Dyno Day

Published in the December 2008 Issue December 2008 Cummins, Duramax, PowerStroke

DMAX TECH

FICM DIFFERENCES

YOU MAY OR MAY NOT BE FAMILIAR WITH THE THREE-LETTER NAMING BEHIND GM'S DURAMAX TURBO DIESEL ENGINES. THEY REPRESENT THE DIFFERENT GENERATIONS OF THE DURAMAX SINCE ITS INTRODUCTION TO GM'S LIGHT-DUTY TRUCKS IN 2001. THE FIRST GENERATION OF THE DURAMAX IS KNOWN AS THE LB7. IT WAS FOLLOWED IN MID-2004 BY THE LLY, WHICH WAS REPLACED IN 2006 BY THE LBZ. THAT WENT HALFWAY THROUGH THE 2007 MODEL YEAR WHEN IT WAS REPLACED BY THE EMISSIONS-CONTROLLED LMM, WHICH IS IN ALL CURRENT NEW GM PICKUPS.

THERE ARE A FEW KEY DIFFERENCES THAT SET THE ENGINES APART. THE LB7'S INJECTORS WERE LOCATED BENEATH THE CYLINDER HEAD, WHILE THE LLY, LBZ AND LMM ALL HAVE THE INJECTORS ON THE OUTSIDE OF THE HEAD. WITH THE EXCEPTION OF A LIMITED RUN OF CALIFORNIA MODELS, THE LB7 DID NOT HAVE AN EGR (EXHAUST GAS RECIRCULATION) SYSTEM, WHICH THE OTHER THREE DO. THE ENGINE BLOCK IS VIRTUALLY INTERCHANGEABLE BETWEEN THE FOUR GENERATIONS.

BUT THE BIGGEST DIFFERENCE BETWEEN THE FOUR GENERATIONS LIES IN THE FUEL INJECTION CONTROL MODULE (FICM). ACCORDING TO WADE BOYD OF CUSTOM AUTO (AND FORMERLY OF ATS DIESEL), THE DURAMAX'S FICM CAN BE COMPARED TO THE EVOLUTION OF THE AVERAGE DESKTOP COMPUTER. THE PROCESSING CAPABILITIES OF THE LB7'S FICM FROM 2000 TO EARLY 2004 WERE ADVANCED FOR THE TIME PERIOD, BUT CAPABLE OF MORE PERFORMANCE. WHEN THE LLY WAS RELEASED IN LATE 2004, IT HAD MORE FUEL MAPPING TABLES ADDED TO IT, BUT WAS STILL LIMITED TO ITS DATA PROCESSING ABILITY. SO WHEN AN EFI LIVE TUNER IS MODIFYING TABLES, HE HAS MORE TABLES TO CHANGE IN AN LLY VERSUS AN LB7.

BUT THE TABLES AND DATA PROCESSING CAPABILITY DIFFERENCES BETWEEN THE LLY AND LB7 ARE ALMOST INSIGNIFICANT COMPARED TO THE ADVANCES IN THE LBZ'S FUEL INJECTION CONTROL MODULE. ACCORDING TO BOYD, THE LBZ CAN PROCESS DATA MUCH FASTER THAN THE LLY, ALLOWING IT TO RUN MORE COMPLEX FUEL TABLES AND OPERATE AT A HIGHER ENGINE SPEED WITHOUT ANY IGNITION, TIMING OR COMBUSTION FAILURES. THE LLY AND LB7 CANNOT OPERATE AT OVER 4,500 RPM BECAUSE THE FICM CANNOT PROCESS THE DATA FAST ENOUGH. AN LBZ CAN HANDLE HIGHER ENGINE SPEEDS. THE LMM'S FUEL INJECTION CONTROL MODULE IS ESSENTIALLY IDENTICAL TO THE LBZ'S.

THIS EXPLAINS WHY LBZ-GENERATION DURAMAX TRUCKS RESPOND SO MUCH BETTER TO MODIFICATIONS AND CAN BE TUNED TO HIGHER HORSEPOWER LEVELS WITH GREATER EASE THAN LB7 AND LLY DURAMAX TRUCKS.

SOMETHING TO KEEP IN MIND IF YOU'RE SHOPPING AROUND FOR A GM DURAMAX TRUCK AND YOU PLAN ON DOING SOME PERFORMANCE TUNING TO IT.

PSD TECH

OVERBOOSTING

A COMMON PROBLEM WHEN ADDING A CHIP OR TUNER TO A 1999-2003 7.3L POWER STROKE IS THE POSSIBILITY OF THROWING A P1249 OVER BOOST CODE.

THE FACTORY MAP SENSOR ON THE 7.3L POWER STROKE SENDS BOOST DATA TO THE TRUCK'S PCM. WHEN THE MAP SENSOR REPORTS OVER 24 PSI BOOST, THE PCM WILL TRIP A "SERVICE ENGINE SOON" LIGHT. WHAT MOST OWNERS DON'T KNOW IS THAT WHEN THAT SPECIFIC TROUBLE CODE IS TRIPPED, THE PCM IS PROGRAMMED TO GO INTO A DEFUEL MODE. THE DEFUEL MODE WILL REDUCE FUELING TO DECREASE BOOST PRESSURES, RESULTING IN LOWER OVERALL PERFORMANCE AND POWER OUTPUT.

WITH MOST OF TODAY'S AFTERMARKET CHIPS AND TUNERS, SEEING MORE THAN 24 PSI BOOST IS QUITE COMMON. TO OVERCOME THE DEFUELING AND OVER BOOST ISSUES, ITP DIESEL OF PHOENIX, AZ (WWW.IT ESEL.COM), HAS DESIGNED A PRESSURE REGULATOR THAT WILL PREVENT THE FACTORY MAP SENSOR FROM SEEING MORE THAN 22-23 PSI OF BOOST.

THE PRE-SET REGULATOR WILL AVOID ANY ISSUES WITH THE P1249 DIAGNOSTIC TROUBLE CODE AND SES LIGHT, WHICH PREVENTS THE PCM FROM EVER GOING INTO DEFUEL MODE, THUS ALLOWING YOUR TRUCK TO MAINTAIN MAXIMUM POWER OUTPUT NO MATTER THE BOOST LEVEL. INSTALLATION OF THE ITP OVER BOOST ANNIHILATOR IS SIMPLE AND CAN BE DONE WITH BASIC HAND TOOLS IN MINUTES.

THE FUEL INJECTION CONTROL MODULE IS AN EXTERNAL COMPONENT ON THE LB7 AND LLY DURAMAX ENGINES (SHOWN), AND IS CONTAINED WITHIN THE MAIN COMPUTER ON LBZ AND LMM ENGINES.

CUMMINS TECH

BLEEDING INJECTORS

IT'S HIGHLY RECOMMENDED THAT YOU NOT RUN YOUR DODGE COMPLETELY OUT OF FUEL. IF YOU DO, YOU RUN THE RISK OF PERMANENTLY DAMAGING YOUR INJECTION PUMP. THIS IS ESPECIALLY TRUE WITH THE SECOND GENERATION DODGE TRUCKS THAT COME EQUIPPED WITH THE VP44 INJECTION PUMP. IF THE VP44 LOSES FUEL SUPPLY FOR EVEN A MOMENT, IT CAN CAUSE WEAR AND DAMAGE DUE TO LACK OF LUBRICATION THAT WILL CAUSE PREMATURE OR EVEN IMMEDIATE FAILURE. HOWEVER, IF YOU DO FIND YOURSELF ON THE SIDE OF THE ROAD, A FEW MILES SHY OF THE NEXT FUEL STOP, YOU'LL NEED TO KNOW HOW TO BLEED YOUR INJECTORS IN ORDER TO RE-START THE TRUCK. THIS APPLIES TO 12-VALVE AND 24-VALVE CUMMINS ENGINES. THE COMMON RAIL ENGINES DO NOT REQUIRE THIS PROCEDURE.

CAUTION: IT'S VERY IMPORTANT THAT YOU WEAR PROPER EYE PROTECTION AND EXERCISE EXTREME CAUTION WHEN WORKING ON THE FUEL SYSTEM. DIESEL INJECTION SYSTEMS OPERATE AT PRESSURES THAT WILL SPRAY FUEL THROUGH YOUR SKIN IF YOU COME IN CONTACT WITH LEAKS OR SPRAY.

AFTER YOU'VE ADDED AT LEAST 3-5 GALLONS OF FUEL TO THE EMPTY TANK, YOU'LL NEED TO BLEED AT LEAST 3 OF THE INJECTOR LINES IN ORDER TO GET THE ENGINE RUNNING ENOUGH TO FORCE THE AIR FROM ALL OF THE LINES.

FIRST, TURN THE IGNITION KEY TO THE RUN POSITION AND BRIEFLY "BUMP" THE STARTER. THEN ALLOW THE KEY TO RETURN TO THE RUN POSITION. YOU SHOULD HEAR THE LIFT TRANSFER PUMP, MOUNTED NEAR THE BACK OF THE ENGINE BY THE FUEL FILTER, TURN ON AND CYCLE FUEL THROUGH THE FILTER FOR ABOUT 20 SECONDS. THIS WILL PRIME THE FUEL SYSTEM FROM THE TANK TO THE INJECTION PUMP. DO THIS A FEW TIMES TO ENSURE THAT YOU'RE GETTING A CONSISTENT FLOW OF FUEL TO THE VP44.

SECOND, USING A _-INCH END WRENCH, LOOSEN THE INJECTION LINE RETAINING NUT ON CYLINDER 1. ASK A HELPER TO TURN THE ENGINE OVER UNTIL YOU SEE THAT ALL AIR BUBBLES AND FOAM ARE PURGED FROM THAT LINE. THE RETAINING NUT SHOULD PUMP AIR, THEN FOAMY DIESEL, AND THEN CLEAR DIESEL. AFTER THE LINE IS PUMPING DIESEL, TIGHTEN THE FITTING BEFORE YOUR HELPER STOPS TURNING THE STARTER. REPEAT THIS STEP NEXT WITH CYLINDER 3 AND THEN CYLINDER 4. AFTER THE INJECTOR ON CYLINDER 4 IS BLED, THE ENGINE SHOULD START TO RUN ROUGHLY ON ITS OWN. IT SHOULD THEN SMOOTH OUT AND RUN NORMALLY AS THE AIR IS FORCED FROM THE REMAINING INJECTOR LINES. IF THE ENGINE DOES NOT RUN AFTER BLEEDING NUMBER 4, CONTINUE TO BLEED NUMBER 5 UNTIL THE ENGINE STARTS.

IT'S A GOOD IDEA TO KEEP THAT _-INCH WRENCH IN THE TRUCK BECAUSE IT MAY SAVE YOU FROM A COSTLY TOWING BILL IF YOU EVER FIND YOURSELF IN A DRY SITUATION.

LOOSEN THE INJECTOR LINE RETAINING NUT TO ALLOW TRAPPED AIR TO ESCAPE.

  • Like what you read?

    Want to know when we have important news, updates or interviews?

  • Join our newsletter today!

    Sign Up
You Might Also Be Interested In...
Share

Send to your friends!