Attention: TDR Forum Junkies 
I submit the following story for everyone's comments.
My '99 second generation 5. 9 diesel 2500 has these modifications: HX35 turbine with HX45 compressor wheel; 16cm housing with BD elbow exhaust brake; 4 inch exhaust; DD stage 3 injectors. Mark Chappel's ECM reflash for increased fueling circia Y2K; Quadzilla boost fooler. Truck dynos at 330 hp and 850 lb. ft. and is used regularly for towing 15K 5er. Truck engine looks entirely stock on exterior, but will smoke on throttle snap test in neutral. Truck never sets any codes even at 330hp towing. Truck has both EGT and boost metering.
Truck began to intermittently loose power about a month ago. When power was down, boost would never rise above 12psi even at full load (it runs 33 psi at full power normally). The truck would make absolutely no smoke when depowered. I estimate the truck would produce no more that 120 hp when depowered. Occasionally the truck would revert back to normal full boost with repeated throttle snaps on the highway.
I attached the laptop to the truck interface port and began monitoring using OBD2 software from Baum Tools. The Engine 21 module was selected and all operating parameters were monitored under highway driving conditions. RPM, Throttle Position, Speed, Measured Load and all other measureable parameters except measured boost were nominal.
Monitoring of Manifold Absolute Pressure indicated the MAP sensor was sending 29. 8 psi ALL THE TIME when the truck was in the failed mode. This corresponds to 0 psi boost and was confirmed by the boost gauge. Also while failed, the MAP continued to signal 29. 8 psi even under full power/throttle with the boost guage showing 12 psi. When the MAP sensor began to operate normally, the MAP signal would show 63 psi indicated at full power, about 33 psi boost as confirmed by the boost gauge, and the truck ran normally.
It was clear that the MAP sensor was faulty (Cummins p/n 4921497 $62-$70) and was replaced by a new unit. The problem was solved.
Now my mind switched to the newly implemented CARB originated smog tests in California. The faulty MAP sensor had SET NO CODES when it was electrically stuck at idle (28. 9 psi). It was clear to me that the electromechanical sensor's internal potentiometer had some worn spots at higher boost. The sensor is a three lead device that uses B-, 5volt B+, and a wiper output voltage proportional to the MAP. What if I could make any MAP sensor fail in this mode and use it to pass SMOG testing? It would be a simple matter to unplug ang replace the MAP sensor prior to a SMOG test, and replace it after testing. All you would need to buy is a MAP sensor and the 27MM deep socket for its removal. (Note: Some older sensors require a 33MM deep socket. ) The ECM just switches to the idle/no boost fueling curve and sets no codes throught the whole process. The truck runs adequately and makes absolutely no smoke on the idle/no boost fueling curve.
Using the old sensor, I removed the o ring and drilled a 1/8 inch hole in the brass slightly outboard from the o ring seat, diagonally into the sensor body and through to the measuring chamber. I was careful not to ram the drill into the measuring diaphram as it broke through. This allowed the sensor to measure only atmospheric pressure, 0 psi boost, just like at idle. Next I tapped the hole that goes into the manifold with a 5/16-20 tap and plugged the hole with a 5/16-20 1/4 inch long allen head set screw.
I replaced the new MAP sensor with the altered sensor and fired off the truck. I was stuck in low power mode with no smoke and no codes! I replaced with the new unaltered MAP sensor and the truck immediately resumed full power bombed operation! Now I have a quick, easy, undetectable way to fully depower the truck for testing for the net outlay of $63. 16 for a MAP sensor and $7. 99 for a deep socket. All with factory parts. Enjoy.
My '99 second generation 5. 9 diesel 2500 has these modifications: HX35 turbine with HX45 compressor wheel; 16cm housing with BD elbow exhaust brake; 4 inch exhaust; DD stage 3 injectors. Mark Chappel's ECM reflash for increased fueling circia Y2K; Quadzilla boost fooler. Truck dynos at 330 hp and 850 lb. ft. and is used regularly for towing 15K 5er. Truck engine looks entirely stock on exterior, but will smoke on throttle snap test in neutral. Truck never sets any codes even at 330hp towing. Truck has both EGT and boost metering.
Truck began to intermittently loose power about a month ago. When power was down, boost would never rise above 12psi even at full load (it runs 33 psi at full power normally). The truck would make absolutely no smoke when depowered. I estimate the truck would produce no more that 120 hp when depowered. Occasionally the truck would revert back to normal full boost with repeated throttle snaps on the highway.
I attached the laptop to the truck interface port and began monitoring using OBD2 software from Baum Tools. The Engine 21 module was selected and all operating parameters were monitored under highway driving conditions. RPM, Throttle Position, Speed, Measured Load and all other measureable parameters except measured boost were nominal.
Monitoring of Manifold Absolute Pressure indicated the MAP sensor was sending 29. 8 psi ALL THE TIME when the truck was in the failed mode. This corresponds to 0 psi boost and was confirmed by the boost gauge. Also while failed, the MAP continued to signal 29. 8 psi even under full power/throttle with the boost guage showing 12 psi. When the MAP sensor began to operate normally, the MAP signal would show 63 psi indicated at full power, about 33 psi boost as confirmed by the boost gauge, and the truck ran normally.
It was clear that the MAP sensor was faulty (Cummins p/n 4921497 $62-$70) and was replaced by a new unit. The problem was solved.
Now my mind switched to the newly implemented CARB originated smog tests in California. The faulty MAP sensor had SET NO CODES when it was electrically stuck at idle (28. 9 psi). It was clear to me that the electromechanical sensor's internal potentiometer had some worn spots at higher boost. The sensor is a three lead device that uses B-, 5volt B+, and a wiper output voltage proportional to the MAP. What if I could make any MAP sensor fail in this mode and use it to pass SMOG testing? It would be a simple matter to unplug ang replace the MAP sensor prior to a SMOG test, and replace it after testing. All you would need to buy is a MAP sensor and the 27MM deep socket for its removal. (Note: Some older sensors require a 33MM deep socket. ) The ECM just switches to the idle/no boost fueling curve and sets no codes throught the whole process. The truck runs adequately and makes absolutely no smoke on the idle/no boost fueling curve.
Using the old sensor, I removed the o ring and drilled a 1/8 inch hole in the brass slightly outboard from the o ring seat, diagonally into the sensor body and through to the measuring chamber. I was careful not to ram the drill into the measuring diaphram as it broke through. This allowed the sensor to measure only atmospheric pressure, 0 psi boost, just like at idle. Next I tapped the hole that goes into the manifold with a 5/16-20 tap and plugged the hole with a 5/16-20 1/4 inch long allen head set screw.
I replaced the new MAP sensor with the altered sensor and fired off the truck. I was stuck in low power mode with no smoke and no codes! I replaced with the new unaltered MAP sensor and the truck immediately resumed full power bombed operation! Now I have a quick, easy, undetectable way to fully depower the truck for testing for the net outlay of $63. 16 for a MAP sensor and $7. 99 for a deep socket. All with factory parts. Enjoy.
