HOW TO DIAGNOSE VP44 FUEL SYSTEM ISSUES
Updated February 21, 2012
Overview
I feel qualified to help you as I owned a full service diesel performance shop specializing in Dodge Diesels, and Freightliner and Ford trucks with the Cummins B series engine, from 1993 through 2006, when I became a website only to specialize in the often misunderstood VP44 fuel system. In 1999 my brother and I were the first to offer a power enhancement device for the VP44 fuel system. During the development of this product we received the only US Patent for enhancing fuel delivery for electronically controlled diesel engines. I felt back then that this experience probably made us a bit smarter than most, but I have to admit that the experience I have gained SINCE then has made me a lot smarter and a much better teacher. As I still answer the phone every chance I get, I am still learning from all of you, to give me way more REAL WORLD EXPERIENCE than others in the industry. I am happy to share this knowledge and experience to help you make an accurate diagnosis of your truck’s VP44 fuel system and direct you to purchase the right part the first time. As I learn more I rewrite this amazing document to make it even better, so keep checking the update date so you are assured of the latest and greatest information.
My REAL WORLD EXPERIENCE has allowed me to really fine tune what works and doesn’t work for diagnosing this fuel system. To diagnose this fuel system requires a unique approach and a sense of humor as you can’t just plug in scan tool for all the RIGHT answers. You can’t get what you need from a shop manual either as it was probably written before the author had the experience necessary to diagnose this unique fuel system. The codes that are in the ECM are a help, but in MOST cases mean nothing unless accompanied by a certain symptom. You only need to read the codes in the ECM as that is the only computer that runs the fuel system. The PCM is for all other systems in the truck. In SOME cases the codes we DON’T get are the most important part of determining an accurate diagnosis. If you follow these diagnostic procedures below you WILL get accurate answers, but not necessarily the answers you like! I am so confident in what I am about to share with you, that I make this promise. If you buy an Injection Pump from me that I have diagnosed with you via email, or you email me and I verify your diagnosis, and our pump doesn’t fix the problem, I’ll take it back within the first week!
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, also known as a TPS or Throttle Position Sensor), Manifold Air Pressure Sensor or MAP Sensor (also known as a Boost Sensor), Fuel Filter, Lift Pump and lastly the VP44 Injection Pump. The ECM and OEM Injectors almost never give any problem in my experience. In fact up until 2009 I had never heard of a bad ECM, even at crazy high mileages, but now that these trucks are getting older I have to change my tune. 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 DIAGNOSTIC HELP on the Home Page. The VP44 Injection Pump is almost always the cause of a drivability issue and or symptom, and can be accurately diagnosed by reading below.
PERTINENT CODES
In my experience the 216 code is not a “Death Code” as some people say. It only tells you the Injection Pump can’t attain full timing advance to provide good fuel mileage and power. If this is the ONLY code and you don’t have any drivability issues, the VP44 does not need to be replaced, and most likely will not put you on the side of the road. If you DO have the 216 code you should check your Lift Pump pressure UNDER LOAD as Lift Pump pressure is what moves the timing piston and advances timing, so if Lift Pump pressure is low, that may be the cause of the 216 code. If the pressure is good, then the code means the housing of the Injection Pump is worn out, which still isn’t a reason to replace it, in my mind.
If the engine won’t start, AND YOU HAVEN’T OPENED ANY FUEL LINES OR REPLACED THE FUEL FILTER SINCE IT LAST RAN, and you have either or both a 1688 or 1689 code, the truck will never start until you replace the injection pump, 99% of the time. If you want to be 100% sure of your diagnosis, follow the No Start diagnosis below. These codes indicate either a serious internal mechanical failure, such as a seized rotor, or that the computer on the top of the Injection Pump is not turning on the high pressure fuel to the injectors. Other circumstances like stray RF (radio interference) can set these codes and therefore confuse or misdirect an accurate diagnosis, so this is where symptoms have more merit than just codes, when diagnosing this fuel system. Code 1693 only means there is at least one code in the other computer, the PCM, which has NOTHING to do with the fuel system or fuel system drivability problems. Sometimes an automatic transmission can cause a drivability issue and appear to be a fuel system issue. In this case codes in the ECM and the PCM should be noted, and COMBINED with the drivability SYMPTOMS and a phone call to me, I can help you differentiate and diagnose the problem. To come up with an accurate diagnosis of this fuel system sometimes, you have to prove all the other components that could cause your problem are indeed good, and therefore NOT the cause of your problem. After you have done that, you have no choice but to condemn the Injection Pump.
Code 123 is truly rare and usually means an ECM problem. 234 means the MAP voltage is too high. 237 means the MAP voltage is too low. 251 and 253 means the fuel solenoid is not working correctly and when associated with a drivability issue is a very compelling reason to replace the VP44. Code 1690 or 336 indicates a signal issue with the Crankshaft Position Sensor, and when associated with a drivability problem, necessitates replacement.
WHY YOU SHOULD CHECK FUEL SUPPLY FIRST
You may think that low fuel supply pressure will cause many or all drivability problems, but NOT SO with this fuel system. Human nature also makes us want to take the path of least resistance, by replacing the less expensive components first, before diagnosing this fuel system correctly. Please know that Lift Pumps have their own problems, but are RARELY the cause of an Injection Pump failure, or a drivability complaint, contrary to what a lot of people want you to believe.
A weak or failed Lift Pump or a restricted Fuel Filter will NOT give any other drivability issues OTHER than a skip, miss or buck at high load/high RPM operation. If you DO experience ONLY these symptoms, replace the Fuel Filter and if you can’t bleed the system, or if changing the filter doesn’t fix the problem, go to our Home Page, then Diagnostic Help, and then to Lift Pump Diagnostics for more answers.
You MAY have to do a Lift Pump diagnosis and or replace the Fuel Filter after you put on a rebuilt Injection Pump because it may make more power than the old one, therefore using more fuel, and therefore lowering the fuel delivery pressure to the point that you then have a skip or miss at high rpm/load. Be sure that you have at least 5 PSI Lift Pump pressure, UNDER LOAD, to be sure it isn’t preventing full power or timing advance, and or causing any harm to an old style diaphragm in your VP44. We strongly suggest installing our Low Fuel Pressure Warning Kit to monitor fuel pressure as a diagnostic tool and a future money saver. It will tell you when restriction in the filter necessitates replacement, which means you will change your filter by restriction, rather than the seat of your pants, and save replacement filter costs! It will also tell you if the Lift Pump fails mechanically or electrically. Go to Products on our Home Page for more info about this money saving product.
READING CODES
If you have a late model year 2000 – 2002 Dodge truck you can read the codes by turning the ignition switch to the “run” position from the “off” position 3 times within 5 seconds and leave it in the “run” position and stare at the odometer. To help your diagnosis, write down the information displayed, so you don’t forget. To be sure the codes read are pertinent to the current issue, I recommend that you clear the codes after you read them, to see if they come back when the problem reappears. As some scanners, as well as the disconnecting both batteries for half an hour trick, do not dependably clear all the codes, I suggest that you REREAD THE CODES BEFORE YOU START THE ENGINE to be sure they are actually cleared. Then drive the truck until the problem reappears, and then reread the codes. If there is no new code, that is very valuable information, and if you do have a newly set code, it is most likely relevant to your symptom. If you have a 1998-99 or a grumpy 2000, reading codes this way will not work, so you’ll have to read the codes with any OBD II compatible scan tool. Most auto parts stores will do this for free for you.
THE SYMPTOMS LISTED BELOW IN RED ARE LISTED IN FREQUENCY OF OCCURRENCE, MOST FREQUENT TO LESS FREQUENT,
TOP TO BOTTOM
DEAD PEDAL, OR INTERMITTENT
LOSS OF POWER
This is THE MOST COMMON DRIVABILITY COMPLAINT and is an intermittent one that happens most often when the truck is hot or working harder, but can occur when cold too. My experience tells me that 4 times out of 5 Dead Pedal is worse hot, but 1 time in 5 it is worse cold! The symptom of Dead Pedal is rarely caused by the APPS (Accelerator Pedal Position aka Throttle Position Sensor) and 90% of the time it is caused by a faulty computer on the top of VP44 Injection Pump. These numbers are NOT an exaggeration. Computer failures are due to the “Lead Free” solder connections on the circuit board becoming crystalline, which causes an intermittent electrical connection and intermittent Dead Pedal symptoms. Its use is mandated by the Federal Government!
There are no codes that specifically diagnose Dead Pedal or that will condemn the computer and therefore the VP44. This is an instance where a lack of codes is most important, and where you have to prove that the only other component that could cause this symptom, the APPS, is or is not the cause of Dead Pedal.
The lazy inaccurate way to diagnose the APPS or TPS as the cause of this drivability issue is to scan or read the ECM (not the PCM) to check for any codes pertaining to the APPS, such as a 121 or 122. Codes 121 and 122 only indicate that the voltage going in or coming out of the sensor was outside of the desired parameters, at least once, since the codes were last cleared. Therefore these codes do NOT tell you what happens to the signal when they ARE within appropriate parameters, which is what really matters. If you DO have either or both of these codes you MAY need an APPS. To diagnose the APPS accurately you need to use an oscilloscope or an ANALOG voltmeter, one with a needle, to measure and monitor the signal voltage on the blue wire with a black tracer, on a Dodge, in the APPS electrical harness plug. A scan tool or a digital voltmeter has too much averaging or buffering of the signal to be useful for this test. First verify the appropriate voltage range and voltage apply rate with the engine off. Turn the ignition key to the “on” position and slowly press on the throttle and slowly release it. You should see voltages from about .6 volt to 3.5 volts, and not ever see a jump in voltage, or the needle bounce. It should go up and down smoothly, directly related to throttle movement. If it repeatedly or intermittently jumps up or down, then replace the APPS. The adjustment of low voltage at idle, or “resetting” or “recalibrating” the APPS is NOT as important as some people want you to think, and does NOT cause Dead Pedal. The ECM learns the range when you do the install of the APPS correctly and does NOT cause any drivability issue in my experience.
As this sensor can be very intermittent, I strongly suggest you ALSO do the same test when driving the truck to prove the APPS is or isn’t the cause of your Dead Pedal issue. Extend the signal wire used in the previous test up to the dash of the truck, hooked to the analog voltmeter, and drive it until Dead Pedal happens and look at the voltage on your voltmeter. If you are holding the pedal still and the voltage drops when the engine drops power, or the needle quivers at the same frequency as the stutter, skip, or miss, you need an APPS. If the voltage stays the same and the power drops, you need an Injection Pump!
IF YOU DON’T NEED AN APPS, AND YOU HAVE DEAD PEDAL SYMPTOMS, YOU FOR SURE NEED A VP44!
If you don’t have access to a scan tool or an analog voltmeter, 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 right off, or if going back to a lesser throttle opening makes the engine run fine, then it is most likely a bad APPS. This usually occurs most frequently, but not always, in cold and or wet conditions. If it is caused by the computer on the VP44, the Dead Pedal or power drop occurs at ALL throttle positions and power comes back only if you let the throttle pedal go to idle for a brief time to re-establish Idle Validation and reset the computer, or push the clutch in, or shut off and restart the engine, or just wait. This kind of Dead Pedal happens most often hot or towing, but sometimes when cold.
TRUCK DIES GOING DOWN THE ROAD
Another frequent 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, or rebuilt pumps that don’t have the upgraded rotor and distributor. The cause of this failure is a poorly "de-burred" rotor according to Bosch. This machining problem has been addressed and apparently solved in later years of production. All of our rebuilt units have these updated upgraded parts. If you run any rotary style pump like a VP44 out of fuel at high RPM you CAN seize the rotor because it runs out of lubrication! This symptom can also be due to contaminated fuel and related corrosion on internal parts of the pump, or an electrical failure of the computer on top of the VP44.
IMPORTANT DIAGNOSTIC FACT:
TO MAKE THE ENGINE START AND IDLE ONLY, YOU DON’T NEED ANY SENSORS OR COMPUTERS OR ELECTRIC LIFT PUMP. YOU ONLY NEED 12 VOLT POWER, GROUND, AND FUEL TO THE VP44.
NO START – TEST #1
FUEL SUPPLY TEST
If the fuel gauge reads 1/8 – 1/4 of a tank, put a few gallons in the tank and bleed the fuel system. I say this because of the famous Dodge fuel tank sender problem. Your gauge may have just failed and be out of calibration for the first time and the tank is actually empty. In this situation air AND fuel is what you are trying to start the engine with! Pressure indicators don’t know the difference between air and fuel pressure, so they make you falsely think all is OK. You will be very glad you did this if your truck runs again and you don’t need an Injection Pump!
If the engine was running BEFORE you CHANGED THE FUEL FILTER or OPENED A FUEL LINE, and it HASN’T STARTED SINCE, or, it started and stalled after doing this, and it WON’T BLEED or restart, and you can hear the Lift Pump running, but won’t fill the filter canister, you most likely have a bad electric Lift Pump. That’s a long complicated sentence, so reread it again slowly for clarification! Please remember when you are doing this diagnosis that the ECM turns on the electrical power to the Lift Pump only for 4 seconds when the key is in the “on” or “run” position. When the ECM sees the “start” signal from the ignition switch it runs the pump for 25 seconds, and when it sees idle RPM it runs continuously. If the pump doesn’t come on, or doesn’t pump fuel into the filter canister when you click the key to the “start” and release it to the “run” position, you can bleed the system to get fuel to the VP44 and get the engine to run again by pressurizing the fuel tank with air pressure, or diagnosing and replacing the electric Lift Pump. The reason this strange scenario happens, is because there is a mechanical lift pump built into the VP44 which works fine UNTIL air gets into the system. This explains why VP44 fueled engines don’t die on the side of the road when the electric one fails.
NO START – TEST #2
ELECTRICAL TEST
Next test the electrical wiring and verify that there is battery voltage getting to the VP44 with the key in the “run” AND ”start” positions. Remove the big plug on the back of the injection pump by wiggling the plug with your right hand pulling toward the firewall and the left hand pulling the indented locking tab toward the fender. When you have the plug in your hand, hold it so it looks like a smiley face, with six pins below the smile and three pins above. Using a test light or voltmeter with its ground connection on the engine, verify battery voltage on the bottom right pin (pin #7, which is a red wire with a light green tracer on a Dodge), during both “run” and “start” key functions. Then verify the ground on the bottom left pin (pin#6, which is a black wire with a tan tracer on a Dodge), by doing the voltage test again at pin 7 with the ground of your test instrument on pin 6 in the plug. If you see no voltage then, it means there is no ground! Use only pin positions, not wire color, when diagnosing a Ford or Freightliner. If you don’t have power at the plug, check the fuse in the PDC (Power Distribution Center, aka fuse box under the hood) for the fuel system, and if that is good, check fuse #9 in the fuse box on the left side of the dash. If they are both good, then try swapping the fuel system relay in the PDC with the one for the horn. Hopefully you find your problem this easily, but if not, get out the schematic for this circuit. If you don’t have one, I can help you. If you have battery voltage on pin #7 in both key positions, and a known good ground on pin 6, cut the black tape off the VP44 plug harness to access the wires going into the plug and reinstall plug. On a Dodge find the light blue wire with a red tracer (pin #5 on other trucks) and verify that there is NOT battery voltage there during either the “run” or the “start” functions of the ignition switch, WITH THE PLUG PLUGGED IN. The ONLY time there should be battery voltage on pin 5, is for about three seconds after turning the key to the “off” position. If there is battery voltage there at any other time, the engine is being told to not start or run by a pissed off ECM. This test is accurate 99% of the time in my experience. It is not unusual and OK to see low voltage, like .2 - .4 volts at pin 5. The important thing here is to NOT have battery voltage there, and if you do have it at the wrong times, I have found cutting that wire and running the truck forever that way, causes no harm!
NO START TEST #3
HOT WIRE TEST - THE FOR SURE TEST
It is very rare, but possible, for a problem with the wiring harness or the CAN bus Wiring to prevent the engine from starting, so if you want to be 100% sure it is the Injection Pump causing the no start, follow the following directions exactly, to be sure of not damaging a possibly good pump. This test POSITIVELY eliminates the possibility of overlooking an electrical problem caused by other components that could affect the start or run function of the VP44, as long as you have verified fuel delivery to the Injection Pump. Remove the electrical plug at the back of the Injection Pump and hot wire the pins on the pump as follows. Get two wires long enough to reach from the battery to the VP44. Install an INSULATED ¼ inch female spade connector onto one end of each wire. Connect one INSULATED connector to pin 7 on the pump, which is the pin on the BOTTOM row of the socket on the Injection Pump, closest to the engine, to preferably fused (10 amp is fine) positive battery power in the PDC (Fuse box under the hood), or directly to the positive battery terminal if you like to take risks!
Connect the other INSULATED connector to the pin directly above the previous connection, the top row of pins, the one closest to the engine, and attach the other end to battery ground. Now try to start the engine and if it doesn’t start, you absolutely positively 100% need an Injection Pump! If the engine starts this way but NOT with the big plug installed on the pump, you know there is something in the harness or CAN bus wiring to the ECM telling or causing the engine to not start. Call me for help if this is the case.
IF YOU HAVE FUEL, POWER AND GROUND, PROVEN BY THE ABOVE TESTS AND STILL HAVE NO START, YOU NEED AN
INJECTION PUMP!
If you want more proof, or really want to know WHY it won’t start, loosen all of the injector lines at the valve cover. Crank the engine for 30 seconds, and if fuel comes out of only one line, better than the others, this indicates a seized rotor, and the engine will never run again until you change the VP44, because only one cylinder is getting fuel. For the engine to start you need HIGH PRESSURE fuel, AND NOT AIR, to get to at least three of the injectors. If you have only a feeble fuel flow from the open lines, you are looking at only Lift Pump pressure, and the engine will never start. To determine if it is or is not HIGH pressure, look for a puddle on the ground after 60 seconds of cranking. No puddle, no high pressure. If high pressure fuel doesn’t come out of the open lines when cranking, the solenoid pintle valve may be stuck, or the pistons may be stuck, compressed in the rotor, due to fuel contamination or corrosion. Low pressure can also be caused by an electrical issue in the computer, where the computer doesn’t energize and close the fuel solenoid to make high pressure, so low fuel pressure going through the injector lines is WHY the engine won’t start. Any of these situations confirms that the engine will not start until you replace the VP44, as long as you have done the other tests above.
LOW POWER, COLD ONLY
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. This means replace the Injection Pump. If you can predict when it is going to do this naughty thing, try heating the computer on top of the pump with a hair dryer for a few minutes, and if it runs fine right off, you know I am right.
HARD START HOT, LONG CRANK TIMES
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 INSTANTLY RUNS SMOOTHLY
This is typically 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 happens because the electric pump pushes air which is always in 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 it rotates enough times to bleed out the air. If it starts better without an electric Lift Pump, it is because the electric Lift Pump hasn’t forced air into the mechanical high pressure pump through the crack or break in the diaphragm, which is what separates the fuel chamber from the high pressure pump. This failure requires a VP44 replacement to fix the problem.
HARD START, LONG CRANK TIMES, USUALLY WHEN COLD BUT SOMETIMES HOT, 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
AIR IN FUEL TEST
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 or not, 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, the water drain seal on the filter canister, or it can be leaking o-rings on the “Fuel Tubes” in the cylinder head. This last one is cool, as it shows its symptoms in a very unique way. If you park the truck facing up hill, overnight, on a fairly steep grade, it will start hard the next morning, but if you face it the other way on the same hill overnight, it will start fine! This is because of fuel drain back, and air getting into the system through leaky fuel tube o-rings and going to the highest place in the fuel system. When it faces up hill, the air goes into the fuel filter. When it faces down hill, it goes to the fuel tank! Call me if you need more help determining where the air is coming from.
INTERMITTENT OR ROLLING SKIP AT IDLE, OR INTERMITTENT MISS AT HIGHER RPM AT LIGHT TO MODERATE THROTTLE POSITIONS
This symptom is almost always caused by an electrical problem with the computer on the top of the Injection Pump, especially if it only happens warm or hot, AND IS INTERMITTENT. If it is consistent, it most likely is an engine mechanical issue, which is very unusual, so we won’t address that here. First, be sure that there is no air in the fuel supply and no relevant codes by doing the appropriate tests. If a relevant code exists, like a 336 or 1690, replace the crank sensor first to be sure to eliminate it as the cause of the skip. If you have a 251, 253, 1688 or 1689 code these only pertain to the Injection Pump and are strong indications the electronics in the VP44 are BAD, and that the pump is junk. With one or any combination of those codes, and an intermittent miss, I would replace the pump. A 216, 234 or a 237 code CANNOT cause a skip or miss, so they are not relevant to THIS symptom. If you want to prove the skip is caused by an electrical issue, hook up an oscilloscope to the ground side of the fuel solenoid and watch the duty cycle, which is the solenoid energized or closed time. If you have the miss at idle, then the test is easy. If you have to increase and hold the RPM at the point it is missing it isn’t as easy. If the duty cycle or time closed varies from one injection event to another, or looks different on the oscilloscope when the skip is occurring, then look at the APPS signal with the oscilloscope to see if that signal is inconsistent, or “dirty”. If it is, that would prove the VP44 is being told to do the skip because of the APPS signal. If the APPS signal is OK then you have to condemn the VP44 computer and replace the pump.
If you don’t have access to an oscilloscope, and the skip is evident at idle, do the Hot Wire test above, and if it idles fine, it means the VP44 is being told to skip. Then you need to diagnose the APPS as best as you can with an analog voltmeter as explained in Dead Pedal, looking for needle quiver at the same frequency as the skip. A scan tool or a digital volt meter DOES NOT WORK for this test, because they have too much averaging or buffering in them to indicate the problem dependably. If the skip only occurs at higher RPMs, then you have to hold the throttle at the point where the skip is evident, and then watch the needle for any quivering. If NO quiver, it Is not a bad APPS, and it is a bad Injection Pump. Another way to determine the cause of the miss or skip WHEN THE ENGINE IS SKIPPING, is to loosen each injector line, one at a time, until you find one that makes the RPM or sound of the engine change LESS than another. The less the change, the less that cylinder is contributing, indicating that is the problem cylinder. If the skip appears to move from one cylinder to another while doing the crack injector test, that’s great news. That is what I call a rolling skip and always is a bad Injection Pump. If it is consistently one cylinder, it might be explained by being a lazy delivery valve on the Injection Pump, but I’ve never heard of it in a VP44. If you think you have a bad injector, which is virtually unheard of, swap the indicated cylinder’s injector with the one next to it and redo the test. If the problem moves, it is the injector. If it doesn’t move, it is a bad Injection Pump.
DOGGY ON TAKE-OFF OR LOW POWER, COLD AND HOT, OR CAN’T MAKE THE BOOST YOU ARE USED TO SEEING
Before doing the voltage tests below, be sure all the silicone boots are securely fastened to the intercooler plumbing, and that you aren’t just experiencing a boost leak somewhere. Don't assume they are fine just by looking at them. Try to twist each one on the pipe to be sure. Look at the intercooler itself, looking for oil stains indicating a leak; check the o-ring at the turbo outlet, check that the sealing plugs under the heating ribbon electrical connections at the intake tube are both there, and check all intercooler plumbing for any signs of a leak.
MAP SENSOR, KEY ON SIGNAL VOLTAGE, TEST ONE:
The ECM wants to only see MAP signal voltage on 1998 - 2000 trucks between .5 and 1.74 volts and 1.0 to 2.2 volts on 2001-2002 trucks. These voltages are the same for a Freightliner or a Ford. If the MAP signal voltage at the sensor on the grey wire with a red tracer on a Dodge, or the MAP signal wire on other trucks, is low to start with, this can cause this symptom, and may or may not set a 237 code. Check the voltage with the key in the "on" position and the engine NOT running. If it is lower than the lower voltage above, it can be due to a bad MAP or BOOST sensor, but more likely it is because the truck has a device on it that attaches to the MAP sensor harness, like a timing box or electronic gauge component, that draws the voltage down below the desired parameters. To determine if one of these components is the cause of the low voltage, disconnect the wires of the device(s) from the engine's MAP sensor harness. You can’t just turn it (them) off, to see if the problem goes away, because any device connected to either the 5 volt supply wire or the signal wire at the MAP sensor, can draw the signal voltage down, even if it isn’t turned on. If the MAP signal voltage is still the same, lower than spec after disconnecting the device(s), they are NOT to blame. Then call me to find out how to give the MAP Sensor an "enema" to fix the low voltage and doggy on take-off drivability issue, which most likely will eliminate the necessity of doing test two.
IF KEY ON VOLTAGE IS HIGH ENOUGH,
THEN DO TEST TWO:
Remember that the ECM wants to only see MAP signal voltage on 1998 - 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, a code 234 or 237 may or may not be set, but for sure the ECM will cut back fuel delivery commands to the VP44 and make the engine run in a de-rated or “Limp” mode. To do this electrical test, make an extension wire connected to the grey with a red tracer wire, or MAP signal wire, at the sensor go up to a voltmeter on the dash of the truck and DRIVE THE TRUCK. You should see close to 1.74 volts on 2000 and older trucks, and close to 2.2 volts on 2001 - 2002 trucks when driving under hard load and high RPM, with NO power enhancement. If the voltages are within limits, then monitor the MAP signal voltage on gentle take off and if the voltage stays low, but above minimum, and then jumps higher and then the truck takes off, you probably need a MAP Sensor. If the voltage rises smoothly and almost immediately as the throttle pedal is applied, and the truck is still doggy, YOU NEED AN INJECTION PUMP! The reason this test is tricky is that YOU have to determine, within the limitations of human error, if the voltage goes up exactly as fast as fuel delivery is commanded, or a while afterwards, to determine where to place the blame.
RPM GOES UP ON ITS OWN OR WAIT TO START LIGHT IS DUMB OR YOU HAVE
A 606 CODE
This is a new one as of 2010. A few callers have remarked that the RPM goes up on its own, so we have them check that the voltage on the blue 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. 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 the wait to start light goes out, or it comes on when driving. New for 2012 is a problem where the sensors that get their supply voltage from the ECM are lower or higher than the required 5.0 volts. SOME of the time a bad ECM with any of these symptoms will set a 606 code to make you feel more confident in your diagnosis! These are the only three symptoms that I have seen or heard of, SO FAR, that necessitates replacing or repairing the ECM. The good news is that these unique symptoms have been eliminated every time by repairing or replacing the ECM. At least one of the symptoms described above has been common to all the very few bad ECMs, as in all 8 of them, that I have found to need repair or replacement. The only way to diagnose an ECM in my experience is to try a replacement, if diagnosing a Dodge. It doesn’t seem to matter what transmission, 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 doesn’t have the above symptoms any more, then you know a replacement or repaired ECM is in your future. I don’t have any experience with Ford or Freightliner ECMs, which may indicate they are better quality, but they are very different and not interchangeable, as they have twice the number of wires going into them.
CONTAMINATED FUEL AND ALTERNATE FUELS
Lastly, is the internal Injection Pump damage caused from using WVO, more than 5% Biodiesel or contaminated fuel. The resulting corrosion 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. 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.
IN CLOSING
To all of you that have spoken with me over the many years to help me get this education and get me to this place, I humbly say THANK YOU!
It has taken me many dollars and 14 years to collect all the information here, research it, and prove what works efficiently and accurately. I hope you can learn almost as much as I know in only the time it takes to read this. I keep updating and or simplifying this as I get smarter, in an effort to help my potential customers make accurate diagnostic and wise purchase decisions from reading this website. If you think you might need a replacement part or component, but aren’t sure of, or want to confirm, your diagnosis after reading the above, or just want to hear it from “The Horse’s Mouth”, please feel free to call and I’ll be happy to help you. It is my sincerest hope that readers of this helpful document and website will feel obliged for all the good information contained herein, and show their appreciation by becoming a customer.
This is copyrighted material and any infringement, copying, plagiarizing or misuse may be prosecuted. However, please feel free to refer people to, or link your site to www.bluechipdiesel.com
Thanks for Reading and Speed Safely,
Chip Fisher, owner of Blue Chip Diesel
Blue Chip Diesel 888-ISB–PERF or 603-966-6459
9AM TO 5PM MONDAY THROUGH FRIDAY, EASTERN TIME