 | HOW TO DIAGNOSE VP44 INJECTION PUMP ISSUES Updated 2/17/08
From 15 years working on only Dodge Diesel Trucks I have acquired lots of experience diagnosing VP44 fueled trucks. I also have extensive experience with the same fuel system in Freightliner and Ford trucks with the ISB Cummins engine. I am happy to share this experience with you to make an accurate diagnosis of your truck’s fuel system and to make sure I sell you the right part to fix your problem. It is impossible to diagnose all VP44 injection pump and fuel system problems by using only a scan tool, regardless of who makes it. There are three DTC codes that absolutely positively condemn the VP44 for different reasons. The 216 code tells you the pump is worn out mechanically, and can’t attain full timing advance, but won’t cause any drivability issues and doesn’t demand immediate replacement. If the truck won’t start, and you haven’t opened any fuel lines, and you have either or both a 1688 and or a 1689 DTC code, the truck will never start until you replace the injection pump. This is because the computer on the top of the injection pump is not turning on the fueling in the VP44. Other circumstances like stray RF (radio interference) can cause false codes and therefore confuse or misdirect an accurate diagnosis. Code 1693 only means there is at least one code in the other computer, the PCM, which has/have NOTHING to do with the fuel system or your fuel delivery drivability problems. Sometimes automatic transmission issues appear to be a fuel issue. Codes in the ECM should be duly noted and COMBINED with the drivability SYMPTOMS and PROCEDURES described below, you CAN accurately diagnose what you have to do to fix your problem. To do an accurate diagnosis, you have to prove all the other components of the fuel system are good, and if you have done that, you have no choice but to condemn the injection pump. There are six components in the fuel system in a VP44 fueled truck. They are the ECM (Engine Control Module), Fuel Injectors, APPS (Accelerator Pedal Position Sensor), MAP Sensor (better known as a Boost Sensor), Fuel Filter, Lift Pump and finally the VP44 Injection pump. The ECM and OEM Injectors never give any problem in my experience. In fact I have never even heard of these components being bad, even at crazy high mileages, so they don’t need further consideration. The APPS and MAP Sensor rarely are a problem, and can be diagnosed with the info below. The Fuel Filter and the Lift Pump have their own diagnostic page that can be accessed by clicking on the link at the bottom of this page. This leaves the VP44 Injection Pump which is almost always the cause of drivability issues and symptoms. I am really lucky to have had the pleasure of listening to over 2000 of you per year, discussing and confirming the symptoms you have, accurately diagnosing your fuel system, and selling you the best product to repair your issues. I have done this for many years now. This experience has allowed me to really find out what works and doesn’t work for diagnosing the various issues accurately. This is what I call my "REAL WORLD" experience. I am very confident in what I am about to share with you; in fact I am so confident that if you buy a product from me that I have diagnosed with you and it doesn’t fix the problem, return it within a week and I will refund your money! CHECK FUEL SUPPLY FIRST A weak or failed Lift Pump or a plugged fuel filter will NOT give any drivability issues OTHER than a skip, miss or buck at high load or high RPM operation. If you don’t have these symptoms keep reading below. If you DO experience these symptoms, replace the fuel filter and if that doesn’t fix the problem, go to "How to Diagnose a Lift Pump" at the bottom of this page and proceed from there. You MAY have to do a Lift Pump diagnosis or replace the fuel filter after you put on a new injection pump as the new injection pump may use more fuel to make more power than the old one, and therefore have these symptoms. Most importantly, be sure that you have at least 5 PSI Lift Pump pressure UNDER LOAD at all times, to be sure you aren’t causing any harm to the Injection Pump Diaphragm, or preventing full power from being attained. We strongly suggest installing our "Low Lift Pump Pressure Warning Kit" to monitor fuel pressure. Go to our Product List or Product Pricing for more info about this inexpensive money saving product. I am going to list the symptoms in descending order of frequency of occurrence below, so you may not have to read all of this to get the answer you need to fix your problem! DEAD PEDAL This is THE MOST COMMON DRIVABILITY COMPLAINT and is an intermittent one that usually happens when the truck is hot or working harder, but can occur when cold too. This symptom is typically caused by either a faulty APPS (Accelerator Pedal Position Sensor) or a faulty computer on the top of VP44 injection pump. The important thing here is to clarify and differentiate the symptoms between the two. Nine times out of ten a "Dead Pedal" is caused by the computer on top of the injection pump. The best way to positively eliminate the APPS as the cause of the problem, is to "scan" the ECM (not the PCM) in your truck to check for any DTC codes pertaining to the APPS. A few discount auto parts stores will do this for free for you, I am told. If there are no DTC codes pertaining to the APPS you DON'T need an APPS. A bad APPS, always, in my experience, sets a code even if it misbehaves for just a second, so if there IS a pertinent DTC code, replace the APPS. A possible pitfall here is if someone turned the key on when the APPS plug was disconnected. This will set an APPS code, so if you think this could have happened, clear all the codes with a scanner, recheck for codes to be sure all codes were cleared, then drive the truck until the drivability issue occurs and see if the APPS code returns. If it does, replace the APPS. Even though you replace the APPS it may not solve ALL your drivability issues, because you may also have injection pump problems. If you don’t have access to a scan tool, and want to trust my experience, let me explain the difference in symptoms between a bad APPS and a bad computer on the injection pump. A bad APPS usually is just a flat spot at a certain throttle opening, usually 65-70 MPH, and smacking the pedal to the floor a few times, usually clears it up. If pushing the throttle just a bit more makes it take off, or if going back to a lesser throttle opening makes the engine run fine, then it is a bad APPS. This usually occurs most frequently, but not always, in cold and or wet conditions. If it is caused by the computer, the "Dead Pedal" occurs at all throttle positions and will only reset and play again if you let the pedal go to idle for a brief time and reestablish "Idle Validation", or push the clutch in, or shut off and restart the engine. The "Dead Pedal" happens most often when hot or towing, but sometimes occurs right after start up when cold. I would say that the APPS is the culprit maybe one time out of 100 times, so replacing it without an accurate diagnosis is a waste of money and time. There are no codes pertaining to "Dead Pedal" that will condemn the computer and therefore the VP44. If the truck has a proven good APPS, and has an intermittent "Dead Pedal" and no codes, YOU NEED AN INJECTION PUMP! TRUCK DIES GOING DOWN THE ROAD Another VP44 failure is when the truck dies driving down the road for no apparent reason, or when you let off the throttle at high RPM, and the engine won’t restart. This is usually a seized rotor in the injection pump and is most common on 1998 and 1999 trucks. The cause of this failure in these two years is a poorly "deburred" rotor, according to Bosch. This machining problem has been addressed and apparently solved in later years. If you run any rotary style pump like a VP44 out of fuel at high RPM or heavy load, you CAN seize the rotor because it runs out of lubrication! Dying for no apparent reason can also be due to contaminated fuel and corrosion on internal parts of the pump. NO START. DO I NEED A VP44 TO MAKE IT RUN? If your truck dies for no apparent reason or won’t start and you want to diagnose it positively and accurately, whether or not it needs an injection pump, do the following. If the truck was running and you have just replaced the fuel filter and IT HASN’T STARTED SINCE, OR, you can’t bleed the system to get the truck to start, you may have to bleed the system by pressurizing the fuel tank because the lift pump is junk. You must have very little or no air in the lines to make the truck start after opening the fuel system or fuel lines. If your truck won’t start and you DIDN’T change the fuel filter, or if you are pretty sure you don’t have air in the lines, do the following. EVEN IF THE LIFT PUMP IS BAD, AND YOU DON’T HAVE AIR IN THE LINES, THE TRUCK SHOULD START! This is because there is another vane pump in the front section of the VP44 that will keep enough fuel flowing to start and run the truck at lower than normal power. This is why trucks don’t die on the side of the road when they have a bad or weak lift pump. Verify that there is battery voltage with the key in the "on" and "start" position, in one of the holes in the removable plug on the injection pump. If you are lazy, you might assume the injection pump is getting 12 volts if you hear the lift pump running as the lift pump and injection pump both run off the ASD relay in the PDC. The lift pump doesn’t run all the time but if you heard it run for a while then you have pretty good odds that the VP44 is getting power. If you are confident that you have electrical power and fuel to the injection pump, loosen three injector lines at the valve cover. Crank the engine a few times for 30 seconds each time, and if fuel only comes out of one line or none of the lines, this indicates a seized rotor, or a stuck fuel solenoid pintle valve. When I say "fuel is coming out of a line" I mean enough to put a puddle on the ground in 30 seconds. We proved that you can not put this pump in a hydraulic lock as the rotor turns, so therefore fuel HAS to come out of one injection line even if the rotor is not turning. If fuel doesn’t come out of any of the open lines, the rotor may be stuck at a closed line. To get the engine to start you would have to see high pressure fuel coming from all the open lines. If the rotor IS turning and the solenoid pintle valve is stuck in either the open or closed position, or the pistons are stuck in the rotor, due to fuel contamination or corrosion, you won’t get fuel out of any line and the engine will NOT run, because the pistons in the rotor can’t compress and develop high pressure and therefore operate the injectors to start the engine. If you have only a feeble fuel flow, this is due to having only lift pump pressure moving fuel through the line, and the VP44 is not creating high enough pressure to pop off the injectors. This is caused by an electrical issue in the computer or a mechanical issue in the VP44. Either of these situations confirms that the engine will not start until you replace the VP44. If you get adequate fuel from all three lines, you should close them and crank the engine until it starts. Then you have to figure out why it ran out of fuel. HARD START HOT OR COLD Other complaints with the VP44 trucks are frequent OR intermittent hard start hot and or hard start cold. If, after either of these problems are observed, when the engine starts does the engine run rough for a while and then clear up and run smooth or does it immediately run smoothly? If the truck runs rough for a while this indicates a fuel delivery problem, such as fuel drainback or air getting into the fuel supply line. If you have rough running briefly after start you probably do NOT have an injection pump issue. If the truck runs instantly perfectly when it finally starts or shows white smoke on start up, your problem is the computer on the top of the injection pump. This component cannot be replaced in the field as it has to be programmed and calibrated to the mechanical part of the VP44. You have to buy a replacement VP44 injection pump to correct this problem. ROUGH IDLE OR MISS AT HIGHWAY SPEEDS LIGHT THROTTLE This is always the computer on the top of the injection pump, as long as there is appropriate lift pump pressure and no codes pertaining to Crankshaft or Camshaft sensors. By now you know what a bad computer means; REPLACE THE VP44! TRUCK IS DOGGY ON TAKEOFF This one is rare AND tricky. If this is the ONLY drivability complaint and the following test is done and the voltages are right, then YOU NEED AN INJECTION PUMP! If it isn’t the only drivability issue then you probably have condemned the VP44 pump already, from another test. Either with a scan tool, or voltmeter on the signal wire of the MAP sensor, verify the MAP signal voltage at .5 volts for 98, 99 and 2000 trucks at idle or "key on" only. This should be 1.0 volts on 01 and 02 trucks. When the truck is driven, monitor this voltage on take off and if the voltage stays low and then jumps higher and then the truck takes off, you probably need a MAP Sensor. If the voltage rises almost immediately and the truck is still doggy, YOU NEED AN INJECTION PUMP! If the signal voltage is low to start with, and or the truck has a fuel enhancing device on it that attaches to the MAP Sensor signal wire, call to find out how to give the MAP Sensor an enema to fix the delayed fueling. CONTAMINATED FUEL AND ALTERNATE FUELS Lastly is the issue of WVO, Biodiesel and or contaminated fuel. If water, condensation or a corrosive situation gets inside the injection pump because of poor quality diesel fuel or alternate fuel use, some of the close tolerance parts inside the VP44 will stick and affect engine performance and cause drivability complaints, such as a high speed skip, low power or no start. These problems can rarely be cured by some sort of fuel treatment being put in the fuel after the truck starts skipping or stops running. The sad truth is corrosion never gets better and a stuck internal part rarely fixes itself. These corrosion problems are the most common reason Bosch denies a warranty claim. Contaminated fuel rusts or corrodes, and therefore destroys, the internal components in these high pressure style rotary pumps. Generally if there are drivability issues due to contaminated fuel, ALL the expensive internal parts of the injection pump will be ruined and have to be thrown out, which renders the pump junk and not worth rebuilding, and therefore not eligible to be a core! These situations are so hard for me to deal with and explain to customers because typically you won’t know you have contaminated fuel until too late, such as when we open up the pump for warranty consideration, failure diagnosis, and or repair. .
If you think you might need an injection pump, or a lift pump, but aren’t sure enough in your diagnosis, give me a call and I’ll happily verify a diagnosis with you. If you really need a pump, hopefully I can sell you an improved unit that has all the latest upgrades to give you the best performance, fuel economy and bang for your buck! Click on "Upgraded VP44 Injection Pump" below for more info or check out the rest of our website for more info. Thanks for reading, Chip Fisher owner Blue Chip Diesel Performance 888-ISB- PERF or 888-472-7373 MON-FRI Eastern Time |
