Attention: TDR Forum Junkies 
I bought a factory service manual on CD-ROM for my '02. THAT is a good manual. And it works very well with Adobe Reader. I spent a little time reading last night and the fuel system section of the manual is pretty interesting. In particular the supply system pressure specs. Dodge says 3, 7 or 10 psi depending on the conditions and what "mode" the engine is operating in. The overflow valve pressure spec is 14.5. So how does the overflow valve ever allow fuel flow to return? Sounds like there must be a transfer pump inside the injection pump as well. I need to get my hands on a "failed" VP44 and see what makes that thing tick. Because what I'm finding interesting about VP44s is that the ELECTRONIC side of the system is VERY similar to that used on Deere 6076s and 6081s with electronic governors. Basically it's juast a P7100 Bosch pump with an electronic "governor" that consists of a rack actuator, rack position sensor and speed sensor. One of those speed sensors took me for a ride on time.
Had a tractor that just DIED on a customer and WOULD NOT START. I'd seen plenty of cranks/won't start problems on them. It was always the engine speed sensor. Replace the sensor and they fire right up. But by the time I got done with that one, I'd learned something that Bosch apparently didn't want us to know, because the diagnostics were VERY vague when it came to the fact that there is ANOTHER speed sensor in the governor. And guess what? On THOSE governors that speed sensor is NOTORIOUS for failing. Which doesn't hurt a THING as long as the engine speed sensor is working. But if the pump sensor has failed and the engine sensor fails? The engine dies and will not start. I wonder just how many VP44 "sudden death" situations are the result of a pump speed sensor that had failed long prior and then having a crankshaft speed sensor fail? Will the engine start and run IF the pump speed sensor is functioning but NOT the crank speed sensor? The manual says it will. It specifically says it will. So do VP44 failure diagnostics include checking the crank speed sensor?
Boy. Wouldn't it be something if Dodge had the same situation as Deere and the pump sensor was failing early on and it was just the engine speed sensor failure that caused the VP44 to "fail"? Hmm. Maybe I should mention that the Bosch diagnostics on the Deere system were not only VAGUE but they specifically tell you to NOT poke any wires. Which is understandable. Don't want to compromise a circuit. But with the tractor I was working on giving me fits and with me having just overhauled the engine and our pump shop having just worked on the injection pump SEVERAL times, I got on the phone with them and raised a little hell. And I learned a couple of things. You CAN diagnose the pump speed sensor with the pump ON THE ENGINE if you just poke some wires or build a breakout harness to do so. Even though Bosch tells you not to poke wires, doesn't mention a breakout harness AND never quite mentions in the diagnostics or principles of operation that a pump speed sensor I would have NEVER known about had the pump shop guys not clued me in - can fail and cause a dies/won't start situation.
I also did a little investigating into various codes and problems and found some info on fuel temps and a spot where the manual says that if you're having high fuel temps, which can cause premature injection pump failure, the problem could be an overflow valve stuck open. Allowing too much fuel to flow throught or fuel to flow through too FAST to cool the pump, I'm guessing. Either that or the lift pump really can't keep up with that giant leak at all times and maybe there's air backfeeding through the return circuit? Also interesting was the extensive diagnostics of the fuel system with a hand-operated vacuum pump. Basically looking for leaks that can let air in but not fuel out.
The VP44 removal and installation instructions are also interesting with the mention of a "keyway" that has to be specifally matched to the pump for proper engine timing. I imagine the "keyway" is an offset key because not only does the "keyway" have to match the pump, it has a 3-digit number that matches a pump number as well AND the keyway has to be installed correctly - pointing in the right direction. Otherwise an offset key is going to throw the timing off TWICE as far as the dimension of the offset to start with. And of course they have to be dynamically "timing" the pumps on a test stand to determine the proper spec. But it turns out that there are TWENTY-ONE different keyways. I wonder how many VP44 rebuilders are going through all those steps and making sure the timing is correct to start with and are then providing the correct matched key with the pump. And I also wonder how many guys are doing all these fuel system "upgrades" to prevent VP44 failure and are causing that stuck-open overflow valve problem in the process? If the factory manual specs 10 psi MAX and you're cranking in 20 or 30? There are going to be some consequences. Especially when the injection pump itself is taking supply pressure and is increasing it anywhere from 50% to 500% inside the pump itself. How about that overflow valve? Do rebuilt pumps come with a new one? If not, is anyone checking the old one if they're reusing it? How many guys are doing the vacuum tests for leaks? How many fuel system modifications do nothing BUT add potential leaks to the system?
My cousin's '99 Dodge went way over 300,000 miles without a VP44 failure and he beat the hell out of that truck. And it always ran good until it died. I have a hard time believing that HE could have such outstanding results, while others who take far better care of their trucks and even "upgrade" the fuel system to PREVENT failures have "inevitable" failures. And 300,000 miles IS decent service life out of ANY mechanical injection pump if that pump is mounted on a high-rpm engine used in a pickup. Even a P7100 can be taking it in the shorts by then if for no other reason than the amount of fuel that's been RETURNED through it. Especially if that fuel is HOTTER than it should be. I know THAT because I sent a LOT of "low-hour" 6076/6081 pumps to the pump shop after replacing weak nozzles to check a low power complaint and then finding that I LOST horsepower on the dyno because the new nozzles had a way higher VOP and were causing a LOT of fuel to bypass back past the worn-out plungers and barrels. And guess what the VOP of those nozzles is? Around 4500 psi. The VOP of VP44 system nozzles? About 4500 psi. Hmm. But the VP44 "sudden death" is just an "inevitable" failure? Sorry. I ain't buying it. Somebody is playing CYA and we're paying the bill. And maybe even buying "rebuilt" pumps that will REALLY "inevitably" to boot because they're "rebuilt" with parts that MAY pass the BENCH TEST and meet Bosch specs, but on the ENGINE they're going to DIE. Just some food for thought...
I'll save my TRANSMISSION revelations for later. Some people aren't going to like them. I'll jjust say that a certain transmission "model" (ROFLMAO at the Dodge codes designating a "model" of transmission) is completely absent from a factory 2002 Dodge Ram 2500/3500 service manual that should DEFINITELY be there since ALL of the aftermarket outfits and "experts" acknowledge its "existence".
Had a tractor that just DIED on a customer and WOULD NOT START. I'd seen plenty of cranks/won't start problems on them. It was always the engine speed sensor. Replace the sensor and they fire right up. But by the time I got done with that one, I'd learned something that Bosch apparently didn't want us to know, because the diagnostics were VERY vague when it came to the fact that there is ANOTHER speed sensor in the governor. And guess what? On THOSE governors that speed sensor is NOTORIOUS for failing. Which doesn't hurt a THING as long as the engine speed sensor is working. But if the pump sensor has failed and the engine sensor fails? The engine dies and will not start. I wonder just how many VP44 "sudden death" situations are the result of a pump speed sensor that had failed long prior and then having a crankshaft speed sensor fail? Will the engine start and run IF the pump speed sensor is functioning but NOT the crank speed sensor? The manual says it will. It specifically says it will. So do VP44 failure diagnostics include checking the crank speed sensor?
Boy. Wouldn't it be something if Dodge had the same situation as Deere and the pump sensor was failing early on and it was just the engine speed sensor failure that caused the VP44 to "fail"? Hmm. Maybe I should mention that the Bosch diagnostics on the Deere system were not only VAGUE but they specifically tell you to NOT poke any wires. Which is understandable. Don't want to compromise a circuit. But with the tractor I was working on giving me fits and with me having just overhauled the engine and our pump shop having just worked on the injection pump SEVERAL times, I got on the phone with them and raised a little hell. And I learned a couple of things. You CAN diagnose the pump speed sensor with the pump ON THE ENGINE if you just poke some wires or build a breakout harness to do so. Even though Bosch tells you not to poke wires, doesn't mention a breakout harness AND never quite mentions in the diagnostics or principles of operation that a pump speed sensor I would have NEVER known about had the pump shop guys not clued me in - can fail and cause a dies/won't start situation.
I also did a little investigating into various codes and problems and found some info on fuel temps and a spot where the manual says that if you're having high fuel temps, which can cause premature injection pump failure, the problem could be an overflow valve stuck open. Allowing too much fuel to flow throught or fuel to flow through too FAST to cool the pump, I'm guessing. Either that or the lift pump really can't keep up with that giant leak at all times and maybe there's air backfeeding through the return circuit? Also interesting was the extensive diagnostics of the fuel system with a hand-operated vacuum pump. Basically looking for leaks that can let air in but not fuel out.
The VP44 removal and installation instructions are also interesting with the mention of a "keyway" that has to be specifally matched to the pump for proper engine timing. I imagine the "keyway" is an offset key because not only does the "keyway" have to match the pump, it has a 3-digit number that matches a pump number as well AND the keyway has to be installed correctly - pointing in the right direction. Otherwise an offset key is going to throw the timing off TWICE as far as the dimension of the offset to start with. And of course they have to be dynamically "timing" the pumps on a test stand to determine the proper spec. But it turns out that there are TWENTY-ONE different keyways. I wonder how many VP44 rebuilders are going through all those steps and making sure the timing is correct to start with and are then providing the correct matched key with the pump. And I also wonder how many guys are doing all these fuel system "upgrades" to prevent VP44 failure and are causing that stuck-open overflow valve problem in the process? If the factory manual specs 10 psi MAX and you're cranking in 20 or 30? There are going to be some consequences. Especially when the injection pump itself is taking supply pressure and is increasing it anywhere from 50% to 500% inside the pump itself. How about that overflow valve? Do rebuilt pumps come with a new one? If not, is anyone checking the old one if they're reusing it? How many guys are doing the vacuum tests for leaks? How many fuel system modifications do nothing BUT add potential leaks to the system?
My cousin's '99 Dodge went way over 300,000 miles without a VP44 failure and he beat the hell out of that truck. And it always ran good until it died. I have a hard time believing that HE could have such outstanding results, while others who take far better care of their trucks and even "upgrade" the fuel system to PREVENT failures have "inevitable" failures. And 300,000 miles IS decent service life out of ANY mechanical injection pump if that pump is mounted on a high-rpm engine used in a pickup. Even a P7100 can be taking it in the shorts by then if for no other reason than the amount of fuel that's been RETURNED through it. Especially if that fuel is HOTTER than it should be. I know THAT because I sent a LOT of "low-hour" 6076/6081 pumps to the pump shop after replacing weak nozzles to check a low power complaint and then finding that I LOST horsepower on the dyno because the new nozzles had a way higher VOP and were causing a LOT of fuel to bypass back past the worn-out plungers and barrels. And guess what the VOP of those nozzles is? Around 4500 psi. The VOP of VP44 system nozzles? About 4500 psi. Hmm. But the VP44 "sudden death" is just an "inevitable" failure? Sorry. I ain't buying it. Somebody is playing CYA and we're paying the bill. And maybe even buying "rebuilt" pumps that will REALLY "inevitably" to boot because they're "rebuilt" with parts that MAY pass the BENCH TEST and meet Bosch specs, but on the ENGINE they're going to DIE. Just some food for thought...
I'll save my TRANSMISSION revelations for later. Some people aren't going to like them. I'll jjust say that a certain transmission "model" (ROFLMAO at the Dodge codes designating a "model" of transmission) is completely absent from a factory 2002 Dodge Ram 2500/3500 service manual that should DEFINITELY be there since ALL of the aftermarket outfits and "experts" acknowledge its "existence".
Last edited:
