Please do not copy and paste this to other forums. ThanksRandy and I had school in Atlanta today. Dodge sent out a guy who has been working with Cummins to get to the root of the problems on 6.7L CTDs. They say most of the problems are fuel injector related. Trash gets in the fuel and prevents the injector from sealing off when it closes. Made a lot of sense. The following is a transcript of the meeting. Pay attention to 2. oil issues. Was told that any CAI must be removed prior to diagnosis.
DIESEL PARTICULATE FILTER
(DPF)
OPERATION
The primary purpose of the DPF found on 6.7L Cummins Diesel equipped Rams is to catch the black particulate matter, (soot or black smoke) that is emitted from the exhaust on a diesel engine. This black smoke is what is typically seen on an older bus, an over the road truck, or a hot rod diesel truck. The more fuel that is added to the diesel engine will typically result in more black smoke being generated.
A DPF failure is usually the result of some other issue and is and never the root cause. It can be loaded (filled) prematurely by over fueling through the fuel injection system, issues pertaining to oil or EGR problems.
The particulate matter that is accumulated in the DPF is removed by adding fuel during the exhaust stroke that will burn off the matter and turn it into ash. The ash will eventually build up and the DPF will need to be replaced. The process of removing the particulate is known as regeneration (Desoot) and these functions are performed automatically with the truck’s onboard computer. A technician can also manually remove the matter through use of a scan tool by performing a mobile or stationary regeneration. It is the heat in the exhaust that removes the particulate. The exhaust outlet temperature at the tail pipe on a diesel is relatively cool at idle; meaning little heat. At road speeds, exhaust temperatures run higher and this higher temperature is needed. Trucks that run constantly at highway speed generally have a lower soot load. They also tend to trigger a Desoot off the timer instead of soot load.
The back pressure in the DPF is measured using a Differential Pressure Sensor (DPS) attached via a metal tube connected at the front and rear of the DPF. From this the fullness of the DPF can be determined. It measures the restriction across the DPF similar to a voltage drop test in an electrical circuit. In the scan tool, under data, the DPS sensor displays a pressure value that is labeled “SOOT DELTA PRESSURE”. A brand new or empty DPF typically will measure 0 or close to it.
To make it easier for a technician to determine the DPF load, the Scan Tool will display the Soot Load in grams. It will be displayed as “ESTIMATED SOOT LOAD BASED ON DELTA.” This should be one of the items you load into your custom display. A brand new DPF will measure 0 or close to it. Sometimes there will be a minimal pressure drop of 2 or 3 grams across a new DPF, especially if the metal tubes going to the DPS sensor are not clean. DPF’s that are cracked internally usually do not show any difference in back pressure or delta.
A 2500/3500 truck will call for a Desoot when the DPF load reaches 47 grams or when the “Soot Removal Time” reaches 24,000 seconds, whichever occurs first. A 3500/4500/5500 Cab and Chassis will signal a Desoot at 57 grams or 36,000 seconds.
Watching the scan tool during this process should display a reading less than 30 grams when completed. There is not a firm number displayed or expectant result at all times because of the ash build up in the DPF over the age of the vehicle. A truck with 100,000 miles may return to the low to mid thirties while a 10,000 mile truck would be in the teens.
When there is something loading the DPF abnormally there are different diagnostic codes generated. The two common codes experienced are P1451 and P242F.
The 1st warning of excess Soot load, a P1451 DTC indicates the DPF is approximately 80% full and will NOT generate a MIL illumination. Freeze Frame should indicate the soot load to be roughly 56 grams. When this soot level is reached AND the CCN is at the “AG”, a message is sent to the Overhead telling the driver that the DPF is at 80% and that he/she should continue driving the vehicle.
The 2nd warning of excess Soot load may set a DTC, P242F, depending on throttle input, anywhere from 76 to 92 grams. A P242F will turn on a MIL lamp. Freeze Frame should always be reviewed to determine what soot level set this DTC.
One other very important indicator is a P200C DTC. This DTC indicates there was an over temperature event in the DPF during the last Desoot. Freeze Frame data of the 3 exhaust temperature sensor should be reviewed. Both the P242F and the P200C DTC’s will suspend the current Desoot event. Once the exhaust temperatures go down, the truck can usually perform a successful Desoot on the next drive cycle as long as the exhaust pressures do not exceed a predetermined mark.
DIAGNOSTICS
NO START
A fully loaded DPF will act just like a restricted exhaust and may cause a no start. The ECM may set a P1451 or a P242F DTC. Removing the DPF per the shop manual instructions will allow the unit to start.
A 6.7L has a number of components that the 5.9L does not that may cause a no-start. We need to keep these in mind when diagnosing a no-start on a 6.7L. They are:
#1) EGR Air Throttle Control Valve - If valve is stuck closed no air will enter the engine. An engine that is a no-start and the valve is stuck closed will sound like a Neon with a broken timing belt. The Scan Tool will NOT identify the correct position of a stuck valve.
#2 Turbocharger VGT – the variable nozzle can stick closed (exhaust brake) and restrict exhaust out of the engine. Look at the VGT position in the Scan tool. Key on, engine off, should read 75-82%. If the reading is 0%, it is a good bet the actuator couldn’t move the VGT (stuck) and the ECM shut off the circuit.
TIP >>> Watch the Exhaust Pressure sensor, the engine will usually not run when the pressure gets into the 115-120 in. hg. range.
#3) DOC/NAC/DPF – these units could just be face loaded. If the Soot Load in grams is 18, the DPF usually is not full; this would indicate a restriction in the inlet of one of these other cats or a stuck turbo.
Other than the above mentioned items, no start diagnosis is similar to the familiar 5.9L Cummins diesel.
BLACK SMOKE
At no time should a 6.7L Ram, ever emit black smoke or have black soot in the tailpipe. This is an indication that the DPF is cracked and must be replaced. The tailpipe is separate from the DPF and is not replaced with the DPF. If the previous technician did not clean the tail pipe when replacing the cracked DPF, the residue will still be there and a DPF may be condemned in error. It is always necessary to inspect the DPF outlet grid for any discoloration.
NOTE: One or 2 black “squares” on the outlet side of the DPF does NOT condemn the DPF, this is considered acceptable.
Injector diagnosis differs on the 6.7 L verses the 5.9 L. The 5.9 L at times may have black smoke out the tailpipe due to a faulty injector that will stop when the leaky injector is capped off during diagnosis. On the 6.7 L the DPF consumes this smoke so capping off the injector will not make a change or can not be used as a diagnostic tool as far as smoke is concerned.
FUEL FILTRATION
The diagnostics of the 5.9L and 6.7L are basically the same except for the aftertreatment system and some minimal tools required for service. A good trait of the DPF on the 6.7L is that it will act as the “fuse” (set a MIL) before we damage the engine, (more on this later). Whereas an injector leaking on a 5.9 L will damage the engine if not serviced in time.
Many of our diesel engine failures occur from customers not changing their fuel filter every 15,000 miles (or earlier if necessary). Dirt may be pulled through the fuel filter and may enter the injector(s). This dirt and/or water entering the injector may result in incorrect spray patterns, injector timing issues, possible injector damage, and most importantly, high soot levels. On a 6.7L the DPF will typically load first with an injector issue, set a MIL, and direct the customer to the dealer, saving a costly engine repair, (hence the “fuse”).
• Severe Duty Filtration Kits are now available for customers exposing their vehicles to harsh conditions. See TSB 14-003-09.
DTCS
P1451, P242F and P200C are all a result of the DPF being loaded abnormally and are not the root cause. There are 6 areas to inspect to determine the root cause. It is also important that the DTC’s are not erased, timers are not reset, or the ECM is not flashed if a stationary regeneration or P2262 test is required on the turbocharger. Listed below are commonly found root causes. They are not ranked in any order of occurrence, but in the order of ease to diagnose.
1. EGR DTC’S OR SOOTED EGR CROSSOVER, HEATER GRID, and EGR VALVE ETC. – A malfunctioning EGR system can cause a DPF to load up instantly with or without actual soot buildup in the crossover tube. A cracked EGR cooler will also place antifreeze in the EGR system and build up soot. When encountering an EGR DTC, the technician needs to ask the question “What caused the engine to overpower or fail the EGR valve?”
2. OIL ISSUES – There are 4 known issues pertaining to oil that will load a DPF abnormally.
• Over filled engine – The engine oil level should only be inspected after the truck has allowed the engine to cool for a minimum of ½ hour. We need to know what the oil level is going down the highway. Whenever the oil level is above the top “Safe Zone” (cross-hatch marks) the oil is over filled. Overfilling the crankcase can cause unexplained turbocharger and O2 sensor DTC’s.
i. REMEMBER >> Best practice is to remove the oil fill cap then remove the oil filter before draining the engine oil. The technician should also allow 15 to 20 minutes for the engine to drain.
Fill with 11 quarts and let it sit 15 minutes before rechecking level. If it falls anywhere in the “Safe Zone”, do NOT add.
• Not using –“Low ash” (CJ-4) oil – adds to the ash level in DPF. Check to see what brand of filter is on the truck and if the customer is unsure of oil rating, change the oil at the customer’s expense. The use of non-ash oil can cause repeat O2 sensor DTC’s. Low ash oil (CJ-4) is required to extend the DPF’s life.
• Restricted breather or air filter – both can be checked with a scan tool. On a normal operating temperature engine the crankcase pressure is typically at .9 to 1.0 in hg. At idle. Readings in the range of 1.8 - 2.0 or higher indicate a restricted breather filter that should be changed at the customers expense. At 2,500 - 3,000 rpm the readings will be typically at -1.0 in hg. The closer they get to - 4.0 the more restricted the air filter and the more likely it is to pull oil over into the air filter box. The air filter and box should also have a visual inspection performed for filter application and correct sealing.
• Oil on the turbocharger inlet – Usually caused by air filter or breather above but it may be coming from the turbocharger itself.
3. AFTERMARKET PERFORMANCE ENHANCERS – Anything that adds more fuel to the engine will cause the DPF to load prematurely. Visually check for modifications or any indicators that suggests some system addition. Also inspect the flash attempt counter in the ECM.
4. OVER FUELING INJECTORS – A 6.7L truck can have “bad stuff” in the fuel, and the day the technician looks at it, it may run perfectly. Fuel issues aren’t always easily identified. Certain DTC’s point us to fuel, i.e. P1451, P242F, P200C, P2262, P0489, P042E, P0402 etc. An engine running rough, can be a result of a customer not changing their fuel filter every 15,000 miles or 6 months. Checking for dirt in the clean side of the fuel system, mainly with the injector return flow will locate the root cause. This dirt is the primary cause of failed injectors and the subsequent loaded DPF.
5. AIR LEAKS IN CHARGE AIR COOLER (CAC) – A diesel engine needs all the air it can get. A leak in the CAC system can cause a decrease in performance plus an engine that generates excessive soot. Pressure test the CAC with the proper tools and procedures.
6. TURBOCHARGER – VGT in the turbocharger may cause a DPF to load. While not common it should be considered.
VERIFICATION OF REPAIR
Verification of the corrective action must always follow the actual repair. This is completed by monitoring the estimated soot load in the DPF on a road test through the scan tool or via wi-Tech with a lap top computer.
In the scan tool, there is a function to reset the regenerative timers back to zero. This is necessary to erase a P242F and perform a mobile Desoot.
Two different paths may be taken when monitoring the estimated soot load. If a mobile desoot is “forced,” the regenerative timers will be reset, the soot load number goes to “zero.” Now the estimated soot load is not a reliable number. Delta pressure now becomes the indicator. If the truck will perform a desoot on it’s own (Soot load above 47 grams or Soot Removal time above 24,000 seconds) then the technician can monitor the soot load as well as the delta pressure.
This verification can only be determined via a road test at highway speeds for an extended period and monitoring the estimated soot load based on delta grams.
The main reason for comebacks associated with the P1451 or P242F, is the root cause of the loaded/failed DPF has not been identified. Just replacing a DPF for a P242F will ensure the truck comes back to someone’s Service Department, because DPF’s ARE NEVER the root cause, they are a result. When the truck is repaired and road tested, the estimated soot load will be less than 35 grams and not climbing and the stationary soot delta pressure will be less than .2 at idle and less than .9 at 2,500 rpm on an engine at normal operating temperature.
BTW, we did get to take a pretty sweet ride to the school.....
Topic: School today and part of what I learned. (Read 18231 times)