Tractorman

So, If I am understanding correctly, you have two fuel returns entering the basket. Where does your lift pump pull fuel from inside the fuel tank? - John

@Royal Squire, I don't know the specific size, but the filler neck tee that was recommended to me by @wil440is 1 1/2" and the tee is 1/2". It worked fine on my truck. - John It seems to me that you return fuel flow must not be entering the fuel basket since your fuel temperatures are so low currently. Is the sump a factory setup? There may be no benefit to adding the filler hose tee in your situation if in fact your fuel is being returned in a location other than the fuel basket. - John

Actually, it is a good question. I really don't think it is an issue. Larger air bubbles would stay at the surface and smaller bubbles would have time to rise to the surface before reaching the suction area. I am sure that fuel sloshing around in the fuel tank while driving down the road generates a certain amount of aeration anyway - probably more than a return line to the filler neck would. Just my opinion, but I think the gains from routing the return line to the filler neck greatly outweigh the risk of problems associated with aeration. - John

I think you are on to something here. I just recently rerouted the return fuel from the VP44 and head to the filler neck on my truck. Previously it returned into the same basket that the lift pump suction drew from. Before rerouting the fuel return, on road trips I would stop and put my hand of the on the FASS DDRP02 lift pump (modified for a frame mount} and the pump housing would be hot to the touch - I estimated to be about 140 degrees (ambient air temperature was 80 degrees) because I could only hold my hand on it for a few seconds before it became too uncomfortable. This was with a full tank of fuel. Yesterday, I had an opportunity to check the lift pump temperature by my hand with the rerouted fuel return line. I purposely ran the fuel tank down to less that 1/4 tank while towing my trailered tractor over 200 mils at 65 mph - combined weight of 16,000 lbs. I stopped at a rest area just before refueling and placed my hand on the lift pump. Much cooler, probably around 110 degrees with ambient air temperature at 75 degrees. I filled the tank about 10 miles and 30.1 gallons later - the lift pump still running cool just before fill up which means there was only about 5 gallons of fuel left in the tank that was cooling the returned fuel. This test clearly shows the results of simply getting the return fuel flow out of the basket. - John

You pose a good question. It is the flow from the internal vane pump that is opening the 14 psi overflow valve as soon as the engine is running. Many VP44 industrial engine applications don't even use a lift pump, but you can bet plenty of fuel is returning to the fuel tank while the engine is running. The internal vane pump builds pressure because its flow output is greater than the total consumption of the the fuel being used by the injectors and fuel returning to the fuel tank, The remaining unused fuel is returned directly to the inlet of the internal vane pump through the internal vane pump pressure regulator (8 – 22 bar (116-319 PSI). The 14 psi overflow valve is important for cooling, but because of its location and the narrow passages that supply fuel to it, it does not impact the operating pressure needed to fill the plunger chamber by the internal vane pump. From Jeeper Jimmy: The first thing the incoming fuel sees in the VP44 is a vane-type fuel pump (called by Bosch the ‘Internal Fuel Pump’) which raises the pressure to “8 – 22 bar (116-319 PSI) depending on the application and RPM” (direct quote from VP44 Service Manual and Bosch Fuel Injection Pump Manual). A pressure control valve at the output of the vane pump bypasses fuel back to its input to control the desired vane pump output fuel pressure and varies depending on RPM. This is a pure spring-loaded mechanical devise; it only depends on vane pump pressure, it doesn’t depend on the VP input pressure nor any electrical signal. The amount the pressure control valve opens depends on how much pressure the vane pump is producing. The vane pump is a positive-displacement pump; therefor its output flow increases pressure as RPM increases. From here on, as long as there is a sufficient volume of fuel available at the VP44 input, it doesn’t matter how much pressure the external feed pump (lift pump) is producing, the VP44’s internal pressure will be controlled at design pressure by the vane pump and the pressure regulator. Since the vane pump output pressure increases with RPM, the amount of fuel bypassed varies to allow a desired, controlled pressure which is dependent on engine RPM (the higher the RPM, the higher the pressure). This higher pressure is necessary in a radial piston solenoid valve controlled injection pump (VP44) because the same cavity of the high pressure pump (the Plunger Chamber) must be filled to a design pressure for each injection, unlike the in-line injection pump which fills each of six cavities in sequence. The higher the RPM, the less time there is to fill the Plunger Chamber, therefore the higher the pressure must be to assure proper filling of it prior to the next injection. @Great work!, thank you for your diligence in looking deeper into the internal vane pump and overflow valve operation. - John

It has been highly recommended, but I never have believed it is true for the reasons I have stated. The fuel circuit is a series circuit. The lift pump feeds directly into the inlet of the internal vane pump. The internal vane pump fills the plunger chamber for the high pressure injection pump. This explanation is simplistic, there is much more going on. It is my understanding that the fuel solenoid cycles rapidly. When it is de-energized, the fuel in the plunger chamber (which is fuel flow from the internal vane pump) is in common with the 14 psi overflow valve providing the fuel return flow. The valve next to the supply inlet is not the overflow valve. It is the pressure regulator for the internal vane pump. See below. Pay close attention to the directional arrows. From Jimmy Jeeper: And that brings us to the Overflow Valve (perhaps the simplest and most misunderstood piece in the VP44).The overflow valve is fed from a separate passageway in the distributor shaft but senses the actual pressure to which the plunger chamber is filled prior to being isolated from the accumulation chamber by the solenoid valve (prior to being pressurized by the high pressure pump). Any excess fuel above the overflow valve set point (about 14 PSI) is returned to the fuel tank by way of the Overflow Valve. The vane pump will always provide more than enough fuel to fill the plunger chamber, therefore there will always be flow back through the overflow valve and, therefore, always cooling flow through the VP44 as long as the engine is running and sufficient fuel volume is available at the vane pump inlet. By design, approximately 70% of the fuel provided by the vane pump will be returned to the fuel tank by the Overflow Valve. Some fuel is also returned to the tank from the injectors. The manual states that “A small amount of fuel is returned from the fuel injectors, while a large amount (about 70% of supplied fuel) is returned from the fuel injection pump”. From Jimmy Jeeper, By design, approximately 70% of the fuel provided by the vane pump will be returned to the fuel tank by the Overflow Valve If an idling engine returns 18 gph and that is 70% of the the internal vane pump flow, then the internal vane pump would be producing approximately 26 gph. The flow would increase to about 78 gph at 2400 rpm. These are just round numbers. Remember, it is unknown how much fuel is being pushed the internal vane pump regulator valve. This would be well within the range of any FASS or Air Dog lift pumps. - John

I don't see how it could. It is not the lift pump that pushes fuel over the 14 psi overflow valve. The lift pump cannot push fuel through the fixed displacement internal vane pump whether the engine is running or not. The lift pump only charges the inlet of the internal vane pump. It is the internal vane pump that supplies the abundance of fuel immediately as soon as the engine is started. thus supplying a strong return flow of fuel to the fuel tank right away. Here is what we don't know about the internal vane pump: * displacement - cubic inches per revolution (volume of fuel being pumped at a specific engine rpm) * is the pressure regulator valve for the internal vane pump always in operation? If so, what is the volume of fuel being returned to the suction side of the internal vane pump during various engine rpm's? * Here is what we do know about the internal vane pump: * it is a fixed displacement pump which means the volume being pumped is directly proportional to engine rpm. * as soon as the engine is idling the internal vane pump is immediately displacing a specific volume of fuel. * we learned from Mopar-muscle, Apr 24, 2001's fuel return flow test that an idling engine produced 18 gph return fuel flow to the fuel tank. This would mean that the internal vane pump is supplying at least 18 gph. BUT, what we don't know is how much fuel is passing over the pressure regulator valve in the internal vane pump circuit? The return fuel flow will significantly increase as engine rpm increases. If engine rpm is raised from idle (800 rpm) to 2400 rpm, the internal vane pump will triple its volume (it has to because it is a fixed displacement pump). The 14 psi overflow valve is in common with the outlet of the internal vane pump - not the outlet of the lift pump. If the engine is running, fuel is being returned through 14 psi overflow valve. Mopar-muscle, Apr 24, 2001 has shown us this: DD2 , DD TTPM (True Torque Power Module) FP volume idle 11 psi 18gph cruise 8 psi 24gph WOT 2 psi 30gph DD2 , TTPM , HOT PE ANY LEVEL FP volume idle 11 psi 18gph cruise 8psi 24gph WOT 0 psi 30gph - John

@W-T, these are the results from the test on my truck from my previous post. I have a background in hydraulic fluid power systems and to me the VP44 fuel system has to follow basic hydraulic principles regarding pressure and flow. It is for these reasons I have never been particularly concerned about low lift pump pressure for the VP44 pump on my truck, especially since the replacement VP44 pump has the Bosch fixes already in place. I expect that this 260,000 mile VP44 replacement is nearing the end of its life, and if it is, it has been a good life, but who knows? As for heat soak on the PSG - what about the ECM that is bolted to the side of the engine block? It has proven to be a reliable electronic device under similar heat soak conditions, but nobody seems concerned to the point of adding additional cooling. W-T, I appreciate what you have brought to the forum and I like you style of writing. - John

Not at all. The return flow would remain the same. I am saying that the return flow is dependent on the internal vane pump flowing fuel over the 14 psi overflow valve - not the lift pump operation.

@Finlandese, just curious - your signature shows 295/75r15 Hankook Dynapro m/t tires. Are they really 15" tires, or is that just a typo? - John

I absolutely agree with this - and don't forget the timing piston, too. I think that blaming lift pump pressure was an easy out for Bosch while quietly fixing the afore mentioned issues without fanfare. At least they fixed them. - John

I believe I've heard someone talking about before where if the motor is not running the fuel will not get pushed passed a certain spot in vp. Vp needs to be turning for fuel to go through. That's what I heard, not sure how true that is I am a firm believer that this is true. The lift pump provides a positive pressure to the inlet of the fixed displacement vane inside the VP44 injection pump. Fluid cannot be pushed through a stopped fixed displacement pump. The best you can get is internal leakage that will dribble out some return fuel - certainly not enough for cooling. Just last week I installed a return line tee into the filler hose for better cooling of returned fuel (which was a success) I believe this modification will provide adequate cooling for the VP44 under all driving conditions. Before I completed the installation I performed two return flow tests into a five gallon bucket. My lift pump is a frame mounted FASS DRP-02. Not sure what the output is, but I know it is less than 100 gph. First test = 3 cycles of bump start (approximately 25 seconds each time for three times - engine not running, lift pump pressure 14 psi) - Results were barely a trickle entering the bucket. Second test = start engine and let idle, fuel pressure at 12 psi - fuel immediately begins pouring into the bucket quickly covering the bottom. I estimated about .3 gpm (about 18 gph) Raised engine rpm to approximately 1800 rpm - flow visibly increased. My truck currently has logged 355,000 miles - 87,000 miles on a warrantied VP44 and lift pump, and now 265,000 miles on the replaced VP44. This VP44 has never seen 14 psi ever at its inlet (lift pump pressure) with engine running. Most of the time it is 10 psi or less. This does not concern me as I know that there is always a positive pressure. I have posted the following copy of a post before, clearly showing the direct correlation between internal vane pump output and engine rpm. This was posted on a different site by Mopar-muscle, Apr 24, 2001, before I even owned my truck. Test # 1 well some of you guys ain't gonna like this , especially those led to believe (and those that believe it) ... the bigger is a MUST theory . spent a couple minutes running some tests with a DIGITAL/mechnical flow meter and a MECHNICAL fuel pressure gauge , items under test ... 2000 RAM , DD2's , DD TTPM on level 2 (??) and a HOT PE , ( all levels tested the same at WOT)factory pickup , factory lift pump , factory fuel filter housing unmodified , all banjo bolts intact and unmodified except the banjo to the input of the lift pump is replaced with a 90* swept areoquip type -6AN hose end , the bolt at the lift pump had the schrader cut off and drilled and tapped to a 1/8 npt ( for the gauge) and the banjo fittings between the lift pump and the fitler housing have been drilled to 9/32nd . again all banjo bolts are not drilled out as i have on my ram ( test conducted on the DTT RAM ) . we installed ( LaserBob is helping me and getting #2 fuel poured on his head ) a Sonnex digital flow meter ( inside ID is 5/16") in the return line back to the tank , cut in right at the trans crossmember . gph numbers are fuel returned to the tank . DD2 , DD TTPM (True Torque Power Module) FP volume idle 11 psi 18gph cruise 8 psi 24gph WOT 2 psi 30gph DD2 , TTPM , HOT PE ANY LEVEL FP volume idle 11 psi 18gph cruise 8psi 24gph WOT 0 psi 30gph yes you read that correctly , fuel pressure went to 0 and the fuel volume back to the tank did not change from WOT with 2 psi . the truck did NOT stumble , buck , spit , fart , fall on it's face , nothing , ran like all heck at 0 psi , i will note , my truck ran the same at 0 psi with the DD3's , EZ and a HOT PE . - John

Since the hydro booster was replaced, wouldn't the spool valve be a different valve? I am always suspicious when a component gets replaced and the problem symptoms don't change. That usually tells me that the original component did not fail. Usually. A couple of questions: Could a malfunction in the antilock brake system cause a intermittent hard pedal symptom? If so, wouldn't a code be set? Could an intermittent blockage of return line flow from the hydro booster cause a hard pedal symptom? This particular problem kind of baffles me. - John

The truck belongs to my brother-in-law in Crescent City, Ca. The truck is a 2002 Quad Cab, 4x4, automatic transmission with approximately 170,000 miles on the truck. Every thing is stock. The problem: After about every 20 or 30 brake applications the brake pedal gets hard and there is no power assist. As soon as he releases the pedal, everything is back to normal. He took the truck to a shop. The guy who runs the shop is a very knowledgeable man and his business has an excellent reputation.. He asked if the power steering worked when the event occurred. My brother-in-law said that he didn't notice anything with the steering, but his focus was on stopping the truck.. The shop could not make the event re-occur. No codes were set. After discussion between the shop owner and my brother-in-law, it was determined to replace the hydra-boost with a remanufactured one. On the first long trip after the repair, the same event occurred twice again. This time my brother-in-law did not release the brake pedal until after he tested the steering to see if the power steering was working normally. It was. Any ideas on the cause? - John

A good read. I didn't realize just how diversified Echlin is. - John

I believe he means Echlin. They are a major brand name in electrical components. - John

After doing a bit more reading, the HY35 turbo may spool better in that dead zone just because it has a smaller exhaust housing. However, exhaust gas temperatures may run hotter under higher rpm loads than the HX35 I guess you will find out when you make the exchange. - John

What is the read axle gear ratio? It is not listed in your signature. It matters. Clearfield, Utah is above 4,000 ft elevation. - much lower air density than at sea level. Most turbochargers are out of their efficiency zones at low engine rpm, especially at higher elevations. Things that will negatively affect getting a turbocharger to spool up under a heavy load.: * 3.54:1 axle ratio vs. 4.10:1 axle ratio * low stall torque converter * 4,000 ft elevation * 2.21 reverse gear ratio vs 2.45 1st gear ratio You may not be experiencing the problem in first gear because you have more torque to the ground just because of the first gear ratio. This equates to less load on the engine. The combination of all of these things could easily put the engine into a condition that the turbocharger cannot gather enough air for efficient combustion when trying to move a heavy load from idle, consequently, lots of black smoke. I am not saying that there is not a transmission problem or another problem; I am just trying to show what is working against you, so that you can take it into consideration. If there is less load on the engine (less weight), there could be sufficient ambient air pressure (available oxygen) combined with a little boost to get the engine above 1200 rpm, which will get the turbo closer to its efficiency zone. Once that happens, the power comes on and the smoke clears. - John

First gear ratio is 2.45:1, reverse gear is 2.21:1. Reverse gear provides less torque to the rear wheels. What is your rear axle ratio? I am guessing 3.54:1. I think you may be correct about this - especially if your rear axle ratio is 3.54:1. I also think that the HX35 turbo would be more suited for the low stall converter than the HY35 turbo. The HX35 should spool earlier in rpm's under load so it would be a better match with a low stall speed torque converter. - John

I think your fan clutch will work fine. There were probably a couple of gremlins living in it while it was on the shelf. They will quickly jump into your wiring harness now that you have installed the fan clutch. In fact, I think they already have, since you mentioned the fan clutch now seems to be working fine. - John

Also, an indicator for left hand thread. I believe the fan clutch nut is marked in this manner. I think I learned this from this site some time ago. - John

I bought one from Geno's 6 years ago and 135,000 miles ago. It is still working fine. I thought my OEM fan wasn't operating properly, but it turned out that it was fine. The dirty oily mess in the in the center of the radiator was the problem. @dripley, I think the steady coolant temperature reading your are seeing after the clutch fan permanently locked up would be expected. There is now a much more stable flow of air passing through the radiator all of the time which equates to less temperature swing, which means the thermostat can regulate the coolant temperature easier. - John

But, if you would have broken a belt halfway back from the moon, you really would have been glad you had the old one under the back seat..., just sayin' - John

I agree that you cannot prepare for everything, but one extra step I take is to remove the serpentine belt and spin all of the accessory pulleys. Check for excessive shaft movement or rough bearings. I even modified the top of the fan shroud to make the belt removal and inspection easy. My brother-in-law's 2003 truck was slated for a long trip, so I showed him what to be looking for. It turned out that the fan hub bearing was very rough when rotated by hand. Couldn't feel it or hear with the truck running. That could have been an expensive catastrophic failure. - John

I am curious as to where that switch would be mounted (just for my own information), whether it is at the throttle in the cab or by the APPS in the engine compartment. I have an older style vacuum operated PacBrake that I wired in myself. I did not use a throttle switch or a clutch switch. I relayed the solenoid valve and the relay is operated with a momentary foot switch that I mounted on the floor right beside where my left foot rests. This setup makes it not very likely to operate the throttle and the exhaust brake at the same time. However, if the PacBrake micro switch would be a reliable setup, I would be interested in mounting one in my truck. Let us know how you resolved your problem. - John