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Here you go...., 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

That should give you all the info for testing the overflow valve on the VP44. Just remember the little hole is always open and some pressure can bleed. The check ball should stay closed completely at 10 PSI. Fully open by 14 PSI.

This is pretty accurate. One of my other cars is an Evo with a stroker engine that was built when I was still stationed in Japan. The builder told me that with the clearances, i need to run 20w50 oil, and that my minimum hot oil idle pressure is 15psi ( factory engine minimum oil press is like 5psi, gas engines are a wee bit different). The builder had used Motul engine oil, but that stuff was CRAZY expensive in Japan. I used LiquiMoly, hot idle pressure dropped by a few psi, still above the minimum, but it dropped. Then I tried ELF racing oil, and that could barely hold minimum psi, car ran noticably rougher. Enter Valvoline VR1. That stuff is AWESOME. I do not know what valvoline puts in there, but its amazing! super resilient against breaking down, holds hot oil pressure even better than Motul. And it is very reasonably priced. Mind you, this poor car gets hammered and abused every single time I drive it. It really brings out the pissed off teenager in me. Lesson here, all these oils were 20w50, and while in theory they should all perform somewhat similar, this couldn't be further from the truth! And now I have a case of VR1 on the shelf at all times. Also, I checked the AMSOil dex 3, and its cold pour point and cold flow performance are FAR superior, but it is synthetic of course. research will continue.

You can tear all of that out. Firewall mat and cowl included. Bad idea from the factory being it dumps all the dust into the engine every time the valve cover comes off. No need to replace.

You're basically covering up a piston ring(s) issue, typically or bad tuning. Why? Well, normally, these trucks will not produce excessive crankcase pressure or blowby gases. Now, someone who runs worn injectors, then your timing could be advanced by the weaker springs in the injectors. Now, you're creating this extra blow by. might see more slobber of oil out of the crankcase vent (gear case vent). I suggest keeping injectors changed out at 100k miles. After that point your rolling the dice. For every 10 bar of pop pressure loss is about 1 degree of advancement. If your injectors haven't been changed in over 100k miles, I'd start there. Yea,h sadly, the only reason I know to add more vent/filter to the valve cover is that the factory breather is not keeping up because of the vacuum line disconnected (added pressure from the vacuum pump), poor rings on the pistons, worn injectors with low pop pressure (less than 293 bar). Now, like Thor, I have a bad ring in Thor, and Thor starts and runs, but the exhaust is white smoke from the low compression, and there is extra crankcase pressure on Thor from the blowby, and the blowby isn't bad, but still it would help to have an extra vent at that point, but... Better to fix the problem. Yeah, I've got plans to rebuild that 2006 in the future. First problem, I need a shop to work in once again. Another trick is you could create a vent pipe to keep the slobbering down some. Remember, this will not fix excessive blow-by.

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

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I became interested in automotive work when I watched my dad work on our family vehicles, then when I had my 1st car...1988 Mitsubishi Precis. I wanted to do some basic maintenance work myself on my car. I had the basic model without most of the electrical features, so it was easier for that car, which lasted until 1998 after finding out my clutch was slipping. Before it went out, I decided to donate the car because it was not worthwhile financially to repair it versus the car's worth. Since then, I have usually taken my cars to a mechanic to do maintenance or repairs on the rest of my vehicles. Now...I have a "personal" mechanic in the family! I married @Mopar1973Man 🥰

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Correct. It's a Cascade system so yes the power steering pump to the hydrobooster. Then it leaves with a second line down to the steering box. There is two low pressure return lines back to the pump which you will see just spring clamps for return lines.

It would be awesome to have a scan tool or Quadzilla to look at the APPS signal to see if its correct. At idle it should show 0% TPS. Which if there is signal above 0% with the Idle validation set then hence the P0121. You not allowed to be throttling with the idle validation set. That new timbo apps should fix it.

Awesome! Thank you much. It will be a bit till I get there, so I might have questions down the road. Excellent write up!

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Hello everyone!! Our progress with all the adversity that smacked us 😲 during 2025 has been gradually getting better. I have been out of the scene due to all the tasks demanding my attention. But...back to concentrating on the responsibility of this website to make it better with some basic housekkeeping. We plan to work on several areas of the website this year. I, myself, will be dealing with one huge undertaking...reviewing the Articles to improve the verbiage in effort to provide clarity or revise the content, of course, with the assistance of the infamously knowledgeable Mopar1973man!! (so many of them! 😳 Yikes!) Gotta get rid of those virtual cobwebs 🕷️😂 So...keep checking the updates or look at my progress notifications. I will notify when I have completed each area...so be patient as I work on them.

Over the past 15 months I have just about completely rebuilt everything on my 2003 Dodge Ram 2500 and the one place which provided me with all the information I needed to solve problems, such as your 48RE failing mysteriously with no warning signs to direct you in fixing it, is the Cummins Forum website -- (39) 03-07 Powertrain | Cummins Diesel Forum There are some very good experienced highly skilled members there who know the 48RE inside and out and I am quite sure they will point you in the right direction. There are many good posts provided on the 48RE. And perhaps the owner of this website will provide excellent advice as well. I have learned a great deal of essential information here such as fixing my torque converter cycling problem using his info and links to other sources which provided exactly what I needed.

I have my 48RE built heavy duty at a local shop which specializes in 48REs which cost about $6K and is now capable of towing the truck's maximum weight and also can handle 1000 hp. However, my truck will never have more than 650 hp, if that. The 48RE when built correctly addressing all known weaknesses is an excellent transmission. I added a Full Send Diesel trans cooler unit which keeps the fluid temps in the 120-140 degree range.

@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

OMG!

Black

Yeah, up here in Idaho, we see upwards of -20℉. Automatics up here are rather rare, and manuals are more typical. The guys here are right that you should consider keeping the factory transmission fluid cooler or replacing it with a more modern transmission cooler in its place. The factory cooler has issues with rusting and leaks over time.

I recommend keeping the heat exchanger but replace the OEM unit with the one Full Send Diesel designed, which is an all-billet solid unit with two totally separate areas which cannot rupture and cause crossover contamination between the coolant and the trans fluid. These units also cooler far more efficiently due to being solid billet design. Combine this unit with their heavy duty high flow transmission cooler and your transmission will remain cool even in the most extreme conditions. My coolant temps with sensor in the deep pan never gets above 150 degree in the month of August in Florida.

Timbo is a repackaged Williams Control. WC 131973/133284 is what they actually are.

That is going to be one of the coolest trucks in history. I took notice of the 11 YEARS this thread has been going on regarding your custom build Cummins truck. I'm sitting here waiting for another bag of popcorn to watch this come together.

Thank you for the kind words. Personally I'm looking for people that are willing to write articles about repairs and information on repairing these trucks. Im going to move forward into 3rd Gen to put Thor at the top of the focus. I need to expand knowledge into newer generations. A lot of info is trapped in my head and needs to get put into HTML5 code for all to see and learn from. Thanks for the comment.

Could a guy put a full flow directional valve in diverting the fluid either through the block mounted cooler during winter months and then shut the valve during summer months? Maybe run the summer hose circuit through a derale cooler with fan under the chassis?

The factory heat exchanger not only cools transmission fluid, but all so heats the fluid to operating temperature in cold weather. With the average winter low temperature of 9°F in your area it would be prudent to retain the heat exchanger for winter drivability.

I would say keep it and replace the damage heat exchanger for the transmission.