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Bad Fuel is the new black.

All the above are samples we have drawn of legitimate “bad fuel”.  Whenever possible, draw a sample yourself – from somewhere – to make sure whatever the shop has for you really came from the subject equipment/vehicle.



It used to be universal truth that if a diesel engine had good timing and no mechanical issues, all you needed to keep it running reliably for almost-forever was clean air, clean oil, and clean fuel.  (And still, for some, that was too much work.)


Things have changed.  Now you need clean diesel exhaust fluid (DEF) which has a shelf life of about two years unless stored where it is exposed to sunlight, synthetic coolant, synthetic motor oil sometimes with a weight that starts at zero, and diesel fuel isn’t what it used to be.  You need dozens of working sensors with sufficient voltage, and you need a driver/operator who will never, ever ignore the check engine light (CEL).


You all remember the claims about ten years ago for “vandalism” to off-road engines in construction, forestry and farm applications when federal regulations mandated ultra-low sulfur diesel (ULSD).  ULSD doesn’t have the lubricity that old-school diesel had and components of the fuel system – mostly pumps and injectors – would explode.  A lot of those claims were easy to resist, because of a recognizable pattern which became predictable, and through failure analysis – especially fluid analysis. 


Well, here we are in 2024 and I’m seeing an increase in claims for bad fuel ending in fuel injection system failures.  Now for the sake of this discussion I am excluding the well-known Duramax and Powerstroke high pressure fuel pump failures of the previous generation engines.  Those fuel pumps were replaced in the new generation engines.  Though, what I saw twice in one-week last month was a surprise.


2018 GMC/Duramax diesel, 30,000 miles:  arrives at the dealer in limp mode, with sooty exhaust and CEL on.  A scan discovers over a dozen diagnostic trouble codes (DTC’s) – mostly related to the fuel system.  Buried in there though, were a few relative to the exhaust aftertreatment.  The shop targeted the fuel system and told the customer he got “bad fuel.”  They saved nothing for evidence.  They said they flushed the fuel tanks (2), the fuel system, changed the filters and confirmed that the fuel regulator – downstream of the pump – had nothing in it.  So they buttoned it up and took it to the fuel station for fresh fuel and test drove it.  Not much improvement.  They told the customer it would cost $10,000 +/- to fix and to call his insurer.


2015 New Holland L230 skid steer/FPT 4-cylinder diesel, 1,830 hours:  arrives at the dealer non-drivable.  A scan discovers over a dozen DTCs mostly related to the fuel system.  With a few for exhaust aftertreatment.  The shop targeted the fuel system and told the customer he got “bad fuel” and needed a whole new fuel system.  They had the machine somewhat disassembled and had not saved any of the fuel they flushed but had one water separator filter reserved with dirt in it, and the secondary fuel filter had not been changed.  During inspection I noted the DEF injector had failed, the leaking injector had bleached the diesel particulate filter (DPF) housing.  Then I noted the selective catalytic reduction (SCR) muffler was removed, and I couldn’t find it.  The service manager confessed the DEF injector had failed, ruining the DPF probably because the SCR was taken to a shop that repairs them and they said it was too far gone and was not repairable.  Is that so?  The fuel water separator filter had tons of dirt in it that the shop pointed to as evidence of bad fuel.  Problem is that the side of the filter you can see into is the clean side – the filter action moves the fluid from the outside in.  So how did that get there?  We removed the secondary fuel filter that was not changed because that has the original fuel in it – or closer to the original fuel than anything they said they flushed – and sampled that for lab analysis.  We sampled the coolant, engine oil, and took a sample of DEF.  The machine was overall pigpen, it was filthy.  The heat exchangers were clogged with filth, the air filters were dirty, it showed a real lack of maintenance.  The engine oil was almost 2x too high over the full mark.  All the fluid samples came back with negative results – except for the fuel!  The fuel was fairly clean, and the analysis report warned us only to monitor it.  We cut open the filter and discovered the filter side was pretty clean also.  Our failure analysis report was sufficient for the carrier to sustain a denial of that claim.


Meanwhile, back to the 2018 GMC.  We had requested all the work orders, including the open WO…customer copies, internal copies, warranty copies – all of it.  We analyzed all the DTC’s and built a case where the DEF injector failed and the aftertreatment caused the ECU to throw all the fuel system codes.  Then we got the paperwork from the dealer.  These revealed that the DEF injector had failed and ruined the NOx sensor – both of which were replaced under warranty.  Further dialog with the shop revealed that they had diagnosed the DPF was ruined by the DEF injector failure.  They did not reveal this to me willingly.  I had drawn a sample of the fuel in the front tank, which proved to be perfectly clean on-road diesel.  Hmmm?  You know how hard it is to perfectly clean a fuel tank?  Research revealed that a faulty DEF injector causes all sorts of turmoil for the engine ECU, which basically recognizes that the engine cannot breathe properly, and it tries to mitigate this by controlling the fuel system, because it just lost control of the only thing it can control in the exhaust system beyond accumulating data – the DEF injector.  It throws more fuel at it, that doesn’t work, it pulls back fuel, it turns injectors on and off electrically, it decreases rail or manifold pressure, all while the CEL is on and the driver is ignoring that.  After a lengthy 3 party dialog including the insured and the shop, the service manager was fired, and the shop was going to repair the truck under warranty.

Tom Fergus handles claims for forestry, farm, construction, and specialty equipment. Service area is all of New England (except Rhode Island), New York: Upstate, Long Island, and Finger Lakes. Desk review on complicated claims outside of my area. Click here to see my mobile office.






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