do valve adjustment?

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It the mean time ...

Like Hammerhead said, slowing down to 63~ish will help -- A LOT!. So will driving by your boost gauge and limiting boost to about 15 psi or so as a good start. I am not saying this as a replacement to any fuel mileage loss problems the engine or truck may have,.. but it will definitely help mitigate losses. This is especially true while you figure out how to get the fuel mileage back up to normal levels. Better driving habits always lead to higher profits and less down time.

Continuing on this subject....
i am having a fuel mileage drop from 8.0 mpg to 7.3, albeit over a 3 year period, but I still don't like it.
I am following some of the tests recommended and this one caught my eye.

"* Has anyone bothered to pressurize the CAC and check it for leaks? -- How about pressurizing the entire engine between the intake filter and the back of the turbo and checking it for leaks as well?"
I have a tool to test CAC, but how do you pressurize the engine between the intake air filter and the back turbo? Any clever ways you guys have to make it easy and practical? Plug it up with rags...?Thanks in advance for your help.

[Rawze]

(04-13-2025 )walterk Wrote:  Continuing on this subject....
i am having a fuel mileage drop from 8.0 mpg to 7.3, albeit over a 3 year period, but I still don't like it.
I am following some of the tests recommended and this one caught my eye.

"* Has anyone bothered to pressurize the CAC and check it for leaks? -- How about pressurizing the entire engine between the intake filter and the back of the turbo and checking it for leaks as well?"
I have a tool to test CAC, but how do you pressurize the engine between the intake air filter and the back turbo? Any clever ways you guys have to make it easy and practical? Plug it up with rags...?Thanks in advance for your help.

using block plates or pipe plugs...
ref: https://rawze.com/forums/showthread.php?...21#pid8321

[walterk]

Inflatable pipe plugs! Super cool! Thanks again. EVAP machine a bit pricy though.

[walterk]

Any way to use that EVAP machine to find air leaks in the truck/trialer air system? I am courious if it would be able to fill all the little air lines with enough smoke to pin point small leaks. Some of the air lines underneth the cab are literally impossible to get to with a soap water and a spryer. Some trailer lines are just as bad. Obiously, that is only if the smoke is harmless to all the internal componetnts. Thanks for any info on that.

[mikkhh]

How good would be to test using AC leak finder sniffer that uses 95% nitrogen and 5% hydrogen gas mix?

Leak sniffer is lile 300 + gas mix and bottle. So I think around 500 would cost the kit. Is it worth considering or trying?

[Rawze]

Soapy water while the system is pressurized is your friend with regard to air lines.