HOW TO DIAGNOSE VP44 INJECTION PUMP ISSUES
First and foremost you have to understand that there is no easy or ACCURATE way to diagnose most VP44 injection pump problems by using only a scan tool. There are no other DTC codes, other than 216 and 1688, that can solely or positively condemn the VP44 as other circumstances can cause false codes and or a bad diagnosis. Codes in the ECM should be duly noted and combined with the drivability symptoms and procedures described below, and with both you can accurately diagnose what you have to do to fix your problem. The sad truth is to do a fair and accurate diagnosis, you have to prove or assume 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. 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 drivability problems.
There are basically only two other components in the fuel system in a VP44 fueled truck and they are the ECM (Engine Control Module) and the injectors. Neither of these give any trouble typically. In 15 years of doing ONLY Dodge diesels every day, I have never seen or even heard of a bad ECM and or OEM injector. This experience, the fact that they have never been an issue, combined with the fact that replacing the injection pump after the following diagnosis, always fixes the problems, I am very confident in what I say below.
If you DO have 5 psi fuel pressure UNDER LOAD and you see the code 216, or if there are certain other injection pump codes, or even if you have NO codes pertaining to the injection pump, AND you have verified ANY of the following drivability complaints seen below, YOU NEED AN INJECTION PUMP!
THE MOST COMMON DRIVABILITY COMPLAINT is an intermittent "Dead Pedal". This symptom is typically caused by either a faulty APPS (Accelerator Pedal Position Switch) 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. 9 times out of 10 a “Dead Pedal” is caused by the computer on top of the injection pump, but since the APPS is cheaper than a replacement injection pump, we recommend getting someone to "scan" the ECM (not the PCM) in your truck to check for any DTC codes pertaining to the APPS.
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, drive the truck for a while, 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 is worse during cold and or wet conditions.
If it is 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 300 times, so replacing it for a quick hopeful diagnosis is a waste of money and time.
Another VP44 failure has occurred when the truck dies driving down the road for no apparent reason, or when you let off the throttle, especially at high RPM. 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 most often a poorly "deburred" rotor. This problem has been addressed in later years. If you run any VP44 out of fuel at high RPM or heavy load, you CAN seize the rotor also! Dying for no apparent reason can also be due to contaminated fuel and corrosion on internal parts of the pump.
If your truck dies for no apparent reason and you want to diagnose it accurately and be sure of what is wrong, to verify if you need a replacement pump, do the following. Verify that there is battery voltage with the key in the “on” position, in one of the holes in the big plug on the injection pump. If you have appropriate voltage, loosen three injector lines at the valve cover. Crank the engine a few times for 30 seconds and if fuel only comes out of one line or none of the lines, this indicates a seized rotor, or 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. You cannot repair either of these problems without replacing the injection pump.
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 an injection line even if the rotor is not turning and the solenoid valve is working correctly. If the rotor IS turning and the solenoid pintle valve is stuck in either the open or closed position,you won’t get fuel out of any line and the engine will NOT run, because the pistons in the rotor can’t develop pressure and therefore operate the injectors. If you have adequate fuel coming from one line only, that proves the rotor is seized. If you have only a feeble fuel flow, this is due to having only lift pump pressure moving fuel through the line. Again, if you have no adequate fuel from any line opened then the rotor is stuck at a line that is closed, OR,,,,,,,,you have a stuck pintle valve in the fuel solenoid due to corrosion or contaminated fuel. 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.
Other complaints with the VP44 trucks are hard start hot and or hard start cold. If either of these problems are immediately followed by rough running that clears up in 5 seconds or so, look for 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 pump to correct this problem.
Lastly is the issue of WVO and or contaminated fuel. If water, condensation or a corrosive situation gets inside the injection pump, some of the close tolerance parts will stick and affect engine performance and cause drivability complaints, such as a high speed skip 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 and these corrosion problems are the most common reason Bosch denies a warranty claim. Contaminated fuel 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 to deal with and explain to customers because typically you won’t know you have contaminated fuel until too late.
If you think you might possibly need an injection 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 bang for your buck! 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