Duramax LBZ and LMM P0087 Low Fuel Pressure code


Summer comes, temps rise and the working trucks with relatively high miles start to set a P0087 code and go into limp mode.  I have been on the receiving end of numerous calls inquiring what to do.  This has prompted me to write this Tech Tip to help explain better what we are finding. 

What is happening to cause this?

The direct answer in most cases:  Injectors.   Simply put, the backflow or return rate is excessive so the pump does not keep up and rail pressure drops.  In some cases it could be excessive demand from a performance programmer etc. so I suggest return to stock programming before troubleshooting. 

How do I troubleshoot this situation?

Step one is simple:  Verify system restriction.  Just changing the fuel filter does not mean that the supply side restriction is OK.  Lines can pinch, get blocked etc.  To test, use our Fuel Filter Restriction Gauge  which is a tool that every Dmax owner should carry along on the road.  Supply side restriction runs normally in the 2-4” hg range on this gauge.  If it is any higher than 4”hg, start with a fresh filter.  If the restriction does not improve then you will need to trace lines back to tank from the filter housing and possibly open the tank to inspect the pickup assembly.  Added note:  Plastic housing fuel filters are cut rate leaky pieces of garbage and should never be used.

Step two:  This is actually a dealer test.  The dealer can use his Tech 2 scan tool to control the injection pump and increase desired rail pressure to max of 160mpa at idle.  The observed actual pressure should follow desired or at least be quite close.  If not then step 3 is necessary to eliminate the rail pressure relief valve as a possible leak.

Step three:  Bottle test.  See this document: http://www.kennedydiesel.com/docs/Shim%20mod%20Bottle%20Test%20etc.htm


Is there a work around fix?

Yes there are a couple of things that have been successful.

Lift pump

 Adding a lift pump setup like my Twin Pump Deluxe Kit has helped in many cases.  What this does is push fuel to the injection pump rather than making it draw the fuel from the tank.  Placing the fuel under positive pressure is a good thing.  This is something that I feel every Dmax should have so it is not like you are just changing parts or adding something on a whim.

ECM Programming

I have developed a tuning fix with my Kennedy Custom ECM Programming  that has been shown to keep the actual fuel pressures in line with desired under load.  I also alter the limp mode parameters to make the truck more useable, but have not deleted the diagnostics or the safety protection.  This tuning change may prove to be more of a band aid than a fix as your injectors are still likely to be in marginal to poor condition, so only time will tell how long it will provide relief.


How do I prevent this from happening to me?

I have no guaranteed answer for you, but what I can say is that the injectors are taking a beating from running dirty, air laden fuel with poor lubricity.  Testing of suspect injectors has shown backflow rates of 2x the factory spec or more.  GM has issued a document PI0474 identifying excessive clearance wear caused by dirt and debris as the cause.  I recommend 3 key things:  Added Filtration, Lift Pump, and Quality Fuel Additive as noted in my Tech Tip Duramax Injector Failures.  I can make no promises that your injectors will last forever, but something needs to be done and if dirt and debris is the cause, these items are a huge step in the right direction.