TECHNICAL QA

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I have a 2001 Sil­ver­ado with 92,910 miles on it. Re­cently I had a re­duc­tion of power. I had some­one check the OBDII sys­tem. The code is a P0093 Large Fuel leak .... The truck is com­pletely stock. I have owned it since it was new.

I checked the oil and it smells Ok and is not above full. I do not sus­pect it be­ing in­jec­tors. Knock on wood; I have not had any prob­lems with them yet. Can you share with me what I should try or eval­u­ate next. I have looked and smelled for fuel leaks. Fuel fil­ter was changed 4,200 miles ago.

Any as­sis­tance would be ap­pre­ci­ated. Re­gards, Scott Via Email The Di­ag­nos­tic Trou­ble Codes P0093 ap­plies to the 2001 model-year Du­ra­max. This trou­ble code was up­dated for the 2002-2004 model year en­gines, and re­ceived a new num­ber - P1093. Each refers to the same problem. P0093/P1093 are de­fined as “Fuel Sys­tem Large Leak De­tected”, which could mean that one or more in­jec­tors are ex­pe­ri­enc­ing a high fuel-re­turn flow rate. Peo­ple usu­ally start look­ing be­neath the truck for signs of fuel when they read this code de­scrip­tion, but this isn't that kind of a leak. Let's have a look at these sort of trou­ble codes to pro­vide a lit­tle more in­sight into what they mean and how to deal with them. Most P0089, P0093 & P1093 trou­ble codes oc­cur due to a problem with the fuel sup­ply or a pres­sure mis­match within the high-pres­sure fuel rail sys­tem. A plugged fuel fil­ter, an air leak in the re­lated fuel lines be­tween the engine and the fuel tank or a de­fec­tive fuel fil­ter base can all pre­vent the Bosch high-pres­sure pump from gen­er­at­ing the de­sired fuel-rail pres­sure that is com­manded by the com­puter. GM added a fuel sup­ply test port to each Du­ra­max 6600 engine – near the al­ter­na­tor on the front of the engine. This port is used to prime the fuel sys­tem at the DMAX fac­tory in prepa­ra­tion for its ini­tial start-up. Ad­di­tion­ally, the test port can also be used to eval­u­ate the fuel sup­ply sys­tem when di­ag­nos­ing an engine start­ing or run­ning problem. The brass Shrader valve is cov­ered by a black plas­tic cap. Pres­sure/vacuum gauges can pro­vide valu­able in­for­ma­tion to aid you in eval­u­a­tion of your truck's fuel sup­ply sys­tem – like that avail­able from www.kennedy­diesel.com. Un­der nor­mal cir­cum­stances, the gauge should read 5” of vacuum or less with the engine idling. Re­place the fuel fil­ter if more than 5” of vacuum is present at the fuel test port. There's a spe­cific fuel-rail pres­sure test that ex­am­ines the fuel pres­sure at 2000-RPM and again at 3000-RPM. The dif­fer­ence be­tween ac­tual & de­sired fuel-rail pres­sure must not ex­ceed 20-MPA (mega Pas­cals), as mea­sured with a Tech II scan tool. If the dif­fer­ence be­tween

MOST P0089, P0093 & P1093 TROU­BLE CODES OC­CUR DUE TO A PROBLEM WITH THE FUEL SUP­PLY OR A PRES­SURE MIS­MATCH WITHIN THE HIGHPRESSURE FUEL RAIL SYS­TEM.

the ac­tual & de­sired rail-pres­sure ex­ceeds 20MPA, the GM ser­vice test pro­ce­dure winds its way through the var­i­ous pos­si­bil­i­ties for a low rail pres­sure, such as high fuel re­turn rates due to faulty in­jec­tors or leak­ing fuel-re­turn lines, a leak­ing fuel-rail pres­sure re­lief valve, and con­cludes with ei­ther an FRP (Fuel Rail Pres­sure) reg­u­la­tor or high-pres­sure in­jec­tion pump re­place­ment.

A more detailed fuel re­turn flow test can be per­formed by the dealer tech where he uses a set of grad­u­ated cylin­ders that al­low for a pre­cise mea­sure­ment of fuel re­turn flow for each bank of in­jec­tors.

Once the cheap and easy items are elim­i­nated (like the fuel fil­ter or ob­vi­ous fuel leaks), the most likely cause usu­ally winds up be­ing the in­jec­tors. Let us know what de­vel­ops. Thanks for writ­ing.

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