ISX mileage dropped suddenly

[Rawze]

(my thoughts)...

The stealers$its are not trained worth a stick to solve fuel mileage issues. Nor will any warranties cover it.

Also, having an OEM certified shop 'do it for free' is likely another big mistake. Its almost guaranteed that most of it was half-arssed repairs at best, as none of the OEM repair shops are worth 3 cents any more.

Putting back the systems typically should also not have caused the fuel mileage to drop a whole 2.5 mpg. It does not matter what you see the EGR valve doing.

The differences between a healthy engine WITH those systems in place vs,. all of them removed (and proper de-mandate programming) is not nearly that much. A healthy engine + healthy Aft-Systems --vs.-- only the healthy engine after, it typically only would be less about 1 mpg or less differences ... but not by a whole 2.5+ mpg change.

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(looking at it the other direction)...

When you see people that claim they have gained 2+ and 3+ mpg after removing those systems, it is because 1 of 2 reasons ...

A)> Their de-mandate program is lying to them now in their vehicle dash (very very common) .. and they have no accurate records of fuel consumption history, so they take things at face value.



B)> .. -- and/or significant engine/emissions systems problems that already existed --

Those emissions systems were already in quite the dire straights, face-plugged, or clogging the heck out of the exhaust, etc. and causing air flow restrictions that drop fuel mileage below normal.

Perhaps the EGR circuits clogged or acting up, and/or perhaps the Doser injector bleeding fuel into the exhaust due to it being leaky, etc.

It can also be due to the EGR piping, bad EGR sensors, maybe bad intake or exh. manifold sensor(s), and very often by a sooted up / restrictive EGR cooler, causing the turbo to over-spool all the time to overcome it. I.E.> old, sooted over EGR components, piping, and clogged engine sensors.

- It can also be other issues like stuck-open EGR valve, and other problems that cause the engine to run far less efficiently all the time.

-- and then when someone removes those systems, it relieves all of these related problems, and then the engine efficiency goes up by 2-3 mpg or more....

- BUT IT IS NOT SIMPLY BECAUSE THERE IS NO MORE EGR GAS!. IT IS NOT SIMPLY BECAUSE THE SYSTEMS ARE NOW GONE, OR HAVE BEEN REMOVED ALONE!!!


If this is truly 2+ mpg 'by the receipts to the pump' changed .. and nothing else external has changed like how heavy its loaded, driving mountains vs flat, etc..etc. and its a genuine comparison.. then yes.. something is most likely wrong.

Solving lower than normal fuel mileage issues starts by not giving it excuses to be low. Things like ...

== Ensuring there are not any fuel leaks, either internally or externally.

== Ensuring the Doser injector is not leaky.

== Ensuring the CAC is not leaky.

== Ensuring the turbo is not out of calibration, and that it is not over-spooling all the time for a number of various reasons.

== Ensuring all of the engine sensors are less than a year old, and are all reading correctly. This especially any EGR sensors like the EGR Delta-p sensor, EGR pressure sensor, the IMAP sensor, and others.

== Ensuring the EGR systems are not buried in soot or in your case, since they were unused for a long time, dried carbon buildup from lack of use... especially the insides of the EGR cooler and various sensor cross channels.

== Ensuring that the cross-piping that feeds the EGR Delta-P sensor, and the Exhaust pressure sensors are not clogged up with carbon/soot, and throwing everything off balance.

An example of this is that, even my own truck, dropped form 7+ mpg down to 4 mpg once just just from a Delta-P sensor reading badly due to soot clogging.


== Ensuring the intake and exhaust flow is unrestricted in any way. Ensuring the Decomp tube is not full of dried DEF fluid due to a leaky DEF injector, etc., and restricting exhaust flow.

== Ensuring that the regeneration cycle is not happening too often vs. driving hours/miles. - What does the regen history in Insite look like so far?.

== Ensuring the intake and CAC are not leaky. Ensuring the exhaust manifold, etc. is not leaky.. and ensuring there is no hidden block-plate still in place, restricting EGR gas flow, etc.

== Ensuring the EGR piping, intake piping, boots, clamps, etc. are not leaky.. and that any block-plates or other mods have been properly removed.

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SO... in your case.. take your pick. You say they 'undid everything' so what was 'undone; and what was replaced with 'new'? ...

Did they install ALL NEW CANS??.

Did they ensure the Doser injector (and def injector) was not leaky?.

Did they clean out the EGR systems and replaced the EGR valve + clean out (or replace) the EGR cooler?.

Did they replace all the intake sensors that were old, etc?.

Did they do proper CAC leak tests, check the DEF injector to ensure its not leaky?.., and chase down all the other stuffs that could have been the reason the systems were turned off.removed in the first place?.

For all anyone knows... it very well could have had some serious issues with those systems initially BEFORE the de-mandate .. and now they have come back. Makes someone ask how much of those systems did they replace ... vs. do the bare minimum to get it working again (and in the possible bad shape is was before someone defeated them).

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Its very reasonable to think that if 'they had to undo it' to get themselves out of some hot water, or get out of some complaints ... then they very well likely could have 'nickel-and-dimmed-it' as much as possible just to barely get the systems somewhat working again. This just to wash their hands of it, ... and in that case .. none of those systems are going to function worth a salt for very long without some serious issues after that.It is highly likely that no one gave a s#it about all the thing that I mentioned above, past getting it barely functional again and spending the least amount possible in the process.

Lastly.. it is VERY VERY EXPENSIVE to 'undo' a de-mandate .. and if it has been de-mandated for several years,.. the costs go up tremendously, especially on the engines that have SCR and DEF fluid. ALL of those pipes, filters, the tank, injector, .. everything that DEF fluid touches goes to s#it real fast after it is no longer used, and this causes big headaches for anyone who later decides to 'undo things'. Chasing down these kinds of issues becomes 10x worse after only a year or 2.

And last but not least.. did they use only 100% genuine OEM replacement parts???.

I.E.> It can be a daunting task with lots of replacement parts + chasing lots of secondary issues towards get the engine and its emissions systems back to a reliable state again long term.

(the beer is talkin')...
Frankly, I just don't see a repair shop doing that, OEM or otherwise, especially for free, or due to a mis-understanding after a sale, doing anything beyond the absolute bare minimum to get it out of their repair shop. This leaves all of the secondary headaches and issues that follow, back in the hands of the vehicle owner to end up footing all the bills for, chasing the rest of it down.