Tractorman

You mean this one? John https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation/engine/electrical/w-t-ground-wire-mod-simplified-r574/?&do=getLastComment&d=4&id=574

Here you go...., John

Any poor electrical wiring or wiring connection starting from the power source, through the relay, and finally ending at the lift pump can cause intermittent or continuous electrical resistance. The same is true for ground wiring or wiring connections between the lift pump and battery ground. Also, intermittent disruption of power can be caused by broken wiring strands, or partially shorted to ground wiring on the positive side of the circuit. I believe that your FASS lift pump draws about 10 amps and FASS wants 10 gauge wiring for the load carrying part of the circuit. I assume that the relay coil is still getting its power from the ECM. That wire can be as small as 18 gauge. If you are familiar on how to perform a voltage drop test, this would be the best test to perform for isolating any voltage drop issues. All voltage drop tests would be performed with the engine and lift pump running. Typically, the positive circuit should see no more that .2 volt (two-tenths volt) drop in the positive circuit - one lead on positive post of battery, the other lead on the positive post on the lift pump. The ground circuit should be no more than .1 volt (one-tenth volt) drop from the negative post of the battery and the case of the lift pump or the ground wiring at the lift pump. The readings should be steady - no fluctuations. John

Sounds like a good plan - thanks for keeping us posted. John

It appears that the lift pump is doing its job. Were you able to hold a specific pressure - say, 15 psi - while you filled the bucket? Overflow valve removal, testing, and installation from the FSM below. No o-rings, just two sealing washers at the banjo fitting. If the sealing washers appear to be okay, I would re-use them - just carefully check for leaks after reassembly. John REMOVAL, TESTING, AND INSTALLATION The overflow valve (pressure relief valve) is located at the outside of fuel injection pump (Fig. 67). It con- nects the fuel return line (banjo fitting) to the pump. The valve has no internal serviceable parts and must be replaced as an assembly. Two sealing gaskets are used. One gasket is located between pump and banjo fitting. The other is located between the banjo fitting and end of valve. A rubber tipped blow gun with regulated air line pressure is needed for this test. (1) Clean area around overflow valve and fuel return line at injection pump before removal. (2) Remove valve from pump and banjo fitting. (3) Discard old sealing gaskets. (4) Set regulated air pressure to approximately 97 kPa (14–16 psi). (5) Using blow gun, apply pressure to overflow valve inlet end (end that goes into injection pump). (6) Internal check valve should release, and air should pass through valve at 97 kPa (14–16 psi). If not, replace valve. (7) Reduce regulated air pressure to 10 psi and observe valve. Valve should stay shut. If not, replace valve. (8) Install new sealing gaskets to valve. (9) Install valve through banjo fitting and into pump. (10) Tighten to 30 N·m (24 ft. lbs.) torque.

I am assuming that there is a return flow line to the fuel tank that is directly connected to the FASS pump. Did you measure fuel flow returning to the tank during your test while the lift pump pressure was at 17-19 psi? This is important. In all of your testing, you have mentioned various fuel pressures, but you have never mentioned flow during the test. Maybe it's flowing lots of fuel at the pressure stated, but we don't know that because you have not mentioned anything about flow. If your return flow was low during the test, it would not necessarily condemn the lift pump - there could be a suction restriction to flow, which could show the same symptoms. If your return flow was high and steady during the test, it would show that the lift pump is performing as it should and that there is no suction restriction (at least for the duration of the test). An idling engine returns about 18 gph of fuel to the fuel tank through the overflow valve. The overflow valve is downstream of the VP44's internal fixed displacement vane pump. This internal vane pump's pressure is regulated at over 100 psi. All fuel must pass through this pump - there is no bypass. Even if the overflow valve offered no back pressure, the fuel return volume will remain virtually the same, consequently lift pump pressure will remain the same. So, I am not saying that an overflow valve cannot be your problem - I am just explaining why I don't think it is your problem. And, your case will be the first one that I know of, if it turns out to be your problem. It is certainly easy enough to remove and test the overflow valve with regulated air pressure. Here you mention fuel pressure, but not fuel flow. Fuel pressure tells you that there is a resistance to some flow, it just doesn't tell how much flow. If the flow is not enough to meet the demand of the VP44 internal vane pump, then fuel pressure will fall. I know you will persevere. John

Long posts are appreciated - especially when they are informative - like yours. I'm leaning toward your new low-stall converter triggering this issue. A stock converter has a stall speed of about 2,100 rpm, so it does not put much of a load on the engine when "drive" or "reverse" is selected. Your new converter probably has a stall speed of around 1,800 rpm, so shifting into gear will load the engine much heavier, especially in cold weather. I vaguely recall that there was an ECM update (referred to as "Anti-stall") around 1999 for these VP44 trucks. I think it was geared for the manual transmission trucks, but possibly the automatic trucks as well. Maybe @Mopar1973Man will chime in on this topic. Have you tried taking the Edge EZ completely out of the circuit? John

You may not be aware, but if you cycle the key switch to the "on" position three times fairly quickly and then leave the key switch in the "on" position, you can read codes from the odometer. This may be what happened to you. The first codes will be from the PCM, then a pause, then codes from the ECM. John

I appreciate you answering all of the questions. It may take awhile to figure this one out. Meanwhile, here is something that you can do next time the engine won't shut off. In preparation to perform the following test, locate and mark the fuel pump relay in the PDC. Have a digital volt meter handy to perform an electrical test. The test - the next time the engine won't shut off, leave the engine running with the ignition switch in the "off" position. Tap on the fuel pump relay to see if the engine shuts off. If the engine continues to run, then remove the relay. The engine should turn off. Using a DVM, check for voltage at Pin # 86 of the relay. There should be no voltage present. If this is the case, try swapping the fuel pump relay with another like relay in the PDC. If there is voltage present at Pin # 86, then this is why the engine won't shut off. Power to Pin # 86 comes directly from the ECM. Something is telling the ECM to power the fuel pump relay. More diagnosis required. Have you heard of, or performed the W-T ground reference modification? This mod deals with potential ground problems with the VP44, ECM, PCM, and PDC. John

P0121 - Accelerator Pedal Position Sensor Signal Volts Do Not Agree w/Idle Validation Signal P0123 - Accelerator Pedal Position Sensor Signal Voltage Too High Any history on how many miles or age on the APPS? Need more detail here. Does this happen immediately when the key is turn on or when the engine is started? What is "hot"? - 200°...., 220°?..., pegged? Are any other gauges being affected when this happens? Does this happen every time? How are you shutting the engine off when it does happen? Please give more detail about the history of your truck (ownership, miles, problems, etc). Did the 3 listed issues just start all at once , or come on gradually and separately? How well does the engine run as far as performance on the road? The ECM switches off the fuel solenoid in the VP44 via the fuel pump relay in the PDC (power distribution panel under the hood) when the ignition switch is turned off. John

@Mopar1973Man , the article is done. It is awaiting your approval. John https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation/transmission-transfer-case/low-range-2wd-cad-conversion-r758/

For those who own trucks with a CAD (center axle disconnect) front axle, this article will explain the benefits of remotely controlling the CAD operation and will also provide information on how to make the modification. For those who are not familiar with a front axle CAD unit, the following description may help. OEM vehicle - manually shifted transfer case (with CAD) - Theory of Operation The CAD front axle has three axle shafts - a driver side axle shaft, a passenger side axle shaft, and a short center axle shaft. The passenger side axle shaft and the center axle shaft can be connected or disconnected by the CAD unit. The center axle shaft is called the intermediate axle shaft in the photo below. The CAD unit is a vacuum motor that controls a splined sliding collar to lock the right axle shaft to the center axle shaft. There is a switch at the end of the CAD unit that allows illumination of the 4WD indicator lamp in the dash. 2WD Selected - front driveshaft does not rotate and CAD is disconnected. This feature minimizes front axle friction at highway speeds. 4WD HI Select on-the-fly - As the transfer case shifter is being pulled into the 4-HI position, a synchronizer in the transfer case brings the front driveshaft up to speed. As the shift is completed, a vacuum valve inside the transfer case actuates the front axle CAD unit and locks the passenger side axle shaft directly to the center axle shaft. 4WD indicator lamp is illuminated. 4WD LO Select - Vehicle must be stopped. Select 4WD LO. 4WD indicator lamp is illuminated. Something worthy of noting - when 2WD is selected, the front drive shaft stops rotating, the left and right axle shafts are still rotating (driven by the wheels), and the center axle shaft is still rotating, BUT in the opposite direction (because of the differential). This is the reason that when 4WD Hi is selected, the synchronizer in the transfer case brings the front driveshaft up to speed first. When the front driveshaft is brought up to speed first, then all three front axle shafts are rotating at the same speed and in the same direction. Now the CAD unit can connect the passenger side axle shaft to the center axle shaft. 2WD-LO Conversion (parts needed) Toggle switch - two position maintained switch with physical lockout Humphrey 4 way / 2 position, 1/8" NPT, spring offset, vacuum solenoid valve Model 410/12 VDC Appropriate length of vacuum tubing and 16 gauge automotive wire and wire connectors. This conversion separates the operation of the transfer case manual shifter and the CAD vacuum controlled shifter. The external vacuum ports of the vacuum valve (inside the transfer case) will be disconnected and plugged. A new vacuum solenoid valve for the CAD unit operation will be installed in a location of choice. A fused switch will be installed to operate the new CAD vacuum solenoid valve. A vacuum supply line will be routed to the CAD vacuum solenoid valve. Two vacuum lines will be installed to connect the new CAD vacuum solenoid valve to the CAD unit. Instructions for operating the new conversion are as follows: 2WD High - The transfer case selector must be in 2WD and the CAD switch must be turned off and locked out. 4WD High - Vehicle must be stopped. The CAD switch must be turned on. The 4WD indicator lamp will illuminate (truck may have to be moved slightly to engage 4WD lamp). From this point forward the transfer case can be shifted from 2WD to 4WD or 4WD to 2WD on-the-fly. 2WD Low - Vehicle must be stopped. Shift transfer case into Low Range. Leave the CAD switch turned off and locked out. The 4WD lamp will not illuminate. 4WD Low - Vehicle must be stopped. Shift transfer case into Low Range. Turn on CAD switch. The 4WD lamp will illuminate (truck may have to be moved slightly to engage 4WD lamp). Tips The 2WD Low Range can be very useful, especially for backing trailers in tight spaces, whether loaded or not. This is true for manual and automatic transmissions. You can basically idle the rig while backing very slowly in tight turns without the wheel hop associated with 4WD. Also, when traveling off-road on very steep and twisty terrain with varying traction conditions in low range, you can shift from 2WD to 4WD or 4WD to 2WD on-the-fly. Just leave the transfer case in 4WD and operate the CAD switch - "Off" for 2WD, "On" for 4WD. Always unload the engine (ease up on the throttle) when making the changes to allow the CAD unit to slide the shift collar easily. The CAD switch has a physical lockout to reduce the chance of accidental operation. When the switch not going to be used, always engage the lockout with the switch in the "Off" position. Enjoy the conversion! View full Cummins article

Will do. John

Personally, I would keep the CAD unit in place. I did so and turned it into a 2WD / 4LO truck - very beneficial for slowly backing heavy loads in tight areas. I purchased and installed a vacuum solenoid valve and a toggle switch with a lockout (switch shown below). I bought my truck new and did this conversion over 20 years ago and over 300,000 miles ago. It has never failed and the 4WD indicator lamp works as it should. John