Dodge Cummins Diesel Forum - View Single Post - VP44 Diagnostic for everyone.
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post #2 of (permalink) Old 01-07-2012, 03:06 PM Thread Starter
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HARD START HOT, LONG CRANK TIMES, and then instantly runs smoothly

Hard start hot is ALWAYS an electrical issue due to heat soak, where the computer gets hot from the latent heat from the engine after the engine is shut off. Cooling the computer by either time or an outside source restores the crystallized and therefore intermittent lead free solder connection(s) on the computer circuit board, and it takes off and starts. To test for this or convince yourself that I am right, try this trick. Run cold water over the computer on the top of the injection pump for a few minutes the next time you know it will be hard to start, and if it starts right up you know you need a new pump.

HARD START COLD, LONG CRANK TIMES, and then instantly runs smoothly

This is most often due to a cracked or broken diaphragm inside the injection pump. To test for this try disconnecting the electrical power from the lift pump BEFORE turning the key on, and see if it starts better. This can happen because the electric lift pump pushes air from the fuel chamber inside the VP44 pump, through the crack or break in the diaphragm, into the mechanical high pressure pump and it becomes air-bound until the mechanical pump rotates enough times to bleed out the air. If it starts better without an electric lift pump, that indicates leak down in the high pressure mechanical pump due to a cracked or broken diaphragm which means VP44 replacement to fix the problem.
HARD START, COLD OR HOT, LONG CRANK TIMES, runs rough for a few seconds after start and then clears up and runs smoothly, or ENGINE SOUNDS DIFFERENT OR LOUDER UNDER LOAD, OR MAKES A CRACKLING SORT OF SOUND


If the engine runs rough for a brief period of time after starting, just a few seconds, or sounds funny when running, this usually indicates air in the fuel supply system, caused by either fuel drain back or air getting into the fuel supply line somewhere. This symptom is NOT caused by the injection pump. Please know that good fuel pressure does NOT mean that there is no air in the supply line, as the pressure sensor doesn’t know the difference between fuel and or air pressure! My latest trick to accurately determine if air is a problem is to get a 12 foot section of clear polyethylene or vinyl 3/8” hose from the hardware store and put it in the steel line between the fuel filter and the injection pump where the rubber section is. For aftermarket plumbing upgrades, figure out how to install it between the fuel filter and the injection pump. Loop it up under the windshield wiper for easy observation while driving and starting. Bleed the system to get all the air out of the newly installed line, and when you know the engine will be hard to start, monitor the line before, during, and after starting, and even driving, to determine if air ever gets into the pump. This test positively tells you that you DO or DO NOT have an air issue which can be very important when diagnosing the VP44 fuel system. If you do have air in the clear line, run the engine from a can of diesel in the bed of the truck with a rubber hose stuck in it, connected to the inlet of the lift pump. If the air goes away, the problem is behind the lift pump. If it is still there, it is forward of the inlet of the lift pump. This can be the lift pump itself, if it is a Fass with a leaky o-ring inside, leaking sealing washers, or it can be the o-rings on the “Fuel Tubes” in the cylinder head. Call me if you need more help determining where the air is coming from.


This is almost always the computer on the top of the injection pump, especially if it only happens warm or hot, as long as there is no air in the fuel and no relevant codes. If those codes exist, diagnose and or replace those components. It can also be an internal mechanical issue. This only means REPLACE THE VP44!


If the truck is gutless when driving for the first little while after start up cold, and then all of a sudden takes off and runs fine, this is always a bad computer on top of the injection pump, IF THERE ARE NO CODES TO INDICATE ANY OTHER COMPONENT, which of course means replace the injection pump. If you can predict when it is going to do this, try heating the computer on top of the pump with a hair dryer for a few minutes when you know it will be bad, and if the heat fixes it immediately, you know I am right.


This one is rare AND tricky to accurately diagnose. The ECM needs to see voltage above and below certain parameters to NOT cutback or restrict fuel delivery from the VP44. The ECM wants to only see MAP signal voltage on 1998 through 2000 trucks between .5 and 1.74 volts and 1.0 to 2.2 volts on 2001-2002 trucks. If the signal voltage is outside of these parameters, the ECM will cut back fuel delivery commands to the VP44 and make the engine run in a de-rated or “Limp” mode. If this symptom is the ONLY drivability complaint and the following tests are done and the voltages are timely and right, then YOU NEED AN INJECTION PUMP! If this symptom 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, which is grey with a red tracer in a Dodge, verify that the MAP signal voltage is at .5 volt for 98, 99 and 2000 trucks at idle and or “key on” and 1.0 volt on 01 and 02 trucks. If the signal voltage is lower than these specs during this test, it can be due to a bad sensor, but more likely because the truck has a device on it that attaches to the MAP sensor, like a timing box or electronic gauge setup, that draws the voltage down below the desired parameters. To determine which component is possibly the cause, disconnect the wires of the device(s) from the MAP sensor harness. You can’t just turn it (them) off, to see if the problem goes away, because any device hooked up to either the 5 volt supply wire or the signal wire at the MAP sensor, can draw the voltage down, even if it isn’t turned on. If the MAP signal voltage is still lower than spec after disconnecting the device(s), call me to find out how to give the MAP Sensor an enema to fix the low voltage and related delayed fueling. If the voltages are right after this test, then attach an extension wire from the signal wire up to the dashboard and read the voltage with a volt meter when the truck is driven.

Monitor the MAP signal voltage on gentle 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! The tricky part of this diagnosis is determining if the voltage goes up exactly as fast as the fuel demand is increased, or a while afterwards, to determine where to place the blame.


This is a new one for 2010. A few of my callers have remarked that the RPM goes up on it’s own, so we have them check that the signal voltage, on the blue wire with a black tracer signal wire (on Dodges) coming from the APPS, doesn’t go up or down when the RPM goes whacky, which confirms it is NOT the APPS. Therefore it only makes sense to blame the ECM. If you hot wire the pump as explained in “No Start” above and the idle is smooth, but if the idle rolls or is erratic with the VP44 plug being plugged in, and the APPS is good, then you have to blame the ECM. The other strange symptom or indicator of a bad ECM is when the truck won’t start until you see the “wait to start” light go out, or it comes on when driving. These are the only two symptoms that I have seen or heard of, SO FAR, that necessitate replacing or repairing the ECM. As these trucks are getting older, and only in the last few years, have I very rarely heard of these symptoms. The good news is these symptoms are unique so far! At least one of the symptoms described above have been common to all the very few ECMs that I have found to need repair or replacement. The only way to diagnose an ECM in my experience is to try a replacement. It doesn’t seem to matter what year or engine rating the test ECM comes from, with or without a crank sensor, as long as the above symptoms go away with the borrowed test unit. I have had many callers do it this way, so I feel confident you won’t hurt anything as long as you remember one thing, PLEASE. When installing any ECM, be SURE to ground it to the engine FIRST, before connecting the big plug. This prevents any problem from static electricity or a voltage spike getting into the ECM which can blow away the software and or computer inside. Yes the test ECM may set codes, but if it runs better and or doesn’t have the above symptoms any more, then you know a replacement or repaired ECM is in your future.


Lastly, is the internal injection pump damage caused from using WVO, more than 5% Biodiesel or contaminated fuel. The resulting corrosion inside the injection pump causes the close tolerance parts inside to seize or stick 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 additive being put in the fuel AFTER the problem is observed.

These corrosion problems are the most common reason Bosch denies a warranty claim. Contamination rusts or corrodes and therefore destroys the internal components in VP44 pumps. Most often if there are drivability issues due to contaminated fuel, ALL the internal parts of the injection pump will be ruined and have to be thrown out, which usually means the pump is not worth rebuilding, and possibly not even eligible to be a core! These situations are so hard for me to deal with and explain to customers, because typically they don’t know they have a contaminated fuel issue until too late, when we open up the pump for warranty consideration, failure diagnosis, or repair.

If you think you might need an APPS, Injection Pump, Low Fuel Pressure Warning Kit, or a Lift Pump, but aren’t sure of your diagnosis after reading all this rhetoric, give me a call and I’ll try to explain it in terms you will understand, to verify an accurate diagnosis with you. If you really do need a replacement part, I surely hope you will consider Blue Chip Diesel to supply you with an improved unit that has all the best and latest upgrades to give you the best performance and bang for your buck. Selling better replacement parts is how I pay the phone bill and support this website!

I hope you can learn in a few hours from this diagnostic sheet what has taken me many years to collect, to research and prove, works efficiently and accurately. I keep updating this as I get smarter in an effort to help my potential customers make accurate and wise decisions, and I want to thank all those people that have learned from this and then became customers. To all of you that have spoken with me over the years to get me to this place, I humbly say THANK YOU!

Any and all suggestions for this awesome document will be gladly received.

Thanks for reading, Chip Fisher

Blue Chip Diesel 888-ISB–PERF or 603-966-6459

Email [email protected]


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Last edited by AmT-yd-; 01-07-2012 at 08:27 PM.
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